3 inch tailpipes hit the shocks and about everything else--you work and work to get them just right then you put a cooler in the trunk or worse someone in the back seat and clankity clank--so for a car you will USE I think it is better with the 2 1/2 in like already stated the mufflers play a bigger role in most applications just no fun with the 3 in 1/16th to a 1/4 in away from the gas tank and same on the shocks etc