What’s in a rating? GVWR GCWR GAWR

Discussion in 'Towing & Trailer Tech' started by Crawdaddy, Jun 21, 2013.

  1. Crawdaddy


    The following is helpful information, rant, and questions, and roughly in that order...My apologies if this wasn't what you were looking for in the first place...

    So, CKNSLS recently got me thinking about towing capacities, GVWRs, GCWRs, GAWRs, and other sorts of technical numbers related to the world of towing. For those that don’t know, my Suburban is a ¾ ton for all intensive purposes despite starting its life and still legally being a half-ton truck. But that’s not important for this discussion. What is important is the response I got back from GM when I inquired about my trailer weight rating for the Suburban in stock form…

    First, a short glossary of what all those acronyms mean to put things into perspective.

    GVWR- Gross Vehicle Weight Rating. This is the maximum weight of the vehicle as equipped and passengers, cargo, fuel, etc. This rating also includes tongue weight of a trailer.

    GCWR- Gross Combination Vehicle Weight Rating. This is the maximum weight of the vehicle and any trailer the vehicle is towing.

    GAWR- Gross Axle Weight Rating. This is the maximum weight that can be put on the respective axle in question. Typically, the rear axle has a significantly higher rating than the front, but not always.
    These ratings can usually be found on a tag inside the driver’s door jamb of the vehicle along with various other important information.

    My 1991 Chevy Suburban’s door tag gives a GVWR of 6800 pounds, no GCWR, and a front axle GAWR of 3250 pounds and a rear axle GAWR of 3968 pounds. So, the door tag doesn’t give me any information specific to towing a trailer. My Suburban has a dealer installed GM trailer hitch with a 4000/400 (total/tongue) dead tow capacity and a 9500/1000 weight distributed capacity. However, that’s simply what the hitch is rated for, not the whole vehicle. So, let’s dig deeper into the situation…

    Friday I placed a call to GM Corporate to inquire about the towing capacity of my truck. After taking down my VIN number, they got off the phone and researched the rating. I got a call back stating that because the truck did not have RPO code Z82 (towing package), that they could only rate the Suburban at 2000 pound towing capacity. Say wha???

    After talking with the agent for some time, she kept telling me I needed to inquire either to my local GM dealer or the hitch manufacturer to get the weight rating that the truck could tow. Ok, so let’s get this straight… you want me to go to a dealer whose technicians probably haven’t ever touched a truck that’s over 20 years old and have them tell me how much the truck is rated to tow? Or I should contact the manufacturer of the hitch (YOU, GM) to find out the weight rating? Either way, neither of these people should be able to come up with a real number as to the towing capacity of my truck.

    So then that got me thinking more. My Suburban is rated to only tow 2000 pounds, yet (for the sake of this argument) U-Haul could sell me a hitch rated for 7500 pounds weight-distributing, and I’m to just assume that’s the towing capacity of my truck? How did they come up with the number 7500? They’re not the manufacturer, and it stands to reason that since I’m buying a hitch from them, that I don’t have RPO code Z82 and according to GM only have a towing capacity of 2000 pounds. How can they in their right minds do that and legally get away with it? I guess they use the standard disclaimer of the end user needing to read the manual to know the weight.

    Then of course we get into exactly what is changed or included to make up RPO Z82. In 1991, Z82 means it gets the weight distributing hitch I have, it gets pre-wired for a 7-way RV receptacle, and it gets an auxiliary transmission cooler. That’s it. I have all of the above and then some, so technically, while it doesn’t include Z82 from the factory, it’s at the minimum equal to one that had Z82.

    So what does all this mean? Well, that’s a tough question. Who should I believe and what should I base my numbers off of? GM’s specs off the factory line, the weight rating on the hitch itself, or some other number? Well, let’s pull some more specs into the mix. This time, we’re going to pull from the official GM Restoration Kit packet. Essentially, the Restoration Kit is just the promotional brochure paperwork from the year the vehicle was built, but it has a LOT of gory details about the vehicles down to frame rail thicknesses and the like.

    On one chart, they list GCWR versus motor, and what gear ratio you need to be at that ratio. With the 3.08 gears the truck had from the factory, the GCWR was only 10,000 pounds. With 4.10 gears and the 5.7L engine, the GCWR is 13,500, but simply saying I have a 7.4L engine changes it to 16,000 which is more than enough for the camper. I don’t understand how getting a marginal amount more engine power can change the GCWR that much, but it does.

    On another chart, it lists the same info that for a given trailer weight, what class truck you need, engine, and gearset. To haul a 9500 pound trailer, they claim you need a 2500 with the 7.4L engine and 4.10 gears. So, according to that chart, I don’t meet the requirements as a half-ton. I’m confident that with my changes I can haul it though. It’s just not that legal, but was VERY difficult to find. Where does the law come into play when dealing with weight ratings?

    So, what’s in a rating? A lot, but it can certainly get muddy at times.
    Last edited by a moderator: Nov 2, 2013
  2. mfleetwood

    mfleetwood Rockstar 4 Years ROTM Winner 5000 Posts

    Lots of great information. I'm saving this thread as a reference in case I do end up towing something one day.

    Thanks for taking the time to post this!
  3. Crawdaddy


    Wow you move and read fast :lol:

    - - - Updated - - -

    For some "show your work", here's the charts I was pulling data from in the last 3 paragraphs.

    Towing Capacity:

    Restoration Kit towing capacity.jpg

    GCWR Table:
    Restoration Kit GCWR.jpg

    These are scans from the Restoration Kit from GM. I didn't scan them crooked, GM copied them crooked before sending them to me.
  4. mfleetwood

    mfleetwood Rockstar 4 Years ROTM Winner 5000 Posts

    It took a whole 3 minutes. I popped it open as soon as you posted it. It was easy reading and organized nicely, thus did not have to figure out things so much in my head. My brain likes to get in my way. :glasses:
  5. McClintoc

    McClintoc ɹoʇɐɹǝpoɯ Staff Member 2 Years 1000 Posts Platinum Contributor

    The odd thing is, doesn't "gross" mean "starting with" and "net" means "final value" after adding or subtracting from the gross? So, shouldn't the GVWR be the NVWR? Or am I taking crazy pills?
  6. Crawdaddy


    I've been doing some research on weight laws, and it seems that there are no weight rules for non-commercial people that really applies. There is a 20,000 pound weight limit per axle law, but virtually no personal vehicle could physically handle that. I have been not been able to find any regulations that state the door tag means anything legally.

    It also seems that while a lot of people say that the insurance companies won't cover you if you're overweight, there are no documented situations where this has happened and that if an insurance company will cover a drunk driver, they should have no reason to not cover an overweight vehicle.

    This thread on RV.net seems to have very good info covering weight laws: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/20577181/srt/pa/pging/1/page/1.cfm

    What's everyone thoughts on this?
    Last edited: Jun 22, 2013
  7. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Many years ago while looking for the same info I found that most of the info was more of a legal disclaimer for the vehicle mfgrs. It was their way of putting a limit of what they "felt" they were responsible for.
    Many of the listings are the lowest weights youll find under local laws, which were normally considered governing laws years ago, since the DOT has stepped up and begun enforcing federal regulations some of the listings you found now really mean nothing, but DOT doesnt go all the way and address privately owned vehicle as much as they should, they concentrate on commercial vehicles.
  8. Crawdaddy


    I started looking at my scale tickets from my previous camping trip (which can be found here) and reading and thinking (which is dangerous :glasses:) and with a little work, I can be perfectly within my front axle weight rating, within 500 pounds of my rear axle rating, and really close, if not within my GVWR.

    I'm not transferring enough tongue weight to my front axle, which once I do, will take weight off the rear, bringing them both close or within spec. I do need to upgrade the actual hitch itself and weight distributing hitch to get within those ratings though. So, I'll be very close to being within the manufacturer specs; probably enough to claim ignorance. Think that'll fly in court?
    Last edited: Jul 2, 2013
  9. Turvok

    Turvok New Member

    Crawdaddy it has to with where the engine gets its torque. Towing has alot more to do with bottom end torque than it does with overall hp rating. Hence why diesels even though they are marginally different in hp ratings. They get their torque at a much lower rpm. The same goes for big gas engines. They tend to have a much longer stroke giving them more torque at a lower rpm.

    Just a reminder hp is a formula. Not a true rating.
  10. Rebel_Bowtie

    Rebel_Bowtie Member

    Ok, this is a thread from the Tundra forum I'm part of. You can calculate it on your own and know exactly what your truck can/can't do. Grab your calculator and hold on....

    When you're looking for a bumper pull trailer the same as above applies except that tongue weights tend to be less than pin weights. Trailers average around 12% of the loaded weight to be carried on the tongue. Some are higher depending on the trailer layout.

    If you want to be safe and stay close to your trucks ratings then you need to load all your passengers and gear that you would travel with in the truck and go weigh it. Then you can figure how much payload you have left for the trailer tongue weight. Keep the gear to a minimum, pack what you can in the trailer.

    Subtract whatever the trucks loaded weight is from 7200lbs (your GVWR) and that is what is left over for the tongue and hitch weight. Then you have an idea what size trailer you can pull.

    When you are looking at trailers don't go by dry weights, nobody travels with an empty trailer. Try to estimate how much stuff you'll put in it and add the weight of options like propane tanks, batteries, AC etc which aren't included in dry weight. Then figure 12-15% of the loaded weight as tongue weight. This number should not be (much) over what you calculated to be left in payload.

    I say much because I wouldn't be too worried being a couple hundred pounds over, as the trucks are under rated, but you don't want to push it and be uncomfortable or unsafe. Plus your weights will vary some for each trip, a proper hitch will transfer some tongue weight back onto the trailer axles etc..

    Here's an example of my situation, I tow what I consider to be heavy for my truck even though it's well under the tow rating. My trailer is a 31' bunkhouse, 6100lbs dry but 6420lbs wet (with options). Loaded to camp it's 7600lbs (no water on board) My Tongue weight is 980lbs (13%)+ 100lbs WD hitch. With my wife, 2 boys and a dog on board we are 250lbs over my CrewMaxs' GVWR. I'm not too concerned as I'm still under the axle and tire ratings (tires were upgraded to E range) which is more important to me than a payload number. It pulls fine but I wouldn't want to go any bigger or heavier with this truck.

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