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?

 

I agree and see where you're coming from. The F-350 DRW is like 23,500 GCWR unless you add the Tow Boss pkg. and it jumps to 26,000. It would make sense that if you regeared to 4.30 on a 3.73 or 4.10 truck, your GCWR should also increase.

 

I agree with the above example. You have increased the capability of the truck so technically you would want to go by the rating so you don't abuse the truck.

What I am wondering is what if you wanted to go to the next step and be legal about it. How would one go about that?

 

Sticker? What sticker? I've never seen a sticker with a GCWR on it on a Ford truck. The data sticker in the driver's door area has GVWR, but it does not have GCWR. The owner's manual is the only place you can find GCWR, and then it is a table if there was more than one gear ratio available.

Changing gears won't change GVWR. That is determined by axle and/or tire rating, though sometimes it's lowered due to some other component.

GCWR is usually determined by vehicle performance. It could be speed up a grade, or it could be powertrain cooling, or it could be braking performance, or a few other things. Changing gearing will help performance and cooling, but not braking.

If the owner's manual shows two axle ratios available and they have different GCWR, then your GCWR will change if you change axle ratios.

 

The way I understand and interpret it, there is no next step. If the truck had an option for a particular setup, if you added or changed to that option, you are maxed out. For example, my truck came with a 3.73 rear end, but had an option and a tow rating for a 4.30. But there was no option for anything beyond that. You could certainly go beyond that, but there is no testing or anything for it, so there are no "official" ratings for that from Ford.

 

A ford engineer explained to me that GCWR is determined by an ratio. here it is.

The weight of the Truck subtracted from the GCWR number gives you tow capacity. So if your tow vehicle weighs in at 6000 lbs and your GCWR is 12000, then that vehicle is design to tow 6000lbs.

Now that being said. Changing gear ratio's, oil or tranny cooler, or any other option, that is not on your tow vehicle but is added to mirror 1 with a higher GCWR would in theory raise that vehicles towing capacity, and GCWR.

 

I'm not sure I understand your question. Obviously, you can take any vehicle and if you modify it enough, you can increase the GVWR or GCWR to whatever you want. But the manufacturer is not going to be involved and their rating is no longer valid.

Except, in a court of law. If a misfortune occurs and you are sued for liability, and the plaintiff claims that you negligently overloaded the truck, how will you defend yourself? Are you an engineer with experience in automotive modifications? Will your insurance cover you?

Obviously your Ford warranty will not cover you for the increased load rating.

So again, what is your question? Liability? Warranty? Or just whether it can be done? I think it is pretty clear that it can be done.

 

The GVWR and GCWR are determined by engineers at Ford. Engine, transmission, chassis, gearing, wheelbase, 2 or 4 wheel drive, cooling, brakes and even tires.

Certainly, you can swap out parts out to make your truck into a vehicle with a higher GVWR and GCWR, but the legal aspect has to be discussed with your local DMV. Each state is different, I've heard a few will have a process to do this.

 

Double post - sorry

 

In the book, then. The b-pillar has all the info (gearing, etc) to go into the book and find the GCWR. My bad for the confusion.

I don't get how you go from :
to :
What are you talking about?

 

GVWR is going to be limited by axles, springs, tires. GCWR is limited by different things, motor, tranny, gearing, brakes, cooling ...

 

It's all about MY comfort with the load. I won't exceed the rated GCWR, but if I'm pushing the upper limits, why not mod the truck a bit (compared to shelling out cash for another rig), to match something that is supposed to be able to handle more. Preventative overengineering?

 

Sure you can, and it's a good idea. It's done all the time on the early SD because Ford rated them really low for 5th wheel towing. Just about everybody who pulls a decent size 5'r on an early SD is over the GCVW.

Go for it.

 

a lot of people get confused on this issue. the gvwr sticker on your truck is a legal number. if youre truck has an 8800lb gvwr, you cannot legally go over 8800lbs. the gcwr from ford is a recommended number. if ford says your truck has an 18k lb gcwr but you can tow 25k lbs and stay within your gvwr then you are still legal. gcwr doesnt become an issue until you exceed 26k lbs.

take this for example. im going to use 10% for bumper pull trailers and 25% for goosenecks. i have a 2000 f250 with a 5.4. my gvwr is 8800lbs and i *think* ford recommends a 15k lbs gcwr. if my truck weighs 6k lbs that means i have 2800lb for payload. say i have a gooseneck trailer that weighs 8k lbs and 25% of the load is on my truck(8k x 25%=2k lb load). currently i have 14k lbs for my gcw and 8k lbs for my gvw.

now say i also want to pull a bumper pull trailer that weighs 8k lbs on the back of the gooseneck trailer(pull two trailers at the same time). 10% of the bumper pull trailer (800 lbs) will be on the gooseneck trailer, bringing the total weight of the first trailer to 8800 lbs(which now makes my gvw 8200 lbs). add my truck and two trailers up and i have a gvw of 8200 lbs and a gcw of 22k lbs. that is 100% legal but exceeds fords recommended gcwr of 15k lbs.

 

but to answer your question about the safety margin of your truck, yes it does help to have the regear and extra changes you made.