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Tires: 35's, 37's and beyond . PSI TP

steffen707

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Just draw a chalk line on the tires and look to see where it wears off, hopefully evenly. Borrow your kids sidewalk chalk.
or see where it sticks? would that work as well? noticed that before, come home from work, drive over their drawing, and its stuck to my tire. Then I can use multiple colors for each test.
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bgenlvtex

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The ability to carry load X is predicated by volume Y and inflation pressure Z

The correct inflation pressure is the volume of air at the required pressure to support the load.

The tire is nothing more than a pressure vessel. Radial tires contact patch does not change appreciably when the tire is mounted on the design or approved rim width over the relatively narrow band of approved pressures, unlike bias or diagonal ply tires.

Look at the load and inflation tables for any specific size tire if you you want to know what the correct inflation pressure is for highway use. While the contact patch changes negligibly over a 5-10psi range, body ply deflection changes substantially and with that deflection comes heat, generated and stored internally. Heat is the enemy of the tire.

Airing down off road has meaningful function, staying aired down at highway speeds significantly increases the likelihood of heat related failure.
 

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What’s the math on cost savings of correct contact patch vs. higher pressure and fuel economy over the life of a tire? Would you save more on tires by airing down, or save more on gas by airing up?
 

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What’s the math on cost savings of correct contact patch vs. higher pressure and fuel economy over the life of a tire? Would you save more on tires by airing down, or save more on gas by airing up?
Don't forget to equate the value of added safety properly inflated tires offers as well as increase comfort from the smoother ride, and likely less wear and tear in the vehicle due to the smoother ride.

:)
 

bgenlvtex

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What’s the math on cost savings of correct contact patch vs. higher pressure and fuel economy over the life of a tire? Would you save more on tires by airing down, or save more on gas by airing up?
Correctly inflated tires will speak to both concerns.

Airing down on the highway will deliver higher rolling resistance, higher operating temperatures, reduced fuel economy, significantly increased likelihood of delamination/spontaneous failure, rapid and/or irregular tread wear. All for an increase in traction that is generally not needed on paved surfaces.

Basically all of the things that airing down off road does for you, are negated when you maintain those same reduced pressures on highway.
 

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Correctly inflated tires will speak to both concerns.

Airing down on the highway will deliver higher rolling resistance, higher operating temperatures, reduced fuel economy, significantly increased likelihood of delamination/spontaneous failure, rapid and/or irregular tread wear. All for an increase in traction that is generally not needed on paved surfaces.

Basically all of the things that airing down off road does for you, are negated when you maintain those same reduced pressures on highway.
My question was actually rhetorical, as I was wondering if the OP considers that what might be saved in tire wear could also be more than lost in fuel economy. Emergency maneuvers (steering and braking) are an additional concern which can’t exactly be quantified unless there is a loss, which becomes significantly more likely on improperly inflated tires.
 
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TennesseePA

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Did anyone who is commenting actually consult the "load inflation table" for their particular tire? ...Neither did I because I couldn't find one for the 37x12.5r17 tires I put on my Gladiator. When I picked it up the tire pressures were (clockwise from left front) 38,41,38,36. Drove like total crap and I was regretting my Gladiator decision. Then I remembered to check my tire pressure so I pulled over found the Toyo tire load inflation table and applied those numbers to my similarly constructed load range D BFGs. According to Toyo my size tire has a load carrying capacity of 2150 pounds at 25 PSI and it goes up to 3005 pounds at 40 PSI. There is no reason in the world to drive your Gladiator around with the tires inflated to carry a 12,020 pound load when you weigh less than half of that. Even the minimum rating of 25 PSI is over a ton more carrying capacity that the maximum GVWR for the Gladiator. The GVWR for the Jeep Gladiator is 6250. SOOO if you have either a load range C or D 37x12.5r17 tire on your Gladiator you are "properly inflated" all the way down to 25PSI, (according to Toyo) and you are way overinflated at the recommended tire pressure for the stock tires. Over inflation will result in drivability issues including wandering on the highway, rough ride and, my favorite, bumpsteer. 25 PSI is the minimum pressure you should run in a tire of this size on the highway so 16 PSI is insanely low, in my opinion, since it is 9 PSI below the lowest referenced load inflation value. I have settled on a cold inflation of 27 PSI on my Gladiator with 37x12.5r17 BFG KO2s on the stock Launch Edition rims. I have 600 miles on the rig (tires were installed at 12 miles) and all drivability issues have been resolved. I plan to tow a small enclosed trailer to FL this weekend and I will be able to test and see if the rear tires need any additional pressure for stability, I doubt that they will but I just wanted to mention that since most pickups have different pressures for front and rear tires. Since our Gladiators are such light weight vehicles, as far as trucks go anyway, lower tire pressures are required to keep them safe on the streets when you upsize your tires.

Link to the Toyo site that I cited included for your reading entertainment.https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf
 

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Did anyone who is commenting actually consult the "load inflation table" for their particular tire? ...Neither did I because I couldn't find one for the 37x12.5r17 tires I put on my Gladiator. When I picked it up the tire pressures were (clockwise from left front) 38,41,38,36. Drove like total crap and I was regretting my Gladiator decision. Then I remembered to check my tire pressure so I pulled over found the Toyo tire load inflation table and applied those numbers to my similarly constructed load range D BFGs. According to Toyo my size tire has a load carrying capacity of 2150 pounds at 25 PSI and it goes up to 3005 pounds at 40 PSI. There is no reason in the world to drive your Gladiator around with the tires inflated to carry a 12,020 pound load when you weigh less than half of that. Even the minimum rating of 25 PSI is over a ton more carrying capacity that the maximum GVWR for the Gladiator. The GVWR for the Jeep Gladiator is 6250. SOOO if you have either a load range C or D 37x12.5r17 tire on your Gladiator you are "properly inflated" all the way down to 25PSI, (according to Toyo) and you are way overinflated at the recommended tire pressure for the stock tires. Over inflation will result in drivability issues including wandering on the highway, rough ride and, my favorite, bumpsteer. 25 PSI is the minimum pressure you should run in a tire of this size on the highway so 16 PSI is insanely low, in my opinion, since it is 9 PSI below the lowest referenced load inflation value. I have settled on a cold inflation of 27 PSI on my Gladiator with 37x12.5r17 BFG KO2s on the stock Launch Edition rims. I have 600 miles on the rig (tires were installed at 12 miles) and all drivability issues have been resolved. I plan to tow a small enclosed trailer to FL this weekend and I will be able to test and see if the rear tires need any additional pressure for stability, I doubt that they will but I just wanted to mention that since most pickups have different pressures for front and rear tires. Since our Gladiators are such light weight vehicles, as far as trucks go anyway, lower tire pressures are required to keep them safe on the streets when you upsize your tires.

Link to the Toyo site that I cited included for your reading entertainment.https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf
I’ll buy this.
28 psi is my preferred pressure with 37x12.50r17 tires on a Jeep.
 
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Ole Cowboy

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Let's talk LIT Load Inflation Tables. I never mention them and there is a reason(s)!

1) Load tables are designed for a specific tire by size, design, plys, and use

2) They do not take into account weight distribution. The table just says the PSI -Tire - weight.

3) Few autos have 50/50 x 50/50 weight distribution across all 4 tires

The result is the data in the LIT is just data points on some specific tire, no more, no less! So where is the real importance and the answer to be found? The contact patch, that tells the tale of the tape. Too much psi and you ride on the center of your tires wearing them out from the center. Too little psi and the tires begin to fold, lifting the center and you are now driving on the edges and sidewalls.

With or without the LIT I still approach proper psi the same, I look at the contact patch! That said the proof is in the tread life. I learned from my father how to find the contact patch...dad's first car was a Model T he paid $10 bucks drive out for in 1928. A tire pressure gauge would cost $3-4 dollars back in those days, a dollar a day was a good wage for a man, think a lot of folks had tire pressure gauges...ya think?

I rotate my own tires, get them balanced regularly and hawk psi and tread wear like a teen boy on a topless beach. I have found in recent times that 'door jam' recommended pressure is very accurate on today's cars. But when you change tire sizes and do so on the order of magnitudes you need a way to ascertain proper tire pressure, I do it on a visual, if you want to use a chart, then do so, your jeep, your wallet and you can buy into whatever feels good.

As a former Test engineer, I trust my eyeballs more than some charts I read. Your mileage may be different.
 

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Let's talk LIT Load Inflation Tables. I never mention them and there is a reason(s)!

1) Load tables are designed for a specific tire by size, design, plys, and use

2) They do not take into account weight distribution. The table just says the PSI -Tire - weight.

3) Few autos have 50/50 x 50/50 weight distribution across all 4 tires

The result is the data in the LIT is just data points on some specific tire, no more, no less! So where is the real importance and the answer to be found? The contact patch, that tells the tale of the tape. Too much psi and you ride on the center of your tires wearing them out from the center. Too little psi and the tires begin to fold, lifting the center and you are now driving on the edges and sidewalls.

With or without the LIT I still approach proper psi the same, I look at the contact patch! That said the proof is in the tread life. I learned from my father how to find the contact patch...dad's first car was a Model T he paid $10 bucks drive out for in 1928. A tire pressure gauge would cost $3-4 dollars back in those days, a dollar a day was a good wage for a man, think a lot of folks had tire pressure gauges...ya think?

I rotate my own tires, get them balanced regularly and hawk psi and tread wear like a teen boy on a topless beach. I have found in recent times that 'door jam' recommended pressure is very accurate on today's cars. But when you change tire sizes and do so on the order of magnitudes you need a way to ascertain proper tire pressure, I do it on a visual, if you want to use a chart, then do so, your jeep, your wallet and you can buy into whatever feels good.

As a former Test engineer, I trust my eyeballs more than some charts I read. Your mileage may be different.
Is your primary goal to save money by prolonging the tire life, achieve driving performance, driving comfort, or something else entirely?
 

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I’ll buy this.
28 psi is my preferred pressure with 37x12.50r17 tires on a Jeep.
ya, I'm at 30 and happy with it.
HUGE difference between 30 and 35.
 
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Ole Cowboy

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Is your primary goal to save money by prolonging the tire life, achieve driving performance, driving comfort, or something else entirely?
The proper contact patch provides performance envelope which contains safety, driving performance, comfort, tire mileage, braking, life of the tire and handling.

Your tires carry the weight of your automobile and the contact patch provides the OPTIMAL coefficient of friction to obtain the above results.

WHY do we air down when we go off road? To INCREASE the size of the contact patch in order to distribute the weight of the vehicle over a larger area and gain more traction points.

Door jamb psi I have found to be very accurate, of course, it does not apply when going to other sizes of tires so you have to find what does. The only way is visual observation of the contact patch.
 

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bgenlvtex

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Let's talk LIT Load Inflation Tables. I never mention them and there is a reason(s)!

1) Load tables are designed for a specific tire by size, design, plys, and use

2) They do not take into account weight distribution. The table just says the PSI -Tire - weight.

3) Few autos have 50/50 x 50/50 weight distribution across all 4 tires

The result is the data in the LIT is just data points on some specific tire, no more, no less! So where is the real importance and the answer to be found? The contact patch, that tells the tale of the tape. Too much psi and you ride on the center of your tires wearing them out from the center. Too little psi and the tires begin to fold, lifting the center and you are now driving on the edges and sidewalls.

With or without the LIT I still approach proper psi the same, I look at the contact patch! That said the proof is in the tread life. I learned from my father how to find the contact patch...dad's first car was a Model T he paid $10 bucks drive out for in 1928. A tire pressure gauge would cost $3-4 dollars back in those days, a dollar a day was a good wage for a man, think a lot of folks had tire pressure gauges...ya think?

I rotate my own tires, get them balanced regularly and hawk psi and tread wear like a teen boy on a topless beach. I have found in recent times that 'door jam' recommended pressure is very accurate on today's cars. But when you change tire sizes and do so on the order of magnitudes you need a way to ascertain proper tire pressure, I do it on a visual, if you want to use a chart, then do so, your jeep, your wallet and you can buy into whatever feels good.

As a former Test engineer, I trust my eyeballs more than some charts I read. Your mileage may be different.
The proper contact patch will be achieved when the tire is mounted on the design rim width, and inflated according to the manufacturers load and inflation chart.

Yes you need to know what each axle weighs, that is a given.

Load and inflation charts BEGIN at a specific pressure, not because the union chart writer is a lazy bastard, but because highway operation below that pressure or exceeding the approved load at that pressure is detrimental to the construction of the tire.

Using the Mk1 mod 0 optical comparator (eyeball) while useful does not tell the whole story. I'm not disparaging you, but the contact patch in a static position is an incomplete representation of what is occurring at speed and/or during lateral loading.

Best answer is use both. Let measurable data points be your friend, and back it up with the Mk1 mod 0.

As tires have developed over the course of the last 4 decades they have become far more reliable, longer lasting, better ride quality, less prone to leakage and punctures both. But with that has come technological changes that require more careful monitoring of pressures, and most importantly that those pressures are correct.

Modern radial tires are highly engineered components you simply cannot treat them like we used to and expect a positive outcome.
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