Tire pressure when changing sizes - Look here

Alxmlr789

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I'm seeing lots of false information both on here and on Facebook regarding tire pressures when going to an LT tire from a P metric so i'd figure I'd post this. The answer is definitely NOT the pressure on the placard, you'll kill both your rolling resistance (MPG) and the outside edge of your tires. Toyo made a chart specifically for this, and it's very helpful. Hopefully, we can make this a sticky!

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

In short , you need to look at your OEM tire size and pressure on the door, take that number to the chart for the weight (don't think the weight is on the placard). Take that weight to your new tire size and you'll have your PSI. In my example, it was 285/45/22 @ 36 PSI = 2416lbs. I made the switch to a 35x12.50x20, so I take that 2416 to that tire size which takes me to 43ish PSI (right between 40-45). I run the front at 48 being a little heavier, rear at 43. When i am towing, i bump the rear up to 50PSI.

Let's take another example. Another OEM tire size is 275/55/20 @ 35PSI - which is 2603. Say you switch to a 295/60/20 (seems to be a common size guys go to) you'd take 2603lbs to the 295/60/20. That weight falls smack in the middle of 40-45. Since these are trucks and are heavier in the front you need to look at the GAW to figure out the true PSI for the front and rear axle. But, at least these tables give us a starting place.

Hope this is helpful!!
 

Stryker6040

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I'm seeing lots of false information both on here and on Facebook regarding tire pressures when going to an LT tire from a P metric so i'd figure I'd post this. The answer is definitely NOT the pressure on the placard, you'll kill both your rolling resistance (MPG) and the outside edge of your tires. Toyo made a chart specifically for this, and it's very helpful. Hopefully, we can make this a sticky!

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

In short , you need to look at your OEM tire size and pressure on the door, take that number to the chart for the weight (don't think the weight is on the placard). Take that weight to your new tire size and you'll have your PSI. In my example, it was 285/45/22 @ 36 PSI = 2416lbs. I made the switch to a 35x12.50x20, so I take that 2416 to that tire size which takes me to 43ish PSI (right between 40-45). I run the front at 48 being a little heavier, rear at 43. When i am towing, i bump the rear up to 50PSI.

Let's take another example. Another OEM tire size is 275/55/20 @ 35PSI - which is 2603. Say you switch to a 295/60/20 (seems to be a common size guys go to) you'd take 2603lbs to the 295/60/20. That weight falls smack in the middle of 40-45. Since these are trucks and are heavier in the front you need to look at the GAW to figure out the true PSI for the front and rear axle. But, at least these tables give us a starting place.

Hope this is helpful!!
so the GAW on my truck is 3900lb on the front and 4100lb on the rear. Is this the number i input into the conversion?
 

Stryker6040

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Nevermind i think i answered my own question factory tires where a 116t so a 2756 load rating at 36psi converted to a lt295-65-20 i should be around 45psi on the new tires. Let me know if im kn the right track
 

Alxmlr789

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Nevermind i think i answered my own question factory tires where a 116t so a 2756 load rating at 36psi converted to a lt295-65-20 i should be around 45psi on the new tires. Let me know if im kn the right track
Yep you got it.
 

Yogi217

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This is very helpful!

I have a question, on this chart my oem at 275/55/r20 is only rated as 111, but on bridgestone it is 113t, which is a higher rating..

I guess we can use this as a rough estimate. I am considering switching from a P to an LT, so this would be helpful.
 
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