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#?

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.

donn0128 wrote:GVWR is the maximum weight that a vehicle cab weigh per the manufacturer.nit 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.Very well stated. Bruce

Weakest link in the food chain down to pavement dictatesStopping to agency mandated distance at max conditions....etcMight just be longevity for warrantyWe on the outside will never know and just guesses...

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.

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.

Question about GVWR. | Good Sam Community

42 Replies

mtofell1
Explorer
Apr 12, 2015
The first response was a perfect answer to the OP's question. Everything else on this thread (other than the 2nd response which was commending the first responder on his post) is splitting hairs and arguing about what shade of the blue the sky is.
45Ricochet
Explorer
Apr 12, 2015
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#?

That is called static vs dynamic weight. When we drive on roads it can change with turns and terrain changes.
Back 10 years ago the ratio was much different than it is today. Most new SRW 35 series trucks have almost a 90% ratio of GAWR vs GVWR. Ten years ago is was about 75%. GVWR sells trucks and I'll leave it at that. Yes the GVWR and GAWR will be the same in the near future :W
Kevin_O_
Explorer
Apr 12, 2015
I don't understand my trucks ratings as well.. My F350 has a GVWR- 9900lbs
GAWR-
REAR- 6830lbs
Front-5200lbs.

I just had my truck weighed at a Cat Scale

Front axle- 4640lbs
Rear axle 3000lbs
That is 7640lbs total which leaves me 2260lbs for payload. but according to the scale slip I still have 3830lbs available on my rear axle...
blt2ski
Moderator
Apr 12, 2015
Then one has to deal with the at cops in th shacks. Which many times depending upon the states, do not care about the tire, spring or Adel ratings. Only that you are below the 20k lbs per Adel, with no less than 20" of tire width per side to support the load, so you do not harm the roadbed ssurface, sub grade etc. You can have an Adel rated to 25 k per the specs shown earlier, but be over weight as you can only load the Axelrod and its components to 20k lbs.

Ive been pulled over here in wa st many times over my manufacture rated Adel capacity, I have yet to get an over weight ticket, as I am under my paid for license, and the max load per axel with out harm's mg the road bed itself.

Choose your poison in how and what to follow, too many rights and wrongs frankly.

Marty
ShinerBock
Explorer
Apr 11, 2015
donn0128 wrote:

"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. Again INCORRECT! The axle ratingnis specified by the axles manufacturer. They design and specifiy the rating of that single component. The body builder specifies the vehicles GVWR based on factors, among them I spelled out earlier.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

Sorry Don, but that is incorrect. Per US DOT and their definition of what they say the GAWR is, it is the whole axle system and not just the axle. The US DOT is the one who makes these regulations on what GAWR is so you cannout say they are wrong since they make the rule.

"GAWR
The Gross Axle Weight Rating (GAWR) means the value specified by the vehicle manufacturer as the load-carrying capacity of a single axle system, as measured at the tire-ground interfaces."

Page 16 file:///C:/Users/owner/Downloads/TP-110T-03_Nov_01_2012_Final.pdf
spud1957
Explorer
Apr 11, 2015
"Again INCORRECT! The axle ratingnis specified by the axles manufacturer. They design and specifiy the rating of that single component. The body builder specifies the vehicles GVWR based on factors, among them I spelled out earlier"

Don, I understand your point but for the sake of this discussion we are referring to the GAWR that is stated on your DOT label. That's all DOT care about. DOT don't give a rats a$$ what AMM rate the individual axle at. It's spelled out pretty clear in the NTSA document.

My axle is rated at over 7000lbs if I had an F350 sticker on my fender.
JIMNLIN
Explorer III
Apr 11, 2015
Atlee wrote:
Why doesn't the Gross Vehicle Weight Rating equal the Gross Axle Weight Rating for the front and rear axle?

Looking at Fords builders spec pages , even Ford say it may;
4) Gross Axle Weight Rating is determined by the rated capacity of the minimum component of the axle system (axle, computer-selected springs,
wheels, tires) of a specific vehicle. Front and rear GAWRs will, in all cases, sum to a number equal to or greater than the GVWR for the particular vehicle."

Lots of RV folks are confused by how much brake performance a vehicle has. Especially our trucks. Brakes are a function of the vehicles axle system.
NHTSA says this about components of the GAWR:
"Gross Axle Weight Rating is the rated load-carrying capacity of an individual axle and wheel assembly. (It represents the load that may be steadily sustained by the components in the system; i.e., tires, rims, hubs, bearing, axles, brakes, suspension, sub frame, etc. with the GAWR limited by the components with the lowest working rating".

and from RMA

• GAWR: Gross Axle Weight Rating (for each axle) -
The maximum weight rating that the components
(tires, rims/wheels, brakes, springs, and axle) of
each axle are designed to support. This is
determined by the lowest design capacity of any
component. In other words, if the wheels have the
lowest design capacity of any component on that
axle, installing tires with a higher load capacity
does not increase the GAWR. By regulation, the
tire load rating times the number of tires on that
axle must equal or exceed the GAWR for that axle.

And for our trailers;
dexter axle;

The Gross Axle Weight Rating (GAWR) of your running gear is determined by the lowest rated component in the assembly. The capacity of the wheel, tire, axle, brake, springs/rubber and hub are all considered.
donn0128
Explorer II
Apr 11, 2015
ShinerBock wrote:
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 handleSorry, INCORRECT! As an example, my truck has an 11.5K rear axle, but the tires are only rated for 10K. 2500 series trucks can have axle ratings around 10K and carry from the factory 6000 pound rated tires.

"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. Again INCORRECT! The axle ratingnis specified by the axles manufacturer. They design and specifiy the rating of that single component. The body builder specifies the vehicles GVWR based on factors, among them I spelled out earlier.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
BenK
Explorer
Apr 11, 2015
Oh, forgot to use my 1996 Suburban's rear axle as an example

GM purchases this axle assembly from AAM.

AAM rates it at 10,000lb GAWR. GM rates it on my Sub and the 1 ton dually of that
year at 6,000lb GAWR

Why and what is/are the limiting factors/components/etc ???

We will never know as outsiders to their Product Design Team. Nor will they
ever provide that info, as I'd guess they consider that company private and
competitive advantage on how they do things

My front axle is rated 4,250lb GAWR by GM. Ordered it with the F60 option (snow
plow prep package) that has 1 ton torsion bars. The 1 ton dually 4x4 has its
front axle rated around 5,400lb GAWR

Should I take the AAM 10,000lb GAWR for mine? Then the 1 ton dually's 5,400lb
as mine also?

That would be 10,000 + 5,400 = 15,400 GVWR?!?...nope I know better, but do
claim, tongue firmly planted on cheek, my 3/4 ton Sub as a K3500.... :)

PS...also forgot that braking ability (repeated on incline, at high temp, etc, etc)
is another mandated performance item from the regulatory agencies. Maybe the
brake sizing for 'that' GVWR can not meet federal spec with higher weights
on it's back...
BenK
Explorer
Apr 11, 2015
IMHO...there is a world of difference between commercial and RV'ing

Professional vs person on the street.

Level of regulation are far apart. How many of us with civilian drivers licenses
are required to take a regularly schedule physical? To keep a log book of your
hours behind the wheel intermixed with required rest time?

Back to the OPs question...first decide if you believe in the ratings system or not

If not, then do whatever...but know that by going over the ratings...you have
taken the OEM off the warranty hook (if there is any left) and the biggie: Liability hook

If yes, then learn how those systems work and pay attention to the fine print.

Fine print is a legal positioning drafted by their corporate lawyers. Some
call it legalize or weasel words...both terms has merit in my book...

To the newbies reading this trying to learn a thing or two...reference Shiner's
posts with links to some of the governing agencies and their laws/acts/mandates/etc

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