REASON WHY THERE ARE NOT FRONT WHEEL DRIVE MOTORCYCLES

Why are there no front wheel drive motorcycles?

It should work in theory, but there are a couple things which would complicate it:

1) As a practical matter, the front wheel needs to steer as well as move up and down on the suspension.  This makes it more difficult to attach a reliable drivetrain to the front wheel, without adding unwanted mass and impeding the action of the front suspension and steering.

2) Traction.  As designed motorcycles apply the driving force at the rear wheel, and the size of the tire is chosen to minimize rear wheel spin. The front tire manages braking forces, since 70-100% of braking force comes from the front tire.  Both tires share the cornering forces.   

If you have driven a front wheel drive car aggressively, you will have noticed understeer, where applying the gas causes the car to push towards the outside of the turn, because the cornering forces plus the driving force exceed the traction limit of the tire, it slides, and the car pushes straight.  On a motorcycle this would cause a lowside crash.

But ignoring this for now:

If you were to drive the front tire, you would need to size it for engine torque, perhaps the size of a standard rear.  This would give heavier steering.  And you'd burn through fronts in half the mileage.

The rear tire, having nothing to do but cornering, could be the size of a standard front tire, or smaller.

Theoretically you could address point 1) with an electric motor, and you could make it safer with traction control.  It wouldn't be as easy, and it wouldn't have better performance, but it would certainly be unique.

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