What is the standard tractor wheelbase required for Cottrell? Because different tractor OEMS can vary on their set back front axle dimensions, we do not work in wheelbases. The standard dimension we require is from the front bumper to the center of the rear drive axle. We typically require said dimension to be 308”. (However that can vary as well so contact your sales representative if you want to make sure you have the correct required dimension for your brand of truck.