Originally Posted by texastech_diesel

I've always wondered this... GCWR is listed on all the Ford docs using engine and gearing combos to delineate the rating of the truck. It would seem logical to the layman that a regear should boost the GCWR, because if the truck had been factory built with those gears, the sticker would have a higher number on it. But people swear up and down the internet that this number is fixed, regardless of how the truck is equiped, or what parts are changed out.

Can anyone actually explain how/why FoMoCo rates an individual truck's GCWR? And why you can't load the truck to a higher GCWR when you modify the equipment to match what a a higher-GCWR truck would have come from the factory with?

Please spare me the "because the sticker says so" lines, and let's just leave liscencing requirements out of this, since those are just numbers printed on legal documents. I'm talking pure mechanics involving the parts installed on the truck. Can you effectively increase the GCWR from a mechanical perspective by modding a stock truck?


Edit: Here's an example of kind of what I'm asking about:

I have an 07 F-250 6.0L w/ 3.73 rear end, a 7500# truck with a 23,500# GCWR. I use it for work to pull an 9k bumper pull trailer, which totals to 15.5k# and is well within all the specs of the truck, hitch, etc. I bump that up to a 15k# gooseneck equipment trailer. At 22.5k#, I'm still within the GCWR of the truck, but I'm pushing the top end here.

So not wanting to buy another truck, I regear to 4.30s, swap out the rear axle internals to the components from an F-350 (bigger shafts w/ more splines), put in the 4" block, and swap in some +2 front coils, up to say 6000# springs. I add in a rear trac bar, overload springs, some airbags, and a B&W 24k flip over ball. My 7500# truck now weighs in at just over 8000#, and I've pretty much maxed out the GCWR with my 15k# trailer.

So think about it. While I might have maxed out the GCWR according to the book, I've basically changed my F-250 w/ 3.73s to an F-350 w/ 4.30s. The 4.30/6.0L combo is rated to 26,000# GCWR. Since I'm almost at, but not to the stock GCWR, I didn't overload the truck according to either the tag or the plates, so didn't I just create a safety margin by modding the truck to a platform, that had it come from the factory that way, would have 2500# more of GCWR?