Help with towing numbers on a 1500 chassis

[bcbickers]

Greetings All,

We used our travel trailer for the first time this weekend. I spent some time at a CAT scale and would like some advice about my vehicle's setup. Here are the numbers. If it matters, weather was clear and 85* F.

Description	Weight - no trailer	Weight w/ trailer
Steer Axle	3380	2980
Drive Axle	3580	4820
Trailer Axle	-	6280
Gross Weight	6960	14080

The Suburban drove fine with no sway or untowards movements. With the Tru-Cool 40k cooler, transmission temps never got over 160* F. Fuel economy was 9.2 mpg (hand-calc'ed) running about 60 mph in the Texas Hill Country. Several of the hills forced a downshift into 3rd and 3,000ish rpms, but some 4.10s will fix that.

My biggest concern is how much overweight the rear axle was (4,820 lbs. actual vs 4,200 lbs. GAWR). I know part of that is an improper WDH setup, since not enough weight was getting transferred to the front axle. I probably should have moved most of our cargo (clothes, food, cooler) to the trailer as well. I'll bet that was at least 200 lbs. Tongue weight also seemed a little high at 1,240 lbs (~17% of 7,120 lbs. trailer weight). I might need to look at what all is in the front compartment and move things around a bit.

So two questions:
1) If I upgrade to a 14-bolt rear axle, does that also increase my rear GAWR and possibly my GVWR?
2) The front GAWR is 3,600 lbs. and the rear is 4,200 lbs. Added together, I get 7,800 lbs. GVWR, but the door placard says 7,400 lbs. Which is the correct number from a capability and safety perspective, not a legal one? Are any of you over GVWR or GCWR, and if so what is your towing experience?

 

[Big Mama]

just curious. How much did the rear sag? Does your rig have rear auto leveling? I sold my Yukon but was amazed at how well it towed but I was only pulling 5500 pounds. I have a Sierra now but want to follow this thread.

 

[intheburbs]

So two questions:
1) If I upgrade to a 14-bolt rear axle, does that also increase my rear GAWR and possibly my GVWR?
2) The front GAWR is 3,600 lbs. and the rear is 4,200 lbs. Added together, I get 7,800 lbs. GVWR, but the door placard says 7,400 lbs. Which is the correct number from a capability and safety perspective, not a legal one? Are any of you over GVWR or GCWR, and if so what is your towing experience?

Short answers:

1) If you upgrade your rear axle, it upgrades your rear GAWR. Nothing else.

2) The GVWR reflects the weakest link in the "chain" of systems in your truck - axles, engine, transmission, suspension, brakes, etc. So yes, based purely on weight ratings, your axles combined can handle more than 7400 lbs. The limiting factor driving the 7400 lb rating is something else - I'd guess either the brakes or your axle ratio.

Long answer:

Regarding your experience/trip aar: One of the reasons your rig was so stable is because of the high tongue weight. And that illustrates the half-ton conundrum. High tongue weight equals stability, but a low rear axle rating makes that dangerous.

Description	Weight - no trailer	Weight w/ trailer
Steer Axle	3380	2980
Drive Axle	3580	4820
Trailer Axle	-	6280
Gross Weight	6960	14080

You can "almost" make the numbers work with your current weights, if you play around with the WD bars and move some cargo around:

Front - 3693
Rear - 4193
Trailer - 6194
Total - 14080

That gets you 13% hitch weight, which is just about perfect. I don't see any reason to spend the coin to upgrade the rear axle. Instead, spend it on a good WDH like an Eqaulizer, get it dialed in and call it good. If you want to do something to the rear axle, get one of those Mag Hytec diff covers with the cooling fins on it, to help keep the axle temp a little lower.

If you plan long road trips, like hundreds of miles per day for multiple days, I'd buy an IR thermometer so you can check on the rear axle temperature. I did a simple test until I upgraded to the 2500 - whenever we'd stop, I'd put my hand on the rear axle - if I didn't burn myself, it was good. We actually did do some middle-of-the-night driving precisely to help keep the rear axle cool.

Welcome to the wonderful world of towing with a full-sized half-ton SUV. Yes, the rear axle is the most commonly overloaded component, and the primary reason I upgraded to a 2500. My 2001 Suburban is wearing rear axle number 4, precisely because I broke it several times (while on vacation) from towing heavy.

Here's the loading sticker for my 2500:

And the rear axle rating? The limiting factor is actually the rear leaf springs. The axle itself is rated to 8600 lbs, and the two rear tires can handle a little over 6,000 lbs. So I no longer worry about overloading it. And notice the axle weights add up to 9680, even though the GVWR is "only" 8600.