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Tire Size, Gear Ratio, Affect on Payload/Towing

PyrPatriot

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So I have been reading up on having larger tires put in. I am thinking of getting 35s for my Gladiator Sport S with Max Tow Package. I came across a few things that I would like some help and clarification on.

When you change your tire size, you change the performance of the vehicle.

https://tiresize.com/gear-ratio-calculator/

If I am reading the chart/tool in that page, and finding similar results in other websites, it looks like putting 35" tires on my Gladiator with a 4.10:1 gear ratio will give better fuel economy, but at the expense of power/towing.

I got the Sport with Max Towing instead of the Rubicon because I wanted the extra payload/towing. How much power/capability will the larger tires take away from my Jeep?

It seems that at some point making your truck more off-road worthy takes away from its ability as a truck. If I wanted 35s with the same approximate overall performance, I'd need a 4.56 gear ratio? I won't be messing with such modifications for a while. And if the towing/payload performance takes too big of a hit from a set of 35s and a 2" lift, I won't be doing those either.

Please advise/clarify
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So I have been reading up on having larger tires put in. I am thinking of getting 35s for my Gladiator Sport S with Max Tow Package. I came across a few things that I would like some help and clarification on.

When you change your tire size, you change the performance of the vehicle.

https://tiresize.com/gear-ratio-calculator/

If I am reading the chart/tool in that page, and finding similar results in other websites, it looks like putting 35" tires on my Gladiator with a 4.10:1 gear ratio will give better fuel economy, but at the expense of power/towing.

I got the Sport with Max Towing instead of the Rubicon because I wanted the extra payload/towing. How much power/capability will the larger tires take away from my Jeep?

It seems that at some point making your truck more off-road worthy takes away from its ability as a truck. If I wanted 35s with the same approximate overall performance, I'd need a 4.56 gear ratio? I won't be messing with such modifications for a while. And if the towing/payload performance takes too big of a hit from a set of 35s and a 2" lift, I won't be doing those either.

Please advise/clarify
If you put on bigger tires it's like changing the gear ratio to a higher ratio (meaning smaller number than 4) . Fine you get fewer engine revs per mile and maybe better MPG - so you put in a different ratio - you are right back where you started with MPG - down again! You can't have it both ways. You either want more umph taking off with a load and give up MPG or get better MPG and give up the umph taking off with a load.
I know - we go back and forth with race cars - you can't change tires to bigger then compensate back with a lower gear ratio (a bigger number - it's inverse) - you end up right back where you started - EXCEPT larger tires may mean more rubber on the road, more friction, and even a taller tire, IF it's wider with a more aggressive tread, could net you the same or LESS MPG.
You have to make it good for one or the other - off-road or highway, strength and power at the low end for crawling, or MPG and ability on the highway.
Taller tires may be the same as going from a 4.10:1 ratio to a 3.87:1 ratio JUST AS AN EXAMPLE. But if the taller is also wider and more aggressive, well...
 

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By the way, in performance cars we talk like this -
Lower gear ratio - that means the ring gear has MORE teeth and the ratio is a BIGGER number. It's inverse.
Higher gear ratio is a SMALLER number - it's the number of turns of the pinion compared to the ring gear. If the pinion turns 4 times for every 1 time for the ring gear it's a 4:1 ratio.
Taller gears is a smaller number and a HIGHER gear ratio.
4.10:1 is a low gear ratio but a bigger number
3.15:1 is what my 73 Javelin has - higher gear ratio - means lower number numerically speaking. That is a taller gear than the 4.10
My Eagle SX4 has something like 2.87 or similar - I'd have to look.
My 70 I just sold came factory with 2.87:1 gears - automatics had taller gears. The dealer put in 3.15s back when the first owner bought it, a lower gear ratio. Man did that engine sing on the highway - 3600 rpm was pretty typical.
 
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By the way, in performance cars we talk like this -
Lower gear ratio - that means the ring gear has MORE teeth and the ratio is a BIGGER number. It's inverse.
Higher gear ratio is a SMALLER number - it's the number of turns of the pinion compared to the ring gear. If the pinion turns 4 times for every 1 time for the ring gear it's a 4:1 ratio.
Taller gears is a smaller number and a HIGHER gear ratio.
4.10:1 is a low gear ratio but a bigger number
3.15:1 is what my 73 Javelin has - higher gear ratio - means lower number numerically speaking. That is a taller gear than the 4.10
My Eagle SX4 has something like 2.87 or similar - I'd have to look.
My 70 I just sold came factory with 2.87:1 gears - automatics had taller gears. The dealer put in 3.15s back when the first owner bought it, a lower gear ratio. Man did that engine sing on the highway - 3600 rpm was pretty typical.
Right. I dont want to affect my towing. I am willing to sacrifice mpgs. My question is: how much power/towing/payload do I lose by putting on 35s?
 

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By the way, in performance cars we talk like this -
Lower gear ratio - that means the ring gear has MORE teeth and the ratio is a BIGGER number. It's inverse.
Higher gear ratio is a SMALLER number - it's the number of turns of the pinion compared to the ring gear. If the pinion turns 4 times for every 1 time for the ring gear it's a 4:1 ratio.
Taller gears is a smaller number and a HIGHER gear ratio.
4.10:1 is a low gear ratio but a bigger number
3.15:1 is what my 73 Javelin has - higher gear ratio - means lower number numerically speaking. That is a taller gear than the 4.10
My Eagle SX4 has something like 2.87 or similar - I'd have to look.
My 70 I just sold came factory with 2.87:1 gears - automatics had taller gears. The dealer put in 3.15s back when the first owner bought it, a lower gear ratio. Man did that engine sing on the highway - 3600 rpm was pretty typical.


javelin photo request lol,,,please, both of yours
 

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All this means that if I win the lottery, I have to buy another Gladiator so I can have one for the highway, one for other fun....... dam............
Right. I dont want to affect my towing. I am willing to sacrifice mpgs. My question is: how much power/towing/payload do I lose by putting on 35s?
You may have more issues on hills - downshifting a lot more, trouble keeping up speed, with "taller tires". The engine will have to rev up more to make power on hills when pulling a load.
I wish my Chevy had a lower gear ratio - it's at 3.42 and that's a pretty tall gear (high ratio) for towing. As a result it downshifts a whole lot on I 80 east heading out of Iowa. If the gears were more like 3.8 or 4.x it would have more power pulling or hauling. It's the same as if the truck had taller tires on it - you cut down the engine revolutions per foot of travel - and put it into a lower RPM - less power. So it has to downshift to get the revs up to compensate. Also taking off with a load is harder with taller tires (or a higher gear ratio)
So if you tow or haul heavy stuff, taller tires will make the truck work harder to get going. You won't win any races taking off from a stop. Hills will tax it.
It will look cool - but will take away some of the grunt at low end.
 
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All this means that if I win the lottery, I have to buy another Gladiator so I can have one for the highway, one for other fun....... dam............


You may have more issues on hills - downshifting a lot more, trouble keeping up speed, with "taller tires". The engine will have to rev up more to make power on hills when pulling a load.
I wish my Chevy had a lower gear ratio - it's at 3.42 and that's a pretty tall gear (high ratio) for towing. As a result it downshifts a whole lot on I 80 east heading out of Iowa. If the gears were more like 3.8 or 4.x it would have more power pulling or hauling. It's the same as if the truck had taller tires on it - you cut down the engine revolutions per foot of travel - and put it into a lower RPM - less power. So it has to downshift to get the revs up to compensate. Also taking off with a load is harder with taller tires (or a higher gear ratio)
So if you tow or haul heavy stuff, taller tires will make the truck work harder to get going. You won't win any races taking off from a stop. Hills will tax it.
It will look cool - but will take away some of the grunt at low end.
Thank you. Any idea as to how much performance hit regarding power/towing it will be hit by? 10%? 20% less?

How come folks dont talk about changing gears when they put on 37s or 40s with the 2-4” lifts? Do they just lose even more power for off-roading?

Does this summarize it well?

https://www.4wheelparts.com/the-dirt/a-guide-to-gearing/

"There are several ways to select the correct ring and pinion ratio. Many methods involve some basic math, formulas, and even charts. But the easiest way to figure out the right ratio is to lower it the same percentage you increased the tire diameter over stock. For example, imagine your 4×4 came from the factory with 32-inch tires and 4.10 axle gears. Upgrading to 37-inch tires would calculate to about a 16 percent increase in tire diameter. Increasing the 4.10 axle ratio by 16 percent would dictate the need of a 4.75 axle ratio to match the 37-inch tires. The exact axle ratio you need probably won’t be available, so it’s okay to round up when selecting the right ring and pinion. In this case, a 4.88 axle ratio would be acceptable. If math isn’t your best subject, don’t worry, there are charts available to help you choose the right axle ratio. Your local 4 Wheel Parts salesman can help you pick the correct ratio for your application too."
 

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javelin photo request lol,,,please, both of yours
I am feeling sellers remorse a bit lately as the 70 is sold and just waiting for the truck to pick it up and take it home to Texas. But it's still in my garage until then so I can visit it for today and I can still look at the pictures.
A few years ago my brother started sending me text messages with pictures of the big body Javelins (the 71-74 years) and asking me what I thought. (at the time he had a 69 Javelin and a 70 Mustang convert) I thought it was looking at another car. I'm the car person in the family...
I'd find things wrong or like them but this or that...... finally he sent me a pic of a pretty nice one not far away and he asked "would you buy this car if you could" and I told him - brother, I can't afford another car now - you know that, it's cool but I don't have the money laying around for another now. I ended up looking at the pics and found that car while nice had been resurrected from parts - and the parts years didn't all match - 71 grill with 73 tail lights, etc.
He sent me another pic and link to an ad - and he again asked- what about this one? I said I love it but again, no way! That's even MORE expensive. He then said - I didn't ask that, I asked if you COULD would you? I said yea, love it and it's a PC Javelin. Then something hit me and I asked him - uh, what are you doing? He said " you told me one time you really liked those cars and wouldn't mind having one some day" I guess I forgot I had said that but I live the curved cockpit design, the dash wraps around the driver.
OK, Scot, why are you doing this?
Because you're my brother, and because I can.
Well this one was over even is budget - so I ended up paying a small amount. He rented a car and drove into WI, drove this car back and signed the title over to me. This is a car I can never sell and I just have to take care of it and do the best I can with it.

pc-rear-seat_01.jpg


Powered by a 377 HP 360 -

73-jav-3507.jpg


And the 70 I just sold -

javelin-new-tires004.jpg
 
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PyrPatriot

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I think I may have found a solution. Someone please verify

http://www.4x4abc.com/4WD101/math_wheels.html

"So, to adjust for larger tires you will need lower gears (numerically higher).

As a rule of thumb you can expect to lose about 3.5% of torque/gear ratio for every inch of tire size increase.

For example, if you replace your stock tires of 28" with 35" tires your loss is 7 x 3.5% = 24.5%. If your stock gear ratio in your diffs is 4.9:1 you will have to get lower diff gears that are numerically about 25% higher. 4.9 x 25% = 1.225 - so, your new gears should be 6.125:1"

So going from 32s to 35s is a 3" difference, that means about 10% loss in power?

Using this tool it seems like going from 32s to 35s without changing the gear ratios will make 55mph be 60mph.
 

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ty kindly, gorgeous javelin

pc-rear-seat_01.jpg


Powered by a 377 HP 360 -

73-jav-3507.jpg


And the 70 I just sold -

javelin-new-tires004.jpg
[/QUOTE]
 

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From a technical aspect, wheels and tires are considered unsprung weight, and as such they do not subtract from payload or towing numbers.

From a practical aspect, taller/heavier tires require more horsepower to keep in motion due to the effect of leverage and mass. So, you WILL lose fuel economy and you also will lose towing/hauling power. Regearing will never get you back to square one again. You will always be turning more weight OR spinning higher RPMs OR both in the case of regearing a Jeep with large tires. Once you leave stock form, there's no going back.

The question, as you noted, is how much power will you lose? My experience was that 35" tires were still doable. The loss of acceleration, braking, etc. was noticeable, but it was still OK and I got used to it. I could still haul and tow, albeit a little more slowly and stopping for fuel more often. But it wasn't miserable.

It all depends on which is most important: form or function?
 

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From a technical aspect, wheels and tires are considered unsprung weight, and as such they do not subtract from payload or towing numbers.

From a practical aspect, taller/heavier tires require more horsepower to keep in motion due to the effect of leverage and mass. So, you WILL lose fuel economy and you also will lose towing/hauling power. Regearing will never get you back to square one again. You will always be turning more weight OR spinning higher RPMs OR both in the case of regearing a Jeep with large tires. Once you leave stock form, there's no going back.

The question, as you noted, is how much power will you lose? My experience was that 35" tires were still doable. The loss of acceleration, braking, etc. was noticeable, but it was still OK and I got used to it. I could still haul and tow, albeit a little more slowly and stopping for fuel more often. But it wasn't miserable.

It all depends on which is most important: form or function?
Who is this guy that knows the term unsprung weight? I never figured to hear that in a forum.....
Absolutely correct - it doesn't do squat for payload especially IF the tires can handle the weight - the load rating, speed rating, etc. So the tires have no impact on PAYLOAD. As far as towing - note the gear ratio used for max tow - it can impact that because of the heat generated by the engine and transmission. But it doesn't change what the springs can handle, the strength of the drivetrain in general, but you are adding changes to the cooling and efficiency of the engine and transmission.
If the transmission is having to shift more, to work harder, it could run hotter - ATF has a limit on temperature.
Engine oils tend to break down and the wear resistance starts to wane at temps of 260 to 270 or so, depending on the oil.
They had trouble getting this thing up to the ratings it has because of the cooling issues with that little engine. The grill, the huge wattage of the fans - that alternator is that big because of the BTUs put out by that engine under load. It was quite a thing to get it to stay cool and give it the load ratings they did.
I'm glad someone mentioned the unsprung vs. sprung weight - because it's a given in automotive design to have the best ride and handling you want to keep unsprung weight to a minimum. That's written in every suspension book I have from college.
Now - wheels and tires are also gyroscopes, and mass has properties like momentum. So you can't expect the thing to handle the same - spinning heavier objects will tend to resist changes in speed and direction than lighter objects.

Basically, apply science, physics, etc. here.

Again, you need to decide what's important and what you'll use it for. Is the appearance worth giving up certain things? Do you prefer xx type of driving over yy? The whole vehicle is a compromise of sorts - thus the three levels, and the various packages - so people can choose what they want to use it for most of the time.
 

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I am feeling sellers remorse a bit lately as the 70 is sold and just waiting for the truck to pick it up and take it home to Texas. But it's still in my garage until then so I can visit it for today and I can still look at the pictures.
A few years ago my brother started sending me text messages with pictures of the big body Javelins (the 71-74 years) and asking me what I thought. (at the time he had a 69 Javelin and a 70 Mustang convert) I thought it was looking at another car. I'm the car person in the family...
I'd find things wrong or like them but this or that...... finally he sent me a pic of a pretty nice one not far away and he asked "would you buy this car if you could" and I told him - brother, I can't afford another car now - you know that, it's cool but I don't have the money laying around for another now. I ended up looking at the pics and found that car while nice had been resurrected from parts - and the parts years didn't all match - 71 grill with 73 tail lights, etc.
He sent me another pic and link to an ad - and he again asked- what about this one? I said I love it but again, no way! That's even MORE expensive. He then said - I didn't ask that, I asked if you COULD would you? I said yea, love it and it's a PC Javelin. Then something hit me and I asked him - uh, what are you doing? He said " you told me one time you really liked those cars and wouldn't mind having one some day" I guess I forgot I had said that but I live the curved cockpit design, the dash wraps around the driver.
OK, Scot, why are you doing this?
Because you're my brother, and because I can.
Well this one was over even is budget - so I ended up paying a small amount. He rented a car and drove into WI, drove this car back and signed the title over to me. This is a car I can never sell and I just have to take care of it and do the best I can with it.

pc-rear-seat_01.jpg


Powered by a 377 HP 360 -

73-jav-3507.jpg


And the 70 I just sold -

javelin-new-tires004.jpg
That 70 is just gorgeous :blush:
 

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Who is this guy that knows the term unsprung weight? I never figured to hear that in a forum.....
Absolutely correct - it doesn't do squat for payload especially IF the tires can handle the weight - the load rating, speed rating, etc. So the tires have no impact on PAYLOAD. As far as towing - note the gear ratio used for max tow - it can impact that because of the heat generated by the engine and transmission. But it doesn't change what the springs can handle, the strength of the drivetrain in general, but you are adding changes to the cooling and efficiency of the engine and transmission.
If the transmission is having to shift more, to work harder, it could run hotter - ATF has a limit on temperature.
Engine oils tend to break down and the wear resistance starts to wane at temps of 260 to 270 or so, depending on the oil.
They had trouble getting this thing up to the ratings it has because of the cooling issues with that little engine. The grill, the huge wattage of the fans - that alternator is that big because of the BTUs put out by that engine under load. It was quite a thing to get it to stay cool and give it the load ratings they did.
I'm glad someone mentioned the unsprung vs. sprung weight - because it's a given in automotive design to have the best ride and handling you want to keep unsprung weight to a minimum. That's written in every suspension book I have from college.
Now - wheels and tires are also gyroscopes, and mass has properties like momentum. So you can't expect the thing to handle the same - spinning heavier objects will tend to resist changes in speed and direction than lighter objects.

Basically, apply science, physics, etc. here.

Again, you need to decide what's important and what you'll use it for. Is the appearance worth giving up certain things? Do you prefer xx type of driving over yy? The whole vehicle is a compromise of sorts - thus the three levels, and the various packages - so people can choose what they want to use it for most of the time.
I want to have slightly more off-roading ability at a reasonable expense in towing. That is, I want to know the trade-off ratio. If I go to 35s and can maybe a 2” lift will I suddenly lose 10% of towing (675lbs)? Based on my “realistic expectations” thread, I dont think the Gladiator can do more than light trails without the larger tires and lift. The lack of that utility kills me. But I got the Jeep that I did because I KNOW one day I will need to tow something in the 5000lb area and will need the 6750lb rating of the configuration I have.

Does that mean all those Rubicons with 37s and 2-4” lifts now only have a 4500lb payload?
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