Determining Rear GAWR

My buddy has a 2014 Ram 3500 SRW/Cummins 4x4.

It has the exact same wheels and tires (size, type, brand) as my truck, but has 500# more rear GAWR (6500# to his 7000#). Must be the springs.

another factor is the diff ring gear dia and the subsequent axle
bearing size. There are TWO 14 bolt diff's that GM puts in +8K GVWR trucks/SUVs

Note that the OEM that supplies the rear axle assembly for my GMT400
rates it at 10,000 lb GAWR

so why does GM rate it for 6,000 lb GAWR?...yes, that is the sum of
the tire's max weight rating, but does that mean if I put in 4,000 lb
rated tires it would now be rated 8,000 lb GAWR?

Mine is also the same axle assembly for the 1 ton dually of my year and it
too is rated 6,000 lb GAWR...so the exact same?

Nope, the MC bores are larger on the 1 ton dually. The rear brake drum
dia are the same, but some 8,600 GVWR Sub's have that same dia, but
2.5" wide shoes/drums...while others and the 1 ton dually has the
same dia drum, but 3.5" wide shoes/drums. The rear brake cylinder bores
are also larger. The brake proportioning valve body are also different

It's not any one component of the 'system', but the whole system that
dictates

And this is what I hate regarding engineering vs marketing vs legal specs!

Any engineer would tell you that if you eliminate the weak spot - tires + wheels, then you should be good for the maximum weight the actual axle is rated for.

So physically, I can guarantee you have nothing to worry about. Legally? Who knows...

I will say, as an engineer myself, if I were ever called into court as a "subject matter expert", I would wholeheartedly defend the guy who put 19.5s on a 3500 SRW, and loaded up the truck to DRW weight limits.

If you dig deep enough, I'm sure you can find the engineering documentation at GM stating the 6200 lbs being a tire limit. If you coupled that with the real axle rating from the axle manufacturer, you'll be able to legally defend yourself.

gmcsmoke wrote:
there's no difference in the wheels the rear axle is derated to fit under the lowered GVWR. The FAWR is the same for both 25/3500 trucks.

Actually, most pickups have GVWRs that are significantly less than the total of the GAWRs.

there's no difference in the wheels the rear axle is derated to fit under the lowered GVWR. The FAWR is the same for both 25/3500 trucks.