# Inline skates

Inline skates are boots with wheels arranged in a single line from front to back, allowing a skater to roll along on these wheels. Inline skates are technically a type of roller skate, but most people associate the term roller skates with quad skates, another type of roller skate with a two-by-two wheel arrangement similar to a car. Quad skates were popularized in the late 19th and early 20th centuries. Inline skates became prominent in the late 1980s with the rise of Rollerblade, Inc., and peaked in the late 1990s. The registered trademark Rollerblade has since become a generic trademark due to its popularity. To this day, "rollerblades" continues to be used in everyday language to refer to inline skates.
In the 21st century, inline skates come in many varieties, suitable for different types of inline skating activities and sports such as recreational skating, urban skating, roller hockey, street hockey, speed skating, slalom skating, aggressive skating, vert skating, and artistic inline skating. Inline skaters can be found at traditional roller rinks, street hockey rinks, skateparks, and on urban streets. In cities around the world, skaters organize urban group skates. Paris Friday Night Fever Skate (Randonnée du Vendredi Soir) is renowned for its large crowd size, as well as its iconic +10 mile urban routes. Wednesday Night Skate NYC is its equivalent in New York City, also run by volunteers, albeit smaller in size.

## History
### Development of wheeled skates

The history of inline skates traces back to the origin of ice skates in prehistoric times, with runners made from animal bones. Steel blades eventually replaced bone runners in the 13th century, with the Dutch sharpening blade edges for better purchase on ice for propulsion. Since then, enterprising inventors have attempted to make boots that could similarly glide on non-ice surfaces, with wheels.
In 1760, John Joseph Merlin, a renowned clock-maker, musical-instrument maker and inventor from Belgium, experimented in London with "skaites" that "ran on wheels". These were the first recorded wheeled skates. Written records left no drawings or descriptions of wheel configurations, however.$^{:7}$
In 1819, Charles-Louis Petibled from France filed the first known patent on wheeled skates. Three wheels in a single line, mimicking a steel blade, were integrated into a wooden foot stand with leather straps. Two wheels sat under the ball of the foot, while one wheel was positioned under the heel. A copy of Petibled's wheeled skates is on display at the National Museum of Roller Skating, in Lincoln, Nebraska, USA.$^{:8}$
In 1823, Robert John Tyers from London was granted a patent for his skates with five wheels in a single line, again mimicking a steel blade. The main body of the skate is called the stock (or foot stand), and is meant to be attached to the bottom of a shoe. A frame with two wheel-mounting sides is secured to the stock. This skate employs a large wheel in the middle, and progressively smaller ones towards the front and the rear, creating a rockered wheel setup that allows skaters to execute turns more easily.
This novelty skate was popularized in London as "Volito" (to fly about, in Latin). A hand-colored print from 1829 in the British Museum depicts a satirical scene where men wearing Volito skates escape chase by men on boots. The National Museum of American History has a Volito skate in its collections.
Robert Tyers was not the only inventor inspired by Petibled to make their own wheeled skates. Many inventors followed suit in the wake of the Petibled skate, including Spence, Lohner and Legrand. Yet another inventor was the famous ice skater Jean Garcin. He filed his own skate patent in 1828, named the Cingar skate, an anagram of his name. This skate, however, was technically similar to Petibled's patent. As a result, Petibled was able to render null and void Garcin's patent in 1832.
Up to this point in history, "roller skates" as a term was not yet used. Inventors simply referred to their contraptions as wheeled alternatives to ice skates. All known novelty skates had wheels aligned in a single line. Skates were simply assumed to have a single runner, whether a steel blade on an ice skate, or a row of wheels on a wheeled skate. This state of affairs continued through 1860.$^{:8–13}$

### Development of roller skates

Around 1860, wheeled skates started to become more popular. Patents on a wide variety of wheeled skates were issued. The configuration of wheels started to depart from previous single-line arrangements. Many of these early patents were titled "roller-skate" or "parlor skate". Indeed, the Oxford English Dictionary dates the earliest printed use of the noun roller skate to 1860. Then, starting in 1870, the popularity of roller skates skyrocketed. Within a decade the term "roller skates" entered the popular lexicon.
In 1860, the US Patent Office granted Reuben Shaler the first US patent on roller skates, titled "Wheel-Skate", with an accompanying drawing labeled "Parlor Skate". The four rollers (wheels) formed a straight line, and were mounted by pins on two side pieces of a hanger that we would now recognize as a frame of a modern-day inline skate. His key innovation was a flexible rubber ring he mounted on each of the four metal roller cores. This allowed his roller skates to gain better purchase on carpeted floors.
In 1861, Albert Anderson was granted a US patent on "Improvement in roller-skates". The accompanying drawings titled "Parlor Skate" showed a two-wheeled skate, with a small wheel under the heel, and a much larger wheel in front of the toes, reminiscent of penny-farthing bikes. The large front wheel overcomes oncoming obstacles, preventing a skater from falling forward. The stock (or foot stand) is inclined forward, with a raised heel section. This is not dissimilar to how some modern-day hockey, freestyle and speed skates pitch a player leaning forward by default, giving a skater greater stability and stronger strokes.$^{:15,21,25}$
In 1861, Henry Pennie was granted a US patent titled "Roller-skate". Its drawing, titled "Parlor Skate" showed a stock supported by two rows of wheels, with 4 wheels on each row, totaling 8 wheels per skate. In the patent specification, Pennie explained that his key innovation was the two rows of wheels. This set his skates apart from all previous roller skates that attempted to emulate ice skates with a single, centered runner. Pennie reasoned that two rows of wheels provided increased support area for better balance, without materially incurring greater friction. Beginners would learn with two rows of wheels, for a more balanced footing. Skillful skaters would move the two rows of wheels increasingly closer to each other, using different widths of washers as spacers, until they graduated to a single row of wheels. Pennie's skate, too, had two side plates secured to the stock, forming what continues to be known as a "frame" today.
In 1863, James Plimpton patented an "improvement in skates" consisting of a stock with four wheels arranged in a two-by-two configuration like a wagon. This was not the first roller skate with two rows of skates, but it was the first double-row skate that could be easily turned by a beginner. Plimpton's key innovation was a mechanism that allowed a skater to turn a skate by simply leaning towards the desired direction. The mechanism converted rocking and canting motions of the skate platform (stock) into movements of the two wheel axles. These axles in turn steered all four wheel into the right orientations for the turn.
Plimpton opened roller skating rinks and aggressively promoted this new sport of roller skating. His wheel-steering invention, together with his business acumen, spread his roller skates far and wide, resulting in a "rinkomania" in the 1860s and 1870s. The editors of the 1876 series of "Historical Notes on Roller Skates" (published in The Engineer) marveled at the number of roller skate patents that resulted from the rinkomania. They compiled a table of roller skate patents issued in Europe and America from 1819 through 1876, showing an exponential growth starting with Plimpton's 1863 invention. Plimpton's skates forever changed the meaning of "roller skates". For the next century, the term "roller skates" no longer referred to all wheeled skates. It became synonymous with the two-by-two Plimpton-style skates, particularly to the masses.$^{:13–14}$

### Adoption of ball bearings

Skates became more practical with the adoption of ball bearings in the wheel assembly. This directly followed the development of precision ball bearings in the 1850s, and the application of ball bearings in bicycles by Albert Louis Thirion in 1862 in England. Ball bearings reduced bearing friction to as little as 10% of former values, greatly improving top speeds of bicycle racers in Europe.
In 1852, Joseph Gidman filed a provisional patent application titled "A skate", where he described a skate with a front wheel, a rear wheel, and two side wheels mounted mid-section. Instead of constructing a wheel with a solid nave, Gidman inserted rollers between a wheel and its axle, effectively applying roller bearings to skate wheels. But Gidman was ahead of his time. He spent 30 years trying to get roller skates with roller bearings mass produced, with little success.
In 1876, William Bown's provisional patent application was allowed, titled "Improvements in the construction of wheels or rollers for roller skates and for other purposes". Bown placed a felt ring, lubricated with oil, between a wheel and its axle to attempt to reduce friction. But this was not substantially more effective, and required constant oil refills.
In 1877, Joseph Henry Hughes' provisional patent application was allowed, titled "Improvements in the bearings of bicycles and velocipedes or carriages". Hughes, a local of Birmingham, described a ball bearing race for bicycle and carriage wheels which allowed for initial adjustment of the system to ensure optimal contact between components, and for subsequent adjustments to compensate for component wear from use. As a successful owner of Bown Manufacturing Company, William Bown persuaded Hughes to sell rights to this patent to him, and to join him on further bearing innovations for the next decade. This led to the successful Aeolus brand of ball bearings, used in the first ball-race-pedals and wheel bearings for bicycles and carriage wheels. Similar ball bearings were subsequently adopted for use on roller skates.
In 1884, two US patents claiming the use of ball bearings in roller skates were issued one after the other. George Burton filed on August 17, 1883, and was granted a patent on November 11, 1884. Levant Marvin Richardson filed on August 6, 1884, and was granted a patent on December 9, 1884. Richardson was more successful in marketing his invention, eventually starting and growing Richardson Ball-Bearing Skate Company to make these skates.
Skates equipped with ball bearings further fueled the Plimpton 2x2 skate craze. Skate manufacturers operated rinks to promote roller skating during the boom period from 1880s through 1910s. Skates made for rink use were referred to as parlor skates or club skates.$^{:19–20,25}$ By 1910, Richardson Roller Skate Company competed with mainstream brands including Henley Roller Skates, Winslow's Skates, Baltimore Skate MFG Co, and Chicago Roller Skate Company.

### Further development of inline skates

Plimpton's two-by-two roller skates took the limelight starting in 1863 and held it for more than a century. But inventors and enterprises continued to bring new roller skates with a single line of wheels to the market, under Plimpton's shadow. For instance, in 1873, Peck & Snyder advertised "parlor or floor skates" with 4 rubber wheels in a single line. These skates had not yet incorporated ball bearings. They closely resembled skates advertised in 1861, which were based on Reuben Shaler's 1860 patent.
Early roller skaters were preoccupied with avoiding rolling backward. E. Edwards and H. Koerner patented heel brakes in 1893 that prevented a single-line roller skate from rolling backward. To brake, a rubber ball was jammed against a rear wheel covered with rubber tire. This skate did not claim its straps, ankle support, or two-wheel configuration, as those preexisted.$^{:6}$
Many single-line roller skates during this period had two wheels. In 1895, the Pneumatic Road Skate Company in London took out a full-page advertisement in the book Figure and Fancy Skating, showing a road skate with two wheels, each covered in hollow rubber tires modeled after bicycle tires. This skate closely resembled the skate shown in the Edwards/Koerner patent. Both provided similar ankle support that was popular at the time. These single-line skates were purported to allow easy turning of skates, without needing the rocking and canting mechanism from Plimpton's roller skates. They were advertised as "road" skates with ball bearings, and were hyped as having great military utilities for moving troops. The company performed a public demonstration before its public offering.
Across the Atlantic Ocean in America in 1904, Peck & Snyder Sporting Goods, which was acquired by A.G. Spalding & Brothers, advertised Racing Roller Skates with two wheels, each mounted with tempered steel ball bearings and supported by a rubber tire. These closely resembled the Pneumatic Road Skates design. However, the American versions replaced the ankle support with a strap, now known as the 45° strap in modern inline skates. Many companies produced similar road skates in this period, often called "automobile cycle skates", after the pneumatic tires. For instance, John Jay Young was granted patents for steel-tired wheels as early as 1872. However, by 1905 he was selling skates with pneumatic wheels instead. The Cycle Skate and Sporting Goods Company also sold these skates in 1906.
Another popular two-wheeled skate set the foot stand below the centers of wheels. This required that the wheels be placed in front of and behind the foot stand. In 1893, the first patent describing this design configuration was granted to A. Sherrif and R. Anderson. In 1899, Augustus Nichols Lindsley was issued the first patent for a telescopic stock for this type of skate, to accommodate different foot sizes. The design employed T-shaped tubing for the telescopic connections. In 1903, Benjamin S Peard filed a patent application on a wheel hub with spokes and fillets to reduce weight while still providing rigidity and strength. The Peard wheel was particularly suited for this skate design.
By 1906, Cycle Skate and Sporting Goods Co. began selling road skates that combined features from Sherif/Anderson (low foot stand), Lindsley (adjustable stock), and Peard (wheels with hub and spokes). In 1912, John Jay Young followed suit and began selling similar skates. These were marketed as "Automobile Road Skates" in 1913 and beyond.

### Precursors to modern inline skates

From the 1910s to the 1970s, many more variations of single-line wheeled skates were patented and manufactured. While still in the shadow of 2x2 roller skates, some of these started to gain popularity amongst ice hockey players, by the 1960s and 1970s, due to their better emulation of ice blades.
In 1925, the US patent office granted Chomin Harry of Canada a patent for a skate frame that gave each wheel axle dual purposes: 1) interlocking with the inner race of double ball bearings, as an axle, and 2) being threaded into one sidewall of the wheel frame, as a bolt. This enabled easy wheel replacement, and allowed an ice blade to be attached in place of the wheels.
In 1938, Christian Siffert secured a patent on a roller skate frame resembling 21st century inline skates, complete with a heel brake. The frame accommodated 3 wheels. This odd selection of wheel numbers was intentional and led to the patented claim. It allowed the frame to be economically cut from a single sheet of metal, where portions of sidewalls were repurposed into parts of toe and heel plates, leaving voids seen on sidewalls. This was one of the very few pre-Rollerblade frames where two sidewalls of a frame were permanently connected. The resulting single-piece frame was lighter, stronger and cheaper than previous designs. This skate was produced and sold by Siffert himself initially in 1941, by Best Ever Built Skate Co. (BEB) thereafter, and later as "Jet Skate" by AFCO Products Inc. in 1948.
In 1966, Gordon K Ware, one of the Ware brothers who founded the successful Chicago Roller Skate Company, obtained a patent for a skate with multiple frame segments that overlapped. In this design, wheel axles served a second purpose - that of securing overlapping segments through specific axle holes. This allowed the frame to adjust to various shoes and sizes. In addition, the front wheel and the rear wheel could be placed higher than the middle two, to create various rockered wheel setups for better turning. Wheels were mounted on double ball bearings. This skate could be customized for different needs from different sports, including figure skating, speed skating, and ice hockey.
The inspiration for this Chicago skate came from off-season training skates used by Russian speed skating teams in the 1960s. Barbara Lockhart of the US Olympic speed skating team brought a pair back to the US. Montgomery Ward commissioned 25,000 pairs of these, and advertised them in 1965 catalogs as excellent off-ice training tools for figure skating and ice hockey. The skate was sold under the name "Roller-Blade", coined by Joe Shevelson of the Chicago Roller Skate Co. Ladies' version came with high-cut leather shoes, and men's version medium-cut leather shoes. Montgomery Ward could not sell the inventory, so the skate was soon discontinued.
Up to this time, almost all roller skates were of the "clamp-on" variety - they were strapped to a skater's own shoes or boots. In his patent application, Ware instead described his skate as explicitly designed to be permanently riveted to any shoes a user desired to use. This borrowed from the ice hockey industry which, by 1908, routinely riveted ice blades to hockey boots, resulting in improved stability and performance for skaters.
In 1975, Morris (Maury) Silver received a patent on a "Tandem Roller Hockey Skate". The key claim of this patent was the single-unit nature of the skate, where a wheel frame was permanently attached to a hockey boot. Prior patents on roller skates did not claim a boot as part of the apparatus. In this patent, the boot was part of the "roller hockey skate". This skate was equipped with larger wheels than those in prior designs. The front wheel was positioned farther forward, and the rear wheel farther back, for enhanced speed and balance, as required for hockey. Both front and rear wheels can be shifted upward in their slotted mounting holes for a rockered wheel setup. The patent and drawings specified the use of roller bearings, when ball bearings had become commonplace by this time.
Silver developed his skate with his friend, Ralph Backstrom, a Canadian hockey player from the Montreal Canadiens. Backstrom briefly played for the Los Angeles Kings from 1970 to 1973, and would train off-season with this skate. Their company marketed the skate under the label Super Sport Skate (or Super Street Skate), as an off-ice training tool for ice hockey players.
Meanwhile, another roller sport, skateboarding, became popular in the 1960s. Avid ocean surfers adopted skateboards with rubber wheels during downtimes. In the 1970s, the increasingly popular sport of skateboarding reached new heights with the advent of polyurethane wheels and their superior performance. Some of these polyurethane skateboard wheels were in fact made by the Chicago Roller Skating Co.$^{:20–22}$
At the same time, in the 1960s, the ski boot manufacturer Lange launched the first molded plastic ski boots furnished with liners. Lange then entered the ice hockey market in the 1970s with similar plastic hard boots, gaining some success. These boots were rigid to provide proper support for aggressive hockey skating. Yet they featured soft inner liners to provide a comfortably fit, despite the use of hard shells. A pivoting cuff is riveted to the boot, allowing a player to forward flex.
Both polyurethane wheels and plastic hard boots would soon be borrowed for modern inline skating, to be combined with the best ideas from precursor skates, leading to the rise of Rollerblade in the 80s and its wide adoption by the general population.$^{:7}$

### Development of modern inline skates

For two centuries, inventors and entrepreneurs attempted to popularize skates with a single row of wheels. By the end of the 1970s, only Chicago Roller-Blade and Super Sport Skate managed to gain limited adoption for training, within a niche community of ice hockey players. It took Scott Olson, his brothers, his friends, and his company, Rollerblade, to perfect these skates, and to make them enjoyable as mainstream recreation for the general population.
In 1979, Scott Olson, an ice hockey player, stumbled upon the Super Sport Skate (or Super Street Skate). Fascinated by these novelty skates, he soon made a living promoting and selling them to hockey players in Minneapolis. As a licensed distributor, Olson traveled on these skates through the city and around the state in guerrilla marketing tours to promote the product. Scott Olson and his brother Brennan tinkered with these skates. They removed the wheel frames from Super Street Skate, and custom-fitted them to customers' old hockey skates for improved ankle support. Wearing plastic Lange boots thus retrofitted, Scott and his friend Mark Lipson skated for 200 miles from Minneapolis to Grand Rapids, MN, in a five-day marketing campaign.
Through tinkering, prototyping and road testing everywhere he could, Scott Olson eventually arrived at a design with an adjustable/expandable frame, polyurethane wheels and double ball bearings. The skate rolled faster, and remained more reliable on road surfaces. But a patent search turned up the Chicago Roller-Blade, which claimed many of his design features. In 1981, Olson persuaded the Chicago Roller Skate Company to give him the patent, in exchange for a percentage of the profit.
In 1981, Scott Olson created a company called Ole's Innovative Sports, and made manufacturing arrangements. Soon, he marketed his own "Ultimate Street Skates" (or Ultimate Hockey Skates), a skate of his own design attached to a hard boot with thick liners similar to the plastic Lange boots. By then, skateboards had adopted polyurethane wheels made by roller skate manufacturers, with standard ISO 608 ball bearings. Scott similarly adopted these roller skate wheels, shaving tens of thousands to fit them to his Ultimate skates. These skates came with a toe brake and had the now-familiar Rollerblade logo imprinted on them, which Scott and his friend designed.
In 1982, Scott Olson started to market his skates as a proper sport in itself, venturing out of the initial niche where they served as an off-season training tool for ice hockey. Scott organized Minnesota hockey players to fly east to play roller hockey teams in New York City, with his team skating on Ultimate Street Skates, and the NYC teams on traditional 2x2 skates. Scott also started to advertise his skates to the masses, in print and in person, as everyday fun activities, where one could "roll over large sidewalk craters without feeling them". Enthusiasts colloquially referred to these skates as "roller blades".
In 1983, Scott Olson marketed a new generation of skates with heel brakes instead of toe brakes, under the trademark "Rollerblade". His company grew from one worker in 1980 to 25 employees in 1985, selling many thousands of units that year. In the same year, the company published a book, Rollerblades: Dryland Training for Ice Hockey, edited by Chris Middlebrook, with chapters written by Randy Gregg, Jack Blatherwick, Laura Stamm, Brad Buetow, Scott Olson, and Brennan Olson. This is the first book that elaborated on the equivalency of inline and ice hockey skates with respect to hockey moves, and the first book that documented wheel rockering adjustments, wheel wear, and wheel rotations.
Around 1986, Ole's Innovative Sports was renamed "North American Sports Training Corporation" (NASTC). As the Rollerblade brand became more popular, the company was eventually renamed to Rollerblade Inc. around 1988.
In 1988, the company released Lightning skates with fiberglass-reinforced plastic frames. The Lightning TRS (Team Rollerblade series) with a cuff buckle was particularly successful, and turned "Rollerblade" into a household name. The company claimed to have up to 75% of the estimated $12 million market in 1988.
The Chicago Roller-Blade patent expired at the end of 1983. Eying the success of Rollerblade, competitors jumped into the race. Another Minneapolis firm, First Team Sports Inc., started manufacturing its Ultra Wheels skates in 1986. More manufacturers joined in, including Oxygen, K2 and Bauer. Then, the Super Sport Skate patent expired in 1992. This allowed even more inline manufacturers to produce skates without fear of infringement.
Rollerblade continued to dominate the market in the 1990s, in the face of competition. In 1990, it had 66% of the estimated $50 million global inline market. Sales peaked in 1996, leaving 1997 with a reported revenue of $106 million, or nearly 40% of the estimated market. According to Rollerblade, by 1997, 20 percent of American households had a pair of inline skates, and a 1998 survey found that 32 million Americans over the age of six had tried inline skates at least once that year.
Modern inline skates became practical for manufacturers to mass-produce, and enjoyable for the masses as a recreational sport, when technological advances such as polyurethane wheels, standard ISO ball bearings, and molded plastic boots arrived on the scene. These skates incorporate double ball bearings with dual-purpose axles from Chomin Harry (1925), single-piece frames from Christian Siffert (1938), adjustable wheel rockering from Gordon Ware (1966), single-unit boot/frame, longer frames and larger wheels from Maury Silver (1975), plus additional innovations.
Both Scott and Brennan continued to refine skates, each having been granted a dozen patent applications for skate-related innovations from 1982 through 1996.

### Rollerblade as a noun

From 1979 through 1990, when referring to his skates in patent applications, Scott Olson called his skates simply "roller skates", "street skates" or "hockey skates". "Rollerblade", as a trademark, was filed on July 25, 1984 with the USPTO, with a first use date of March 1983. But when promoting them in the early 1980s, "Rollerblade" was often used as a noun for this new type of skate, exclusively sold by Ole's Innovative Sports. For instance, the 1985 book edited by Chris Middlebrook and published by the company, was titled Rollerblades: Dryland Training for Ice Hockey, with a plural "Rollerblades". The Oxford English Dictionary dates the earliest printed uses of "Rollerblade" to the publication of the trademark in 1985 by the USPTO Gazette, and to this 1985 book.
By the late 1980s, Rollerblade, as a company, started to relabel roller skating of this style as "in-line", in order to preempt "rollerblading" from becoming a new verb. This was reflected in Brennan Olson's 1987 patent, which he titled "In-line roller skate with frame".
By 1990, newspapers and the media had generally adopted "in-line skating" as the name of this new recreational sport. In 1991, Rollerblade Inc. used "in-line" in the subtitle of its official guidebook Wheel Excitement: "Official Rollerblade® Guide to In-Line Skating". In the same year, "Rollerblade In-Line Skate Association" (RISA) was founded, but quickly changed its name to the International Inline Skating Association (IISA) shortly after.$^{:4}$
When comparing modern inline skates to the 2x2 Plimpton roller skates, enthusiasts referred to the latter as "quad skates". But the term "quad skates" never took hold among the masses.

## Anatomy and function

All modern inline skates share a common basic blueprint. A skate comprises a boot, worn on the foot. To the bottom of the boot is attached a frame, the most rigid part of the skate. The frame holds a number of wheels in place with wheel axles. In between a wheel and an axle are two bearings. Bearings allow a wheel to rotate freely around its axle. Finally, a rubber brake typically attaches to the frame of the right boot, on recreational skates.$^{:17–27}$$^{:14–39}$$^{:41–51}$
For many skaters, the frame is never removed or replaced. But wheels are consumables, as they wear down with use, and require periodic mounting rotations and even replacements.$^{:81–86}$ Inline skates usually come with a skate tool for wheel, bearing and frame maintenance. The tool will have a hex wrench or a Torx wrench for removing wheel axles from a frame, and wherever applicable, for removing bearings from a wheel, and for removing a frame from a boot.$^{:39–45}$$^{:39–51}$
In the 1980s and 1990s, all inline skates had hard boots, borrowed from ski boot designs. A removable liner in a hard boot provides a snug yet comfortable fit between a skater's foot and the hard shell. Around 1996, K2 introduced soft boots with an exoskeleton. These provide the most comfortable fit, at the expense of reduced rigidity. In the 2010s, hybrid (soft) boots with an endoskeleton were introduced to the high-end market. A hybrid boot has an integrated, non-removable liner. This is glued to a rigid endoskeleton shell integrated with the sole, providing direct power transfer from the foot to the wheels.$^{:142}$
All three types are able to secure a foot in them without slack, with proper closure systems. Soft boots are often laced, and hard shells are usually secured with buckles. Velcro straps are also common in all types of boots. Well-designed boots provide proper heel support and ankle support to a skater.$^{:14–39}$$^{:47–52}$$^{:142}$
The length of a frame positively affects stability and negatively affects turning agility. Longer frames accommodate more wheels, and taller frames larger wheels; both positively affect top skating speed. Modern inline skates are equipped with polyurethane wheels. Harder wheels are suitable for smooth indoor surfaces, while softer wheels are more comfortable for rough outdoor surfaces. Beginners skate with all wheels touching the ground, for enhanced stability, known as a "flat" wheel setup. Advanced skaters may choose to configure wheels in a "rockered" setup for enhanced maneuverability. The weight of a skate is an important consideration for some disciplines. Lighter boots, frames, and wheels are preferred. However, weight reduction is only achieved with escalating costs and diminishing returns.$^{:14–39}$$^{:19–33}$

### Heel support

Heel support refers to the ability of a boot to keep a skater's heel comfortably seated and firmly locked down in the heel pocket of the boot, even during aggressive maneuvering.
A heel pocket is formed by the shell, inner liner and sole of a boot. A properly-designed boot has a heel pocket that hugs the heel, with an anatomical contour. A proper closure system causes the "facing" (where eyelet tabs are) to push the instep against the heel pocket, preventing the foot from shifting or lifting during maneuvers. As a result, the heel remains in contact with the footbed at all times.$^{:15–18}$
Proper heel lock serves as a stable foundation for the entire foot. It allows a skater to adopt an athletic stance for skating by flexing the lower leg forward, without raising the heel. A snug fit means reduced movement of the foot within the skate, and thus reduced opportunity for friction to cause blisters. At the same time, the whole skate becomes transfixed to the foot as an extension of it, allowing efficient strides with a faithful transfer of power from the foot to the ground.$^{:35–36,79–80}$

### Ankle support

Ankle support refers to the ability of a boot to prevent sideways movement of a skater's ankle and lower leg, while allowing the shin to flex forward into an athletic stance. In some skates, such as recreational and aggressive skates, this is achieved via a hinged cuff. In other skates, such as hockey skates, this is enabled by rigid, and anatomically-shaped quarter panels that lock both ankle bones in place, from two sides, leaving the shin to freely pivot forward.$^{:5,15–18}$
Proper ankle support allows a skater to keep a skate upright as a straight extension of their entire leg, when observed from the front. Without rigid support on both sides of the ankle, the foot may wobble within the boot, causing the skate to tilt inward or outward. This creates pronation, making it harder for a skater to glide on a single skate at best, and resulting in sprains and other injuries at worst.
A properly-designed boot does not hinder the mobility of the ankle joint, allowing a skater to pivot the lower leg (the shin) forward, adopting a squatting (athletic) stance. This forward flex (or forward leaning) is known as dorsiflexion of the foot. It places the center of body mass atop the ball of the foot, a balancing skill crucial to most skating moves. Without such a squatting stance, the leg and the skate form a 90° angle, placing the entire body weight of a skater on the rear wheel of the skate. This is dangerous for a beginner because a small backward shift of the upper body will cause a skater to pivot their entire body on the rear wheel, and thus fall uncontrollably backward.$^{:67–77}$$^{:57–59}$

## Types

There are a variety of ways to design and make modern inline skates. Different types of inline skates reflect needs specific to different inline skating disciplines, such as recreational skating, urban skating, roller hockey, street hockey, speed skating, slalom skating, aggressive skating, and artistic inline skating.
However, skates are not equivalent to disciplines. Often a particular type of skate can be used in several disciplines, with varying degrees of efficiency and comfort. For instance, when specifically-designed skates are not available for freestyle slalom skating, a skater could use recreational skates, aggressive skates, hockey skates, or even speed skates. But some of these alternatives are more suitable for slalom skating than others. Hockey skates, in particular, most closely meet the needs of slalom skating, due to the shared requirement for rigorous turning and edging maneuvers in both roller hockey and slalom skating.$^{:31–32}$$^{:15–19}$$^{:140–142}$
In some cases, a skate launches a whole new discipline. For instance, the Rollerblade Lightning TRS has been widely credited for enabling aggressive inline skating as a sport, with its durable boot and nylon-reinforced frame, suitable for skaters to perform grinds on street obstacles.$^{:134–138}$
Disciplines and skates continue to evolve over time. In 1985, Roller Zetra wheels were advertised as much faster than the Pro-line wheels.$^{:81,84}$ But by 1988, 64mm Rollerblade Zetra 100 and BladeRunner wheels had become the slower wheels, compared to faster, larger, and higher-end Lightning wheels, now at 70mm in diameter. Around 1995 to 1999, a normal wheel size for recreational skates was 70-72mm, and large wheels for speed skates meant 78-82mm.$^{:20–21}$$^{:22–24}$$^{:315–316}$ By 2024, the standard wheel size for recreational skates had increased to 80-84mm, and large wheels for speed skates ranged from 90mm to 125mm.
For simplicity in advertising, manufacturers and resellers generally classify inline skates based on disciplines. Some types named this way are significantly distinct from one another, with their own unmistakable features. For instance, "aggressive skates" have signature soul plates and H-blocks (or grooves), for grinding on urban street and skatepark obstacles. "Speed skates" have low-cuff boots with long frames and large wheels, for gaining absolute top speed. "Hockey skates" have reinforced quarter panels instead of hinged cuffs, for better ankle support.$^{:30–38}$
Some disciplines are not large enough to warrant their own classification. Thus, dissimilar disciplines with similar equipment needs are grouped under a single skate category. For instance, freestyle skating, slalom skating, wizard skating, city commuting, and urban skating may be crammed into a single "urban skates" category.
Then, there are the rest of skaters who casually skate, skate for fitness, or skate for cross-training. These purposes constitute 90% of actual inline skate sales. Skates suitable for these activities are often grouped together as "recreational skates". Some makers instead call them "fitness skates". Others split them into two or more categories: recreational, fitness, and cross-training. Usually, the fitness and cross-training categories reflect increasing cost and thus quality of skates.$^{:90–105}$$^{:30–38}$$^{:30–32}$

### Recreational skates

Recreational skates constitute 90% of the inline skate market. The label recreational encompasses not only casual recreational uses but also fitness skating, which involves more frequent skating over longer distances, and requires more robust and efficient skates. Often the recreational skates category also caters to cross-training needs, with even hardier boots and frames, plus a wider range of options for wheels, among other features. Boundaries between these disciplines are blurry, with manufacturers and resellers marketing their skates in inconsistent ways.
This category can be better understood as "unspecialized" inline skates, or generic skates. All other types of skates can be thought of as specialized deviations from this basic type. Recreational skates usually come with four wheels of average size, and a frame of average length, which is just slightly longer than the boot. This places the front wheel halfway ahead of the toe box, and the rear wheel halfway behind the heel pocket, a design that remained unchanged since Scott Olson's adoption of Super Sport Skate from 1979.
Recreational skates are the default type of skates that a beginner finds comfortable and stable to skate on. The cheapest skates fall under this category. They are not necessarily of lower quality; they are simply mass-produced. As a beginner progresses, more expensive recreational skates are available with the same unspecialized characteristics, but now upgraded with more durable materials and hardware, possibly providing improved heel support, ankle support, and an enhanced skating experience. For instance, soft boots with an exoskeleton are usually the least expensive. Hard boots with removable liners are often priced higher. Hybrid boots with an endoskeleton are high-end models. Often, the higher-end models are marketed as fitness skates or as cross-training skates.
Recreational skates are equipped with heel brakes. These allow beginners to learn to stop rolling, with a simple pivot of a foot on its heel. Heel brakes can usually be removed once a skater learns to stop rolling without them, using a skating move such as the T-stop.$^{:25–26,44–45,52–57}$$^{:87–96}$
Casual skaters and fitness skaters can be seen rolling alongside a creek, a lake, or a park on paved bike paths. Some also take to the streets, skating on bike lanes and paved roads.$^{:131–135}$

### Aggressive skates

Aggressive skates are the most specialized inline skates, in contrast to recreational skates. They are designed for one specific purpose only: grinds. Grinding is the art of sliding on street obstacles such as stairs, rails, benches, curbs, ramps and walls. To support a skater performing these stunts, aggressive skates are built with strong hard boots based on ski boots, as Olson originally did with his Ultimate Street Skates. These are bolted to thick frames which are fitted with the smallest wheels in all of inline skating. The smaller wheels bring the boot closer to the ground, making tricks and grinds easier to perform. To help a skater lock onto an obstacle of interest during a grind, an aggressive skate provides channels and surfaces such as H-blocks, frame grooves, backslide grooves, grind plates, soulplates, etc. Transitioning between these stunts, a skater often jumps considerable heights, or rides down a long flight of stairs (known as stair bashing). Thus, aggressive boots are often fitted with shock absorbers to dampen shocks upon landing.$^{:134–163}$$^{:33,156–168}$
Aggressive skates co-evolved with the discipline which started as inline stunts. It then turned into streetstyle skating, and finally into aggressive inline skating.
Soon after the Rollerblade Lightning TRS was released in 1988, skaters experimented with extreme stunts on inline skates. Many took the axle wrench that came with Lightning TRS, and bolted it onto the frame as a makeshift grind plate. In the early days, frame grooves were formed on frames by the continuous grinding of frames on street obstacles.$^{:137–138}$ Inline skating books published on or before 1995 treated the discipline as stunt skating or street-style skating, following nomenclature from skateboarding. The word "street" in street-style meant that skaters performed tricks on and over street obstacles.$^{:98–110}$$^{:6,64–77,170–174}$
In 1993, the movie Airborne came out, showcasing streetstyle inline skating to an entire country. In 1994, the video The Hoax: An Inline Crime was released by T-Bone Films, featuring icons such as Chris Edwards, Arlo Eisenberg, Chris Mitchell, Jess Dyrenforth, Pat Parnell, and others. Both videos inspired a new generation of young aggressive skaters.$^{:134–136}$ While skaters were still custom-modding their skates for aggressive skating, the Aggressive Skaters Association (ASA) was formed in 1994. Shortly after, ESPN X Games adopted aggressive inline skating in 1995 and ran aggressive competitions for 10 years, cementing the discipline.
Over time, aggressive skates evolved to incorporate even more mods by skaters. The frame walls were thickened to provide rigidity, and to allow skates to be inclined further during grinds, without incurring wheel bites. Frame grooves became a standard, and H-blocks were integrated. The two middle wheels were spaced farther apart, creating a larger split between these two wheels, to enhance grinding experiences.$^{:151–152}$
In 1996, Roces M12 (Majestic 12) was launched, with small wheels, a boot closer to the ground, a large gap between two middle wheels, and an H-block. Soon, the M12 became synonymous with aggressive skates. In 1997, makers such as USD introduced integrated soulplates (also soul plates, from sole plates), providing a platform for soul grinds using the bottom of the boot, rather than the frame. Backslide grooves were eventually introduced, to allow even greater skate inclination during grinds. By 2003, the soulplate became a single-piece, flat platform in Roces M12, with an even wider boot bottom to further enhance soul grinding. From then on, inline skating books dedicated entire chapters to aggressive skates and skating.$^{:156–168}$
In 2001, aggressive skate manufacturers standardized on UFS (Universal Frame System), the first replaceable mounting standard for inline skates. Most UFS frames accommodate small wheels up to 60mm. Some aggressive frames with frame grooves and H-blocks are designed with thick walls to prevent wheel bites. These frames can be used with a flat wheel setup, where all wheels touch the ground. Other frames without prevention measures against wheel bites can be set up with an anti-rocker wheel configuration. The second and third wheels are replaced with even smaller "grindwheels" (or "antirockers") made of hard plastic that are resistant to wheel bites. Some skaters go one step further, eliminating the two inner wheels altogether. Instead of wheels, "juice blocks" are installed to keep the structural integrity of the frame walls.
Aggressive skates come with no brakes. It is assumed that skaters are able to stop without brakes, as they grind on street obstacles (termed street skating), perform stunts at skateparks (termed park skating), and take to the air at the top of ramps (termed vert skating). Brakes only hinder aggressive maneuvers.$^{:33,156–168}$
The name "aggressive" has been controversial outside the core community of aggressive skaters. Even within the core community, debates continue to this day on alternative naming. Many in the community call aggressive skating rollerblading (or simply blading), and thus members bladers. Others call it aggro.$^{:134–163}$ Some skate manufacturers eschew the label "aggressive", choosing to market their aggressive skates instead as street skates or park skates. For instance, Rollerblade Inc. called this discipline "extreme skating" in its 1991 official guidebook, Wheel Excitement.$^{:98–110}$ Even after the aggressive competitions from X Games in 1995, Rollerblade Inc. continued to call it "extreme skating", in its 2000 book: Superguides: Inline Skating.$^{:40–41}$ The company marketed these skates as "Street Skates" all these years, to this day, almost 30 years after the X Games.

### Hockey skates

In the 21st century, skates for inline hockey (roller hockey) use a construction process for the boot that differs significantly from other inline skates. They are mainly made by ice hockey manufacturers such as CCM, Bauer (Mission), True, Marsblade, etc.$^{:37–38}$ In many instances the same boots are fitted with a blade holder for ice hockey, and an inline frame for roller hockey. As a consequence, inline hockey skates continue to use the same rivet-based mounting system from ice hockey. This is unlike other inline skates which have largely moved on, now adopting standard mounting systems such as UFS, 165mm, 195mm and Trinity, with replaceable frames for all but entry-level skates.
Hockey frames, wheel choices, and wheel setups reflect the specific needs of the game. Hockey skates adopt some of the shortest frames in all inline skates, to allow a player to turn hard on a dime, and to do crossovers unhindered. Hockey boots are kept as low to the ground as possible, only allowing their frames to accommodate smallish wheels, in order to deliver the best stability for hard edging maneuvers. The largest wheels used are 80mm which would be the smallest ones found in recreational skates. Wheels with a rounder profile are preferred, to support sharp edging and turning, without the skate sliding out from under a player.$^{:37–38}$$^{:19–24}$
Hockey skates often incorporate a hi-lo wheel setup through the deliberate use of wheels with different diameters (e.g. 80-78-76-74mm), or by having its frame explicitly support such setup (typically 80-80-76-76mm). A hi-lo setup places larger wheels at the rear, and smaller wheels in front, while all wheels touch the ground. This raises the heel higher, and pushes the toe cap lower, thus the name hi-lo. It causes a player to forward flex naturally, for greater stability and stronger strokes.
Inline skates started as a wheeled equivalent of ice hockey skates, when Olson adopted molded plastic hockey boots that Lange just introduced to the ice hockey world. This type of hard boot construction, with a pivoting cuff and a removable liner, as typified by the 1988 Rollerblade Lightning, evolved into many types of inline skates over four decades. Yet ironically, neither ice hockey nor roller hockey ended up adopting hard-shell boots nor hinged cuffs.
The rigor of a hockey game requires that inline hockey skates be made as lightweight as economically possible. At the same time, these skates must deliver superior heel support and ankle support. In addition, power transfer from foot to wheels needs to be direct and instantaneous. Traditional inline hockey skates achieve these by creating an unyielding wall, with anatomical contours that hug the heel and both sides of the ankle. This wall is known as a quarter package comprising left and right quarter panels, and it is bolted to a rigid outsole platform. The wall and its connection to the outsole is reinforced, often with an injection-molded thermoplastic piece sewed into the wall, and then nailed, tacked or glued to the outsole.
The rest of the boot is built around the quarter package, with a thick tongue to support the shin for an aggressive athletic stance, along with an reinforced toe cap. The entire boot is thus designed to protect a foot from flying pucks. The boot is furnished with an integrated and non-removable liner with varied thickness at places, to further deliver an anatomical fit. Hockey skates use eyelets and laces, not buckles or straps. Players often use waxed laces which stay unyielding around eyelets, to selectively tighten certain eyelets and loosen others, based on needs. Usually the toe area is laced comfortably, the middle eyelets are laced tight for proper heel lock, and the upper eyelets loose for ankle mobility (forward flex).$^{:1–3}$
Thus, traditional hockey boots are not hard boots with removable liners. They are not soft boots with an exoskeleton. Traditional hockey boots may be constructed in a fashion similar to hybrid soft boots, but they are not soft anywhere, and eschew hinged cuffs for contoured quarter panels. Hockey boots are in a class of its own.

### Speed skates

Speed skates (or race skates) are purpose-built inline skates with a single goal: speed. To this end, speed skates need to enable a racer to generate the most efficient strides and to glide with the least amount of friction. The distance for a race ranges from a few hundred meters to 100 kilometers. And a race may take place indoors on tracks, or outdoors on paved roads. World records for outdoor races exceed 27 miles per hour. For instance, Joey Mantia holds the world record for the outdoor 10-kilometers race from 2009, at 13 minutes and 46.801 seconds.$^{:3–9,283–318}$
Speed skating differs from other inline disciplines in that a speed skater tilts her body trunk forward for up to 60° when racing, positioning her head far ahead of the skates in order to reduce her body profile with respect to air resistance. A speed skater bends her knees aggressively for up to 80° in a deep-seated squatting position, much more than other disciplines. Such body configuration requires a deep forward leaning of the shin (dorsiflexion) for proper balance. This deep squatting posture produces the most powerful push-offs, with the farthest displacement of the pushing skate.$^{:5–11}$
Because of the need for a deep dorsiflexion, speed skates have no eyelets, buckles, or straps above middle eyelets at 45° angle which is the minimum requirement for proper heel lock. Indeed, speed skates have no shafts and cuffs commonly found in other inline skates. In order for racers to freely flex their foot around ankle bones, speed boots are cut the lowest among all inline skates, around or below the ankle bones.
A skater compensates for the lack of lateral ankle support from boots by strengthening muscle support for proper ankle movements such as dorsiflexion, pronation and supination, which are essential for double push strides with aggressive push-offs and precise transitions from outside to inside edges. The removal of shaft and cuff significantly reduces a boot's weight, a key advantage to a skater in a game where a saving of fractional seconds makes a difference.$^{:75–79}$$^{:17,34–36}$$^{:3–30}$
A speed skate boot is close-fitting, without much padding, and usually made of leather, carbon fiber, or other strong and lightweight composite materials. For best performance, the boot must conform closely to the shape of the foot to prevent it from moving inside the boot. Thus, most boots are custom-fitted or else heat-moldable.
The frame may be made of aircraft-quality aluminum, magnesium, or possibly lightweight carbon fiber. All frames flex during skating. A stiff frame flexes very little, so it transmits power from the foot to the wheels more directly. A shorter frame navigates tight curves at smaller tracks better but may become wobbly at high speeds. A longer frame provides stable tracking at high speed and increased power transfer, useful for long-distance events.$^{:311–314}$$^{:18–20}$
The length and height of a frame determine the number and size of wheels it can accommodate. More wheels and bigger wheels increase mass, making acceleration harder and slower. But once rolling at speed, a skater can more easily maintain top speed given the rotational inertia. In the 1990s, speed skaters preferred a frame with five wheels, usually 80mm in diameter (i.e. 5x80mm). In the 21st century, wheel size ranges from 90mm to 125mm. A setup with four 110mm wheels (4x110mm) is typical for competitive speed skating, and three 125mm wheels (3x125mm) for marathon skates at marathon events.$^{:311–314}$$^{:22,24,34–36}$
Speed skates generally adopt either the 165mm or the 195mm mounting standard for securing a frame to a boot. Short speed frames for short track racing use the 165mm standard, while long frames for marathon use the 195mm standard in order to better accommodate larger wheels. Both of these 2-point mounting standards feature a built-in heel lift that pitches a skater forward, creating forward flex.
Speed skating generally adopts harder wheels than other disciplines. Harder wheels minimize energy lost to elastic hysteresis when a skater's weight deforms wheels upon ground contact. Speed skaters prefer wheels with high rebound, which returns the compression energy back to the skater. Speed wheels have a pointy bullet profile that reduces friction from drags, when a skate glides and its wheels touch the road upright. The elliptical profile, however, affords greater contact surface for improved traction and control, when a skate is inclined on an edge during push-offs.$^{:18–19}$$^{:51–52}$$^{:316}$$^{:24–26}$
Speed skaters pay close attention to the quality of ball bearings and their periodic maintenance. High-quality bearings with precision ratings are the minimum requirement. Regular cleaning and lubrication of these bearings remove trapped dirt and restore them to their optimal performance, which is essential in the pursuit of ultimate speed.$^{:128–130}$

### Urban skates

Urban skate is an umbrella term created by the industry to describe a type of skate suitable for several niche inline disciplines: freestyle skating, slalom skating, wizard skating, city commuting, and urban skating. These activities take place on relatively flat ground, but the surface may not always be paved or smooth.
Freestyle skating is named after its counterpart in skateboarding, just like aggressive street, park, and vert skating are named after street, park, and vert skateboarding, respectively. Freestyle skating is the art of performing skating tricks on relatively flat ground, free of obstacles. Freestyle slalom skating is a form of freestyle skating where tricks are performed around slalom cones. This is standardized by the International Freestyle Skaters Association (IFSA) and World Skate as freestyle slalom to distinguish it from speed slalom, which is a form of speed skating around cones on flat ground. Freestyle skating requires skates that support rigorous turning and edging maneuvers, with characteristics similar to hockey skates. A rockered setup with 76-80mm wheels on a relatively short frame is common for freestyle skating.$^{:15–25}$
Urban skating and city commuting take the activity to the street. But the term 'street skating' is already taken as a subdiscipline of aggressive skating, for grinding on street obstacles. Thus, this niche market is variously promoted as skating on paved roads or commuting to work on skates. These activities demand longer frames and larger wheels for higher cruising speed, stable tracking, and more comfortable rides on uneven surfaces, similar to speed skates for marathon events. Common wheel setups include 4x80mm, 4x90mm, 4x100mm, 3x100mm, 3x110mm, and 3x125mm.
In terms of skate construction, urban skates overlap with the high-end segment of recreational skates. A hard shell is standard for urban skates. Higher-end models feature hybrid boots with carbon composite shells (endoskeleton) that are heat-moldable. Despite sharing some design goals with hockey skates and speed skates, urban skates are not built like them. Unlike speed skates, urban skates provide strong ankle support with traditional hinged cuffs. Unlike hockey boots, urban boots are not built around a quarter package, nor do they have frames riveted onto them.
Indeed, most urban skate boots support either the 165mm two-point or the Trinity three-point mounting standards, allowing a skater to mount a variety of compatible frames to a boot that best fits them. The same boot can thus be customized with a short frame and average-sized wheels for slalom skating, or with a long frame and large wheels for long-distance road skating.
Both the 165mm and Trinity standards have their heel mounting platforms raised higher than their toe mounting platforms. This difference in height between the raised heel and the lowered toe is known in the shoe industry as a heel-to-toe drop. Such a drop causes a skater to lean forward by default, simulating a slight forward flex. This is similar to the purpose of the hi-lo wheel setup in hockey skates.
Wizard skating is named after the company Wizard Skating, founded by Leon Basin in 2014. Leon and his aggressive inline friends from @Mushroomblading popularized this new form of skating. Leon himself performed flowing footwork from freestyle, slalom, and figure skating while blazing through roads, rolling over curbs, skating up ramps, bashing down stairs, and parkouring on walls. Leon perfected a type of "Wizard" skate for this sport, featuring a long frame, large wheels, and a rockered wheel setup. For a skate size of EU43, these Wizard skates are available with either a 4x100mm or a 5x80mm setup.
Wizard frames utilize the UFS mounting system from aggressive skates. Wizard frames are thus not compatible with other urban boots where 165mm and Trinity mounting systems dominate. Unlike the flat aggressive frames from which UFS originated, a Wizard frame does include a built-in heel-to-toe drop, similar to 165mm and Trinity systems.

## Boots
### Hard boots

Hard boots dominated the inline skate market in the 1980s and 1990s at the inception of modern inline skating. They are made of plastic, fiberglass, carbon fiber, or other solid materials. A removable liner in a hard boot provides a snug yet comfortable fit between a skater's foot and the hard shell.
Hard boots use a combination of velcro straps and plastic buckles as closures. Some also use laces for the facing of the boot, while others have a front strap (or buckle) instead of or in addition to laces. The front lace and top buckle secure the foot inside the boot. To achieve proper heel lock, the liner is shaped to fit the heel, and the 45° strap (or buckle) presses the instep of the foot against the contour of the liner.$^{:15–18}$
Hard boots have a high cuff (or shaft) to provide proper ankle support. In order to accommodate dorsiflexion, the cuff is made to pivot near the ankle bones. As a skater leans their shin forward, the hinged cuff rotates to follow the lower leg while continuing to provide lateral ankle support.$^{:15–18}$
Molds used in plastic injection molding are expensive to make. As a result, plastic hard boots are usually available only in so-called "dual sizes". One hard shell is made for two US and EU shoe sizes (e.g. US 9-10, and EU 42-43). A thicker liner is provided for US 9 and EU 42 to fill the gaps, while a thinner liner is provided for US 10 and EU 43. Some manufacturers offer "dual fit" liners, where the same liner can accommodate two shoe sizes using elastic parts, memory foam, and other compressible space-filling materials.$^{:15–18}$

### Soft boots

K2 introduced soft boots to inline skating in 1993 with its Exotech line of recreational skates, marking the company’s entry into the sport. Building on this innovation, K2 later released the legendary K2 Fatty, an aggressive skate featuring the same soft-boot design. Since then, similar soft boots have come to dominate the recreational skate market.
They are akin to hiking shoes, made of textiles, mesh, neoprene, and other soft materials. Liners are integrated into the soft boot, and are thus not removable or replaceable. A soft boot is reinforced in strategic areas with a plastic exoskeleton for structural support.$^{:15–18}$
A soft boot uses a pivoting cuff to support the lower leg, like hard boots. Otherwise, its exoskeleton covers only a small area of the foot. This allows the boot to provide superior airflow through its fabric for moisture extraction, to keep the foot cool.
Soft boots use closure systems similar to those of hard boots. These include laces, velcro straps, and buckles. These include laces, velcro straps and buckles. Lacing the front of the boot is key to securing the foot within the boot, due to the lack of exoskeleton support in this area. On the other hand, the flexible front of the boot readily accommodates different shapes of foot. Soft boots thus provide a more comfortable fit at the expense of reduced rigidity and support, making them suitable for beginners and casual skaters. Committed enthusiasts, however, generally avoid soft boots due to their lack of direct and immediate response to skating moves, which is caused by elastic hysteresis.
Soft boots are lighter and generally less expensive than hard boots. They are easier to make for specific shoe sizes, compared to hard boots. Unlike hard boots, which usually come in dual sizes, soft boots are available in half sizes for US shoe sizes (e.g., US 9.5, 10 and 10.5), and even for some EU shoe sizes (e.g., EU 39.5, 40 and 40.5).$^{:15–18}$

### Hybrid boots

Hybrid boots, also known as hybrid soft boots, look superficially similar to soft boots, complete with soft materials covering a large part of the boot. Unlike soft boots, however, hybrid boots have no exoskeleton reinforcement apart from the pivoting cuff. These boots have an endoskeleton instead, in the form of a composite shell. The shell serves as the sole of the boot, with shell walls extending upward from the sole. The soft upper part of the boot is pulled taut over the shell and glued onto it.
Hybrid boots are lighter than hard boots and soft boots. Yet they remain rigid where the foot meets the boot. Integrated liners in hybrid boots can be made thinner than removable liners in hard boots. In higher-end hybrid boots, the integrated liner is heat-moldable for the best custom fit, and the shell is made of carbon fiber. A hybrid shell sits much closer to the foot than a hard shell or the exoskeleton of a soft boot. As a result, hybrid boots provide more direct and responsive power transfer from a foot to wheels.
Hybrid boots trace their origin to carbon shell development in speed skates of the 1990s and 2000s. Powerslide is a manufacturer offering hybrid inline skates in the 2020s, including Hardcore Evo, Tau, and Swell. However, the label "hybrid" is not yet universally embraced. These boots are often marketed as high-end soft boots.

### One-piece carbon boots

One-piece carbon boots were developed for speed skating in the 1990s. These are boots built around a carbon fiber-reinforced composite shell, where the shell almost completely surrounds a foot. After eyelet holes are punched out of a shell, the shell is usable as a functional boot if laced.
In the 21st century, hockey skate makers began to experiment with composite shells inspired by these advances in speed skates. For instance, in 2004, Easton Sports filed for a patent on an "unitary shell" made from fiber-reinforced resin, with sections of integrated walls arising from the sole. Easton's Synergy 1300C came out in 2005, with a unitary shell made with carbon and aramid fibers. This is widely recognized as the first retail hockey skate with a composite shell.A rigid shell exacerbates inherent conflicts arising from key design goals for a hockey skate: being lightweight, economical, a firm support structure comprising an outsole and a quarter package, and lastly, fitting this support to the different foot shapes of individual players. The fitting issue can be mitigated by adding a layer of heat-moldable materials to the quarter package, such that a player can finish the final molding process of a boot at a skate shop or at home. Heat molding became possible in 2006, with the Easton Synergy 1500C.
Other hockey makers take it one step further, creating a single, unbroken composite shell that also incorporates the "facing" portion where eyelets are located. These one-piece monocoque shells are almost usable by themselves as functional skate boots, if laced and mounted with inline frames. With the advent of "one-piece" shells, the traditional hockey boot construction is now known as employing a two-piece shell, comprising a quarter package attached to an outsole. A heat-moldable monocoque shell requires no breaking-in, unlike traditional hockey skates. All tuning needs are done by baking skates in an oven before wearing them, as often as needed.
The use of monocoque shell in hockey skates traces back to Scott Van Horne who started to make and sell custom composite speed skates in the 1990s. He incorporated VH Footwear in 1999, and made custom speed skates in the 2010s. Van Horne worked with Dave Cruikshank to file hockey skate patents in 2009 and 2011, on a composite shell and removable tongue / tendon guard. This shell foreshadowed that used in inline skates with a hybrid soft boot in the 2020s, and became the basis for the retail MLX Skate released in 2010 by Cruikshank's new company. Easton Sports bought MLX in 2011, and worked with Cruikshank to release a new Easton Mako skate in 2013, based on the MLX Skate. Easton was later acquired by Chartwell Investments which subsequently sold it to Bauer.
By then, Van Horne had gone back to perfecting custom speed skate boots. In 2012, he created tooling and a process to 3D-scan a skater's foot, and to 3D-print a custom last based on which a speed skate boot is shaped. By 2015, VH Footwear had adopted the same tooling and process for hockey skates, filed a patent application, and marketed them under the brand VH Hockey. True Temper Sports bought VH Hockey in 2016, and started to mass produce retail hokey skates with heat-moldable monocoque shells, as well as scaling up 3D scanning of feet at retail stores for custom True hockey skates, leading to inline hockey skates such as the TF9 Roller Skate, and the TF Pro Custom Roller Skate in 2020.

## Frames

An inline frame is also known as the chassis in some disciplines, notably hockey. A frame interfaces with the ground via wheels mounted on it, and with the foot through the boot.
Frame length, also known as wheelbase, refers to the distance between the centers of the first and last wheel axles. Several factors influence the choice of frame length. The number and size of wheels determine the minimum wheelbase required for a given wheel setup. In disciplines like hockey and slalom, skaters use short frames with closely-packed wheels to enhance maneuverability and enable fluid footwork. In contrast, speed skating relies on longer frames, which space out the wheels to provide greater stability at high speeds. Ideally, frame length should be proportionate to the skater's boot size for optimal control, stability, and safety. However, some skates use a one-size-fits-all frame across multiple boot sizes, which can compromise performance.$^{:18–24}$
Frame height, deck height, and ride height are related but loosely defined terms in inline skating. All three describe how low a boot can be positioned relative to the ground in a given setup, considering the number and size of the wheels. Ideally, a skater wants the boot as close to the ground as possible, while allowing enough clearance between the sole and the wheel tops for free rotation. For example, with four 80mm wheels in a flat setup, the boot should ideally sit just above 80mm from the ground. A lower center of gravity enhances control and stability. However, factors like frame thickness, mounting platforms, bolts, and other design elements often raise the boot higher than desired.$^{:311–314}$$^{:18–24}$
The term deck height sometimes refers to the distance from the frame's deck (i.e. mounting platform that the sole rests on) to the wheel axle center, excluding wheel size. In other cases, it is defined as sole-to-ground distance, incorporating both the structure of a frame and of actual wheel size. Adding to the confusion, some sources use ride height or frame height interchangeably for either of these measures. For UFS frames, which have two mounting points at the same height, a single deck height value suffices to describe the sole-to-axle distance. However, for 165mm and Trinity frames with a built-in heel lift, deck height must be specified as "front" or "rear." Notably, in Trinity-mount skates, "front deck height" does not measure the sole-to-ground distance. The two front mounts are positioned alongside the front wheels, allowing the ball of the foot to sit nearly as low as the wheel tops.
Frame rigidity is essential for an efficient transfer of power from a skater's foot to the ground—a rigid frame does not suffer from elastic hysteresis.$^{:18–21}$ For this reason, even entry-level inline skates now use fiberglass-reinforced plastic, instead or softer but cheaper plastic to make frames. For a stiffer yet lightweight frame, aircraft-grade aluminum alloys such as the 6000 and 7000 series are used. Hockey and speed skating often call for magnesium frames, which are even stiffer and lighter than aluminum. Some speed skaters use carbon fiber frames that are the most rigid and lightweight frames available.$^{:23–24}$

### Frame materials and rigidity

In general, stiffer frames require more expensive materials and manufacturing processes. The cheapest options are plastic frames, which are injection-molded with PVC, polypropylene, polyurethane or nylon. These are soft and flexible, thus not suitable outside of low-end skates. Fiberglass-reinforced plastic is more rigid, and is widely used in recreational frames.
Metal frames are produced from aluminum, magnesium and titanium alloys using a variety of processes. Folding a metal sheet is the cheapest option, resulting in a frame less rigid compared to other processes. Die casting is a step up from folding, but the resulting frame is more brittle. Extrusion followed by finishing milling is much more expensive, but produces a very rigid frame. The most expensive option is to run computer-controlled milling (CNC) on a block of metal, called a billet, and carve a frame out of the block.
Rigidity of a frame is an important factor in choosing one. However, other considerations, including cost and weight, also influence the decision. Sometimes, a discipline's needs trump many of these factors. For instance, aggressive skaters exclusively use fiberglass-reinforced plastic frames for their superior performance and consistent friction when grinding against all types of surfaces.$^{:19–20}$$^{:138}$ Some of the most rigid frames, such as those made of carbon fiber, can be too brittle for hockey. These frames shatter rather than deform under impact or extreme stress due to their low fracture toughness. In addition, some skaters value comfort, which is at odds with rigid frames; increased rigidity transmits all imperfections of the road surface to the skater unattenuated, reducing comfort.

### Rockerable frames

Wheel rockering can be achieved by using wheels of different diameters, or by using a frame with built-in support for a rockered arrangement of identical wheels. Modern inline skates of the 1980s came standard with oblong mounting holes as a standard feature on their frames. These holes allowed skaters to configure their skates with the same wheels in either a flat setup for long-distance skating, or a banana-rockered setup for highly maneuverable disciplines like hockey, with sharp turns and quick footwork.$^{:81–86}$
Skate manufacturers subsequently devised various toggleable hardware for quick and reliable switching of wheel setups. These involved the use of frame spacers, axle guides, mounting hole inserts, or axle bolts that fit oblong mounting holes in two or more ways, in order to shift the axle’s center to a preset position.$^{:44–45}$$^{:20–21}$$^{:28}$
With the advent of mounting standards and easily-swappable frames in the 21st century, some inline frames now eschew toggleable hardware in pursuit of reduction in complexity, weight, and number of components. Each brand specifies exact locations for mounting holes to create a wheel assembly profile that it deems optimal. For instance, the Endless 90 Trinity frame presents a flat setup when configured with three 110mm wheels, and a slightly banana-rockered setup with four 90mm wheels. Wizard frames have a similar fixed setup that mimics an even milder banana rocker. Wizard frames are, in general, even longer than Endless frames. Therefore, even though both shift the two middle mounting holes by similar amounts (1mm to 2mm), the rockered profile on Endless is further attenuated.

### Non-standard frames

Modern inline skates started as off-season training tools for ice skaters. Many early inline frames were designed to be length-adjustable, so that each skater could have inline skates tailored to their individual shoe size. For instance, inline skates made for the USSR speed skating team in the 1960s accommodated differences in shoe sizes by using a variable length connector between the front and rear mounting platforms, and by allowing wheels to be mounted at different locations on the frame. This tradition continued and was further expanded in the 1966 Chicago Roller-Blade and in Rollerblade skates from the early 1980s.
There were no standards for boots, frames, or the way frames were mounted onto boots. The 1962 USSR skate and the 1966 Chicago Roller-Blade were designed to be mounted onto a flat sole, or an equivalent dress shoe with a front sole level with the heel. On the other hand, the 1975 Super Sport Skate was modeled after ice hockey skates, and had a frame with a raised heel mount, resulting in a built-in heel-to-toe drop (or heel lift).
These early inline skates featured frames that were riveted to the boots, mirroring the construction method used in ice skate manufacturing. The lack of standards and the fixed-mounting process made it hard to mix and match boots and frames. For instance, early 1981 prototypes of the Ultimate Hockey Skate by Scott Olson had a flat Chicago frame mounted onto an ice hockey boot. This required that an artificial heel disc be inserted in between the frame and the boot to make up for the heel lift designed into the hockey boot.
Non-standard inline frames still dominate the entry-level market. Many such frames are not replaceable. Most cannot be adjusted to compensate for a skater's ankle pronation or supination. Some beginner skates, such as the Powerslide One Zoom in 2024, continue to use riveted frames. These skates are fixed at the factory, and cannot be further customized.
Outside of the entry-level market, inline skates have largely consolidated around a few mounting standards. Aggressive skates and Wizard skates follow the UFS standard. Most speed skates use the 195mm two-point standard. The rest generally adopt the 165mm two-point standard. The Trinity standard with three mounting holes was created in 2016. It has been gaining popularity in urban skating, where skaters wish to mount bigger wheels with a minimal increase in frame height.
Only one type of inline skate does not follow any of these standards: the hockey skates. Inline hockey skates continue to use the same riveted mounting process as their ice hockey counterparts. All hockey skates, from inexpensive to high-end custom-molded ones, have proprietary frames that cannot be replaced or adjusted.

### 165mm and 195mm frames

In 1974, Inze Bont, founder of the speed skate manufacturer Bont, created fiberglass-reinforced boots for short track racing, featuring 2 mounting holes spaced 165mm apart. An adjustable ice blade was attached to the boot using these holes. As inline skating gained popularity in the mid-1980s, companies like Darkstar, Mogema, and Raps began producing inline frames designed to mount onto these short track boots. This led to the establishment of the first inline skate mounting standard.
The 165mm mounting standard incorporates a height differential of approximately 10mm between the front and rear mounting points. This creates a heel lift, also known as pitch or heel-to-toe drop, allowing speed skaters to achieve more powerful push-offs through deeper dorsiflexion. Due to this height difference, the two mounting platforms on a frame are usually not contiguous. The standard does not specify frame width or exact mounting locations on the boot. In practice, these result in relatively small contact surfaces between the frame and the boot compared to traditional rivet mounting. However, this is not an issue for rigid speed boots made from fiberglass, and even less so for Bont’s later innovations - kevlar boots (1986) and carbon fiber boots (1989).
Roces Impala skates from the mid 1990s were the first to adopt the 165mm 2-point mounting standard outside of speed skating, paving the way for other inline skate manufacturers to follow. This standard became widely used across various inline skate disciplines, from recreational and aggressive skating to slalom skating. However, unlike speed boots, these disciplines do not rely solely on composite boots with extremely rigid soles. On softer soles, the small mounting platforms can cause the frame to wobble under load. To mitigate this, some boots reinforce the mounting areas with metal plates.
The 165mm standard, also known as SSM (Standard Speed Mount), was developed when speed skates primarily used five small wheels (e.g. 5x80mm). However, as longer frames with fewer but larger wheels became popular (e.g. 4x100mm), the positioning of the mounting bolts interfered with some wheels, forcing frames to become taller. This increased a skate's center of gravity and reduced a skater's performance. Some speed frames relocated middle wheels or reduce their sizes to fit the standard.$^{:311–316}$
To address this, the 195mm 2-point standard was introduced in 2003, also known as LSM (Long Speed Mount). By increasing the interaxial distance to 195mm, this standard prevented bolts from interfering with middle wheels, enabling the use of larger wheels and longer frames without increasing frame height. This design provides a stable ride at high speeds by maintaining a relatively low center of gravity in proportion to the longer wheelbase.
The 195mm standard retains the same heel lift as the 165mm standard. In general, only speed skating boots use 195mm, while most other inline boots continue to rely on 165mm. However, many inline frames include dual mounting slots on the front mount to accommodate boots of either standard.

### UFS frames

The ESPN X Games introduced aggressive inline skating in 1995, propelling the sport into the spotlight. As its popularity grew, more enthusiasts took up aggressive skating, prompting companies to develop their own specialized skate lines to meet the rising demand.
In 1996, K2 released the Fatty, a legendary skate that integrated the wheel frame into its soulplate for the first time. In this early stage of its evolution, the soulplate still consisted of two separate platforms, a design inherited from the toe and heel mounting platforms of riveted boots, as seen in the Rollerblade Lightning TRS. However, the K2 Fatty reduced the height difference between these platforms, with its frame now forming a solid rectangular bar, eliminating distinct mounting protrusions.
In 1998, Roces too, released an aggressive skate featuring a combined soulplate and frame: the 5th Element. This design not only incorporated a rectangular frame without distinct mounting protrusions but also featured a completely flat soulplate with no height difference between the front and rear sections. This flat sole significantly improved soul grinding and was soon adopted by other skate manufacturers. Additionally, the 5th Element’s integrated soul/frame unit could be easily removed from the boot by loosening just three screws.
In 1999, Salomon, along with USD, Razors, Kizer, 7XL/Able, and Fifty/50, collaborated to establish a standardized mounting system for aggressive skates: the Universal Frame System (UFS). This standard capitalized on the emerging trend of flat soulplates, requiring a single, flat rectangular mounting surface 41mm wide and long enough to accommodate two mounting holes spaced 167mm apart. In 2001, Salomon introduced the Aaron Feinberg Pro Model, the first skate to feature the UFS mounting standard. The model quickly gained popularity and set a new industry benchmark.
Unlike other mounting systems of the time, UFS eliminated built-in heel lift, positioning the heel level with the toes for the first time. However, most brands followed Salomon’s lead in incorporating a thick shock absorber at the heel, providing better impact support for hard landings from high jumps, and accidentally reintroducing a small amount of heel lift.

### Trinity frames

The 165mm mounting standard, originally from speed skating, has dominated the inline skate market since the mid-1990s, except in aggressive skates that use UFS mounting and hockey skates that rely on rivets. However, not all inline boots are made from the stiff carbon-composite materials typical of speed boots. The small 165mm mounting area can lead to frame wobbles on boots lacking a rigid sole or reinforced mounting platforms.
As larger wheels gained popularity in the 21st century, 165mm frames evolved to accommodate setups with bigger and sometimes fewer wheels. Some manufacturers increased frame height, which negatively affected stability and performance. Others relocated or downsized middle wheels to avoid interference with mounting bolts. Some brands even shifted the mounting platforms forward or backward to fit specific wheel setups, causing front-to-back centering issues when mixing and matching boots and frames. For instance, Rollerblade Twister and certain Seba boots have unconventional 165mm mount placements, making it difficult or even impossible to achieve proper longitudinal centering with aftermarket frames. To meet demand for these popular boots, Endless Blading released a version of its Endless 100 frame specifically-tweaked to fit them.
The 195mm standard, introduced in 2003, better supported larger wheel setups without increasing frame height, relocating middle wheels, downsizing middle wheels, or shifting mounts. However, it also spread the mounting points farther apart—beyond the optimal heel-to-ball length that best supports an average foot. The 195mm standard required exceptionally stiff soles and boots, which were unavailable outside the speed skating market until the late 2010s. As a result, only speed boots made of carbon fiber adopted the 195mm standard.
In 2016, Powerslide introduced the Trinity mounting system to accommodate a wide range of modern wheel setups while addressing the shortcomings of both the 165mm and 195mm standards. Demonstrating its versatility, Powerslide launched Trinity-mounted boots and frames across multiple disciplines, including recreational, urban, speed, slalom, hockey, and off-road skating.
The name "Trinity" reflects its three mounting points, in contrast to the two-point systems used in 165mm, 195mm, and UFS. Trinity features two front mounting points positioned on the sides with a longitudinal offset, avoiding the centerline where the two frontmost wheels are located. The vacated centerline allows front wheels of any size or configuration to be placed within millimeters of the boot sole. The rear mount is elevated by 10mm, creating a heel lift similar to the 165mm standard. Positioned under the heel and in line with the rear wheels, the rear mounting bolt remains unobtrusive due to the 10mm rise. The longitudinal offset positions the two front mounts asymmetrically under the medial and lateral sides of the ball of the foot. The three mounting points create a triangular configuration with sides measuring 150mm, 135mm, and 55mm. This design provides structural support tailored to a typical foot, ensuring optimal heel-to-ball alignment.
A Trinity frame generally exhibits less wobble than 165mm and 195mm frames when comparing boots with similar sole rigidity and mounting platform strength. This is because a 165mm frame depends on the boot sole to function as a cantilever beam, with each side extending outward and applying bending forces to the centrally located mounting bolts. In contrast, a Trinity frame distributes structural support across the full width of the ball of the foot, much like a hockey blade holder with two front mounting wings. This broader support reinforces the sole and shortens its effective cantilever length on each side of the boot, resulting in better transfer of power from foot to wheels and support for weight transfer when leaning into an edge.
A Trinity frame typically has a lower "front" mount height than its 165mm counterpart when using the same wheel setup. This is because the front mount of a Trinity frame can be positioned significantly lower than the tops of the front wheels due to its open centerline. However, a reduction in mount height alone is not a meaningful metric for skaters. The true advantage of a Trinity frame lies in its ability to position the front of the boot as close to the ground as the front wheels allow, effectively lowering the skate’s center of gravity. This improves control and stability, resulting in a safer and more responsive skating experience.

## Wheels
### Polyurethane wheels

Modern inline wheels are made of polyurethane, a material that revolutionized skating. Before the widespread adoption polyurethane, roller skates and skateboards used composition wheels made from clay or rubber mixed with sawdust and other fibers. These composition wheels were prone to swelling from moisture and could shatter on impact, contributing to a decline in skateboarding by the late 1960s.
In the early 1970s, roller skaters experimented with polyurethane wheels, but they proved too grippy and slow for roller rinks with wooden floors, where composition wheels performed better. However, by the mid-1970s, skateboarders repurposed polyurethane wheels from roller skates, shaving them down to fit skateboards. These wheels excelled on streets and urban terrain, offering greater durability and impact resistance compared to their predecessors. Their elasticity provided a smoother ride over rough surfaces, helping to spark a resurgence in skateboarding after its late-1960s slump.
In the early 1980s, Scott Olson similarly repurposed polyurethane wheels from roller skates, shaving down tens of thousands to fit the skates sold by his company, Ole’s Innovative Sports—later known as Rollerblade. The same qualities that made polyurethane wheels ideal for skateboarding, such as durability, impact resistance, and a smooth ride, also benefited inline skating. This innovation helped bring inline skating out of obscurity and transform it into a popular outdoor sport during the 1980s.
What truly set polyurethane (or urethane) apart from previous wheel materials was its versatility. As an elastomer, it could be molded into any shape and formulated to achieve a wide range of properties including color, hardness, grippiness and rebound. This adaptability allowed for the development of specialized wheels for different inline skating disciplines, from large, hard wheels with pointed bullet profiles for outdoor racing to small, soft wheels with rounded profiles for indoor hockey.$^{:20–26}$
Another remarkable aspect of a polyurethane compound is that it can be formulated to achieve high elasticity, regardless of the desired values for other properties such as hardness. In material science, this elasticity is known as resilience, but in the inline skating industry, it is referred to as wheel rebound. A wheel with high rebound efficiently converts energy from a skater's stride into acceleration, while a wheel with low rebound dissipates much of that energy, leaving little to propel the skater forward. High-rebound wheels are beneficial across all inline skating disciplines, enhancing performance and efficiency.$^{:24–26}$

## Parts
### Bearings

Ball bearings allow the wheels to rotate freely and smoothly. Bearings are usually rated on the ABEC scale, a measure of the manufactured precision tolerance, ranging from 1 (worst) to 9 (best) in odd numbers. The ABEC standards were originally intended for high-speed machinery, not skating applications, and do not account for the quality of steel used, which is very important for how long bearings last. While higher rated bearings are generally better in overall quality, whether they automatically translate to more speed is questionable. Since at least 2007, Rollerblade brand amongst others have begun using their own rating system. For instance, Rollerblade brand is currently using a SG1 to SG9 rating system, whereas TwinCam brand is using its own "ILQ" (inline qualified) rating system and Bones brand is using its own "Skate Rated" rating system.
A mistake that is often made in purchasing bearings is that spending more translates to more speed. Generally, clean inline skate bearings contribute about 2% of the rolling resistance that the best urethane inline skate wheels produce, so there is very little opportunity in improving speed by spending more money on bearings. Newer bearings on the market have been offered that use ceramic ball bearings instead of steel, which are more expensive than traditional steel bearings but made of harder material.
Two bearings are used per wheel. The bearings slip into openings molded into each side of the wheel hub, and a flange molded into the wheel hub holds the bearings the correct distance apart. Additionally there is an axle spacer either machined into the axle or that slides over the axle (depending on the axle system used). Since the outer race of the bearing contacts the wheel spacer and the inner race of the bearing contacts the axle spacer, it is critical that the relationship between these two spacers is correct. If the wheel spacer is wider than the axle spacer the bearings will bind when the axle bolt (or bolts) are tightened.

### Wheels

Wheel sizes vary depending on the skating style.
* 44–72 mm (1.73–2.83 in) for aggressive skating.
* 47–80 mm (1.85–3.15 in) for roller hockey skating.
* 68–72 mm (2.68–2.83 in) for artistic inline skating.
* 72–80 mm (2.83–3.15 in) for freestyle slalom skating and downhill skating.
* 70–90 mm (2.76–3.54 in) for urban skating.
* 72–100 mm (2.83–3.94 in) for general recreational skating.
* 80–90 mm (3.15–3.54 in) for downhill inline skating.
* 100–125 mm (3.94–4.92 in) for tri-skating, mushroom blading, and speed skating.
* 125–150 mm (4.92–5.91 in) tires for off-road skating, and downhill mountain blading with inflatable tires.
Wheels are nowadays almost universally made of polyurethane (a kind of durable plastic). Most other plastics and rubber either wear down too quickly or have too much rolling resistance. In general, the bigger the wheel, the faster the skate. A bigger wheel rolls over road imperfections smoothly thus the less bumpy the skating. On top of that, an inline skater trips far less on large wheels. However, large wheels take more energy to start rolling. Smaller wheels allow faster acceleration, maneuverability, and a lower center of gravity.
Wheel hardness is measured on the A scale (see Durometer) and usually ranges between 72A-93A (lower numbers are softer, higher numbers are harder). Harder wheels are not necessarily faster but tend to be more durable; soft wheels may have better grip and are generally less affected by road bumps. Harder wheels (which grant minimal elastic hysteresis energy absorption) maintain rolling speed far better while softer wheels (because they grip the surface) accelerate more straightforwardly when striding. In the 1990s, wheel rolling resistance (CRR – coefficient of rolling resistance) tended to be minimized with wheel hardness in the 78A durometer range, with rolling resistance dramatically increasing below 75A durometer and above 85A durometer. In the early 2000s, urethane compounds improved significantly, allowing skaters to use harder compounds to get better wheel life, and get the lowest rolling resistance in the 82A–84A durometer range.
Wheel profiles and thickness again vary by application. Elliptic profiles were thought to minimize friction for a faster ride; however, they were intended to mimic the knife-like properties of an ice blade. They helped define the inner, central and outer edges. Elliptic profiles made the wheel quite maneuverable when turning or otherwise crossing over. More rounded profiles provided lower rolling resistance due to the greater "belly" or tire that increased resilience (or "rebound"); and these wheels were perceived as having better grip and being more stable (less like an ice blade), but were heavier than elliptical-profiled wheels and were often used in downhill racing (such as the Hyper Downhill racing wheels) and in recreational skates. Another advantage of rounded profile wheels is longer wear life due to the increased urethane amount on the tire. To increase stability at high speed, skates intended for downhill skating usually have five or six wheels, in contrast with recreational skates, which typically have four wheels. This advantage of more wheels having less rolling resistance has been largely negated by the 100–110 mm (3.9–4.3 in) diameter wheels with 4-wheel trucks. A flat profile allowed the wheel to be even far stabler than the rounded profile. This profile is almost exclusively used on aggressive skate wheels. On the flip-side, the squared-off shape caused cornering to be tremendously harder, seeing how edges are non-existent with a flat profile. In fact, a flat profile has only a center edge preventing the skater from leaning over.
The core's general design i.e. material, shape, and flexibility/sturdiness degree at the wheel's hub determine the wheel's properties as well. In a classical point of view, wheels on older skate models (during the 1980s and early 1990s) contained no core feature whatsoever. The core is a result of the gradual technological improvement inline skating underwent. Above all else, a wheel lacking a core is prone to deformation. This deformation is a hindrance to the skater's striding ability since in such a case it minimizes the skater's top speed. The core is inserted to hold the polyurethane firmly in place. Despite the setback, markets still distribute special wheels without a core. Core designs vary among open, full or semi-open. 'Spokes' are an element seen in wheels whose cores are open which generally increase overall wheel lightness. These are inserted into the hubs of wheels for inline speed skates, fitness skates, recreational skates, some slalom skates and artistic/figure inline skates. Apart from spokes, other open-cores can be hollowed out internally. The main disadvantage about an open core is that their design does not permit sturdiness hence they are highly likely to snap under too much pressure i.e. when jumping. Another trade-off with open cores is the lesser amount of polyurethane around it to compensate for the spoked or hollow shape meaning they last shorter. Full cores are entirely solid, akin to a pipe's cross-section. This core design is mostly favored amongst aggressive skaters whose leaps off higher levels strain the wheels when landing. Of course, these cores (alongside the extra polyurethane) tend to add weight on the wheel. Some even disfavor the full core design for its rigidity that feels uncomfortable. The question still stands on whether a full core improves power transfer. Semi-open cores are a hybrid between the two previously mentioned cores seen on wheels for urban skates, slalom skates and inline hockey skates. Minuscule holes are typically punctured into these solid cores to provide a semi-open design.

### Heel brakes or toe stops

A hard rubber brake attached to the heel of the frame allows the skater to stop by lifting the toes of the skate, forcing the brake onto the ground. Learning how to use the heel brake is very important for beginners, as it is the easiest way to stop in emergencies and to control speed on downhills. Also, with practice, beginners realise if the heel brakes are better placed for them on the left/right foot.
Heel brakes can interfere with a useful technique called a crossover turn, in which a skater crosses one leg over another to make a sharp turn without losing much speed; for this reason, most intermediate to advanced users prefer not to use heel brakes. Skaters in the freestyle slalom and aggressive inline skating disciplines do not use heel brakes, since they limit the skater's ability to perform tricks effectively. Aggressive inline skates and racing skates generally have no heel brake, thereby permitting extra speed and control.
Inline skaters lacking a heel brake can use various other methods to stop, such as the T-stop in which the skater moves one skate perpendicular to the other, making a "T" shape to increase friction and reduce speed, or the more advanced maneuver of a hockey stop/snow plow stop, in which the skater quickly moves both skates perpendicular to the path of motion.
For artistic roller skating purposes, inline figure skates can also feature a "toe stop" which aids in performing figure skating jumps.

## Wheel setups
### Flat setup

A flat setup is the most common setup used on inline skates. Almost all non-aggressive inline skates are sold with a flat wheel setup. Flat means that all the wheels touch the ground at the same time when resting on flat ground. Flat setups are not the most maneuverable but what they lack in maneuverability they make up for in speed. Flat setups tend to be the fastest setups, compared to setups such as the Hi-Lo or anti-rocker. The presence of two middle wheels matching the diametrical size of the rest increases contact points with any surface. They also minimize the rate at which the skater's loading weight deforms the wheels. This minimizes the wheel's footprint thereby minimizing rolling resistance. Speed skaters and marathon skaters normally use flat setups. This setup also allows for a powerslide, an advanced braking method.
Aggressive skates are sometimes sold with flat setups, but with a small space in the middle for grinding. With aggressive skates, the flat setup obviously leads to better control on the ground when either accelerating on a push or decelerating on a drag because of increased traction. It also grants a faster speed, translating to faster grinds, more powerful pumps in a skate ramp, and higher heights ('airs') off the edge of a vert ramp. Indeed, flat setups are quick save for the likelihood that they will be heavier and the two standard central wheels tend to 'bite' when grinding. Similar to skateboarding in certain respects, 'biting' is a common hindrance during grinding whereby friction between the wheel(s) and surface it comes into contact causes the wheel(s) then entire boot to suddenly reach a halt and the momentum throws the aggressive inline skater off the rail or ledge. Again, the aspect of wheel profile is key here. A harder wheel on a flat setup will slide and 'bite' less than a softer wheel. Likewise an elliptical profile (Undercover's Dustin Werbeski 'super bullet' wheels for example) possesses less surface area hence it will not bite as much either. Adjusting to a flat setup can even out shock when landing jumps. In doing so, an inline skater's hardware like wheels, bearings, axles and the frame itself are twice as much to be spared damage.
It is worth noting that having a flat setup is just one factor in a fast skate setup. A long frame, low resistance bearings, and good technique all contribute greatly to a skater's speed.

### Full 'crescent/banana' rocker

Full rockers are used by skaters who favor maneuverability when skating on flat ground. Freestyle skaters, freestyle slalom skaters and artistic inline skaters tend to use this setup. Inline hockey players no less can customize their wheels to implement this setup (especially those who favor nimble change in direction over sheer speed during a match). This setup is called "crescent" or "banana" because it is curved, and mimics a curved ice blade profile. On flat ground this setup will only have 1–2 wheels touching the ground at any one time. This makes the skate much easier to pivot but lacks stability so it is harder to balance on. To attain balance when learning to skate a full rocker, it is recommended that pressure and weight are deposited on either the two middle wheels or the two wheels in the back. Avoid applying pressure on the two front wheels when taking strides since this is what will cause instability. In addition, a full rocker is slower than a flat setup in terms of top speed. Worst of all at high speeds, skates with a full rocker setup can experience a speed wobble, where they oscillate uncontrollably. The skater may lose control and crash to the ground.
Flat setups generally wear into a 'natural' rocker. This is because the front and back wheels seem to receive the vast majority of wear on inline skates.
Having a short frame (230–245 mm [9.1–9.6 in]) in combination with a full rocker is optimum for achieving the highest maneuverability when skating.

### Front rocker

Front rockers are often used by street skaters who want to combine the ability of a full rocker to handle imperfections in the ground with a flat setup's sheer speed. Having a smaller wheel at the front encourages the front wheel to guide the rest of the skate over ground imperfections, rather than digging in and tripping up the less experienced skater. Maintaining a flat profile at the back allows the skater to transfer power through the rear of the skate efficiently to maintain a good speed.

### ‘Hi-Lo’ setup

Some hockey skates inline speed skates include a Hi-Lo setup. Hi-Lo setups resemble a flat setup in that all 4 wheels touch the ground at the same time. Unlike a flat setup, however, different wheel sizes are used. The front two wheels will be smaller than the back two wheels. This is possible because of the location of the axles on the frame itself. One example is a Bauer frame that has two wheels in the front that are 76 mm (3.0 in) and two wheels in the back that are 80 mm (3.1 in). Another example is a 74–76–78–80 mm (2.9–3.0–3.1–3.1 in) wheel arrangement. This drastically changed the pace at which inline hockey players accelerated. Furthermore, by transferring weight forward, the skater could sprint explosively off the toe section and reduce instances of falling backwards. If the hockey skate is used recreationally outside the arena, the skater will find climbing slopes much easier than on a flat setup. As inline hockey skate manufacturers design frames with varying axle hole placements or even raise the frame's back bolt to be higher than the front bolt nowadays, wheels of the same diameter (like 80 mm [3.1 in]) can be used entirely.
Beyond inline hockey, the Hi-Lo setup was an experimental component seen on K2's VO2 100 X Pro where the manufacturers believed that the two smaller wheels (90 mm [3.5 in] each) in front would increase stability and rate of acceleration while the two bigger wheels (100 mm [3.9 in] each) in the back would maintain high speeds. Essentially this K2 skate model married both wheel size properties. A Hi-Lo configuration on an inline speed skate employs three large sized wheels and a smaller sized wheel between the first and third wheels beneath the ball part of the foot (see speed skates). An example is a 110–100–110–110 mm (4.3–3.9–4.3–4.3 in) arrangement beginning front to back. This increases efficiency now that the foot pushes on a smaller wheel. The smaller wheel lowers deck height off the ground improving stability and keeps the frame length shorter improving maneuverability and comfort amongst speed skaters having a smaller foot size. This is desirable seeing how wheels on inline speed skates are enormous enough to occupy a lot of room in frames. Unfortunately, top speed for a Hi-Lo setup is far less than that for a flat setup where same sized large wheels are used.

### 'TriDi' Hi-Lo setup

Another variant of the setup in which there are three diameters of wheels. It is supposed to emphasize the same benefits as the HiLo system but with greater maneuverability due to the smaller front wheels. The configuration is 72 mm (2.83 in), 76 mm (2.99 in), 80 mm (3.15 in), 76 mm (2.99 in). It allows one to pivot on the third wheel similar to the brand Wizard Skates. This system is also used by some hockey skaters as it pitches the foot slightly forward.

### Aggressive Hi-Lo setup

A few aggressive skate frames (most notably Rollerblade's Switch Frame, Ground Control's Bullet Frame, Oysi Frame and Joe Atkinson Sola Frame) are designed so that there are two big outer wheels, and two small inner wheels, rockered so that they all touch the ground. This gives the benefits of a flat setup, while keeping the frame as low as the height of the smaller inner wheels. It also retains room for an H-block in the center. But out bigger outer wheels give some of the benefits bigger wheels offer such as speed and stability.

### Anti-rocker

Anti-rocker is the most popular setup for aggressive skaters. An anti-rocker wheel is a small hard wheel that replaces the two middle wheels. Anti-rocker wheels almost never touch the ground except in cases where the terrain is uneven, such as skating over a ramp. Anti-rockers can be made of plastic, or high density polyurethane. Some use bearings so that they can spin. As they can spin, the anti-rockers wear out more evenly when grinding. Anti-rockers containing bearings can effectively roll over uneven ground or features like steps, lessening tripping hazards. Others do not use bearings so that they are lighter. The anti-rockers themselves lock the H-block onto the ledge or rail a skater grinds. There is a minor nuisance to anti-rocker hardware in which the items emit a loud noise upon fastening into a grind that some aggressive skaters find unbearable. The anti-rocker setup altogether makes maneuvering harder (since the standard wheels slip more), wheel life shorter, overall speed slower, a rougher ride, and a wider turning radius, but because of the extra space in the middle, it makes grinding objects much easier than with a flat setup.

### Freestyle

The freestyle frame is another setup used by aggressive skaters. This setup simply has only two wheels – one in the front and one in the back. In between the two wheels is an area of solid material, resembling a large "H Block", which is used for grinding. Freestyle frames have nearly identical advantages to the Anti-rocker. Since large space is freed up in the middle, the skater can not only grind wider surface areas like an entire ledge but also the frame's weight is lighter. Likewise, the Freestyle frame shares its disadvantages with its Anti-rocker cousin already listed. As opposed to anti-rockers which securely lock grinds, aggressive skaters should train themselves to remain balanced when sliding across narrow rails or edges on a Freestyle frame. Worse still, when not being careful, a Freestyle setup can easily hook on vertical surfaces including steps, coping, and funbox edges if one rolls over them, leading to tripping incidents. This is why the technique to 'bash' (see Flat Setup) a staircase is almost impossible on a Freestyle setup. Freestyle frames can be purchased, although removing the two inner wheels of a flat or anti-rocker frame technically makes it freestyle, however this would not be very durable due to the lack of solid grinding material. Originally invented by Fifty-50 (an aggressive inline skate frame company), Juice Blocks allow the skater to convert their flat or anti-rocker frames into proper freestyle frames. Juice Blocks are simply solid grind blocks inserted into the axle holes where two middle wheels or anti-rockers are found.

### Tri-rocker

Tri-rocker (not to be confused with the 3-wheeled frame/chassis seen on Tri-Skates) is used by some aggressive skaters. It is another method of making grinds easier. A frame with a tri-rocker setup has only one wheel in the middle, either in the second wheel position or in the third wheel position, depending on what kinds of grinds the skater plans on doing. The remaining axle has an anti-rocker wheel, a special grind block, or is just left empty.
The purpose of a tri-rocker setup is to give the skater good speed and maneuverability, like on a flat setup. But because of the extra space, grinding is also a little easier than a flat setup.

## Candidate images for illustration

This is not a gallery. This is a list of pictures that may be useful for illustrating parts of this article. Images will be removed from the list as they become used in the article during the rewrite. This list will be removed after the rewrite is finished.
* One wheel removed showing axle and bearings
* 110mm 85A speed wheels
* Wheel and bearings
* bearings
* Cross section of a wheel
* Frame and wheels
* 5-wheel speed skating frame
* Inline skate wheels (hi-lo 80mm/76mm)
* Soft boot
* Hard boot
* Hard boot
* Falling with protection gear
* Falling at a slalom skating event
* Skating protection gear
* Protective gear: helmet, elbow pads, wrist guards, and knee pads.
* Heel brake
* New heel brake
* Worn-out heel brake after 205km of skating
* Worn-out brake vs new brake
* Inline figure skate with a toe brake
* Urban skating
* Off-road inline skates
* Police on skates
* Boot detachable from the inline frame