i would suppose its because the weight in which they carry must be distributed on 18 wheels instead of 4, 4 wheels would not workEach wheel has a specific load rating as does the axle. The more tires...
Well if the 1998 truck bed is 8 feet and the 2008 is a 6.5 feet the answer is no.How big is the 1998 trucks bed and how big is the 2008 trucks bed.You need to measure length and width.