You'll have to look at the rope company website, but I think most recommend 7/8-1" for vehicles weights like Jeeps, 1/2 ton trucks and average size SUVs. Length is going to be somewhat your choice. In rocky and/or tight environments, the shorter 20' might be better. Mud/sand/snow the 30' will give you extra distance. Personally, I carry a 20' kinetic rope and a 30' tow strap which could be linked together if needed in an effort to have the best of both.