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Old 08-22-2013, 05:35 AM   #29
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I would also argue exceeding the published company ratings (towing capacity, GCVWR, axle weights, payload, and tongue weight), even with after market modification, is unsafe.
While I agree with payload and axle weights, I'd argue that GCVWR and towing capacity are numbers arrived at by the marketing rather than the engineering department.
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Old 08-22-2013, 06:25 AM   #30
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While I agree with payload and axle weights, I'd argue that GCVWR and towing capacity are numbers arrived at by the marketing rather than the engineering department.
Anything the marketing department does will be more optimistic than the engineering department which normally will be fairly conservative. This was a constant battle where I used to work
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Old 08-22-2013, 07:28 AM   #31
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While I agree with payload and axle weights, I'd argue that GCVWR and towing capacity are numbers arrived at by the marketing rather than the engineering department.
I agree. That's why I believe exceeding the towing capacity/GCVWR is unsafe, because those figures have already been inflated by the marketing department (hence some people use the 80% rule in deciding the towing capacity). Until all car companies start using the same standard in determining the towing capacity (SAE standard is a good start), those numbers do not mean much. For example, Toyota Sequoia was rated at 10000# towing capacity. After SAE standards was implemented by Toyota, it towing capacity dropped to 7400#. Many other cars/trucks will follow suit if they implement SAE standards (hence their refusal to implement it).
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Old 08-22-2013, 08:32 AM   #32
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It is my belief that both towing capacity and CVWR numbers have close to zero engineering backup. This belief is backed up by the observation that vehicles from one manufacturer using the same components, i.e engines, brakes, transmission etc, frequently have very different values assigned to them, depending on their intended use.

There's just too many inconsistencies for any of this to make any sense of any kind. For example, a 1999 Honda Odyssey, which is a totally different vehicle from a late gen Odyssey, has the exact same stated towing capacity, 3500lbs.

This despite the fact that drivetrain, engine, body, brakes, transmission, pretty much everything about the entire vehicle has been re-engineered, strengthened, improved during the last 15 years.

My suspicion? Nobody has even looked at changing the value, it just got transferred from the second gen Honda Odyssey onwards. (I believe the first gen stated capacity was 2400lbs)

Payload and axle weight count and should not be ignored. As a result, these are the numbers I care about.
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Old 08-22-2013, 08:57 AM   #33
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Back to the original point about GCWR, if you can't adequately pin down to how it was derived, measured and tested then you have no hope of using it in any legal argument.
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Old 08-22-2013, 09:02 AM   #34
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I would also argue exceeding the published company ratings (towing capacity, GCVWR, axle weights, payload, and tongue weight), even with after market modification, is unsafe.
But to back your argument you will need evidence, both on the derivation of said ratings and to show that exceeding them is actually unsafe. I'm not sure that evidence exists.
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Old 08-22-2013, 09:47 AM   #35
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Adding the vehicle GWR and the actual trailer weight as opposed to the towing capacity should give you credible numbers for the GCWR. On the way to this campsite, I weighed the '13 GC and 25' Safari and it came to 12,182 pounds. If you add the GWR and the towing capacity as some here are doing, this combo would approach 14,500 GCWR. I've towed this Safari with an F-250 V-10, GMC 2500 HD and a Silverado 2500HD. Quite frankly, the GC is more comfortable, has better torque that the 6.0 liter GM products, stops better and is far more comfortable than any pickup.

In the early seventies, I experimented with ads in Trailer Life and Camper Coachman offering speed equipment redesigned for towing. This was an offshoot of a program designed to produce more power for racers traveling cross country with ramp trucks or tow trucks. This program was a hit right out of the box. My clients included makers of intake manifolds, electronic ignitions, exhaust headers, clutches/flywheels and cam grinders.

There were several magazine tests using a combination of these products that proved to vastly improve the towing performance of late sixties, early seventies passenger cars and pickups of the era.

In as much as emission controls were starting to become standard on cars of that era, several tests actually showed that in some cases that emissions were actually reduced. Sadly, brake performance never matched up to the improved engine performance.

I do keep a weight certificate in the glove box with the insurance card and registration.
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Old 08-22-2013, 11:34 AM   #36
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I don't doubt the power of marketing departments in coming out with dumb claims. The power of marketing over engineering is what led US manufacturers down the road to poor quality and overstimulated marketing. Consumers figured it out and bought foreign made vehicles.

Toyota adopted the SAE standards. That is a good sign and US manufacturers will be forced to adopt them fairly soon as the market realizes what is happening. I always thought the Sequoia was overrated. It is heavier than the Tundra and has a softer suspension.

For those of us without engineering credentials and testing equipment, we have to accept that the ratings are fairly accurate and if we own a Toyota, more accurate than other manufacturers' claims. If involved in a lawsuit, you can say you saw the manufacturers' numbers and having no way to test them (unless you work in a testing facility), had no other way of knowing the scientific truth. If you derate the vehicle yourself—using the 80% "rule"—so much the better as a defendant. Your insurance company will handle the argument anyway because they have to provide you with an attorney, and they will probably settle to avoid litigation costs.

I and others have said before we want to see more testing of RV's. But the RV market is not big enough to attract the kind of money necessary to properly test RV's and tow vehicles. Some attention grabbing accidents with many children killed and intense media coverage might change that, but no one hopes for that outcome. The manufacturers don't have a good reason to do the testing as long as most people don't pay attention. The only thing that can make such testing happen is for the government to require it and there doesn't appear to much interest for that these days. We should congratulate SAE for trying to do something. I don't anticipate RV testing to happen any time soon and we will be forced to speculate and threads debating these topics will be a constant for the future.

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Old 08-22-2013, 03:45 PM   #37
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But to back your argument you will need evidence, both on the derivation of said ratings and to show that exceeding them is actually unsafe. I'm not sure that evidence exists.
We in this forum are not automobile engineers. We have not been involved in the design and development process of the tow vehicles we drive. Nobody has evidence regarding the tow ratings of our vehicles, but the manufacturer. Hence, the ultimate authority on the towing specs is the car company.

You should call Toyota, tell them that you have modified your car (transmission cooler, beefed up the hitch, etc). Then ask them if it is safe to tow more than the 3500# Sienna is rated for. I bet you they will tell you its unsafe and you should not do it. I believe and trust what Toyota (the biggest auto maker of the world) says. But, to each their own.
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Old 08-22-2013, 05:22 PM   #38
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I'd like to tow our 20 flying cloud with a car but, we have a Tahoe because we live in the desert southwest and we need to climb out of the Los Angeles basin to get anywhere. The summers are hot and our Tahoe with our current trailer pulling a 7% grade, Grapevine, Cajon pass and others such as Sherwin summit out of Bishop, the Tahoe temperatures go up rather fast. The transmission tops out at 230F the collant tops at 250F the car is serviced when we get back because I'm afraid the fluids have degraded. The Tahoe has the factory tow package and is rated to tow 7500lbs. I could not see a car tow our 20 ft without major overheating it. I'd like to down grade to a Traverse for example but, I'm afraid I could get over these major climbs.
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Old 08-22-2013, 06:24 PM   #39
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Borrowed from another poster, BradB, but worth posting here too - a 1987 Airstream brochure:

I wonder what the tow rating on this TV would be, happily married to a 34' triple axle. What I do suspect, strongly, is that my 2008 Honda is superior in any way to the car on the Airstream brochure - payload, engine, brakes.

(I didn't grow up in North America, so I have no idea what car this is. Perhaps somebody else can dig up the numbers)
That car is a Chevrolet Caprice Classic with a 105 horsepower 5.0 liter v8. It was as good a tow vehicle as any in its day. It was not out of place in its time as all cars were weak and underpowered.
Average v6 cars now have nearly double the horsepower and better brakes
I still don't think people should exceed the tow rating or payload of a vehicle.
The new Nissan Pathfinder commercial showing the Pathfinder towing a big old Airstream that is heavier than the tow capacity of the Pathfinder with no umbilical cord, no weight distributing hitch, and no sway control is a joke..
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Old 08-22-2013, 08:03 PM   #40
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150 horsepower...

Good ole floatin' boat.
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Old 08-23-2013, 12:20 PM   #41
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We in this forum are not automobile engineers. We have not been involved in the design and development process of the tow vehicles we drive. Nobody has evidence regarding the tow ratings of our vehicles, but the manufacturer. Hence, the ultimate authority on the towing specs is the car company.

You should call Toyota, tell them that you have modified your car (transmission cooler, beefed up the hitch, etc). Then ask them if it is safe to tow more than the 3500# Sienna is rated for. I bet you they will tell you its unsafe and you should not do it. I believe and trust what Toyota (the biggest auto maker of the world) says. But, to each their own.
Toyota will stand by their ratings, especially as they won't endorse non-factory modifications. Whether they can say if a specific set up is safe or not is another thing; I'd suggest that they don't have the technical data to make that claim for either a modified of non-modified vehicle because their original ratings are not based in engineering and won't have been tested. As an interesting side note, a member of the SiennaChat Forum recently asked Toyota what the GCWR was for his Sienna as it's not posted on the door post sticker or in the manual. Toyota's response was that they "did not have that information". Make of that what you will.
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Old 08-23-2013, 12:36 PM   #42
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Some of the Forum members are engineers and a few worked in the auto industry. A few others worked in auto and truck service departments and eventually managed the departments. So there is some expertise around.

Sorry to hear your Tahoe's cooling system gets so hot subfan'. For comparison's sake, our Tundra never overheats going over Colorado mountain passes. Different manufacturers have different standards for their cooling systems. Tow ratings may be done on level roads at sea level.

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