Development of Shock Absorbers for Snowmobile Racing

ProductIntroduction

Development of Shock Absorbers for Snowmobile Racing
TANAKA ShinIntroduction

KYB Motorcycle Suspension (hereinafter "KMS")
designs and manufactures shock absorbers (hereinafter“SA”) for domestic and overseas motorcycle manufacturers. KMS also designs and manufactures shock absorbers
for snowmobiles and ATVs and has been in business withBRP Inc. Note 1) and BRP Finland Oy. Note 2) over 30 years.
They lineup snowmobiles called Ski-Doo and Lynx Note 3)
known as a major brands in North America and NordicCountries and they gained to have a majority share of theglobal market in 2020. 1) High-performance SA used in thehigh-end snowmobiles of both brands are designed andmanufactured by KMS.
As snowmobiles have become technologically innovative, many state-of-the-art technologies have beenreflected in their SAs. All of these technologies wereoriginally developed for snowmobile racing and they canbe found everywhere in today’s mass-produced SAs forsnowmobiles.
This paper introduces development of technologies thatcan be found in our high performance SAs.
Note 1) BRP Inc. originated with the invention of the first evervehicle that can travel on snow by Joseph-Armand Bombardier at Valcourt in Quebec, Canada. L’Auto-Neige
Bombardier Limité was established in 1942. In 1959, theSki-Doo brand was born. In April 2003, Bombardier Inc.
announced the sale of the Bombardier Recreational
Products division.
Note 2) A forerunner of BRP Finland Oy was Nordtrac, which
was the only snowmobile manufacturer in Nordic countries and became BRP Finland in 2005, it has continuously produced the Lynx brand. Lynx is still the only
snowmobile brand in the Nordic countries.
Note 3) Ski-Doo and Lynx are the trademarks of BRP.

2Snowmobiles Information

2.1 Vehicle Lineup
Snowmobile manufacturers offer a wide variety ofvehicles that suit riders’ preferences such as sport/utility
models used as heavy duty work horses on snow, comfort-able touring models, trail models for high-speed aggressive rides on groomed trails, crossover models that shine
both on and off the trails, and deep snow models specifically designed for riding in the steep mountains covered
with deep snow. Many package options are available foreach model and industry’s first semi-active SAs (KADS 2))
can be selected as an option for high-end package of trail
and crossover models in order to have advanced shock
absorption, handling and stability control. Weight savingsare critical for deep snow models so lightweight highperformance SAs are chosen to improve maneuverability
in the mountain terrain with steep slopes. Characteristics
of snowmobile SAs required in various riding conditions
are shown in Fig. 1.

Weight → Light1

Shock Absorption/Stability Control → HighFig. 1

Characteristics of snowmobile SAs for each models

2.2 Suspension designSnowmobiles are quite different from motorcycles orATVs because they have skis and track to be able to driveon the snow (Fig. 2).
The skis will float and steer a snowmobile to be able tobe controlled by a handlebar on the snow. Generally, skis
are suspended by double wishbone suspension. This
design makes it possible to have a wider ski stance while
ensuring longer suspension stroke in order to achieve
higher steering stability. The right and left skis are bothsuspended by independent suspensions and front shocks
are mounted on each side.
The track will make it drive forward on snow using its― 42 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Front Shocks

RailTrackSki
Center ShockFig. 2Rear Shock

Components of snowmobile suspension

lugs while keeping it floating on the snow by enlarging thecontact area. There are many track styles that suit any
riding conditions. Some have studs in order to have traction on hard, icy trail surfaces while some have longer
lugs in the paddle form to be able to run on deep snow.
Center and Rear Shocks will control the movement of therail to keep the track in contact with rough, bumpy trails.
2.3 SA Structure
Snowmobiles are equipped with gas filled shock absorbers (hereinafter “Gas SA”) that use a steel or aluminum
monotube cylinder as a standard package. (hereafter "gasSA"). All Gas SAs have Spring Preload adjuster but also
some have Rebound adjuster to control Rebound Damping
Force. (Fig. 3).
For the high-end package, Remote Gas SAs or Piggyback Gas SAs that have Base Valve with Compression
Adjuster are equipped since much more shock absorption
and stability controls are requested. (Figs. 3 and 4).
Regardless of which package they are used for, all SAs
are using specially developed parts in order to be operated
in specific environment conditions. The examples are inthe following.

Gas-filled valve
Springpreloadadjuster

Compression
adjusterSpringpreloadadjusterGas-filled valve
Aluminium light-weightcylinderRebound adjuster
Rebound adjuster

Fig. 3

Lightweight aluminium single cylinder gas SA (left)
and piggyback gas SA (right)

・ Ice scraper:
Integrated Ice Scraper in the seal head to scrape off
frozen snow on Piston Rod surface (Fig. 5)
・ Oil:
Specially formulated to ensure fluidity in freezing condition
Compressionadjuster

Rebound adjuster
Oil

Base valve

Low Temp Compatible Seal
Ice Scraper

Spring preload adjuster

Fig. 4

Piggybackguide cylinder

Base valve

Components of piggyback gas SA― 43 ―

Development of Shock Absorbers for Snowmobile Racing

・ Low-temperature seal:
Carefully chosen seal material to keep Oil in SA in
freezing condition

Fig. 6

Fig. 5

 rozen ice covered Center Shock at the racing
Fpaddock
Fig. 73

Ski-Doo MXZx 600RS Note 4)

Types of Snowmobile RacingLynx Rave 600RS Note 4)

Note 4) MXZx, Rave and 600RS are trademarks of BRP Inc..

There are various kinds of snowmobile races as in thecase of other motorsports. The following describes major
categories of snowmobile races.
3.1 Snowcross
Snowcross was derived from the sport of motocross.
Like motocross, riders compete with each other on manmade racetracks with tight turns, banked corners, steep
jumps and obstacles.
Today, Snowcross are held are held at many locations inNorth America and Nordic countries. Courses in North
America include consecutive jumps and tight corners,
thereby requiring harder braking and rapid acceleration.
On the other hand, many of the courses in the Nordic
countries make use of original natural terrains. Since thesecourses are usually wide, racers are likely to run at higher
average speeds. The International Series of Champions(ISOC) Snocross, which are held around Great Lakes inNorth America, are participated in by famous competitors
not only from North America but also from the Nordic
countries. The world's premium race riders compete in a
total of 17 races at eight racing venues every year vyingwith each other to clinch the championship title.
Both Ski-Doo and Lynx have lineups for the racingready snowmobile specific for Snowcross called 600RS
that is only available for snowcross competitors (Figs. 6and 7). They are developed based on Trail snowmobiles
but equipped with a fine-tuned 600cc two-stroke engine
and race-proven special suspension system.
KMS has been providing specially designed SAs called“Factory Shocks” to BRP Racing Department and joining
BRP’s Racing program to develop better SAs by supporting them technically.

3.2 Hill Climb
Riders compete on how fast they can climb up ski slopes
with specially modified Deep Snow snowmobiles. The
most famous race is the World Championship Snowmobile Hill Climb that is held at Jackson Hole in March.
3.3 Cross-country
Competitors run a long distance toward a specified
destination with the Crossover snowmobile like Dakar
Rally. The most famous race is the Iron Dog in Alaska.
Competitors race over 4,000 km in a week and may berequired to ride on dirt, grass or skipping over frozen
rivers.
3.4 Others
Oval racing competitors corner on icy oval racetracks atthe highest speed with specially modified, lowered snowmobiles. Drag racing can record the highest speed on ashort, straight course. Snowmobile racing is not only heldin winter; Watercross is getting popular, competitors skip
snowmobiles on a lake to race like snowcross.

4

Development of SA for SnowcrossThe following are the major functions that are required
specially for Snowcross SA.
4.1 Front ShockTo prevent rolling moment during high-speed corneringin order to keep skis in contact on the trail, Front Shocks
need to provide a certain amount of damping force fromlower piston speed range. In addition, Front Shocks have
longer shock strokes to accommodate the larger gaps andjumps found on recent racetracks.

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4.2 Center and Rear Shocks
Center and Rear Shocks will stabilize the snowmobile
by controlling the rear suspension system and keep therail tracks on bumpy racetracks. Center Shock attached to
the front of the rail needs to be supple enough to help therail to follow the rough track surface while maintaining acertain amount of Ski pressure to have good handling.
However, it also needs to get stiffer to absorb energy toprevent harsh landing after jumping. Thus its damping
force will have progressive characteristics that can generate less damping force at lower piston speed range but
generate more damping force as it gets higher. Rear Shockis attached on the rear end of snowmobiles to control thevehicle pitching moment during acceleration and braking
by providing a certain amount of damping force at lower
piston speed balancing with Front Shocks. To provide
higher damping force at a higher piston speed range toabsorb landing impacts after jumps, it has the longest
stroke than the other SAs. So it is essential to have higher
rigidity construction to withstand its harsh use condition.
4.3 Adjuster
In Snowcross racing, competitors need to race all day
for several rounds of races; qualifying in daytime and thefinal at nighttime. SAs need to have many kinds of adjusters in order to quickly adapt to any kinds of racetrack
conditions because it changes depending on the weather
moment to moment.
4.4 History of Development of SA for 600RS
4.4.1 Development in the Early 2000sBefore the 2000s, aluminum monotube Gas SAs wereused because of its lightweight construction but they onlyused to have a rebound adjuster. In the early 2000s, riding
style has drastically changed from old-school “sit-on seat”
style to revolutionary “stand-up” style that suits modern
racetracks. To adapt this, a new chassis; REV and front
suspension system; RAS were developed. At that time,
BRP requested to develop new Remote Gas SAs in orderto improve shock absorption by adding Base Valve andFig. 8 lair Morgan’s racing snowmobile built forBX-Games in 2006

Compression Adjusters that can generate higher dampingforce (Figs. 8 and 9).

Fig. 9Remote Reservoirs of Front Shocks werefixed in the hood

Later in 2004, piggyback Gas SAs were developed andintroduced in all SAs years later by replacing Remote Gas
SAs. To further improve shock absorption, the piston
diameter got larger from 36 mm to 40 mm and rod diameter was also enlarged for higher strength and rigidity.
These racing technologies developed and validated werelater used in SAs for consumer models and they are stillused in today’s SAs.
4.4.2 Development in recent years
For the Snocross Pro Open; premier class in Snocross,it had been permitted to modify engines, pipes and chassisof racing snowmobiles to gain performance. But in 2018,
the regulations were revised to limit the modification.
This gained even more attention on the development of
the stock racing-ready snowmobile; 600RS. Particularly,
improving the suspension performance was considered asa critical challenge to ride faster on modern racetracks.
To do so, suspension linkage mechanisms were fully
redesigned and more performance improvements of SAs
were strongly requested. As a result, peripheral parts for
suspensions have been improved every year and SAs havealso been improved every year from 2018.
Following technologies were originally developed for
Snocross Factory Shocks and adapted for 600RS.
① Larger diameter piston for Center and Rear Shocks
As stated above, revision of regulations were taken as
an opportunity to improve performance of the rear suspension system. Larger Diameter Pistons were alreadyintroduced for Factory Center and Rear shocks but evaluation swung into high gear to find good setups. Riders
soon highly valued its stability and improved impact
absorption performance to prevent harsh landing after bigjumps. It was adapted for Center shock of 600RS MY2018
first and for Rear shock of MY2019 later.

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Development of Shock Absorbers for Snowmobile Racing② Integral adjuster
An integral adjuster, originally used for motocrossracing shocks, was introduced for Factory shocks to beable to be fine-tuned to rider’s preferences in a tight racing
schedule. It made it possible to adjust high-speed rebounddamping force quickly from outside that used to be hard toadjust via conventional adjusters and normally required
re-valving (Fig. 10). The characteristics of the check valve
were re-calibrated for Snocross after being introduced forSnocross. As a result, it will settle shock movements tomaintain a good ride height when shock rebounds from afully stroked position which gives better handling whenriders enter corners right after a jump landing. It showed
its value on the racetracks with many jumps and was more
useful than conventional adjusters. Finally, it was adaptedin all SAs from 600RS MY2020.
③ Larger diameter piston for front shocks
Since the larger diameter piston used for center and rearshocks had been highly valued as stated above, a request
arose to apply it for front shocks as well. However, it waseven harder for the front shocks because they had to be fit
in a very limited space around them. To solve this, relatedparts needed to be redesigned from ground up. A brandnew guide cylinder and bearing were designed and firstly
used in 2018-2019 season (Fig. 11) They reduced rider’sarms fatigue by absorbing landing impact after huge consecutive jumps and provided better stability that leads togreat advantage during racing. Development was further
continued to find good setup and the reliability was provedon racetracks. They firstly debut for 600RS MY2021 andalso selected as production shocks for high-end Lynx Trailmodel (Fig. 12).

GaschamberHigh Speed
Rebound Damping
AdjusterFig. 10Base valve

Check valve

Rebound Oil flows in the Integral Adjuster andHigh Speed Rebound Damping adjust circuit

Brand new design
guide cylinder

Integral adjuster
optimized forSnocrossBrand new design
bearing
Large diameter
piston/cylinder

Fig. 11

A brand new Front shocks with large diameter
piston debut in 2018-2019 season

Fig. 12First production trail snowmobile adopted front
shocks with large diameter piston

4.4.3 Current Development
They are equipped with new technologies that are
expected to be adopted for the next generation of SAs for
600RS and production shocks. Our technologies had
already been verified by great racing results as follows.

5Major Racing Results

2020-2021 Season#200 Elias Ishoel
Three consecutive championship in Pro Class of ISOC
Snocross (Fig. 13)
Won Race 1 and finished 6th overall in FIM SnowcrossWorld Championship 2021

― 46 ―KAYABA TECHNICAL REVIEW No. 64 APR. 2022

Finally, I would like to express my deep respect to ourpredecessors who were involved in the past development
and brought those technologies of racing shocks into production that had built the foundation of today’s technology and cordially thank all those from the internal related
departments who extended their cooperation to us. I am
committed to develop products that are even more attractive to riders all over the world and hopefully our latest
technologies will be their advantage.

ReferencesFig. 1361) Power Sports Business, 2020 Market Data Book, p.61,Worldwide Snowmobile Market Share.
2) UEMURA, KOJIMA, SUGAWARA: Development of "KADS"- An Electronically -Controlled Suspension System forMotorcycles, KYB Technical Review No. 63, (October 2021).

Elias Ishoel won the three consecutive
championship along with our technicians;
Tim (left) and Gilles (right)

In Closing

I would like to take this opportunity to thank all theengineers of BRP and BRP Finland who extended theircooperation into the development field as well as thetechnicians from Enzo Canada who have been joining ourracing support program and provided technical support on
our factory shocks for more than 20 years.

Author 
TANAKA Shin
Joined the company in 2015.
Group 2, Design Sect. No.2,Formerly engaged in design anddevelopment of motocross racing
suspensions and later engaged indesign and development of SAs forsnowmobiles and ATVs

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