3500 SRW vs DRW: Non-obvious differences

[bickford]

There is a 6000 lb. difference in tow rating between 2015 Duramax SRW and DRW trucks (24,500 vs 30,500 GCWR). Increased pin and hitch weight capacities are very different for SRW and Dually.

Are there non-obvious differences between SRW and DRW pickups? Are cooling, braking, or anything else internal different?

[CoyleJR]

My first thought is that the weight rating for a single tire compared to a dual tire is a major factor for the different weight ratings. Additionally, the wheels would also be rated for a much lower capacity on a single wheel truck. There probably isn't much of a difference between the truck in terms of the actual parts.

[bickford]

It seems that tire size is a significant part of the difference in towing capacity between SRW and DRW pickups. Chevrolet uses 3.73 gears for both, yet DRW tires have a smaller diameter. This means that a DRW pickup has more driveshaft revolutions per mile.

Higher number rear axle ratios are generally associated with higher towing and GCWR numbers, and DRW pickups have a higher effective gear reduction behind the driveshaft.

This is assuming that the transmission gears are the same for the two.

[Kennedy]

My take is that the SRW to DRW are largely the same with the exception being wheels/tires, hubs.

My SRW has the extra overload "slapper" springs like a DRW.

Oh yeah-No TPMS on the 1 tons! At least not in 2012...

[DickWells]

I've never thought much about it, but our wagon master for the Alaska tour in 07 had a DRW Dura Max and claimed that the wheel bearings were much wider in his full-floating hubs than in a SRW. I've never taken the time to confirm this, even though my son has an 03 3500 DRW. Well, he also asserted that "You'll never get 50 K miles out of your truck tires, towing." My last set of Michellins got more than 54 k before the wear bars touched. Can one of you guys confirm that the DRW rear end has heavier bearings? To me, it would stand to reason.

DW

[DickWells]

Got curious and went to Rock Auto's catalog and checked both 2500 and 3500 outer RW bearings. I didn't see any opportunity to specify SRW, or DRW, but the result was that they spec the same dimensions for both. Doesn't make much sense, to me. I'd think that you'd need a much wider bearing to take all that extra dish. ???

[a5150nut]

Got curious and went to Rock Auto's catalog and checked both 2500 and 3500 outer RW bearings. I didn't see any opportunity to specify SRW, or DRW, but the result was that they spec the same dimensions for both. Doesn't make much sense, to me. I'd think that you'd need a much wider bearing to take all that extra dish. ???

Dick,

I would think the center of balance would take care of the extra dish. There are deep spacers on the front to compensate for the wheel. I have seen kits to put duels on a 3/4 ton and they are studs, spacers, and the wheels.

[DmaxMaverick]

Got curious and went to Rock Auto's catalog and checked both 2500 and 3500 outer RW bearings. I didn't see any opportunity to specify SRW, or DRW, but the result was that they spec the same dimensions for both. Doesn't make much sense, to me. I'd think that you'd need a much wider bearing to take all that extra dish. ???

AAM (the axle manufacturer) rates the GM D/A 2500/3500HD 11.5" axle capacity at 10,500 pounds, all by itself, and make no condition to how that weight is applied. The only difference between the different GM 2500/3500HD axle applications is the tube and axle shaft length. They are interchangeable, otherwise.

As far as the "dish" goes, the wheels are installed, opposed, so the weight bearing center is still at the hub surface. The same location that may be applied on a single wheel. Just for discussion (not the same geometry as the rear axle), the front hubs are extended, but the weight bearing center is inboard, because the dual-dish wheel is installed convex, with the weight bearing surface about the same as with a SRW front axle.

[DickWells]

Yes, I understand about the location of the center of mass, but used "dish" in an attempt to express what I perceive as a wider load bearing area to put more force to the single bearing, both from inside and outside, like when the inner tire rolls over a pot-hole while the outer one hits a bump, for instance. Seems I'm not giving those bearings, front, or rear, enough credit. And, my wagon master, from 07 was wrong, as well.

Thanks for the info.

DW

[DmaxMaverick]

Yes, I understand about the location of the center of mass, but used "dish" in an attempt to express what I perceive as a wider load bearing area to put more force to the single bearing, both from inside and outside, like when the inner tire rolls over a pot-hole while the outer one hits a bump, for instance. Seems I'm not giving those bearings, front, or rear, enough credit. And, my wagon master, from 07 was wrong, as well.

Thanks for the info.

DW

Equally distributed load vs. leveraged load. I understand what you're saying. Either the bearings and design (of all mfg's) is adequately over-engineered, or the millions of us have been very lucky. While premature wheel bearing failure does happen, it's rare, and can almost always be attributed to abuse, (lack of) maintenance, or mfg defect. I'm not aware of any reports, from any mfg's, when DRW bearings fail at a higher rate than SRW bearings, front or rear. I really don't think we are all that lucky. I know my luck doesn't run in that direction.

[bickford]

Here are the numbers from the 2016 Chevrolet Order Guide:

SRW tire: LT265/70R18E
DRW tire: LT235/80R17

Michelin lists the SRW tire diameter as 32.7" and the DRW 31.8"

The 3% difference in diameter helps, but doesn't explain the 24% difference in GCWR!

[gimpyhauler]

There is a 6000 lb. difference in tow rating between 2015 Duramax SRW and DRW trucks (24,500 vs 30,500 GCWR). Increased pin and hitch weight capacities are very different for SRW and Dually.

Are there non-obvious differences between SRW and DRW pickups? Are cooling, braking, or anything else internal different?

Does it make a difference when it goes over 25,000#? Doesn't anything over something like 25,000# have to stop at the scales?

[DmaxMaverick]

Does it make a difference when it goes over 25,000#? Doesn't anything over something like 25,000# have to stop at the scales?

26K is actually the limit, making a greater combined load commercial, requiring USDOT compliance, in every regard. Non-commercial below that isn't normally required to scale. There are exceptions, however. Local ordinance and state laws may also skew it some. Some states require a non-commercial CDL at specific weight combinations as well, for recreational transport.

[Mark Rinker]

Having owned and towed extensively with both, I ended up favoring the SRW version for the extra unloaded MPG and better ride with the truck alone.

For towing goosenecks, obviously the DRW setup allows for more weight transfer to the truck.

Very application specific, but amazed at how stable the SRW trucks were, despite less contact area.

Rotating tires for max mileage out of a set is MUCH easier with SRW as well.