GVWR? IS this number picked out of the air? :-)

[budwich]

I was looking at trying understand what or maybe why the GVWR is what it is.

I see in 2008 (my year) that a 2W vehicle has a GVWR of 5550 lbs while a 4W has a rating of 5750. I think that the difference is probably that addition of the extra drivetrain stuff. BUT doesn't the GVWR limits have constraints related to braking and suspension among other things? These don't get upgraded for 4W versus 2W so shouldn't the GVWR remain the same (just as the GCWR).

 

[IllogicTC]

Drivetrain (though this is more toward GCWR, it can affect GVWR), suspension, frame, axle ratio and strength, wheel bearings, shocks, tires, rims, brakes... all the stuff that involves bearing the load factors in. So having a different style of rim even on a similarly-equipped vehicle may alter this rating.

How do you know suspension isn't upgraded? There's literally tons of RPO codes available in the TB/Envoy just on individual springs for each corner alone. Apparently the standard "premium ride suspension" meant that rather than taking a one-size-fits-all approach, there was a computer that calculated how much weight was at each corner by way of checking through the options list, and selected the appropriate spring to install at each particular corner in an attempt to make it "ride evenly." It can also be assumed that the computer could have been set up to dial the spring selection up a little more for 4x4-equipped vehicles, as this would be trivial.

 

[The_Roadie]

I've never understood this technically either. I think the ratings were fiddled to make sure the 2WD and the 4WD had the came CARGO and PASSENGER WEIGHT capacity even though the naked weight of the 4WD truck is higher.

If I was able to look deeper into the minds of the design team, I'd only run screaming away in horror twice as fast as I already feel like doing.

 

[IllogicTC]

I've never understood this technically either. I think the ratings were fiddled to make sure the 2WD and the 4WD had the came CARGO and PASSENGER WEIGHT capacity even though the naked weight of the 4WD truck is higher.

If I was able to look deeper into the minds of the design team, I'd only run screaming away in horror twice as fast as I already feel like doing.

Again, I would suspect it may come down to the computer-picked suspension. The only way to know would be to find two of the same year with the exact same options installed, except one in 2WD and one in 4WD. The RPO codes would tell the story then.

 

[BlazingTrails]

The gross vehicle weight rating (GVWR), or gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer[1] including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers.[2] The term is used for motor vehicles and trains.
The weight of a vehicle is influenced by passengers, cargo, even fuel level, so a number of terms are used to express the weight of a vehicle in a designated state. Gross combined weight rating refers to the total mass of a vehicle, including all trailers. GVWR and GCWR both describe a vehicle that is in operation and are used to specify weight limitations and restrictions. Curb weight describes a vehicle which is "parked at the curb" and excludes the weight of any occupants or cargo. Dry weight further excludes the weight of all consumables, such as fuel and oils. Gross trailer weight rating specifies the maximum weight of a trailer and the gross axle weight rating specifies the maximum weight on any particular axle.

Pulled this from wikipedia......

Edit: 2005 Trailblazer LS SWB Specs
Weights: gross vehicle weight rating (lbs) 5,549, curb weight (lbs) 4,418, gross trailer weight braked (lbs) 5,300 and max payload (lbs) 1,133

 

[gmcman]

Does the 4WD model have specific spring rates? The XL does so maybe the 4WD does..I agree if there's a set weight for the platform, common sense would state that the 2WD would have a higher payload.

 

[IllogicTC]

Mine:
TrailBlazer 2005 SWB I6 4WD, pretty-well loaded up.

GVWR 5750
Max payload: 1058
Front GAWR: 2950
Rear GAWR: 3200

Suspension codes:
6HP 7HP 8NT 9NS

It would make sense to use heavier springs to compensate for the extra weight to "keep things even," if the 2WD and 4WD used the same springs you'd expect the 4WD to actually ride a little lower, which would be counter-intuitive of course. The use of a weaker spring (whether it has less material or what I don't know) for lighter vehicles makes sense when buying in bulk like GM does/did, as this can represent cost savings if the deal is negotiated well. If they make their own springs, then obviously less material means less cost.

 

[IllogicTC]

I am poring over the "Vin Comparisons" page on the OS. 4x4 SWB seem to have 2,611 KG as the gross rating a lot, while 2WD SWB has them generally in the 2500 range. The suspension codes seem to line up somewhat to what I expected, too, with a common set of codes showing up for 2WD vs 4WD. I believe that there was a target payload they wanted to hit (at or a little over 1000 pounds onboard), regardless of options.

GCWR changes with axle ratios. SWB goes as follows, and is regardless of 2WD or 4WD:

3.42 - 10000
3.73 - 10500
4.10 - 11000

It should be noted that the amount of weight the trailer is allowed to have on a particular axle is 200 pounds less for the 4WD version vs the 2WD version. This further supports my theory of changing suspension selection as appropriate (100kg difference between 2WD and 4WD GVWR is about 220 pounds, which is then subtracted from trailer allowance to come up even on GCWR).

 

[blazinlow89]

If I was able to look deeper into the minds of the design team, I'd only run screaming away in horror twice as fast as I already feel like doing.

That is a place I would not wish upon my worst enemy.

Realizing this, I have exceeded that capacity, substantially many times.

 

[budwich]

Thanks for the comments. Certainly interesting. My recent "weigh in" puts my vehicle loads at just over 5700 lbs (trailer "tongue", two bodies and 7/8 tank of gas). Its close. Travels well. Probably need to fill rear waste tanks with some water to help move weight off the hitch a bit. I guess based on the discussion,a question would be what happens as you get near this "magical" 5750?

Further with this, GM indicates the GCWR is 10000 for combined towing but this figure seems to conflict with the GVWR.... in that they appear to "suggest" that the tow will be a "point load" with no impact (no hitch weight) towards the GVWR. Looking at the guide, they suggest max trailer of 5200 lbs but basically a TB with one adult plus "fluids" is at 4700ish... ie. a moving vehicle. So related to this discussion, is it possible that they consider the two limits "independent". That is in a "no tow" situation the GVWR (unit weight) is one number and in a "tow situation" the GCWR is the guide knowing already the base/curb weight of the vehicle.... of course, no withstanding the limits of the axles limits.

 

[gmcman]

Also, I'm not 100% on this, but isn't the trans rated for 6000 pounds for towing? I know this is slightly conservative but the "60" designation I believe is for 6K lbs.

 

[blazinlow89]

I think that would have more to do with gearing and equipment. The Avalanche uses a 4l60e, m ax toeing is 8000lbs. If I use a weight distributing hitch, it is around 12k.

 

[IllogicTC]

Thanks for the comments. Certainly interesting. My recent "weigh in" puts my vehicle loads at just over 5700 lbs (trailer "tongue", two bodies and 7/8 tank of gas). Its close. Travels well. Probably need to fill rear waste tanks with some water to help move weight off the hitch a bit. I guess based on the discussion,a question would be what happens as you get near this "magical" 5750?

Further with this, GM indicates the GCWR is 10000 for combined towing but this figure seems to conflict with the GVWR.... in that they appear to "suggest" that the tow will be a "point load" with no impact (no hitch weight) towards the GVWR. Looking at the guide, they suggest max trailer of 5200 lbs but basically a TB with one adult plus "fluids" is at 4700ish... ie. a moving vehicle. So related to this discussion, is it possible that they consider the two limits "independent". That is in a "no tow" situation the GVWR (unit weight) is one number and in a "tow situation" the GCWR is the guide knowing already the base/curb weight of the vehicle.... of course, no withstanding the limits of the axles limits.

GCWR is what the engine, transmission, and axle can handle. This is under the assumption that you've already held up the GVWR end of the bargain (by not having a ton of weight toward the front where the suspension would be overloaded (and following the front and rear axle ratings).

GVWR is the total absolute maximum the vehicle itself can weigh. Lessening the payload in the vehicle will allow more weight to be in the trailer, up to the GCWR. By the figure of "vehicle with one passenger is ~4700", if you add 5200 pounds on the hitch you're still coming up at just 9900 pounds.

And what is meant by "weigh in," was this an unofficial calculation of some sort or an actual weighing on a certified scale? I'll have to see if I can find a place to get mine weighed, but I would imagine a rough estimate of weight (not sure if dry weight, or with all fluids) would be the GVWR minus the rated payload.

 

[budwich]

The "weigh in" was an official scaled measure of all axles. Anyways, I think GM is somewhat "mis-stating" (ie.unrealistic) in their statement about maximum trailer towing numbers and it kind of gives one somewhat less "confidence" about their other numbers which is kind the "jest" of my post.

 

[IllogicTC]

I believe the maximum towing numbers to be rather appropriate, however if I remember correctly it is also warned in that same section of the manual that GCWR is not to be exceeded.

I would trust the official weigh-in calculating GCWR as your go-to number first, followed by the trailer towing limits as a rough guideline of how much crap you can pack in the trailer before you should go get weighed and see how close to GCWR you are. After all, the figures for trailer limits may be talking based on base-equipped vehicles. Getting all the fancy stuff adds weight.

Even then, if I figure my GVWR at 5750, less my rated payload of 1058, that makes my rough-estimate vehicle weigh in at just under 4700 pounds. My GCWR is 10500, less 4700 is 5800 left, with a maximum trailer acceptance of 5600 my numbers appear to check out.