An electric bike conversion uses a typical bicycle, and with an electric motor and a battery, converts the bike into an electric bike. Electric bike conversion can be done with four basic types of conversion. The hub motor, the mid drive, the friction drive, and left side drive.
The left side electric bike conversion typically uses a brushed motor to drive the rear wheel from the left side. The rear wheel may have a chain and sprocket attached to the left side, or the motor may drive the wheel by pushing on the spokes. This type of conversion was common in the 90’s and early 2000’s. The inexpensive but inefficient brushed motor kept costs low. Most ran on 24v battery that limited speeds to a relatively slow pace.
The friction drive electric bike conversion was also more common in the 90s and early 2000’s. In this type of conversion, a brushed motor powered a roller that rubbed on the bike tire, propelling the bike. Friction drives of the 90s also ran on 24v, and did not propel the bike very fast.
Modern electric bikes today use a more efficient brushed motor, and usually take the form of a hub motor, or mid drive. Today’s electric bikes generally run on 36v or 48v batteries, and can reach speeds at least as fast as a highly trained athlete could pedal the bike.
The mid drive electric bike conversion uses a motor built into the bottom bracket (the pedals) of the bike. In this way the motor actually helps the rider pedal, and the motor’s power can be used in any gear on the bike. In some cases, inefficient operation can occur if the rider selects too high a gear and the motor is low powered. Chain and gear wear can be increased as well. Installing a mid-drive typically requires special tools for changing the pedals spindle.
The hub motor electric bike conversion is, by far, the most popular choice for electric bikes. In this type of conversion, either the front or the rear wheel is replaced with another wheel. This hub motor wheel has a high efficiency brushless motor built right into the hub of the wheel. This makes the hub motor electric bike conversion very easy to install, requiring no specialty tools or extensive bike mechanics knowledge. The gears of the bike remain the same, and no extra chain or gear wear results. The bike can still be pedaled normally in any gear, with the motor on assisting the rider or the motor off.
Hub motors for electric bike conversions come in two basic types. Planetary geared motors and direct drive motors. Both types can be used to replace the front wheel, or the rear wheel. Rear motors come with the normal external freewheel that most bikes use for shifting gears with a derailleur. A “geared hub motor” has gears inside the hub that allow a smaller motor to spin faster pull harder. This means a lighter motor can develop excellent torque and efficiency. The geared motor is a good choice for most riders because it climbs hills well, and is very efficient in stop and go city riding. It’s lighter than direct drive motors, which helps if the bike must be carried up a few stairs, or put on the bus bike rack for last mile rides on a commute. The geared hub motor conversion also has an internal freewheel, that makes the hub motor coast with zero drag when the motor is not in use. So it coasts better than a direct drive.
A direct drive hub motor is the simplest and most durable type of electric bike conversion. In a direct drive motor, there is only one moving part in the motor. No internal gears or clutch inside to wear out. Theoretically, a direct drive hub motor could run forever. The only wearing part is two sealed bearings on the axle. Direct drive motors are heavier than geared motors, but this extra weight is in the form of larger magnets and larger copper coils, which can pull hard for a longer duration without overheating. Because of this robust construction, direct drive is the motor of choice for heavier bikes, such as tandems, cargo bikes, or towing a trailer.
Batteries provide the power to run the electric bike conversion. Two basic types of batteries are used. Lead, or SLA type batteries, and Lithium type batteries. Batteries are usually listed by volts and amp hours, such as 36v 10 amp hours, or 48v 10 amp hours. Amps is how the flow of electricity is measured, so a flow of one amp for one hour is one amp hour. Thus, amp hours are a quantity of power, like cups are a quantity of liquid. Regardless of the voltage, a 10 ah battery can run for 10 hours at one amp, or 1 hour at 10 amps. Riding a 36 volt electric bike 20 mph generally takes about 15 amps, while 15 mph traveling will take only half that much. The slower you go, the more of the power needed can be provided by pedaling. Also wind drag greatly increases as speed increases.
Lead batteries are affordable, but heavy. They are after all, made of lead. They are ideal for electric bikes that are used less often, and ridden shorter distances between charges. The usable lifetime for lead batteries is typically one year, but careful use with frequent charging can make them last longer. Lifespan of lead batteries is extended by never discharging them much more than half way. So a lead 12 ah battery is best used by thinking of it as a 6 ah distance battery. At 20 mph, a 36v battery will use about one ah per mile. At 15 mph, about one ah per 2 miles. Lithium batteries are the first choice for the modern electric bike conversion. A lighter battery is a huge benefit. But even greater benefit, is that lithium batteries can be discharged all the way without greatly affecting the batteries lifespan. So the effective range is increased. Lithium batteries have a battery management system attached, that prevents too deep a discharge, and helps the smart charger achieve a perfect charge every cycle. Lithium batteries can theoretically have lifespans of 10 years, but in real world use on electric bikes, 2 to 4 years is typical, even when used daily.