Help me understand weight limits...

So, I've recently started pulling a travel trailer and I have a CAT Scale 2.5 miles from where I'm parking my trailer (less than 10 miles form my house). Being the data-geek that I am, I find myself really curious about some of the vehicle weight limits and how all this stuff works together.

First off, let's air the limits of the 2020 TRDOR. GVWR is 5600 lbs. GCWR is 11,360.

I've done a modest amount of stuff to my truck, but am nowhere near as built out as some. I do have an OME suspension and haven't noticed any issues on or off road. I took the truck across a scale today with me, a full tank, and nothing in the bed. My (GVWR) weight was 5600 lbs.

This weekend, with the trailer hitched up, and driving across the same scale with two humans, dog, weekend load out, and trailer, the GCWR weight was 10,120 lbs. I am running an OME suspension, which carries the weight well.

What I'm super curious about is how do people manage with much heavier overland builds with bed racks, drawer systems, rooftop tents, etc.? If I'm already at the rated GVWR, then quite a few others' builds are clearly over that. Is this primarily a matter of suspension?

I can understand how the GCWR matters as at that point one it up against drive train and drive line components, break system, etc. But, if suspensions are upgraded, is that only the weak point regarding GVWR.

Finally, it is quite possible that none of this makes sense... just thing out loud a bit.

Thanks y'all.

 

This implies that either the scale is way off, or you weigh over 1100lbs, as the curb weight of your truck is less than 4500lbs.

 

It was at a certified CAT Scale, and I have bumpers, winch, nerf bars, aluminum under armor, lights, roof rack, awning, tonneau cover, stuff in the cab, suspension upgrade, 33" tires, me, full tank of gas, and stuff in the cab storage.

I'm pretty sure that is accurate. I'm also pretty sure many grossly underestimate actual weights.

Also, I know there are people with WAY heavier builds than this.

 

That makes more sense.

Your original post only mentioned you and a full tank.

 

Absolutely not!
Wheels, tires, brakes, cooling system, engine, transmission, etc all come into play. Suspension is one factor (and probably the least important).

Take for example two identical trucks, Ford F-350s...If you spec one with heavy duty 18" wheels and upgraded tires the GVWR will go up over 1,000 lbs (!) compared to the standard 17" lighter duty wheel/tire combo. Suspension is the same in both and has zero impact on improving GVWR.

You can spec a 1/2 ton full size truck with different GVWR doing something similar. In addition, GVRW is only one spec you need to worry about, the others included cargo capacity or payload (not always the same thing!) and other weight measurements.

Want to carry a slide in camper in your Ford F-150? You need to spec a different engine (5.0) otherwise Ford will not issue the camper certificate with COG measurements. The 2.7 and 3.5 ecoboost engines are not certified to haul a camper.

Best would be to spend some time with the VERY informative section your owner's manual has regarding towing/hauling. Your manual has an excellent section on the different calculations and terms you need to be aware of.

To be blunt: All those "overlanders" are hugely overweight but since they crawl around in the middle of nowhere at 30 mph nobody has come down hard on them. Yet.

 

Everything matters like was well said above. Also, you cannot increase GVW, only the manufacturer. HOWEVER, you can increase carrying capacity! How? Go on a diet. Your truck has to go on a diet too. While you might think you need all that stuff you hung on your truck, you proba ly don't. I'm sure it looks cool and all that but...
There is a reason people who use trucks for work get the stripped version. Having no options means less weight which means more payload.

 

I dig what you’re saying, but, if the drive train, cooling system, brakes, etc. can handle the GCWR of 11,360 lbs, and configured to move that mass, what is the weak point in having that mass distributed on the truck?

That’s what has me asking the question.

If could have a 5600 lb GVWR vehicle (the limit) and pull a 3000 lb trailer with no breaks and be within spec. What is the fail point at a 5800, or 6200 lb vehicle? I don’t see how it could be the drive train, breaks, cooling system, or transmission. Maybe the suspension, or frame, but clearly with a GCWR at over 11k, the truck can deal with more mass than 5600.

Again, just thinking out loud trying to understand more deeply. Thanks for taking the time for a thoughtful reply.

 

This is the second truck I’ve built and, this build is a lot lighter than my 2nd gen, which served me well for 197k miles before it was sold to a friend who is even more avid of an off-roader than me. Everything on it serves a purpose, none of which is to “look cool”.

Maybe I opened a can-o-worms I shouldn’t have. ;-)

 

The truck isn't really dealing with the weight of whatever you are pulling (the thing that is giving you a max GCWR). The thing you are pulling is dealing with the mass. It has it own set of brakes (required). It has four steel rims, four tires and with the (required) WD hitch, you are putting maybe 600 or 700 lbs of weight actually on the truck (tongue weight). The rest of the weight is being carried by the trailer.

Think of it this way: Load 500 lbs of dirt in a wagon. Try to pull it. You can probably drag it across the driveway with no problem. Next, grab five, 100 lb weights and try to carry them on your back across the same driveway. Not gonna happen. In the first instance you had your weight (think GVWR) AND the GVWR of the dirt-filled wagon combined (equaling your GCWR) and probably had no problem moving it. Because it was distributed. When you didn't distribute it (put 500 lbs on your back) you couldn't even move.

Soooo..In that silly example your GCWR is your weight and the weight of the little red wagon filled with dirt. You could move it. BUT, when the weight was put entirely on you, taking even one step was impossible.

You should have two weight stickers on your driver's door jamb. One is the nice, factory installed one that is on every vehicle sold. But, look kinda under it and you should see a small round, yellow sticker that gives you the truck's true payload. It is put there after your truck is built and will subtract from the door sticker the weight of your options. My bare bones SR had a payload sticker of 1,300 lbs. But, I had one or two factory options and the weight of those options were listed on that yellow sticker with a warning to subtract that weight from the 1,300 lbs that the "standard' sticker showed

 

No this is a good discussion. Building a truck for off road is quite a bit different than building one for work.
For example, a Raptor or a Power Wagon both have much lower payloads than their stable mates. They are great offroad, suck at carrying a load.
Setting up a truck to do either requires a much different setup. If you try to build a truck to do both, it will be full of compromises and do neither very well.
However, most pickups are full of compromises. The ones that aren't are trucks like a Tacoma SR... or a GM WT... or a Raptor. They are built for a specific purpose.

 

Another thoughtful post, but I have to disagree with some of the physics. Let me try and break down my thinking a bit more.

If we take a truck with a GVWR of 5600 lbs, and a GCWR of 11,360, this is a bit different that a human lifting that same mass. Our system is a vertical system and our legs and core probably most closely relate to the up and down forces of piston rods on the crank shaft.

If a vehicle at 5600 lbs can safely tow a trailer of 2500 lbs (less than where trailer brakes are required), the engine, transmission, drive axel, and brakes are capable of handling that 8100 lbs. That is different than loading 2500 lbs in the bed, but once vertical forces of the piston hit the crank shaft, all of way through the drivetrain into the wheels and on the pavement are now rotational forces. At that point, this is why I would think things like the frame and suspension are more of the limiting factor to how that mass is moved (and stopped) while on the road.

The same things happened when towing at the 11,360 GCWR. It's the same rotational force coming out of the engine, through the drivetrain, into the rear diff, and ultimately onto the pavement. In that case that load would obviously exceed limits where trailer brakes were required, to assist in stopping the mass... but it's the same engine and drivetrain propelling that mass that far exceeds the GVWR.

Thus, I still find myself curious of what the actual limiting weak link that defines GVWR... frame, suspension (which is weak in the stock config), maybe the stock tires, possibly something else... and for some odd reason and late at night, I find this a burning curiosity.

 

Brakes.
Tires.
Frame
Wheels
Cooling
All those put together. In addition, the SAE spec that sets the standards has a lot of rules.
Plus, you have to remember that we are dealing with dynamic, not static forces. That 1K load you are carrying at one mph is quite a bit different at 70 mph.

 

Correct, and that same 5600 lb truck at GVWR pulling a 2500 lb trailer = 8100 lbs of dynamic force at 70 mph... and that is well within 11,360 GCWR.

 

No. Use the formula 1/2mv^2.

 

Two identical appearing Ford F-150 trucks are in front of you. The ONLY difference is the rims and tires. One has a 7,600 lb GVWR and the other has a 6,400 lb GVWR.

Two identical Ford F-350 trucks are in front of you. The ONLY difference is one has dual rear wheels and the other has single rear wheels. The dually has a GVWR of 14,000 lbs and the single rear wheel has a GVWR of 11,400.


The frame, engine, brakes, etc are identical. In those examples, the "weak link" is (obviously) the rims and tires of the trucks. That is what is determining GVWR.

Remember we are talking about one single measurement (of many): GVWR which is actually not a very good indicator of capacity to either haul or tow since those two things rely also on ......

............ other measurements that are not static (GVWR is static and does not change). Payload changes, wet weight changes and other measurements probably also change. Saying a Tacoma can tow 6,500 lbs is true, if and only if a bunch of conditions are met. These conditions are terribly hard to meet though!

It is possible (and likely) that two trucks with the same exact GVRW will have different payloads, towing capacities, and GCWR..

For example: Payload is the function of two numbers: Gross Vehicle Weight Rating minus the wet weight of the vehicle. If your truck has a heavy diesel engine and I have a lighter gas engine, my GVWR and yours will be the same, but my payload will be a quarter-ton more. In this case, the "weak link" in your payload capacity is your diesel engine (!) Got lots of armor on the Taco? That weight must be subtracted from your payload, just like the convenience group wacked 8 lbs from my Taco's payload.

Sooooo depending on what particular measurement you are after, the weak link will vary. As posted, it is pretty much everything: Engine, Frame, Brakes, Rims, Tires, even the options on a particular truck impact some (not all) measurements. I saw a builders guide put out by Ford which listed the weight of every single option available on a SuperDuty truck. Power folding mirrors? Subtract 18 lbs....Glass moonroof? Wack off another 89 lbs. Got navigation? You lose another 2lbs of payload. The weight doesn't come off the GVWR but from what you can put in the bed or tow. That is why I can spec out a Ford F-350 that will carry more weight than a F-450 (!).

SAE J2807 calculates towing specs and if you look at it and understand it you will realize there isn't a Taco on the planet that is actually designed to tow 6,500 lbs or whatever their max tow rating is. In fact, every single tow rating is wildly optimistic for all the manufacturers (since they all subscribe to the SAE J2807 spec). That is why most normal people suggest if towing with the Tacoma to cut the max weight number in half if you want to be safe and comfortable.

 

Excellent post!

 

My truck is a 2018 DCSB manual transmission that is pretty stock as far as what I see on this forum:
- 275/70/17 KO2 E rated
- hard tonneau cover
- swingcase full of recovery stuff in the bed

I weighed my truck on a certified Cat scale today with a full tank of gas and my 192 lb self in it, and believe me my truck is not a Lotus:

 

I'd say it's Toyotas legal team. Nothing is rated at it's failure point, you could probably load 2000 lbs in the bed and hook up a 7000 lb trailer and go down the road without breaking anything. It wouldn't be safe, legal or good for any components but you could do it.

 

It is actually Toyota's engineering team. You will find very few lawyers with a background in vector mechanics, material strengths, system dynamics, or mathematics. The LSAT is all about reading...and talking ;-)

There is a reason why lawyers are a dime a dozen..the bar isn't very high ;-)
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