JIMNLIN wrote:
John wrote:
Often times GVWR is limited to less than f+R awr due to brakes. We know the frame is designed for the full rating at each end, so there is something else limiting it.
There are times where exceeding GVWR isn't a big deal, and other times where it is. It really just depends on what your using.
Actually brakes on a vehicle ( our trucks or trailers) are determined by the axle rating;
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".
This is one big reason dot allows us to use the sum of the vehicles axle rating as the vehicles GVW (if required) and another reason GVWR doesn't determine how much load the truck can carry safely/legally.
Many times its not the tires that is the weak link in any size truck. looking at tire/wheels/spring rate spec on Fords 150/250/350 trucks shows the wheels with the lowest rating on some trucks and others its the spring pack.
Not so true on 3/4 and 1 ton pickups.
The axle on my pickup is the same axle, and same brakes, as the one used on a DRW. The GAWR has a difference of 3150lbs, but only a GVWR difference of 2300lbs.
Ford even discusses that brakes are sized to the GVWR in their towing brochure. "Towing vehicle’s braking system is rated for operation at GVWR"... which on any HD pickup is less than the sum of front and rear.
On my TT the 5200lb axle has the same brakes as a 6K, 7K, and some 8K lbs axles. The brakes are not the limiting factor there, even the bearings are the same as the 7K axle, but a different tube/hub are on the 7K (and some 6K have the 8 lug hub). Brakes are not a determining factor on my trailer axles.
This is why one must research their truck/trailer if they plan to exceed GVWR.
All my research on pickups has lead me to the conclusion than brakes are based on GVWR, not FAWR+RAWR... The only time I have found it to not be true is looking at multiple GVWR's with the same brakes.. i.e. a 3/4 Ram has the same brakes as a DRW Ram in my year... or some cab configurations change GVWR for the same components. So the brakes are designed for the highest rated application.
As far as DOT is concerned they don't care, at least here in Idaho, about any GVW or GAW... simply what I have registered for and what tires I have (and under 20K/axle). Beyond that it's up to me to be smart about loading. I know I have 9K worth of tires on my front axle, and I also know the axle itself can't go that high.
Looking thru specs there isn't a single 3/4 or 1 ton SRW truck I can find that isn't tire limited. That takes everything into account. Most 1/2 tons are axle limited these days... in years past they have been tire limited but with all the 17-22" rims out there the tires hold a little more, even as LRB.