Join Date: Oct 2007
Location: Newark, CA
Re: Weight math
This might be a good time to repost information I posted to the Yahoo groups a long time ago. I have a friend who was the tech editor for a couple of RV and trailer magazines. I e-mailed him back in 2003 after weighing our van. It was fully loaded with gas, water, LP, etc. Since we were headed out for a trip, the refrigerator was loaded and we had some clothes, fly fishing gear, etc. However, I was completely surprised to find that, without people, it came in at 9760 lbs. My post to him stated:
"If you add two people, that puts it at about 10,060 lbs, compared to a GVWR of only 9400 lbs., 600 lbs. overweight. This surprised me since I figured that we were well under the GVWR. When we picked up our van, Sportsmobile included a form in which they filled in the GVWR, subtracted the weight of gasoline, LP, 4 passengers, water, and the van itself to get the CCC or cargo carrying capacity which was about 1100 lbs. We figured that, even with lots of things (lounge chairs, warm clothes, etc.), we wouldn't have that much stuff. However, I now suspect that the van weight listed in the form was the weight of the stripped van and not the completed conversion. I can't see how we can eliminate 600 lbs of stuff from the van and, in fact, suspect that the van, with the winch, custom bumpers, cabinets, water heater, etc., etc., etc., was very close or maybe even over the GVWR when we picked it up even without the clothes and food and things that we packed when we got it home.
My question then, is, what is the consequence of exceeding the GVWR? I have larger, BGF tires and recognize that the van takes a mile or so to brake from 60 mph to 0 (<g>). I also realize that additional strain is put on the frame when going off-road. Anything else to worry about?"
His answer was:
"This is the kind of question we hear all the time. In your case, you aren't overloaded enough to seriously worry. This isn't a Monty Python movie where one pound over GVWR gets added to a rig and it bursts into flames. You're right about how Sportsmobile calculates its weights, in that no matter how responsible the manufacturer is, they all tend to fudge when it comes to the weight question.
Truck manufacturers don't add in a "safety factor" per se, in that they establish a gvwr and figure people will exceed it by XX amount, so they cut it back for safety's sake. The GVWR is based on all the load or power-bearing capacities of the parts, including brakes, steering, bearings, transmission, engine cooling ability, springs -- all these details -- and it's usually the weak link in the chain that establishes the GVWR. In many cases, the GVWR is based on adding up both front and rear axle GAWRs (gross axle weight rating), and the GAWR is based on tire capacity. A typical E range tire is rated at 3,042 lbs capacity at XX pressure, so two tires equals 6,084 lbs capacity, and that's a very common axle rating on 3/4 and 1-ton vehicles. Check your doorjamb sticker for your GAWR figures.
GVWR is also established based on durability, or service life, and warranty work. For example, Ford could give it a higher GVWR, but that could mean 10% more warranty work in the first three years and that's a big $$$$$ for Ford. They strike a balance between usability, competition with the other brands, and cost.
As long as your replacement tires are rated as high or higher than the tires you removed, you have no worries in the tire-rating area. Compare your total tire carrying capacity to your weight figure."
As for the rest of the rig, the potential long-term problems would be accelerated wear and tear on the parts listed above, or possible overheating. Again, your setup is only overloaded a little bit, relatively speaking, so you shouldn't see any real-world effects for a very long time. For example, the engine and tranny you have are the same ones used in the much-larger F-series pickups rated to tow huge trailers, so powertrain durability isn't an issue. My suspicion is that you're a far more savvy driver than the average user, so you can probably "get away with more" than the average guy."
Food for thought...
'01 Ford EB50p Quigley 4WD