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37”s and air pressure

Discussion in 'Ford Raptor Exterior Forum [GEN 2]' started by Wfo, Apr 15, 2019 at 9:11 AM.

  1. Wfo

    Wfo Full Access Member

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    5635014E-E403-46DA-B179-B97CC03D58D9.jpeg I just mounted up my method mr105 beadlocks with 37” Mickey Thompson mtz. What air pressure are people with 37s running for road and off-road?
     
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  2. jzweedyk

    jzweedyk FRF Supporting Member Supporting Member

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    Go to the dealer or online and get the pressure/load carrying chart for the tire. Then you can see how low you can go for highway. When I ran 37 KO2 E range tires, the Jeep was only about 4,200 pounds, and I could go as low as 16 and still be rated for the road. I normally ran 24 psi most of the time.

    Once you find how low you can go, you can experiment with different pressures until you find the best one. My GUESS is around 28.
     
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  3. Wfo

    Wfo Full Access Member

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    Mickey Thompson doesn’t have any info regarding pressure and load chart. Just maximum pressure.
     
  4. Sunchild714

    Sunchild714 Member

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    28 seems excessively low. I deflate my 37's to 20-25 when off-road. For regular highway use, I put them to about 48 so they are just over 50 when hot.
     
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  5. BigGriff023

    BigGriff023 Full Access Member

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    I run my 37" Nitto AT Tires at 38 front, 37 rear. I got that psi doing a chalk test. It also depends on what you're going to carry in the bed and other weight factors.
     
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  6. Wfo

    Wfo Full Access Member

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    Thanks for the input!! I am at 33 front and 31.5 rear now for road use. I will add some air. These tires are too expensive to wing it.
     
  7. jzweedyk

    jzweedyk FRF Supporting Member Supporting Member

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    With all due respect, 20-25 for off road is way too high. I do a ton of off road in Jeeps and RZRs and now the Raptor. Even with my C range 35s on the Raptor, I go down to 14-15 off road and they are fine. The reason to deflate is two fold, one a more comfortable ride as the sidewalls flex more and absorb the bumps better and two to increase the tire patch on the ground (for climbing obstacles). If you do research on tire patch, you will find out it is a geometric curve. Very little contact patch change for a long time (like from 38 to 25 PSI) and then it starts to increase geometrically. The only problem with going lower is the possibility of "blowing" a bead. That is why rock crawlers use bead lock wheels. I have never seen anyone blow a bead unless they had less than 10 pounds in their tires. I can't go below 14 or so in the Raptor because the tires are C rated (very flexible side walls) and the truck is heavy. When you come down a steep rock face and the truck is pointing down, all the weight is on the front tires and if you go too low they can wrinkle up to the wheel, which is not good. Stiffer sidewall tires, like load range E tires, need to go down lower in PSI to increase the tire patch area, and can handle the weight better. The only other thing you need to be aware of is that at higher speeds, the tires flex faster that can build up heat and cause damage. The rule of thumb with rock crawlers, is when the tires are deflated they generally don't exceed 45 mph for any sustained time. So the pressure you can use for road and off road is determined by the load range of the tire, and the weight of the vehicle. I run my RZR at 6.5 pounds with out bead locks and it does fine off road, 14 on road. The Raptor 34 on road and 14 -15 off road. My 6,000 pound Jeep with C range 40" tires and double bead lock wheels, 28 on road (which is does not do much of) and 11-12 off road.

    My 2 cents.
     
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  8. 500mag

    500mag FRF Supporting Member Supporting Member

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    I run my 37 KM3s at factory (38). Southern Off-Road mounted them at 40, but I went ahead and dropped them since the dealer will anyway when I take it in for service, and for a little better ride (in theory). Still getting 16MPG overall.
     
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