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Old 01-02-2014, 06:18 PM   #1
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Calculation of towing capacity, et. al.

My question deals with correct interpretation of towing capacity. TV is a 2006 Chevy Express 3500 conversion van with 6.0L and 3.37 RAR. The vehicle door jam lists GVWR at 9,600 lbs and owner's manual lists max towing capacity at 7,700 lbs and GCWR of 14,000 lbs. Curb weight of vehicle is listed at 6,009 lbs. Have not yet purchased a TT.
Using the above, is my analysis in the following example correct?



Example: GCWR of 14,000 less tow vehicle curb weight of 6,009 = 7,991 lbs. Subtract weight of passengers (350), 30 gal fuel (250), and gear (200) = 7,191. Subtract trailer dry weight of 6,500 lbs = 691 lbs for trailer cargo and liquids in tanks. Say 100 for propane, 335 for water, gray water, black water (40 gal), leaving 256 lbs for cargo in the trailer. Still under max towing capacity of 7,700 lbs at 7,191 lbs. Make sense?


Now for the bonus round. How does tongue weight figure into the calculations? Assume tongue weight is 800 lbs.



Thanks much.
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Old 01-02-2014, 07:12 PM   #2
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When the trailer is connected to the tow vehicle, tongue weight is payload applied to the tow vehicle. Some people forget to add the weight of the hitch and sway control to this weight when calculating load on the hitch receiver.

Calculate tow vehicle payload capacity by subtracting actual vehicle weight from GVRW. All fluids should be at full when weighing the tow vehicle to establish actual weight. The reason to weigh; any accessory that has been added to the tow vehicle makes additional payload capacity less.
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Old 01-02-2014, 07:39 PM   #3
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Does a conversion van mean that it has been customized by a non-OEM company? If this is the case, you may want to weigh your van at a CAT scale to find the actual curb weight of the van before you start calculating your capacities. The van could have a considerable amount of the payload capacity taken by the customizing work.

In any case, I would think that a 3500 van should be a very stout tow vehicle. The 6.0 engine GM engine is the one I have had in three of my trucks. I have been very happy with that engine. I imagine your towing capacity is based on the 3.37 rear axle ratio. A 3.73 rear axle would probably jump your towing capacity to 9700 lbs. A 4.10 would probably carry you to 10,000 lb towing capacity. There is information about this on the Trailer Life site.

A weight distributing hitch will also shift part of the trailer tongue weight back to the trailer axles. I can't remember the rough percentages of weight shift with a WD hitch. Someone will chime in a give the rough percentages for the weight shifts.
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Old 01-02-2014, 08:18 PM   #4
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Thumbs up

As noted the best weigh to get the weights is to weigh.....sorry, hard to resist.
But it is very important NOT to guess.


There is a sticker on the driver door jamb that will give you both the front and rear axle weight ratings(GAWR)..very helpful in determining payload and adjusting weight distribution.

Also take note of your tire load rating.

Bob
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Old 01-02-2014, 08:53 PM   #5
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correction

Correction: TV rear axle ratio is 3.73:1, not 3.37
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Old 01-04-2014, 01:58 PM   #6
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Thanks + more musings

Thanks to all who responded. I will take to heart the suggestion not to rely on door frame posted weights ('curb' or 'dry' weight) and have the trip outfitted vehicle weighed on a scale. Even though the base vehicle was a passenger van, the conversion package must have boosted the factory specs (hightop roof, power folding 3rd seat, inverter, entertainment system, and assorted trim gejaws). I will report back with results.

I am still toying with the idea of swapping out the 3.73:1 rear axle for a 4.10:1. That will boost towing capacity by 2,000 lbs to 14,000 lbs. However, some say MPG drops significantly; some say only 1 - 2 MPG less. I do not plan to tow beyond 60 MPH. Gear Vendors is an interesting option, but much less so at $4,000 (including installation). I believe the rear gear swap would run approx $1,200. I will be getting a quote from a shop experienced in all matters drive train.
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Old 01-04-2014, 02:19 PM   #7
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Thumbs up Weigh first.....

.....excellant plan. You may be surprised how much of the payload was used on the 'conversion'. You will also know how much weight is on each axle and exactly what you have to work with.

IIWY...I would tow first as you are, then decide if the up-grade to 4:10 is needed.
Remember the gearing gives you more towing ability but does nothing for payload.

My experience....
The tongue weight for a 25' AS will be between 900-1200 lbs depending on load and equipment.

Bob
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Old 01-04-2014, 02:41 PM   #8
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Quote:
Originally Posted by ROBERT CROSS View Post
.....excellant plan. You may be surprised how much of the payload was used on the 'conversion'. You will also know how much weight is on each axle and exactly what you have to work with.

IIWY...I would tow first as you are, then decide if the up-grade to 4:10 is needed.
Remember the gearing gives you more towing ability but does nothing for payload.

Bob
I agree with what Bob has to say about gears, the door sticker, and taking your van to the scales. The owners manual is a reference but the door sticker is the gospel as far how your van was first delivered.

Is your van a short wheel base or long wheel base? That makes a difference for towing capacity on a table I have looked at. Below is the trailer life towing guide for 2006 vehicles.

http://www.trailerlife.com/wp-conten...Guide-2006.pdf

It appears that the payload capacity on your van was over 3000 lbs before the conversion process.
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Old 01-05-2014, 06:43 AM   #9
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@Ridgerunner3: The van is a short wheelbase (135").

@Robert Cross: Good point about load capacity not being the same as towing capacity.
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Old 01-05-2014, 07:55 PM   #10
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Just remember, load capacity equals total capacity of vehicle minus load of trailer's tongue weight and everything will be just fine...

Everyone checking their door stickers rights about now...
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Old 01-05-2014, 08:24 PM   #11
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Door stickers are not always correct.
In the instance of a conversion van where the vehicle has been modified, which the original poster asked about.
Another, I have a brand new 2014 pickup that has an incorrect door sticker, checked on two certified scales and both confirmed the error.

Only weighing can confirm actual vehicle weight.
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Old 01-10-2014, 03:40 AM   #12
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GVWR: The van (and everything inside it) plus the tongue weight must be below this.

GCWR: The van (and everything inside it) plus the trailer (and everything inside it) must be below this.

GAWR: Each individual axle must be below these numbers. Tongue weight will be multiplied on the rear axle. If you use a weight-distributing hitch, weight will be distributed from the rear axle to the front axle and trailer axles.
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Old 01-10-2014, 08:14 AM   #13
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You will have you weigh the van before so that you know what the conversion has added in weight.Then you know what you have remaining.
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