[KenWittlief]

Ted has a good point - if you end up hitting something, or another bot is pushing you backwards, you wheels will either be slipping (spinning) or turning backwards or both

but either way, you are already lost - so you might as well assume you are going in the direction you set your motors to. once your wheels slip your position based on wheel turns is useless.

and if you are using wheel rotation to close the loop on motor speed, buy the time your wheels end up being pushed backwards your PID loop would have them at full power forwards anyway