Wheel & Tire Weight vs Towing Capacity

[EricStanley]

I have a 2020 Rubicon gas auto. From the factory, the GCWR 12,450lbs and towing capacity is 7,000lbs. It's had a lot of work done including a lift and other heavy mods. According to the spec, the curb weight bone stock is 5,050. I recently weighed it on a CAT scale. No cargo, full tank of gas, me, and my wife. The total was 6,540lbs, a total increase of 1,490lbs. For kicks & easy math, let's say that 450 of that is the passengers. That means the current curb weight with the modifications is about 6,090lbs. So the total added weight of the after-market stuff should be about 1,040lbs. The mods include bigger (and way heavier) wheels and tires (38x12.5 on 22x12). I have a way to quantify the increased weight of the wheels & tires alone, but it requires a ton of work. Before I do that - my question is this: since the entire weight of the truck is ultimately resting on those wheels & tires does that added weight really matter when calculating what my reduced towing capacity actually is? Let's pretend for a minute that the weight of the 5 wheels & tires is 500lbs more than the stock ones. If that's true, does that 500lbs contribute to the reduced towing capacity since the entire weight of the vehicle is resting on those wheels and tires? If it does contribute to the reduced towing capacity, then there's no point in going through the process of determining the added weight. If it doesn't contribute to reduced capacity, then I may very well go through the giant hassle. As it stands now, if I'm doing math right (and there's no guarantee that's true), then the current tow capacity is 5,910lbs (GCWR of 12,450lbs minus the CAT scale confirmed weight of 6,540lbs). So... if the increased weight of the wheels/tires does NOT contribute to the reduced capacity, then (again, for giggles we'll say the added weight is 500lbs), then my new towing capacity should be 6,410... but if it does then the tow capacity is 5,910... right?

So, the somewhat simple question here... does added rotational weight (wheels/tires) get included in the math when determining reduced tow capacity or not?

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[MattKay]

Curb weight is curb weight so yes it would be included.

 

[PuddleJumper]

I have a 2020 Rubicon gas auto. From the factory, the GCWR 12,450lbs and towing capacity is 7,000lbs. It's had a lot of work done including a lift and other heavy mods. According to the spec, the curb weight bone stock is 5,050. I recently weighed it on a CAT scale. No cargo, full tank of gas, me, and my wife. The total was 6,540lbs, a total increase of 1,490lbs. For kicks & easy math, let's say that 450 of that is the passengers. That means the current curb weight with the modifications is about 6,090lbs. So the total added weight of the after-market stuff should be about 1,040lbs. The mods include bigger (and way heavier) wheels and tires (38x12.5 on 22x12). I have a way to quantify the increased weight of the wheels & tires alone, but it requires a ton of work. Before I do that - my question is this: since the entire weight of the truck is ultimately resting on those wheels & tires does that added weight really matter when calculating what my reduced towing capacity actually is? Let's pretend for a minute that the weight of the 5 wheels & tires is 500lbs more than the stock ones. If that's true, does that 500lbs contribute to the reduced towing capacity since the entire weight of the vehicle is resting on those wheels and tires? If it does contribute to the reduced towing capacity, then there's no point in going through the process of determining the added weight. If it doesn't contribute to reduced capacity, then I may very well go through the giant hassle. As it stands now, if I'm doing math right (and there's no guarantee that's true), then the current tow capacity is 5,910lbs (GCWR of 12,450lbs minus the CAT scale confirmed weight of 6,540lbs). So... if the increased weight of the wheels/tires does NOT contribute to the reduced capacity, then (again, for giggles we'll say the added weight is 500lbs), then my new towing capacity should be 6,410... but if it does then the tow capacity is 5,910... right?

So, the somewhat simple question here... does added rotational weight (wheels/tires) get included in the math when determining reduced tow capacity or not?

yes it still counts. rotational weight even more so because its dynamic load not static like a bumper per se. but for simplicity sake, curb weight is curb weight, regardless of how you got there. on the bright side your towing capacity is still pretty close to a stock Mojave with a matching tow package. you could still haul a 19.8ft NOBO empty and have some wiggle room left.

 

[bleda2002]

Yes, gcwr is everything between both vehicles including passenger tires etc. Someone will come in and mention that you basically have no payload left, but heavier tires and rims aren't really payload so you can probably fudge that a bit. That said I'm on 38s as well and with 5.13s and I wouldn't want to tow a camper more than my nobo 19.8 (~4600 pounds loaded), not because of the way it handles but because of the lack of power.

 

[TestMule]

Yup, all items added to the vehicle as noted in your post count as an addition to your vehicle weight. So, given the calculation you use to determine towing capacity, you use that revised weight value.

 

[EricStanley]

So we’ve concluded that the max weight I can tow in its current state is 5,910lbs. Got it.

Now, how about tongue weight? Tongue weight seems to contribute to payload, right? With the max payload being 1,245lbs and the max tongue weight 700lbs, it seems like a bit of a sliding scale. Meaning that for every pound over 545 pounds of payload, that’s one reduced pound of max tongue weight. Right?

if that’s true, and the actual payload of the modifications (not including wheels and tires) + people + gas + stuff is 815lbs (for example), then the max tongue weight is now 430lbs… right?

 

[ShadowsPapa]

Yup, all items added to the vehicle as noted in your post count as an addition to your vehicle weight. So, given the calculation you use to determine towing capacity, you use that revised weight value.

None of that is towing, it's payload.
Towing will be greatly reduced due to reduced braking, higher center of gravity and more, but that can't be calculated.
Basically, it's not a great tow vehicle and has nothing much left for payload.

So we’ve concluded that the max weight I can tow in its current state is 5,910lbs. Got it.

no, you haven't, because all of those numbers are payload - not towing.
You can't calculate reduction of towing by mods - just know it's reduced. And the the higher it sits, the heavier the tires, the taller the tires and so on, the more it's reduced.
I'm not sure where you are getting that these numbers are towing.
Look again at that sticker on the door frame - it's payload, weight the vehicle can carry on itself.

 

[asrricklin]

Your door sticker will have both gvwr and max payload as your truck came out of the factory.
Go to a truck stop and weigh your truck as it sits now. Weigh it with the people who are going to be in it as well as a full tank of gas.
Subtract the current weight from the gvwr and you get your remaining/new payload capacity.
Subtract the actual vehicle weight from the gcwr and you get your max trailer weight.
Now your tongue weight cannot exceed your remaining payload. So you may need to reduce the trailer weight accordingly.

Subtract your tongue weight from the new payload number and you get the weight available for anything else you want to put in the truck.

I'm going to guess that you'll exceed your payload capacity before you meet your gcwr.

 

[hepcat]

Here's the real issue here: every pound you add to the truck deletes a trailer pound from the GCVWR number.

 

[ShadowsPapa]

Here's the real issue here: every pound you add to the truck deletes a trailer pound from the GCVWR number.

Yes..
But people leave out the other things that these had to pass testing for - acceleration, braking, steering, and more.
So lifts impact steering and even braking.
Heavier, larger tires impact braking and steering.
You can go by numbers - math, to get numbers for an unlifted truck on stock tires, but then when you swap tires and lift it, you reduce those numbers even more - in ways you can't use a calculator for.

This has been covered to death in dozens of threads here - people make tons of mods, then think about towing and payload later. They should consider all uses before modifications.
It may not be illegal, but it can wind you up in a real tangled up mess should there be an accident. Someone is going to just look at a highly modified lifted truck with huge tires and see dollar signs in event of an accident.

Bigger tires cut braking considerably and change how the truck will handle if you have to avoid something in the road or someone cuts you off, or you get into sway.
The electronic sway control won't be able to work as well in a lifted truck with huge tires, so don't count on it to be as much help as stock.

Subtract the current weight from the gvwr and you get your remaining/new payload capacity.
Subtract the actual vehicle weight from the gcwr and you get your max trailer weight.

^^^^
This - for raw numbers.
Then deduct some more for the lift and big/heavy tires because of reduced braking and steering abilities, and a higher center of gravity. I need to find the video from a 4x4 shop that explains this perfectly - and how and why lifts matter.

Basically, people build these and they end up being a compromise for something - might be great for the rocks and ravines, but the ability to tow and handling on the road are cut way down. These are already a compromise vehicle from the factory. Then we change them and swing that pendulum in one direction or another.

Factory payload is based on GVWR minus curb weight.
Curb weight is the weight of the vehicle with all fluids, stock, from the factory, a full tank of gas, all coolant and oil levels where they should be. That's curb weight - it does include a full tank of fuel.

 

[EricStanley]

Your door sticker will have both gvwr and max payload as your truck came out of the factory.
Go to a truck stop and weigh your truck as it sits now. Weigh it with the people who are going to be in it as well as a full tank of gas.
Subtract the current weight from the gvwr and you get your remaining/new payload capacity.
Subtract the actual vehicle weight from the gcwr and you get your max trailer weight.
Now your tongue weight cannot exceed your remaining payload. So you may need to reduce the trailer weight accordingly.

Subtract your tongue weight from the new payload number and you get the weight available for anything else you want to put in the truck.

I'm going to guess that you'll exceed your payload capacity before you meet your gcwr.

Take a look at the original post. All of that was covered, including a screenshot of the result at the CAT scale.

 

[EricStanley]

None of that is towing, it's payload.
Towing will be greatly reduced due to reduced braking, higher center of gravity and more, but that can't be calculated.
Basically, it's not a great tow vehicle and has nothing much left for payload.

Yes, it's payload. And payload affects towing capacity.

And to say that it can't be calculated isn't really true. It can be calculated - just need to know the factors.

no, you haven't, because all of those numbers are payload - not towing.
You can't calculate reduction of towing by mods - just know it's reduced. And the the higher it sits, the heavier the tires, the taller the tires and so on, the more it's reduced.
I'm not sure where you are getting that these numbers are towing.
Look again at that sticker on the door frame - it's payload, weight the vehicle can carry on itself.

Again, payload affects towing capacity. I know it's a long read, but read the first post again.
And yes, it can be calculated - literally everything discussed here can be calculated, it's just a matter of knowing the factors that contribute, how they contribute, and determining the math that solves the riddle. It's more about availability of information than it is inability to calculate.

Either way, I still would like to determine tongue weight or hitch weight capacity.

 

[asrricklin]

Take a look at the original post. All of that was covered, including a screenshot of the result at the CAT scale.

You are missing the gvwr....it's not much over the 6500lbs the vehicle weighs. You don't have 500lbs available for tongue weight.

 

[ShadowsPapa]

Again, payload affects towing capacity. I know it's a long read, but read the first post again.
And yes, it can be calculated - literally everything discussed here can be calculated, it's just a matter of knowing the factors that contribute, how they contribute, and determining the math that solves the riddle. It's more about availability of information than it is inability to calculate.

If you are an engineer, you can calculate it. Better yet - computer simulations of the forces involved with the various weights, speeds and center of gravity.

Yes, payload affects towing - not your payload number on the sticker, but what you put in or on the truck.

If the combined weight rating is xxxxx and you toss in 600 pounds of concrete blocks, you have reduced what it's able to tow by 600 pounds.
That's a given. Any book on towing, or the GM truck web site, towsafe, etrailer, REDARC, all of them have calculators and so on.

What can't be figured here is how much more you lose with your mods. Jeep figured it out, and then passed all of those SAE tests to prove it.
It's far more than just weight.

People try to get internet buy-in, or validation. The math is simple, you know that. Figure how much you've added to the truck, do the math, and figure your lift and tires will reduce it farther -
where's the problem?
...............People trying to validate or get approval for going over, above and beyond.

Not sure why there are so many threads on this when it's in the books.

 

[DylanM]

You are missing the gvwr....it's not much over the 6500lbs the vehicle weighs. You don't have 500lbs available for tongue weight.

^^This.^^

When you added almost 1500lbs of "stuff" to the curb weight of your JTR you effectively used up all of your GVWR. In other words, you have nothing left for the tongue weight of a trailer without overloading the vehicle, regardless of how much remaining weight you have in your GCWR.

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