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Old 06-10-2021, 11:14 AM #1
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Tire inflation pressures

I just did the chalk test on my 5th gen 4Runner with nitto Ridge grapplers 255/80R17, new tires, load range E. I have all tires inflated to 32 PSI cold pressure. The chalk test on the front tires showed perfect even wear across the tread. The chalk test on the back tire showed more wear in the center of both rear tires as opposed to the outside. This inflation pressure is the recommended inflation pressure for the stock vehicle, but I've added extra weight and I have changed the tires to load range e versus a passenger tire. I don't really want to reduce the pressure more than that, but the chalk test results suggest I should reduce it in the back tires. I assume this is because of the higher weight on the front end versus the rear despite having cargo in the rear at the time of the test. Additionally, it seems in most vehicles that the pressure is recommended to either be the same all the way around or increased in the rear tires and comparison to the front tires if there is extra cargo. Again, this test was done with a moderate amount of cargo in the rear. What would y'all advise?

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Old 06-12-2021, 08:24 AM #2
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32 PSI is safe enough and with tall aspect ratio you don't want to run low pressure or that back end will move around too much especially while towing. Just rotate them as recommended and it'll be all right.
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Old 06-12-2021, 10:19 AM #3
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You definitely jumped down a huge rabbit hole with E rated tires. lol Thats why i went with C rated tires and even that was annoying with air pressure, but at least i could run a wide range of air pressure to meet my needs.

If you are proactive in your weight calculations per tire you can modify your air pressure accordingly. I also wouldn't 100% rely on the chalk test, rotate often and that recommended inflation on the door is now meaningless with E rated tires and the new load index of the tire. What's your load index?


This is what i did to make sure i met the important points.

I went with C 112Q rated Duratracs.

4R RGAWR (rear) = 3439 lbs /2 = 1720 lbs (no load) per tire and since 112 load index = 2469ea at 50psi i can run the C 112Q rated Duratracs at ~38+ psi and exceed the actual RGAWR still. If i need additional weight capacity i just bump up the air pressure up to 50 and get the full 2469 at max capacity of each tire exceeding the stock required load index.

Last edited by Ripper238; 06-12-2021 at 05:17 PM.
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Old 06-16-2021, 03:50 AM #4
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I would put 32-35 psi for that tire size.
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