Here are the current tire chain ratings. Some new trucks tell you to use type S on the front as there isn't enough clearance for U's. My Dodge 2500 is that way but by using narrower tires, I can run U's without any problems.
SAE class S:
Regular, non-reinforced passenger tire chains and cables for vehicles with restricted wheel well clearances.
SAE class U:
Regular, non-reinforced and lug-reinforced passenger tire chains for vehicles with regular, non-restricted wheel well clearances.
SAE class W:
Passenger tire chains that use light truck components, as well as some light truck chains.
