Out of interest I've just done a few rough calcs based on the following assumptions (I haven't got a scales to hand so the weights may not be accurate.)
2wd
Tyres weigh 50g each with 45mm effective radius
rotor weighs 100g with a 7mm radius and a gearing of 10:1
acceleration from 0 to a motor speed of 50000rpm in 3 seconds.
Without reproducing the calcs in full, the answers I get are as follows:
The torque due to inertia of the motor is approx 10% of the torque due to the inertia of 2 wheels, which is actually more significant than I was expecting.
For the acceleration above the torque generated by the inertia of the wheels is 35.3 Nmm.
So for a typical wheelbase of 275mm the instantaneous effect of the torque due to the tyres on a 2wd is the same as taking 13g from the front axle and moving it to the back axle of the car.
So take 10% of 13g and that will be the change in load due to the inertia of the motor. i.e. 1.3g
So changing the motor direction by adding a gear to the transmission results in a maximum difference in load of 2.6g for a 1500g car or 0.2% of the cars weight.
Which is a difference that I personally am not good enough to notice.
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