It amazes me how misinformation and folklore spreads and soon becomes 'fact'. For example, no doubt you have heard that if your rear wheel is driven with a chain then when you accelerate the rear-end of the bike will squat while if the rear wheel is shaft driven it will rise. You may also have heard that you cannot do either a 'wheelie' or a 'stoppie' if your bike is shaft driven. WRONG!

Observe the diagram to the right. It shows a rear wheel and its swing arm. The swing arm, you will note, is joined to the bike frame via a pivot which is higher than the hub of the wheel. (This configuration is normal. There are a few bikes which do not even have a swing arm and fewer still that have the swing arm connected to the frame at a point lower than the wheel hub.) Wherever the swing arm attaches to the frame, it is behind the bike's Center of Gravity.

Whether the motorcycle is chain driven or uses a shaft, the connection of the rear wheel to the frame of your bike is as described. Your rear suspension system connects the frame of the bike to the rear wheel by attaching one end of your shocks to the swing arm.

So let's look at what happens when you accelerate. This diagram shows that as the wheel turns (clockwise) it moves to the right. In doing so it exerts a force to the frame thru the swing arm. Since that arm is angled upwards, the force exerted is divided between a forward component and an upward component - it is NOT simply pushing the motorcycle forward. As a result, the motorcycle moves forward and, because the upward force is behind the bike's CG, the rear-end of the bike moves UP. (You will also observe if you look closely that as the angle of the swing arm increases, the wheelbase decreases.)

The top of the engine, particularly on chain driven bikes, tends to torque towards the rear of the bike when accelerating. This, at once, tends to compress the rear shocks and extend the front ones. This is rarely sufficient to offset the effect of the swing arm described.

Finally, weight shifts towards the rear on any bike while it accelerates. But, your shocks are not infinitely compliant. That is, when any load is applied quickly to your rear shocks they 'stiffen' before compressing. In other words, the rear-end of your motorcycle will rise first, then it will squat because of weight transfer.

So why should anyone care?

Because just as it is almost always true that the rear-end will rise when you accelerate, the rear-end will squat when you use the rear brake. This, because when the rear brake is used the swing arm is pulled level with the road (ie, front end of it will move down.) This lowers the Center of Gravity and lengthens the wheelbase at the same time. In other words, it makes the bike easier to control. It becomes more stable.

You want to make the job of riding slowly easier? Use the rear brake.

As to 'wheelies' and 'stoppies', both are accomplished as a function of how high the CG is relative to the bike's wheelbase, not whether the bike is chain or shaft driven.

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