Automobiles squat when they accelerate. If a motorcycle squats when it accelerates, that’s a problem.
Motorcycle rear suspension is different from automobile suspension in one important respect: When an automobile accelerates, it squats in the back because weight is being transferred from the front to the rear as a result of the tires pushing the vehicle forward at ground level while the mass of the vehicle is above it. That tends to tip the vehicle to the rear.
If a motorcycle were to squat down in the rear as you began to accelerate off a corner, that would take weight off the front, which would not steer as well as before-you would try to steer into the turn and the bike would drift to the outside. When you came into the pits at the end of practice, you would be asking your crew chief for a solution.
The force that opposes squat in a correctly designed motorcycle comes mainly from the drive chain, which is not parallel to the swingarm’s central plane but at an angle to it. And the tangent of that angle determines an anti-squat force. When you hear that a certain sportbike has an adjustable swingarm pivot height, it is at this problem that feature is aimed.
By varying the height of the pivot and therefore the droop angle of the swingarm, you alter the angle between the chain when it’s tight and the swingarm itself, thereby changing this anti-squat force. When that force is able to completely balance the weight shift caused by acceleration, you can accelerate off the corner without squat and push.
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