The Pros are marked "DOT", and "FOR COMPETITION USE ONLY...NOT FOR HIGHWAY USE", but I use them on the street (which is not a highway ). The Pros I bought in 2005 are still soft and have no cracks in them...probably because they have spent too little time on the road since the car has been apart and on jackstands for the last few years. Had the standard version before, and the Pros are softer.