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Why are Rebel Tire Pressures so High?

Eltaco

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Forgive my ignorance here, doing my best to learn on this subject.

I have a 2020 Laramie with ORP, but just swapped from my factory wheels/tires to a set of Rebel takeoffs. Trying my best to determine what new pressures I should be running. I know the Rebels come from the factory with a 55/45psi door sticker.

My factory wheels and tires:
Falken Wildpeak AT: 275/55/R20 113T
Door sticker: 32/32psi

New Rebel Takeoffs: LT275/70R18 E

Running load calculators and charts, I believe I come out to somewhere between 36 to 40psi on the new tires. I can’t figure how the Rebel door sticker recommends 55/45psi F/R. Curious what I’m missing... I don’t think our weights are likely too much different.
 

BostonBLS

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In the same situation as you. Been reading through threads and has to do with E rating of tire. But interested to see responses. I am running 50/40. Curious to see how tire wear is but rides good.
 

securityguy

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Forgive my ignorance here, doing my best to learn on this subject.

I have a 2020 Laramie with ORP, but just swapped from my factory wheels/tires to a set of Rebel takeoffs. Trying my best to determine what new pressures I should be running. I know the Rebels come from the factory with a 55/45psi door sticker.

My factory wheels and tires:
Falken Wildpeak AT: 275/55/R20 113T
Door sticker: 32/32psi

New Rebel Takeoffs: LT275/70R18 E

Running load calculators and charts, I believe I come out to somewhere between 36 to 40psi on the new tires. I can’t figure how the Rebel door sticker recommends 55/45psi F/R. Curious what I’m missing... I don’t think our weights are likely too much different.
Click on the "What Tire Pressure to Run" link in the attched:

calculator
 

Eltaco

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Click on the "What Tire Pressure to Run" link in the attched:

calculator

Thank you. I did this earlier today and came up with 36psi, if I recall correctly.

I can’t figure why the discrepancy between the 36psi calcd here or around 40psi from Toyo as compared to the Rebel door sticker of 55 front / 45 rear.
 

mel22b

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Funny, i wondered the same thing about my truck. Works ok on road, however its almost mandatory to lower psi once off pavement.
 

bingo23

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Thank you. I did this earlier today and came up with 36psi, if I recall correctly.

I can’t figure why the discrepancy between the 36psi calcd here or around 40psi from Toyo as compared to the Rebel door sticker of 55 front / 45 rear.

Although LT tires can carry more load, they typically need a higher pressure vs a passenger tire to carry equal load.

The difference you're seeing with the Toyo chart and the calculator is that the calculator is taking into account that the vehicle manufacturer had to increase the load capacity of the passenger tire by 10% because it was going on an SUV or Truck. If you're changing to an LT tire then you don't have to keep this added load capacity. The calculator states this in red writing when doing the calculation for 275/55R20 113 to LT275/70R18 E. It also explains this on the Toyo chart pdf on page 11.

36 psi in the LT275/70R18 E tire should match the load needed from the 275/55R20 113 passenger tires on the truck. 40psi would match the exact same load capacity, but it isn't needed when going to an LT tire supposedly.

The reason for the Rebel using 55/45psi, I'm not sure.

The real test is how the truck feels/drives with whatever psi, and how the tires wear.
 

Eltaco

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Although LT tires can carry more load, they typically need a higher pressure vs a passenger tire to carry equal load.

The difference you're seeing with the Toyo chart and the calculator is that the calculator is taking into account that the vehicle manufacturer had to increase the load capacity of the passenger tire by 10% because it was going on an SUV or Truck. If you're changing to an LT tire then you don't have to keep this added load capacity. The calculator states this in red writing when doing the calculation for 275/55R20 113 to LT275/70R18 E. It also explains this on the Toyo chart pdf on page 11.

36 psi in the LT275/70R18 E tire should match the load needed from the 275/55R20 113 passenger tires on the truck. 40psi would match the exact same load capacity, but it isn't needed when going to an LT tire supposedly.

The reason for the Rebel using 55/45psi, I'm not sure.

The real test is how the truck feels/drives with whatever psi, and how the tires wear.

Thank you for your detailed information.

To me the contact patch looks very large on the LTs at the same pressure, and the truck felt loose / bouncy. Not sure exactly how to explain it but definitely didn’t feel as tight.

I’ve upped it to 50/45 and the truck feels very good on road. I’ll get some more feedback from the truck when I stop babying it and bring it onto some gravel. I wanted to get some running boards and mud guards for paint protection before doing so, tho.

I really can’t explain the Rebel recommendations other than that truck has different shocks. Perhaps the characteristics of that setup is so substantially different that it benefits by such high pressures? Unsure.
 

go-ram

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Thank you. I did this earlier today and came up with 36psi, if I recall correctly.

I can’t figure why the discrepancy between the 36psi calcd here or around 40psi from Toyo as compared to the Rebel door sticker of 55 front / 45 rear.
.
First, each size/model/manufacturer of tire has a different type of construction and uses different materials, hence requires a very different inflation pressure to achieve their stated load rating. Second, Ram has full responsibility for your safety under all conditions at the maximum load at which the truck is rated for both payload and towing. If Ram put 32-36 PSI on the door jamb sticker, and you go out and load the vehicle to the maximum GVWR, etc. the tires would likely fail, and Ram would be legally liable. Toyo (or any tire manufacturer) has it very simple by comparison. They only care about passing the load rating for their tire, i.e. a single tire loaded by a specialized testing machine in a lab environment. Ram has to worry about a LOT more than Toyo does.
 

Eltaco

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First, each size/model/manufacturer of tire has a different type of construction and uses different materials, hence requires a very different inflation pressure to achieve their stated load rating. Second, Ram has full responsibility for your safety under all conditions at the maximum load at which the truck is rated for both payload and towing. If Ram put 32-36 PSI on the door jamb sticker, and you go out and load the vehicle to the maximum GVWR, etc. the tires would likely fail, and Ram would be legally liable. Toyo (or any tire manufacturer) has it very simple by comparison. They only care about passing the load rating for their tire, i.e. a single tire loaded by a specialized testing machine in a lab environment. Ram has to worry about a LOT more than Toyo does.

Understand the liability concern.

My door sticker says 32psi
Rebel says 55psi
GVWR and payload between vehicles are nearly identical.
Toyo chart suggests a 10% increase due to tire size/construction
The Ram stickers suggest a 72% pressure increase.

It’s odd to me, even as an engineer, how those two recommendations can vary so wildly. I suppose I’ll set pressures somewhere in between as my basic concern is for best wear rate.
 

go-ram

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Understand the liability concern.

My door sticker says 32psi
Rebel says 55psi
GVWR and payload between vehicles are nearly identical.
Toyo chart suggests a 10% increase due to tire size/construction
The Ram stickers suggest a 72% pressure increase.

It’s odd to me, even as an engineer, how those two recommendations can vary so wildly. I suppose I’ll set pressures somewhere in between as my basic concern is for best wear rate.
.
I suggest you pose the question to Sean Holman at [email protected]. If anyone knows and can give a clear answer, it's Sean. He's a hard-core truck guy, a hard-core four-wheeler, and he has more high-level contacts in the auto industry (both engineers & executives) than any other automotive journalist I know of. He's a solid, straight-up, stand-up guy, and he drives more different vehicles in a year than any of us will ever drive in a lifetime. If you haven't already subscribed to The Truck Show Podcast, you might consider it. They get a wee bit silly sometimes, but all in good fun, and overall they have a ton of very high-quality, technically-minded guests to learn from.
.
 

Eltaco

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I suggest you pose the question to Sean Holman at [email protected]. If anyone knows and can give a clear answer, it's Sean. He's a hard-core truck guy, a hard-core four-wheeler, and he has more high-level contacts in the auto industry (both engineers & executives) than any other automotive journalist I know of. He's a solid, straight-up, stand-up guy, and he drives more different vehicles in a year than any of us will ever drive in a lifetime. If you haven't already subscribed to The Truck Show Podcast, you might consider it. They get a wee bit silly sometimes, but all in good fun, and overall they have a ton of very high-quality, technically-minded guests to learn from.
.

Thanks for the contact. Always open to learning from individuals smarter than me (and there’s a lot) on these subjects.
 

19TXLimited

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I would like to know the same. Although I went from a 285/45/22 to a 285/55/22. New tires are LT E-rated tires. Seems that have a large contact with pavement as you noted. I am running 39-40 PSI right now. Door jam says 36PSI for stock. Wish I knew what pressure is going to provide best wear, MPG and ride quality...???
 

19TXLimited

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I would like to know the same. Although I went from a 285/45/22 to a 285/55/22. New tires are LT E-rated tires. Seems that have a large contact with pavement as you noted. I am running 39-40 PSI right now. Door jam says 36PSI for stock. Wish I knew what pressure is going to provide best wear, MPG and ride quality...???

I am now running 45psi. Still rides well and I’m sure will ride even better once I get the Daystars on.
 

Trich_Rebel

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For the people choosing to run under recommended pressure... does the tire light being on bother you?!
I hate that I need that much tire pressure just to keep the light off. I'm really not a fan of running that high of pressure anyway with no load or hauling anything, not to mention the roads down here will knock your liver loose.
I'm thinking of contacting my local dealer to see if its possible they adjust and re-calibrate my tire pressure setting to something lower.. not sure they would. But I'd like to run around 36-38 psi with no tire light on my dash.
 
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RebelWraith

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For the people choosing to run under recommended pressure... does the tire light being on bother you?!
I hate that I need that much tire pressure just to keep the light off. I'm really not a fan of running that high of pressure anyway with no load or hauling anything, not to mention the roads down here will knock your liver lose.
I'm thinking of contacting my local dealer to see if its possible they adjust and re-calibrate my tire pressure setting to something lower.. not sure they would. But I'd like to run around 36-38 psi with no tire light on my dash.
Dealership will not do it. You need AlfaOBD or some sort of tuner in order to change tire pressure minimums.
 

19TXLimited

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For the people choosing to run under recommended pressure... does the tire light being on bother you?!
I hate that I need that much tire pressure just to keep the light off. I'm really not a fan of running that high of pressure anyway with no load or hauling anything, not to mention the roads down here will knock your liver lose.
I'm thinking of contacting my local dealer to see if its possible they adjust and re-calibrate my tire pressure setting to something lower.. not sure they would. But I'd like to run around 36-38 psi with no tire light on my dash.

With most cars/trucks this can be done from the comfort of your own home...I'm not sure that's the case with the Ram, but I'm sure someone will chime in.
Dealership will not do it. You need AlfaOBD or some sort of tuner in order to change tire pressure minimums.

Well that's stupid. Although after talking to a buddy who works at the dealership here in Houston it seems that even changing tire size is unavailable other than changing to a different models tire size. I.E. you could have the dealer change to show that your truck has Rebel wheels and tire, but not able to adjust to a 34" or 35" tire size.
 

evskie53

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Anyone tried doing the “chalk test” to find the right pressure for your tire set up? I’ve done this in the past with aftermarket set ups and it really worked well. Worth a try here?
 

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