Mel,
I generally like to have the front tires just touch the track to help reduce some of the drag on the guide just a little bit. It’s a fine balance. If you have the tires riding up and all the pressure on the guide you might be slightly slower because of the friction/drag.
I agree with Russell’s statement – If it ain’t broke, don’t fix it. Many a slot car racer has fallen victim to messing with their car too much and watching the performance go backwards.
Best of luck with it!
Marty