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Old 10-18-2011, 09:19 AM   #1
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Towing Math Example: Tundra pulling '79 31ft Sovereign

My AS research has now led me to an advanced degree in physics and math, AKA calculating the required tow vehicle. I'm learning numbers such as trailer dry weight, hitch weight, and the tow vehicle ratings, including curb weight, GVWR, payload (which I think is GVWR minus curb weight), and finally tow capacity and Gross Combination Weight Rating (GCWR).

As an example, let's take a 2008 4x2 5.7L Toyota Tundra Standard Bed pulling a 1979 31' Sovereign Center Bath.

The Sovereign dry weight is 4810 lbs and the hitch weight is 545 lbs.

The Toyota Tundra numbers are:
Curb weight 5235 lbs
GVWR 6900 lbs
Max payload 1665 lbs
Towing capacity 10300 lbs
GCWR 16000 lbs

Assuming these numbers, is the following correct:

- With 545 lbs of hitch weight, does this take the Tundra payload remaining to 1665 - 545= 1120 lbs
- 1120 lbs needs to cover the passengers (let's say 180 x 4= 720 lbs), so 400 lbs left for two Honda 2000i generators, gas totes, a gray water waste tote, and miscellaneous other suplies in the truck bed?
- with 10300 lbs of towing capacity, that leaves 5400 lbs of tow capacity to spare. Even assuming full water tanks and supplies in the AS, can you shift items to the AS storage spaces and have plenty of tow capacity and Tundra payload capacity to spare? As along as you stay well below that GCWR?

Thanks in advance to furthering my education.

Cheers
Jim S
Arlington, VA
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Old 10-18-2011, 09:35 AM   #2
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You are correct on your towing math.
Usually on half ton tow vehicles, the practical limit is the gross combined vehicle weight limit as manufacturers base their tow ratings on a nearly empty tow vehicle.
Still, your Tundra should have plenty of capacity to tow an old Airstream with a gvw of approximately 6000 lbs.
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Old 10-18-2011, 09:42 AM   #3
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Your thinking sounds correct to me.
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Old 10-18-2011, 09:54 AM   #4
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Yes, you can transfer some cargo to the trailer, with the caveat that you balance the load correctly in the trailer. You don't want to reduce the tongue weight, especially as you're increasing the net weight of the trailer with cargo. A too-light tongue will contribute to squirrely behavior from the trailer. Also, there's no substitute for actual measurement of the weights... a tongue scale is a good start, but commercial truck scales will tell a more complete story.
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Old 10-18-2011, 10:28 AM   #5
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At trip to the local CAT scale is well worth the time and effort. You can get a complete weight of both the combination and individual weights of the truck, the tailer, and the tongue weight. I think it cost around $10 for the first weight and then $1 for each reweigh during a 24 hour period. When I did mine I unhooked the trailer and put the tongue on one pad and the trailer on another. You can also get a weight for each axle. Might want to go at a time the truck stop is not too busy. I have used the CAT scales 3 times and at each location the folks were extremely helpful, especially when they saw my old Trade Wind. At catscale.com you can find a location near you and also there is a guide on how to weigh.
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Old 10-18-2011, 10:48 AM   #6
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Quote:
Originally Posted by DKB_SATX View Post
Yes, you can transfer some cargo to the trailer, with the caveat that you balance the load correctly in the trailer. You don't want to reduce the tongue weight, especially as you're increasing the net weight of the trailer with cargo. A too-light tongue will contribute to squirrely behavior from the trailer.
An absolute good point! Load any trailer evenly. Redistributing load to behind the axles can lighten tongue weight to the point of instability. Standard axle location in the US calls for 11-13% of the trailer gross weight to be on the hitch. Lighten below that and you'll get a very squirrely tow. Imagine throwing an arrow butt end first -- it will try to change ends. Just like a trailer with too-light tongue loading.
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Old 10-18-2011, 10:57 AM   #7
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Originally Posted by JBSVirginia View Post
My AS research has now led me to an advanced degree in physics and math, AKA calculating the required tow vehicle. I'm learning numbers such as trailer dry weight, hitch weight, and the tow vehicle ratings, including curb weight, GVWR, payload (which I think is GVWR minus curb weight), and finally tow capacity and Gross Combination Weight Rating (GCWR).

As an example, let's take a 2008 4x2 5.7L Toyota Tundra Standard Bed pulling a 1979 31' Sovereign Center Bath.

The Sovereign dry weight is 4810 lbs and the hitch weight is 545 lbs.

The Toyota Tundra numbers are:
Curb weight 5235 lbs
GVWR 6900 lbs
Max payload 1665 lbs
Towing capacity 10300 lbs
GCWR 16000 lbs

Assuming these numbers, is the following correct:

- With 545 lbs of hitch weight, does this take the Tundra payload remaining to 1665 - 545= 1120 lbs
- 1120 lbs needs to cover the passengers (let's say 180 x 4= 720 lbs), so 400 lbs left for two Honda 2000i generators, gas totes, a gray water waste tote, and miscellaneous other suplies in the truck bed?
- with 10300 lbs of towing capacity, that leaves 5400 lbs of tow capacity to spare. Even assuming full water tanks and supplies in the AS, can you shift items to the AS storage spaces and have plenty of tow capacity and Tundra payload capacity to spare? As along as you stay well below that GCWR?

Thanks in advance to furthering my education.

Cheers
Jim S
Arlington, VA
Remember though, years ago, big cars pulled Airstreams. every where, and with rare problems.

Today's thoughts are gross overkill.

Since vehicles, we all know are better today, then we can say that a half ton truck, properly equipped can pull up to a 31 foot Airstream, at least as good as they did 40 years ago.

But, we now have a 34 foot trailer. That should be towed with a 3/4 ton,properly equipped truck.

To use dually's, 1 ton, 4 X 4 trucks, is absolute overkill, for towing even the largest Airstream.

But, it still comes back to an individuals choices, some good, and some not so good.

Safety is always the issue, and that being the case, perhaps everyone should use a Peterbilt.

Andy
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Old 10-18-2011, 11:02 AM   #8
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Jim

I have a Tundra identical to yours. I consider the max tow rating and the GCTW to be pretty much worthless figures. They only apply if you are towing an empty trailer by yourself, naked and about to run out of gas. The figure that will get you first is the rear axle weight rating of 4,100 lbs. It is on the drivers door jamb. The second that will get you is the GVWR of 6,900 lbs. Load up your trailer the way that you would like to tow and then visit a CAT scale and make whatever adjustments are necessary. The education continues.

Dan
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Old 10-18-2011, 11:17 AM   #9
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Jim

I weighed my Airstream and Tundra set up to go camping by myself when I carry my motorcycle. The margin between actual and gross ratings were 460 lbs for the rear axle, 260 for the gross vehicle and 4,940 for the gross combination. see the following link:

http://www.airforums.com/forums/f161...ams-81920.html

Dan
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