Finding Towing Capacity

wandering1 wrote:
The manufacturer has the only correct, factual, legal towing spec for your truck, the rest are funny figures. Contact the manufacturer.

Hardly. 99/100 times you ask a dealer what the GCWR is and they'll say, "huh?". You really have to do it yourself in the way it's described a few posts up.

Here's a good towing capacities calculator that helps.

Michelle.S wrote:

GM never had a 5 speed auto Huh, wonder what the 5 gears were that were in my 2005 K3500 Dually. Or don't you consider overdrive as a gear, if that's the case they still only have a 4 speed, but with 2 over drive gears.

Did you have the 8.1L engine in that truck? If so, you had the Allison 1000 transmission which was definitely a 5-speed tranny.

Through the 2001-2007(old body style) model year the engine/transmission/gear/axle options in 2500HD and 3500HD trucks were as follows:

Duramax - Allison 1000 - 3.73 gears - AAM 11.5" full floating axle

Vortec 8100 - Allison 1000 - 3.73 or 4.10 gears - AAM 11.5" full floating axle

Vortec 6000 - 4l80E - 4.10 gears - AAM 10.5" full floating axle

Any van model with the 8.1L got the 4L85E transmission. The van body did not leave enough room to fit the Allison.

To Wandering1's suggestion of going to the GM for exact info.... That's a decent idea but the OP shouldn't be surprised if GM doesn't get back to him quickly regarding questions on a 10 year old truck. The local dealership might be an option, but the quality of info there can vary too depending on knowledge of the service or parts department. Several years ago I was shopping to find a limited slip or locking differential to install in my truck. It is a 2WD and came originally with an open differential which meant I got stuck in just about any wet condition. Long story short, the dealership (fairly large I might add) couldn't decipher from the VIN if I had the 10.5" or 11.5" axle. Only through a lot of research across multiple sources was I able to find all the information I listed above.

KJ

deltabravo wrote:

rgeisler wrote:
... 5 speed automatic (I think), with Tow/Hauling button,

GM never had a 5 speed auto.. For the year your truck is, it's a 4 speed.

Your automatic transmission is a 4 speed. It's a 4L80E.

...and later year trucks had a 6 speed - a 6L80E, but I don't know what year the 6 speed auto replaced the 4 speed. (I'm talking gas trucks, not diesel)

GM never had a 5 speed auto Huh, wonder what the 5 gears were that were in my 2005 K3500 Dually. Or don't you consider overdrive as a gear, if that's the case they still only have a 4 speed, but with 2 over drive gears.

rgeisler wrote:
... 5 speed automatic (I think), with Tow/Hauling button,

GM never had a 5 speed auto.. For the year your truck is, it's a 4 speed.

Your automatic transmission is a 4 speed. It's a 4L80E.

...and later year trucks had a 6 speed - a 6L80E, but I don't know what year the 6 speed auto replaced the 4 speed. (I'm talking gas trucks, not diesel)

The manufacturer has the only correct, factual, legal towing spec for your truck, the rest are funny figures. Contact the manufacturer.

rgeisler wrote:
Does anyone know how to find the actual towing capacity of a vehicle? Every source that I look at gives a different answer. I have a 2004
GMC Sierra 2500 HD 6.0 Liter, 5 speed automatic (I think), with Tow/Hauling button, Extended Cab/Long bed. When I look at the 2004 Towing Guide it gives several different ratings, I think based upon the Axle ratio, which I don't know, but it appears to be listed as 10,100 lbs. When I look up the VIN # at a site called Decodethis.com, it shows a maximum of 15,500 and a standard tow rating of 9900 lbs. I have no idea what the difference between the maximum and standard towing capacity is.

Nearly Identical truck to mine. You will have a 10.5" AAM full floating axle with 4.10 gears (RPO code GT5) and a 4L80E 4-speed transmission. That was the only gear and axle combo offered with the 6.0L/auto tranny.

Your GVWR will be 16,000 lbs, so yes, go weigh the truck and subtract that amount from 16K to find your max tow capacity. My truck is 2WD crew cab. Empty bed with a full tank and 2 adults it weighs 6,300 lbs. so I have about 9,700 lbs tow capacity.

The RAWR (rear axle weight rating) is 6,084 lbs, which is a limit of the OEM tires. These tires are rated at 3,042 lbs per tire @ 80 PSI. AAM rates the axle itself at 10,000 lbs, so that means your only limitation is the tires and/or the springs GM put on the rear.

If you're getting a ball-tow trailer be sure you ARE NOT using the OEM hitch receiver that came with the truck. These are a known poor design and there was much discussion about these years ago. Get a good Class V Receiver that has the receiver welded into the cross tube. When I towed with my OEM receiver I had a lot of porpoising and poor weight distribution even when using my WD hitch. After installing a Curt Magnum V receiver the towing experience was vastly improved.

The 6.0L engine needs to rev to make good power. There is a great torque band between 3200 RPM and 4400RPM where the engine pulls extremely well. I've towed all over central Illinois (yes very flat), southern Indiana, and made multiple trips to Bristol TN. You have to let it rev, but I've never felt outmatched by our 7,500 lbs TT.

Oh, one final thing, watch the exhaust manifold bolts. After making hard pulls the front and rear bolts on both sides tend to snap. You'll eventually develop an exhaust leak and will notice significantly reduced power. You can fix the problem by swapping in hardened bolts. I chose to install stainless steel shorty headers from Gibson and the kit came with new hardened bolts. I didn't take any measurements for power output pre or post installation, but it does seem the engine will rev a little quicker with the headers. That faster revving means I reach that magical 3200 RPM quicker so I'm hitting that torque curve faster.

I hope this info helps.

KJ

GCWR minus the actual weight of the truck = towing capacity.

The numbers published in the owner's manual are a good starting point, but they don't reflect the actual as-built weights of the vehicle.

Agree with most of the advice given and add

The below diagram will help you understand, decipher the HOW2 figure it
out to do the simple math towards finding your actual rating numbers

First, here is the diagram of how the ratings system looks like in a
graphical form. Hope you can see that if you go over any *ONE* rating,
that the rest of the system can be within, but that one overage becomes
the weak link....limiting factor

howmuchcanitow howmuchshoulditow


You also need to load and weigh your TV as suggested. That is the basis
for all in this scheme

On that, you need to decide for yourself whether you believe in the
ratings system or not

If not, then all of this is academic and do whatever you wish, but know
that you then have taken all the OEMs off the warranty and liability
hook. You will now own both warranty and liability

If yes, then read up, ask questions to learn HOW2


This is an old chart that shows how GM's tow ratings looked like back
in 2001 or whenever they printed these documents

NOTE that there are BILLIONS of bucks behind it, but so many...most
people take any individual number as an absolute. Meaning that there
are other factors...and most of that is embedded in the fine print
Not just this OEM, but *ALL* OEM's do this, as that is the only way
they can compete for your dollars.

GCWRchart

Do wish the OEMs would have continued to publish charts like the above
As today's info is much tougher to find...many times wonder if it is
so well organized today... Personal opinion...the OEMs no longer have
marketing folks who understand towing heavy anymore. Plus their demographics
surveys no longer show 'enough' buyers towing heavy...so an almost lost
art in building TVs for heavy towing

Also note that was back then and now things have changed. Mainly in
the sciences embedded (design, engineering, process, material, etc)
have gotten better. Mine is a GMT400 series truck. The above GCWR
chart is for a GMT800 series truck, yours is a GMT800 series truck

Too many will only see the three variables listed on that chart

• Transmission type
• Engine type & size
• Differential ratio

But there are many more attributes (factors) embedded that are NOT
clearly shown that folks are ignorant of, ignore or don't care to
consider. Somewhere else in the OEMs documentation will be reference
to the basis for all ratings...'curb' and one driver...that one driver
is the proverbial 150lb person from insurance actuary tables from
decades ago... A PS on that 150lb person...boating industry (Coast
Guard driven) has changed that to define that person as a 180lb person now

The door label referenced by others is the ratings for 'your' vehicle
Here is mine, a 1996 Suburban.
mydoorlabel



So, after you have weighed your fully loaded and ready to go camping TV

Plug that weight into the diagram

Then find the actual weights of the trailer you are considering. If no
actual, then use it's max rated weight (GVWR) and use that with the
percentage tongue/PIN weight of the 'dry' trailer. That will give you
the trailer's GVWR tongue/PIN weight

The GCWR will then be the bottom line comparison for your risk management
decision (AKA gamble) on how much design margin you wish to have (AKA safety factor)

Contact the manufacturer and ask. All the other sources mean nothing.

kaydeejay wrote:
Have you looked in your owner's manual? It will give you tow ratings for the different engine/axle ratio combinations.

X2!

You need the owners manual to help sort all this out. If you do not have a copy of your manual, search Google, GM has a lot of them going back about 10 years, for older ones there are reliable sites that have them as do many of the user forums.

So you need:

• Your owners manual
• The sticker in the door so that you know what your cargo capacity is, and a few other relevant numbers
• The sticker in the glove box to find all the options you have so you can decipher in your manual what your real towing capacity is.