DaveInDenver
Middle Income Semi-Redneck
What SAE standard applies to GVW? The FHWA has classified vehicles based on GVW for decades, as does the EPA for emissions and mileage rules.
How important is GVWR?
- Thread starter jornvango
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Well ********! Have to toss that one on the trailer. Prolly a good thing I just tossed new wheel bearings in this past Tuesday!
True. But I see 2 different camps on this issue.
One camp thinks the taco is basically a hilux with a different engine and can take the same levels of abuse.
The other abides by the OEM’s ratings to be safe.
I think the latter camp has more credibility.
Anyone who overloads their truck is doing so at their own risk. The engineers may know exactly how much extra punishment those trucks can take. The average overland enthusiast doesn’t.
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DaveInDenver
Middle Income Semi-Redneck
In this case I don't know we can assume it's solely an engineering question.
The way vehicles are classed in the U.S. makes Hilux GVWR practically unnecessary. We can say prior to 1995 that the number on the door jamb was arbitrary. A U.S. truck with 5,300 GVWR would receive a 3,000 kg rating as a Hilux. There wasn't any difference other than perhaps spring rates with those trucks. So the GVWR on a U.S.-spec 79-95 truck was probably a combination of marketing and safety, e.g. they couldn't sell one as a 3/4 truck with the regulations and laws in place to dissuade import trucks and even if it could do it without breaking doing so in the U.S. was uniquely unsafe. It's one thing to bounce a Hilux at >6,000 lbs at slow speeds and another thing at 70 MPH on the Interstate.
The Tacoma was designed with the U.S. market restrictions in mind so it's not apples to apples. But there are similarities and I know we disagree about the definitions of platforms and families. The reality is it lies somewhere in the grey zone. Dimensions are similar, many parts are the same or similar. Most of what I've read about Hilux is they ride very rough and so are likely sprung much more truck-like. But Toyota also sold a commercial version of the Tacoma in Canada and Mexico with uprated rear leaf springs (which we could get in the U.S. under a TSB for excessive rear spring sagging), so it's not completely far fetched to think there's extra capacity still built-in.
We just simply can't know without direction from Toyota. With stronger rear springs there may be a couple hundred pounds on the table. If you reinforce the rear frame where the Tacoma is open-C vs. Hilux boxed perhaps the real difference would then only be based on dimensions, curb weight and center of gravity. There's a point where no matter how strong the truck is you're limited by physics of track width, wheelbase, etc, and how long you want your truck to last carrying the weight.
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We don’t know for sure. That’s why the wise choice is to abide by OEM ratings rather than overload with the assumption that the Taco has extra capacity.
It’s not just a matter of switching out the rear springs and shocks. The Tacoma’s chassis is mostly unique to NA. Your not going to get hilux-like payloads simply by swapping the suspension.
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It’s not just a matter of switching out the rear springs and shocks. The Tacoma’s chassis is mostly unique to NA. Your not going to get hilux-like payloads simply by swapping the suspension.
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s.e.charles
Well-known member
I watched a documentary about a group from New Zealand (I think) that restores WWI planes. they try to be as authentic as possible, shunning most "modern" materials citing the damage which might incur if one part of the plane was strengthened disproportionately. I guess "domino" effect would be the layman' term. i'll try to dig it up. probably a Netflix.
NOVA: First Air War https://www.amazon.com/Nova-First-A...pID=51bH2HGYk2L&preST=_SY300_QL70_&dpSrc=srch
NOVA: First Air War https://www.amazon.com/Nova-First-A...pID=51bH2HGYk2L&preST=_SY300_QL70_&dpSrc=srch
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DaveInDenver
Middle Income Semi-Redneck
On what basis do you suggest that isn't the case? Do you have information that documents how and where they differ in performance? I would very much like to see such analysis if it exists.
Point is it's all speculation, no real engineering data. Toyota could be building in excess capacity since they don't void warranties AFAIK on trucks with Ride-Rite airbags, which shouldn't be necessary if everything is engineered with no margin as you suggest.
Anyway, when you load the truck to the maximum axle weights listed in the manual, which is 2,755 front and 3,110, that yields a 5,865 lbs total vehicle weight. But my GVWR is listed at 5,350 lbs. Even stock if you load only the rear to the 3,110 lbs you'll still be around 150 lbs over GVWR with everything stock in front (which was roughly 2,400 lbs on my truck).
If I was to guess the engineering department may have designed a truck that the marketing department could sell as carrying the stated payload with fuel and passengers. IOW, most people buying recreational trucks aren't going to be savvy or even care to really do the math to understand curb weight, GVWR, etc. So in effect my argument is therefore that there's an implicit ~450 lbs with a full fuel tank and two 150 lbs people that may account for the discrepancy if you were to drive on a scale to check axle weights.
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Toyota could be doing that, but no one here can prove that. I just think its stupid for for people to overload their Tacoma's based on vague assumptions on what Toyota could be doing. Honestly, many Tacoma owners don't even think that much about this issue. They just overload their trucks because they don't know any better.
And no truck is going to get its warranty voided simply for using airbags. The factory can only deny warranty repairs if they can prove that a malfunction occurred because of said airbags (or other modification).
GVWR is important. If you're going to surpass it on a regular basis, get a different truck. That's all there is to it.
DaveInDenver
Middle Income Semi-Redneck
Sure, manufacturer's specs mean something but why do you view it as an absolute number? What is it that Toyota has told you that indicates its importance?
They provide that GVWR so that owners have a guideline on how to safely operate their vehicles.
Dave, I'm sure OEM's build in some leeway with those ratings. My point is, none of DIY, self-appointed internet engineers know exactly how much leeway there is. I adhere to the OEM's GVWR not because I believe it is some absolute number, but rather because I have more faith in the OEM's recommendations than those provided by the internet.
DaveInDenver
Middle Income Semi-Redneck
Just curious why that one number is so important but we're cavalier about tire size, suspension, whatever else. Your own signature indicates you plan to modify your 4Runner but you don't suppose GVWR only is meaningful if you change nothing on your truck? When you mod isn't then your responsibility to then understand how that changes the OEM's guidelines? The point I'm laboring on is the supposition is GVWR is only about frame deflection or whatever but isn't just as likely it's due to handling or maximum operating speed? So with taller springs the GVWR should go down given a set of parameters to reduce roll-over risk? Perhaps the actual GVWR is up to you to determine if you decide that 75 MPH is an unnecessary top speed and by governing yourself to 65 MPH you might absolutely be safe to go beyond the GVWR in the book? That's what I'm getting at with the discrepancy between GVWR and GAWR in the owner's manual. The truck is capable of some mechanical number, e.g. the axle ratings, but that doesn't mean it's not a roll over risk at that combined mass. It's ultimately your responsibility to understand this stuff, at least I think so.
mezmochill
Is outside
Downhill braking especially.
JaSAn
Grumpy Old Man
I spent the odd hour last night searching for an explanation of how GVWR is determined. Nothing of any substance was found. I did find an article that at least gave some idea of how GCWR is determined: http://www.trucktrend.com/news/163-0910-truck-towing-capacity/
At least they talked to people who know. As far as I could surmise from my reading GVWR is determined by a combination of engineering, marketing and voodoo. In SAE J2087 (trailer towing spec) there are five things they look at: structure, propulsion, thermal, handling, and braking. Manufacturers are not bound by SAE specs.
The thing about GVWR is it is a legal limit, whether or not it is enforced for LDTs. There is a legal risk in exceeding it. Tire size, aftermarket springs, et.al are currently not legally restricted. IIRC there was an attempt in congress to limit or outlaw most modifications to vehicles not sanctioned by the manufacturer sometime in the '80s.
jim
At least they talked to people who know. As far as I could surmise from my reading GVWR is determined by a combination of engineering, marketing and voodoo. In SAE J2087 (trailer towing spec) there are five things they look at: structure, propulsion, thermal, handling, and braking. Manufacturers are not bound by SAE specs.
The thing about GVWR is it is a legal limit, whether or not it is enforced for LDTs. There is a legal risk in exceeding it. Tire size, aftermarket springs, et.al are currently not legally restricted. IIRC there was an attempt in congress to limit or outlaw most modifications to vehicles not sanctioned by the manufacturer sometime in the '80s.
jim
The number of people who are going to properly understand / calculate that is likely statistically insignificant.
Yes, modifying things results in changes in capability -- but ultimately, keeping weight at or below the factory recommendation is always going to be safer than deciding you can go heavier.
kletzenklueffer
Adventurer
My Tacoma has a number of aftermarket pieces added by the PO to include Icon stage 4 suspension and OME heavy leaf packs and a camper shell.
There is a sticker in the door jamb that states "Modifications to this vehicle have reduced the original load carrying capacity by 2 kg or 5 lbs." The decal has the VIN number on it, so I'm not sure who generated it. I wonder how they determined that it was 5 pounds and not 10 or 40 pounds?
There is a sticker in the door jamb that states "Modifications to this vehicle have reduced the original load carrying capacity by 2 kg or 5 lbs." The decal has the VIN number on it, so I'm not sure who generated it. I wonder how they determined that it was 5 pounds and not 10 or 40 pounds?