How important is GVWR?

[Bayou Boy]

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?

Weigh the stuff taken off. Weigh the stuff put back on. The new stuff weighs 5# more than the stock stuff. Pretty simple.

 

[kletzenklueffer]

sounds simple enough, but the PO added nearly 300 pounds of skid plates, a contractor camper shell, an ARB with 10K lb winch, tire carrier rear bumper, dual batteries and extensive wiring and a fridge with slide out. items removed were the stock skid plate, stock suspension and front and rear bumpers. no way that's only a 5# difference. More like 5 or 600# difference.

Would spring rates factor into GVWR? I would think so since it increases the weight the suspension can handle

 

[Dalko43]

Just curious why that one number is so important but we're cavalier about tire size, suspension, whatever else.

Well, to be perfectly frank with you, I don't think overlanders should be so cavalier about changing out major components in their rigs. After all, some of those components you mention (tires, suspension) are a big determining factor in the OEM's GVWR. And there are plenty of horror stories of how people spent thousands of $ swapping in bigger tires and a lifted suspension, only to find that their vehicle rides like crap as a result.

Any modification should be done only after careful consideration of the pro's an con's, and only quality parts should be used. Too many aftermarket companies out there who offer marginal performance (in some cases worse than stock) for high $.

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.

There is a discrepancy between GAWR and GVWR, likely for several reasons. One reason you already addressed (roll-over risk and COG issues). Another would be that the axles, by design, need to have a higher weight rating than the GVWR in order to accommodate the combined payload and vehicle weight as the suspension cycles.

I think its stupid to assume that we, as semi-informed 4x4 owners, can make an exact determination, or even a rough guess, on how much extra payload capacity is afforded to us by the GAWR leeway. If someone wants to overload their Tacoma and drive slower and more deliberately in order to safeguard against potential handling issues, that's their choice. I don't see the point in that. Safety and legal concerns aside, I just have no interest in overloading a truck for daily or travel use. There are almost always other options which are designed, from the ground-up, to accommodate those heavier payloads...Just buy those and avoid the worry and hassle.

 

[RoyJ]

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.

That's a VERY good point that I've brought up in depth in an older thread. To quote:

"Keep in mind if we go by hard technical specs, just about every mod we do renders the legal GVWRs and GAWRs useless:

• Bigger tires and or wrong wheel offset? Boom, there goes your axle rating, as it could over stress your bearings and brakes.
• Larger diameter tires? GVW, payload, GCWR all invalid due to gear ratio change.
• Lower brake pad friction rating (i.e. OEM is FF and you use ceramic EE pads)? Axle rating is gone.
• Lift kit? Every weight rating out the window.
• Winch bumper? A good lawyer can ding you bad if you hit a person, as it doesn't meet federal pedestrian safety standards!

I am not advocating careless over-loading, not at all.

But due to the nature of our hobby, we have to rely on our own safe judgement. If we "go by the book", then just about thing we do is technically "illegal", short of driving absolutely stock vehicles... "

https://expeditionportal.com/forum/...ssues-with-excess-weight.147752/#post-1919659

If we play by the book in this hobby, might was well call it quits before we even head out on a journey!

 

[RoyJ]

There is a discrepancy between GAWR and GVWR, likely for several reasons. One reason you already addressed (roll-over risk and COG issues). Another would be that the axles, by design, need to have a higher weight rating than the GVWR in order to accommodate the combined payload and vehicle weight as the suspension cycles.

If that was the case, then why does EVERY commercial truck have a GVW = sum of GAWRs?

I'm talking every Peterbilt, Volvo tractor, dump truck, cement mixer, mobile crane, tour coach, you name it. In fact, if you look up a say, a Kenworth T880 manual, it doesn't even list a GVWR. All you have are the different axle options (13.2k, 14.4k, 16k, 20k front, 38k, 40k, 46k heavy spec rear, etc.) Not only that, with a overload permit, I can easily (and legally) exceed just about any weight rating of my truck when hauling commercial.

Axle, tire, and suspension load ratings are all based on dynamic, not static rating. If it were static, then every pothole would severely over-load the axle. Depending on your damper, a shock load can be 5 - 10 times the static load.

More likely, commercial load ratings are rarely based on marketing, as they know it'll be driven by commercial drivers, abiding by commercial DOT regulations. Whereas for a recreational vehicle, the legal team knows in a worst case scenario (improperly loaded and poorly driven), our sue-happy society will always blame the OEM.

A commercial driver, especially a heavy hauler, is expected to know his/her tire and axle loads at all times, and the tire load rating for any given psi. You're also expected to know how much you can safely "overload" a tire at a lower speed (tire OEMs all publish this data). Can you imagine expecting the same from a soccer mom in a crossover?

But we all follow the same laws of physics on this planet, so if we take the same precautions and educate ourselves like a commercial heavy hauler, why can't we at least load up to our GAWRs?

 

[Dalko43]

If that was the case, then why does EVERY commercial truck have a GVW = sum of GAWRs?

That's a good question for the manufacturers of those commercial vehicles. I'd imagine the average operator has a better understanding of vehicle payload is constrained by a different set of reg's. The OEM's indicate what the axles can take in terms of payload and the operators are expected to load their vehicles appropriately within those guidelines.

Axle, tire, and suspension load ratings are all based on dynamic, not static rating. If it were static, then every pothole would severely over-load the axle. Depending on your damper, a shock load can be 5 - 10 times the static load.

Thank you for further proving my point. The axle rating needs to accommodate the vehicle (and payload) under dynamic conditions, not just static conditions. That, in addition to COG issues, would be my guess on why the OEM's of pickups build in some leeway between the GAWR and GVWR.

 

[redthies]

It is because they spell “tonne” differently over there. The extra “n” plus an “e” tacked onto the end means you can carry more.

It’s also because a “tonne” is actually more than a “ton”. 2200 lbs vs 2000lbs.

 

[DaveInDenver]

If that was the case, then why does EVERY commercial truck have a GVW = sum of GAWRs?
-snip-
Axle, tire, and suspension load ratings are all based on dynamic, not static rating. If it were static, then every pothole would severely over-load the axle.
-snip-
A commercial driver, especially a heavy hauler, is expected to know his/her tire and axle loads at all times, and the tire load rating for any given psi. You're also expected to know how much you can safely "overload" a tire at a lower speed (tire OEMs all publish this data). Can you imagine expecting the same from a soccer mom in a crossover?
-snip-
But we all follow the same laws of physics on this planet, so if we take the same precautions and educate ourselves like a commercial heavy hauler, why can't we at least load up to our GAWRs?

The OEM's indicate what the axles can take in terms of payload and the operators are expected to load their vehicles appropriately within those guidelines.
-snip-
The axle rating needs to accommodate the vehicle (and payload) under dynamic conditions, not just static conditions. That, in addition to COG issues, would be my guess on why the OEM's of pickups build in some leeway between the GAWR and GVWR.

So the astute owner and mindful driver can therefore use GVWR as a guideline and the combined axle ratings as the hard limit.

 

[DaveInDenver]

The number of people who are going to properly understand / calculate that is likely statistically insignificant.

Being ignorant doesn't exempt us from the consequences.

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.

This is implicit in my argument, if the GVWR specified is based on handling dynamics, which is likely very much so, then taller tires and suspension may reduce your safe GVW. We always assume we're increasing it but unless we know the formula or do the engineering ourselves we can't assume that higher spring rate has anything to do with increasing your safe payload capability. That would be the reciprocal of saying the factory GAWR/GVWR may increase just changing from a P-rated tire to an E-rated LT type.

 

[DaveInDenver]

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.

The legality has been mentioned and I can't find anything that says there's any legal ramification for adherence to GVWR for non-commercial drivers (which is itself an operator license type, not a vehicle) under 26,000 lbs.

There's liability assumption with your insurance or in the event of an accident and there's maybe a license & registration component (the Colorado light truck plates I run on my truck limit me to 16,000 lbs or less empty weight, for example). We have an option for a recreational truck plate here for 10,000 lbs or less empty vehicles. They are technically not allowed to carry cargo, although I suspect that stipulation is probably meant "for hire".

And even that licensing part only affects trucks or vehicles licensed as trucks, an SUV without a bed would be classed as a passenger car and I don't think there's any limits technically on them.

 

[Dalko43]

So the astute owner and mindful driver can therefore use GVWR as a guideline and the combined axle ratings as the hard limit.

No...for reasons you and I have already highlighted. GAWR needs to have a higher rating than GVWR for reasons of COG/rollover mitigation and cycling of suspension (or 'dynamic loads' as @RoyJ referred to it).

You can exceed your GVWR to some degree and it is very reasonable to assume that neither your frame nor your axles will suddenly snap and break. But don't fool yourself into thinking that your vehicle will ride and handle the way it was designed to.

GVWR is the 'hard limit' if we really want to call it that. GAWR needs to be higher in order to accomodate the truck's combined weight for different driving situations. Also, it is possible to exceed the GAWR of one of the axles (either front or rear) while still keeping the overall payload below GVWR. A GAWR informs the owner how much weight is acceptable over either axle. GAWR's really aren't intended to advertise any extra payload that the OEM was holding back on.

 

[DaveInDenver]

No...for reasons you and I have already highlighted. GAWR needs to have a higher rating than GVWR for reasons of COG/rollover mitigation and cycling of suspension (or 'dynamic loads' as @RoyJ referred to it).

No, that's not what he said. Heavy truck ratings don't assume any dynamic loads. The GVWR is the sum of the axle ratings because the driver will load and operate appropriately.

There's no way the manufacturer can know dynamics otherwise they'd have to dictate other variables, speed over terrain, load position and height, tire pressure. You seem to be saying it both ways, that GVWR is and isn't critical. It seems to me for light trucks the number is a SWAG that gives the manufacturer room for marketing (bigger is better!) and liability (reducing for reality of uncritical owners, for which they probably do assume so-called dynamic margin for things like poorly secured loads and driving too fast).

GAWR is just want it is, the amount of weight the vehicle can put on that axle. It doesn't have to be higher or lower than anything, that's just how much the chassis, axle, hub, wheels, tires and brakes can tolerate. The individual axle weights and the total combined weight are the only two things you can measure with any consistency by driving on a scale and those will both be static numbers. The real dynamic forces will be a lot higher than a few hundred pounds implied in the GVWR vs GAWR differences.

If I had to make my own SWAG the reason the Toyota manual has a combined GAWR higher than GVWR is that the assumption is you've bolted in a camper and so the load is secure. They assume GVWR based on the occasional user who's put grandma's dining room set in the back and holds it fast with bungie cords. If loaded under GVWR and it shifts the truck's handling has enough margin that mostly likely won't result in a roll over.

 

[RoyJ]

No...for reasons you and I have already highlighted. GAWR needs to have a higher rating than GVWR for reasons of COG/rollover mitigation and cycling of suspension (or 'dynamic loads' as @RoyJ referred to it).

What I meant is GAWRs already have dynamic load leeway built into them; no need for additional leeway by artificially chopping GVWR.

We can talk about frame limitation, chassis dynamics, etc. But until an OEM engineer show me hard proof, I'll keep on referencing back to the Power Wagon:

It has a chassis that's proven to work on a 14,000 lbs GVW 3500 dually. Same axles. The only limitation are the springs. So if I upgrade them, why can't I take it up to the axle / tire limit?

 

[Dalko43]

What I meant is GAWRs already have dynamic load leeway built into them; no need for additional leeway by artificially chopping GVWR.

We can talk about frame limitation, chassis dynamics, etc. But until an OEM engineer show me hard proof, I'll keep on referencing back to the Power Wagon:

It has a chassis that's proven to work on a 14,000 lbs GVW 3500 dually. Same axles. The only limitation are the springs. So if I upgrade them, why can't I take it up to the axle / tire limit?

That's a distinction I made early on. The Power Wagon very likely has additional payload to be gained by adjusting the suspension because the underlying platform is mostly the same as what's used for the 2500/3500's with higher GVWR's. Now I'm not necessarily saying its wise to exceed the OEM's recommended payload for the PW.

The same argument can't be made for the Tacoma; there is no factory-produced variant of the Tacoma with a higher payload. The GVWR is what it is.

Edit: By the way, the 3500 dually has a different axle from the SRW 2500/3500.

 

[mathers420]

Did I read that people here think the Tacoma and Hilux should have the same GVWR?

Have you guys ever looked at the difference in the frame between a hilux and tacoma?

The hilux frame is fully boxed front to rear. The Tacoma frame is 1/3rd C channelled. That alone would be a huge difference in the payload they can support. I'm sure the differences don't end there.