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Weight ratings and safety factors

by James 0 Comments
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Modern 3/4 ton trucks are very well built, and similar to 1 ton trucks in most ways. As far as parts, the only differences between a 2015 2500HD and a 2015 3500HD SRW (single rear wheel) are the wheels and an extra leaf on the rear spring pack of the 3500HD. There is a hard 10K GVWR (gross vehicle weight rating) limit because the manufacturers cram the 3/4 ton trucks into Class 2b, so the 2500HD is always going to be hard capped at that limit. Does that mean it is incapable of more? Of course not. But it also means that you need to be very considerate about what you do with it, when pushing or exceeding those limits, as you can’t legally increase the payload capacity of a truck. We’re going to go out on a limb here and throw the GVWR out the window. The rear axle is the same for both the 3500HD SRW and DRW, but the rear axle weight ratings for those are 7050# and 9375#, respectively. The 2500HD is a much smaller 6200#. Assuming wheels, tires, and suspension are up to the task, we should be okay up to the GCWR (gross combined weight rating, for both truck and trailer) for the 2500HD of 25100#.

These aren’t the numbers for my exact truck, but I pulled them off a forum for one that is similarly equipped.

Gross 7980#, front axle 4780#,  rear axle 3200# with a full tank of fuel and a 200lb driver. Subtract the gross from the GVWR, and you have 2020# left for everything else.

I have aftermarket bumpers and steps on my truck, and we can estimate those at 300#. For us, dogs, and some gear, you can add probably another 250# to the cab. I have a toolbox that weighs about 150# with tools, and it holds up to 375# in fuel. And the fifth wheel hitch for my trailer comes in at 240#. If we run with the toolbox full of fuel, we’re have 1315# cutting into that 2020# before we even add a trailer.

A fifth wheel trailer will put 20-25% of its weight on the rear of the truck. The trailer we’ve been running had a dry pin weight of 2000#, and we can assume cargo took that to 2250#.  We’ll look soley at rear axle numbers, and assume that 10% of the payload is shifted to the front axle (which is rated the same at 5600# for all 2500HD and 3500HD Duramax models) without looking at the specifics of the heavy bumper in the front, etc. It should give us a good ballpark figure. Here are the payloads:

  • Bumpers: 300#
  • Cab creatures/contents: 250#
  • Toolbox: 150#
  • Fuel: 375#
  • Hitch: 240#
  • Trailer (our old one, not the new one): 2250#

Total of all that together: 3565#. Assuming 10% of that goes to the front axle, that adds 3028.5 to the 3200# rear axle weight, for a axle weight of 6228#, or just barely overloaded for a 2500HD.

To address those concerns I added Air Lift Ultimate 5000 airbags, an onboard compressor, and upgraded my tires to ones that have a 3750# capacity instead of the stock 3100#ers, that the axle was derated to. That in theory should give me plenty of additional capacity, but there is most likely a good reason Chevrolet does not offer the 20″ wheels I have on the 3500HD models. From my research, they most likely are rated to 3400#, which means I’m alright with my 3114#/tire (6228#/2) weights.

However, the new trailer has a dry pin weight of 2485#. I added a 290# Onan generator and a 200# washer and dryer set, right in the front. We’ll be carrying a bit more gear with us for longer trips, so lets assume 400# of gear weight transfers to the pin. Now instead of a payload of 3565# we’re looking at 4690#. If 90% of that stays over the rear tires, our rear axle will now have 7421# on it. That’s 3710# per tire if we’re fully loaded. The axle can handle it, the suspension can handle it (worse-case, we can add a leaf to have the same rear suspension as the 3500HD DRW), but the wheels are a definite weak spot. 3500HD SRW wheels have the same issue, at 3525# each.

For now, I’m pulling out my tools and not filling up the toolbox. We’ll be fine for the trip home as there is plenty of wiggle room in the specs, but I wouldn’t want to push it for extended travels. The solution here is to either buy a new truck, or go what they call super single. I’m unwilling to trade my truck for a dually because I don’t want one, and I’d probably take a loss on the trade, so I’m going the super single route.

Super single is when you upgrade your wheels to support F, G, or H rated tires. I’ll be going with the Vision 81 Heavy Haulers that will handle 4500# per wheel. I’ve chosen the machined clear coat finish. I’m still debating on tires, but will most likely go with Michelin XDS2 tires in 245/70r19.5, which is almost exactly the same diameter as the stock tires but a almost an inch narrower. They’ll stick out further due to wheel backspacing, though, so I don’t think it’ll look too strange. I’ll be getting them match mounted and dynamically balanced, and run Centramatic automatic balancers. These tires are very heavy, but have approximately 60% thicker sidewalls, and are rated to support up to 4940#. They’ll only come in about 10# heavier per corner than my current combos because of lighter wheels and smaller tires. The wheels will once again be the weak point, but at 4500# per wheel, I will not have to worry about capacity at all. I will still be under the ratings for all axles and the combined vehicle weight. The disadvantage is they’re very expensive, difficult to balance, negatively impact ride quality, and aren’t very good off road due to hard rubber compounds. The ones that are good off road squirm a lot because they have to use deep lugs. The XDS2 is kind of like a mild all-terrain, so it’ll do limited off pavement, and shouldn’t introduce too much squirm.

Doing anything over the factory supplied payload ratings for your truck is a controversial subject, but after a plethora of research, I’ve decided it is the right decision to make in our specific case. These 2500HD trucks are heavily derated due to the 10000# GVWR cap for personal vehicles, and are just as capable with a few modifications as their 3500HD counterparts. I’m looking forward to getting these ordered tomorrow when tire shops open and I can finalized a few prices.

Update 1:

I ordered the tires, mounted and balanced, shipped to a local freight depot today. Prices ranged from $3000 to $5800(!) depending on the vendor. The place I went with was not only one of the least expensive, but they also were one of the only ones who match mount, force balance, and shave the tires if required to make them balance properly. Leave a comment if interested in the vendor. They were expensive, but I consider them and the hitch investments in safety.

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Consider them an investment in safety.

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