[Taylor]

Depends on the drive train setup. We've put a pair of 4" duraomnis on the front of our 6WD and have had no problems whatsoever. I was personally surprised at how well they've worked; I was expecting them to slide sideways on the slick ramp. However, we've found that the grippy kit wheels in the middle and back keep the robot steady.
Our chassis is just under 28" long.
However, I would not expect the same results with a 42" long 4WD system.