I had a 60" rake on a 16 horsepower 4WD tractor with ag tires, and it seemed to pull it pretty well. When I would pull gravel up a steep hill, if it got pretty loaded, I'd start to lose traction. I think, worst case, going too wide will lower the speed you can work at, unless it's a traction problem. And you're lowering the speed but taking fewer passes, so at worst the effects will cancel out.