MOD 1 pinion question

[its me]

Originally Posted by lincpimp

&xl on 4s will be plenty, 5s will be too much motor rpm.

What vehicle, tires size(overall diameter in inches) do you have. That will make it much easier to advise on a pinion.

I should have asked sooner, why is 5S to much for the 7XL? is it because of material quality/bearings or will it just cause to much heat in the motor?