One pair (2 units) of MAXTRAX will usually do the job but two pairs (4 units) make vehicle extraction even easier. We recommend two pair if you're crossing a desert or heading into remote areas, or towing a trailer or a boat. That way you get instant traction on all four wheels, then once you get moving, the rear wheels of the vehicle gain an extra spurt of momentum from the front pair of half-buried MAXTRAX. If you're towing, the trailer wheels then gain traction on the rear pair of MAXTRAX.