What Are Torque Arms and Do You Need Them?

If you have ever thought of converting a normal road bike into an e-bike you could well have read that you probably need something called a “Torque Arm”. These are special supports for normal road bikes that provide increased support at the axle and are used to prevent the axle from ever “spinning out” inside the dropouts. Both front and rear-wheel e-bike conversions require torque arms.

When you accelerate your motor, a torque (turning force) is generated. If the wheel axle is held securely in place then this turning force is transferred to the wheel and it will turn. However, if the wheel axle is loose then there’s a chance that the wheel might stay put and the wheel axle itself turns. This is called “spin-out” and it can be a common problem with electric bike conversions, especially if your motor is particularly high-powered. If you’re not careful, spin-out can cause serious damage to your bike and conversion kit.

What Causes This?

Spin-out happens because standard bike forks are not often designed to grip the wheel axle sufficiently firmly to stop it from rotating. The solution is to install an additional gadget, called a torque arm, which fits over the wheel axle and clamps to the bike frame, holding the wheel axle securely in place. A usual torque arm is made of two components. The first is the “head”, which fits over the wheel axle, and the second is the “arm”, which is attached to the head by a bolt and fixed to the bike frame with a hose clamp. With a torque arm in place, the wheel axle is unable to rotate and spin-out is avoided.

Do I Really Need these?

The best answer we here at EB-UK can give you is that it is better to be safe than sorry. Most new e-bikes don’t come with them and to be honest, most e-bike conversion kits run a lot smoother these days and don’t cause this issue. But on older kits and older bikes being converted we once again stick with the line “better to be safe than sorry”.