Question about GVWR.

Also maybe add that the rating is for the respective truck's "standard" equipment. Meaning optional equipment does not change the GAWR.

Example, my truck's rear is 6100 because of the 17" tires. I have optional 18s with a greater rating, I also have the optional overload spring, which is standard on the 350, but my axle rating is still 6100.

I guess from an administrative point of view, it's much easier to have one axle rating for each model.

donn0128 wrote:
GAWR is the weight rating for one single component the axle.

This is false. The GAWR is defined by the NHTSA and DOT to be the measure of the limit of the axle system which includes suspension and tires. It is not just what the axle itself can handle

"The Gross Axle Weight Rating (GAWR) is the maximum weight that the designated axle system is designed to carry. It is set by the OEM and noted on the vehicle's original certification label. Alterers must determine whether their modifications affect the manufacturer's stated GVWR or GAWR. If they do, the alterer must specify the new GVWR or GAWR on the alterer's certification label (see 49 CFR 567.7). Note: A modifier or dealer should never accept an altered vehicle that does not have an alterer's certification label."

http://www.nhtsa.gov/cars/rules/adaptive/Inoper/Fre_ask_Ques.htm

"GAWR (Gross Axle Weight Rating) – The GAWR is the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system. Each axle on a truck (and trailer) has a maximum allowable weight capacity. As previously noted, the GVWR of a truck is usually less than the combined GAWRs of all of a truck’s axles. The GAWR is limited by the weakest link in the axle system which also includes the suspension and the tires. For example, an axle with a design rating of 21,000 pounds may be rated lower due to the rating of the selected suspension (springs) or tires. When calculating the design load on an axle, make sure to take into account any weight transferred to the axle from a trailer (tongue weight) and the potential placement of cargo."

https://www.ntea.com/content.aspx?id=20194


If the GAWR set on manufactured trucks was just the axle, then the 11.5" AAM axle in my truck would have a GAWR of it's rated 10,000 lbs instead of its axle system rating of 6,500 lbs.

http://en.wikipedia.org/wiki/10.5%22_Corporate_14_Bolt_Differential#11.5_AAM

Atlee wrote:
Why doesn't the Gross Vehicle Weight Rating equal the Gross Axle Weight Rating for the front and rear axle?

Take my F150 (heavy) pickup for example. The FGAWR = 4,050#. The RGAWR = 4,800#. Yet the GVWR = 8,200#. Why shouldn't the GVWR = 8,850#?

In your case, the reason why your truck is not rated over 8,500 lbs GVWR has more to do with the DOT class that it is in than the actual weight it can handle.

The US DOT(Department of Transportation) and EPA(Environmental Protection Agency) classifies on-highway vehicles in 8 different classes with class 2 being broken down into two different segments. The classes for the light duty(yes an F350 is considered light duty) are as follows;

Light Duty
Class 1: 0 - 6,000 lbs GVWR (small cars and midsize trucks)
Class 2A: 6,0001 - 8,500 lbs GVWR (150/1500 trucks and vans)
Class 2B: 8,501 - 10,000 lbs GVWR (250/2500 trucks and vans)
Class 3: 10,001 - 14,000 lbs GVWR (350/3500 trucks and vans)

The GVWRs for the rest of the classes can be found here.


So as you can see, if Ford gave your truck a GVWR of over 8,501 lbs, then it would be considered a class 2B truck which is where their F250s are. The class system that we currently have was made a long time ago and in my opinion is outdated. There are some classes (like class 1 and class 2b) that most trucks that are in them are limited due to the class they are in rather than what they can actually handle. Keep in mind that for most manufacturers, their GAWR is the weight that the axles AND suspension/tire components can handle.

Take a look at class 1 midsize pickup trucks. Every one of the V6 models have a max GVWR of 6,000 lbs. This isn't because all the manufacturers got together and figured that was the most they would rate their trucks. It is because of the class those trucks are in is maxed out to 6,000 lbs GVWR therefore they cannot make it higher even if the truck can handle more.

Take a look at the 250/2500 trucks as well(especially the diesel trucks). Almost all of them are maxed out at 10,000 lbs except for a few with small engines yet most have a GAWR that would put them into the 11,000 - 12,000 lbs GVWR range. Again, this is not because all the truck manufacturers agreed to max their trucks out at that limit or even because that is all that truck can handle by its specs. It is because 10,000 lbs GVWR is the max each manufacturer can apply to their Class 2B trucks going by the DOT and EPA trucks classification system.

Yes, the system is outdated and you would probably see all 250/2500 trucks automatically raise their GVWRs without changing a thing on the trucks if the Class 2B was raised to 12,000 lbs GVWR, but that will likely never happen given the bureaucracy of our government. So your truck cannot be given an 8,850 lb GVWR even if it could handle it due to government regulations.

Because the whole is less than the sum....just check out 'Why Einstein's famous formula tells us that the whole, as far as mass is concerned, is often less than the sum of its parts'

donn0128 wrote:
GVWR is the maximum weight that a vehicle can weigh per the manufacturer. It is based on the assembled components including the weakest link. GAWR is the weight rating for one single component the axle. Loading to GAWR would likely overload the weakest link in the chain. Usually tires, but could also include things like springs, drive shaft, frame, wheels heck even safety equipment like seat belts. There is a retired GM engineer on the forums whos job was as a certification engineer. His basic job was to submit certification requests to the Feds for vehicles. He is very knowledgable in the process and what it all entails.

Good description Don.
What I can add is the perspective on how a truck owner would load the vehicle so precisely that the actual axle weights would total that GVWR number. There is some leeway to move the load a little fore & aft such that axle ratings are not exceeded when GVWR is reached.

Atlee wrote:
Why doesn't the Gross Vehicle Weight Rating equal the Gross Axle Weight Rating for the front and rear axle?

Take my F150 (heavy) pickup for example. The FGAWR = 4,050#. The RGAWR = 4,800#. Yet the GVWR = 8,200#. Why shouldn't the GVWR = 8,850#?

For commercial purposes it actually is used as the trucks GVWR.
As rjstractor mentions this is the way you will use the same truck if you were towing commercially. And its safe to do so.
The truck makers may choose any GVWR number he wants as long as it doesn't exceed the sum of the vehicles certified GAWRs.

Lots of theories as to why the truck makers choose a particular GVWR.
Some say for a nice long warranty.
Or for IRS tax issues.
Or for licensing issues.
Lots of other opinions.

Over loading the rear axle is mentioned by some as a possible reason GAWRs don't = GVWR.
We have the same over load problem with some (not all) of the new higher GVWR numbers with those low RAWR numbers.

Just stay under your trucks 4800 RAWR. Your front axle isn't a big player in a hitch weight so its not a concern.

Edit; GCWR to GVWR....Jim

If only axle weight mattered, they could hang a dually axle under a Ranger and say that it is good for 12,000 pounds. GVWR is the rating for the "Total" vehicle, including frame, suspension, tires, transmission, engine, etc. etc.

I think you will find that for most light trucks the gross vehicle weight is less than the combined axle weight. GVWR is also a function of how well a vehicle will stop loaded up to that rating. GVWR is not caclulated by adding up the axle ratings or even tire ratings. Consider a dually, it has more than 12,000 pounds rear tire capacity, a rear axle that is around 9500 pounds and is on a vehicle with perhaps a 12,000-14,000 pound GVWR. Add in the front axle and two front tires and soon it is very apparent that if you try to make the numbers add up they won't.

It seems as though vehicles intended for the consumer market are that way. This is my theory, and it's just a theory, I have nothing really to back it up with- Say your truck's GVWR is actually the sum of FGAWR and RGAWR, so 8850. Say your truck weighs 5500 empty, giving you a max payload of 3350. The average consumer might see that number and assume they can just throw 3000 pounds in the bed. The problem with that is the RGAWR would be exceeded substantially. Therefore the OEMs give some "wiggle room" with GVWRs and payload ratings to help avoid exceeding axle ratings by a wide margin.

The GVWR on trucks for the commercial market typically is FGAWR+RGAWR. My theory on that is a commercial user is more likely to pay attention to axle weights, and the OEMs leave it to the truck user to determine how to load the truck.

Weakest link in the food chain down to pavement dictates


Stopping to agency mandated distance at max conditions....etc

Might just be longevity for warranty

We on the outside will never know and just guesses...