-4mm: Swingarm pivot

The swingarm pivot affects the rear-end geometry of the motorcycle and is mainly used to control anti-squat. If the motorcycle accelerates out of a corner, weight is transferred to the rear wheel (squat). A certain amount of squat is beneficial to load the suspension and hence improve traction, however, too much and the front wheel becomes unloaded and hence will affect how you finish the corner (by running wide). In order to avoid that, you need what is called anti-squat: something that works against the weight transfer.

Since the swingarm is not perpendicular to the ground, the force that drives the rear wheel when you accelerate also lifts the back of the motorcycle (creating anti-squat). The amount of angle has an affect on how much force is actually transferred into lift.

Now...there are other forces that play a role in anti-squat such as the chain pull which actually has a greater influence (even more-so when using different sprocket sizes). The secret is to combine these forces to allow for the "perfect" amount of squat/anti-squat to let the motorcycle accelerate out of a corner most efficiently.

In regards to the 959, lowering the swingarm pivot (lowering the angle to the ground and subsequently decreasing the amount of lift) as well as using a different sprocket size proved to provide a better squat/anti-squat balance and hence allows to accelerate harder and more stable out of corners...