I have reversed the Robochallenge wheels on both of our new machines. It makes it 25mm shorter; 40 if you go by the wheel position.

But caution! I found that when driving the wheels would tighten onto the front face of the motor. This happened to one and it burnt out the motor in a massive cloud of smoke! The way to stop this is to add a M8 washer onto the shaft and remove all the plastic up to the bolt on the inside of the wheel. The means as the wheel tightens if comes to rest on the washer, not the motor.

If these new wheels do the same thing but are designed for it, I will probably swap to make the set up more reliable!