The two main ways you'd have to do it are either to run one set of wheels (either back or front) off the drill motors and connect the other set of wheels via pulleys or chains, geared in such a way that the small wheels turn faster than the bigger wheels, thus covering the same amount of ground each in one rotation, or if going for four motors, run the rear motors on a higher voltage so that they spin faster than the front ones. This method is a bit trickier as batteries tend to come in set voltages so it can be difficult to get an exact voltage match.