For some reason, Light duty trucks are rated some 10-15% less than the sum of the axels. Meanwhile most medium and ALL heavy duty trucks, ie over class 4 trucks to class 8, will have the gvwr BE the sum of teh axels. This makes more sense to me. Now why the class 3 ie 1 ton/35 series and smaller trucks are derated.......your guess is as good as mine.
Meanwhile, if one wants to get into the legal side of things. A SW CC diesel truck with a 9900 gvwr, and a tare wt of 7500 lbs will be licensed for 12K here in Wa st, and it will be legal to run down the road at 12K lbs too! Door sticker be dammed! GCWR in most states, is also a non legal measure/rating. It is only from a warranty purpose that these ratings will be an issue. Along with a civil court case, but from an LEO stand point.....nada!
marty