Applies to All Model Years Correct pressure for beefier tires

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  • 1 Post By vulcan_classic

Thread: Correct pressure for beefier tires

  1. #1
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    Correct pressure for beefier tires

    Hi everyone. I'm looking for advice on tire pressure for city driving. With stock tires Subaru recommends 33 psi front / 32 psi rear.
    I switched to Toyo AT2 215/75R15 and 33psi looks pretty flat. It looks more round at 42 in the front and 36 in the rear so that's what I'm running for now. Is there any more scientific way to determine proper pressure?

    P.S. I'm talking about city driving here. Off-road I vary between 18-30 depending on the terrain.

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  3. #2
    Senior Member Paul4Runner's Avatar
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    Tire pressure is entirely objective but as long as you do not go over the maximum PSI on the side of the tire. If you go offroading then maybe you'll want maximum traction thus lower the PSI to 20 or better gas mileage on a road trip but also firm (teeth rattling) go to 45 PSI. I like a firmer tire, my '18 Crosstrek I have the OEM Falkens at 36 but the Falkens WP AT3W on my 4Runner I have a 34, anything over that then the ride is too harsh.

    Are your Toyos LT or P? Where did you buy them from?

  4. #3
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    I'm using the P type, I bought them from a local shop. I'm happy with it so far, but this if my first AT tire. I suppose a taller sidewall generally requires higher pressure to stay round.

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  6. #4
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    The toyo has 100 load index so by right does not need much different tire pressure. If you are ok with rear at 36 then you can try 37 at front. Certain AT tire will not be round due to focus to be used on low speed. Of course if sidewall is too soft you can increase a few psi as long not to exceed the maximum pressure stated at the tire

  7. #5

    Correct pressure for beefier tires

    Based on TRA inflation charts my P-rated 225/55-18 OEM Falkens (2019 Limited) have a load rating of 1609# at 35 Psi; the LT 215/75-15 BFG AT KO2 is rated 1605# at 45 Psi (within 1% , 1609/1605=1.002)

    So doing the math, the OEM 33 Psi front/ 32 Psi rear works out to be 42.43 Psi front/ 41.14 rear. I’ve only been running the new setup couple days so I will monitor performance.

    P charts start on p.13 and LT charts on p. 20, see link below

    https://www.toyotires.com/media/2125...s_20170203.pdf



    Sent from my iPhone using Tapatalk

  8. #6
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    Correct pressure for beefier tires

    Quote Originally Posted by vulcan_classic View Post
    P charts start on p.13 and LT charts on p. 20, see link below

    https://www.toyotires.com/media/2125...s_20170203.pdf
    Thanks for the link, that's exactly what I was looking for! But these numbers don't make sense or I'm reading it wrong.
    OEM tires are P225/55R17 at 32psi in the rear, so according to this table the load rating is 1477 lbs.
    I look up my replacement P215/75R15 and it says 1510 lbs at 26 psi. At 26 psi these tires look very flat and and are well suited for rock crawling or sand, but there's no way I would drive on the highway like that.

  9. #7

    Correct pressure for beefier tires

    Quote Originally Posted by llamafilm View Post
    Thanks for the link, that's exactly what I was looking for! But these numbers don't make sense or I'm reading it wrong.
    OEM tires are P225/55R17 at 32psi in the rear, so according to this table the load rating is 1477 lbs.
    I look up my replacement P215/75R15 and it says 1510 lbs at 26 psi. At 26 psi these tires look very flat and and are well suited for rock crawling or sand, but there's no way I would drive on the highway like that.
    Based on the tables your stock 225/60-17 (assuming you meant that size not 225/55-17) and the P rated 215/75-15 AT tire can both handle 1587# load at 32 Psi and 29 Psi respectively (slightly stiffer sidewall of the AT tire can handle same load with slightly lower pressure)
    You could try 30 front and 29 rear and go from there


    Sent from my iPhone using Tapatalk

  10. #8
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    I meant what I said, my stock Geolandar tires were P225/55R17. Anyway, I've been running the Toyos at 44 psi front and 38 rear because it looks right visually and handles well on the highway.

  11. #9
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    You could use Water and a Paint brush to set the tire pressure. Start with the max air pressure recommended for your tires and plan on letting air out of the tires. On your driveway or in a parking lot use the brush to paint a 4 inch wide strip on the driveway surface. Then drive over it, the tire will pick up the water then with 1 rotation the tire will make it's pattern back on the driveway. Adjust the air pressure in the tire down till you see full contact of the tire tread pattern on the ground. Once you determine full contact of the tread pattern that should be the correct pressure for those tires and the weight of your car. How I always set the air pressure on my oversized Jeep tires.

  12. #10
    Quote Originally Posted by vulcan_classic View Post
    Based on TRA inflation charts my P-rated 225/55-18 OEM Falkens (2019 Limited) have a load rating of 1609# at 35 Psi; the LT 215/75-15 BFG AT KO2 is rated 1605# at 45 Psi (within 1% , 1609/1605=1.002)

    So doing the math, the OEM 33 Psi front/ 32 Psi rear works out to be 42.43 Psi front/ 41.14 rear. I’ve only been running the new setup couple days so I will monitor performance.

    P charts start on p.13 and LT charts on p. 20, see link below

    https://www.toyotires.com/media/2125...s_20170203.pdf



    Sent from my iPhone using Tapatalk
    Just realized the OEM tires are not P- rated but are SL standard load rated (98H) so using the SL tables the numbers will very slightly. (no more than 1-1.5 psi)

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