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  1. #1
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    LBS to Kilos to PSI

    LBS to Kilos to PSI - Watched a few videos on PSI and gathered the common preference is having a 5 PSI difference between the front and back tire. Then I also gathered it's best not to go over the PSI which is fine.

    Then it got a bit more involved on the LB to Kilo conversion which is easy for you just reference a chart but still don't get the KILO to PSI ratio.

    I am a big boy so not willing to share my weight, but I am going to do this on my MB, Hybrid, and Gravel.

    Thanks.

  2. #2
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    Quote Originally Posted by uncaged View Post
    Thanks.


    You're welcome!
    I brake for stinkbugs

  3. #3
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    You mean a formula to calculate what psi your tires should be based on rider weight? I wouldn't bother. Just keep lowering it until you get rim strikes, pinch flats, or tire squirm then add 1 psi at a time until you don't have those issue. Front to rear difference in psi depends on the bike's weight distribution and what tires you're running.

  4. #4
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    Quote Originally Posted by jeremy3220 View Post
    You mean a formula to calculate what psi your tires should be based on rider weight? I wouldn't bother. Just keep lowering it until you get rim strikes, pinch flats, or tire squirm then add 1 psi at a time until you don't have those issue. Front to rear difference in psi depends on the bike's weight distribution and what tires you're running.
    And keep track of all this in Excel.

    Then when you change tire size, apply a simple formula to keep constant casing tension.

    Keep track of how much pressure change you need for different terrains (rocky vs hardpack for example)

    It's an iterative process.

  5. #5
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    Oh just forget it. I will just go by feel and visual.

  6. #6
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    Don't forget the faster you go on rough terrain the more pressure you need to avoid rim strikes and pinch flats .

    Calculators are good for a starting point that that's all. Start high, it will be uncomfortable but it's just a starting point. I used to session a somewhat short section of downhill trail and drop my pressures little by little until it felt good or until I got a flat/rim strike. Try to include some hard corners to see if the tires feel squirmy. Your ideal pressure will be different than someone else's ideal pressure even at the same weight.

  7. #7
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    and just wait until you start doing jumps or drops!

  8. #8
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    Quote Originally Posted by uncaged View Post
    Oh just forget it. I will just go by feel and visual.
    That's my motto.
    "...rhetorical hyperbole..."

  9. #9
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    Any formula people have come up with is totally pointless with how sidewall stiffness affects how much PSI you need. I have Bontrager and Schwalbe tires that are in the exact same volume, the Schwalbe with Snakeskin sidewalls is dramatically stiffer and thus requires a lot less pressure (about 25% less) for it to feel "right"

  10. #10
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    Quote Originally Posted by idividebyzero View Post
    Any formula people have come up with is totally pointless with how sidewall stiffness affects how much PSI you need. I have Bontrager and Schwalbe tires that are in the exact same volume, the Schwalbe with Snakeskin sidewalls is dramatically stiffer and thus requires a lot less pressure (about 25% less) for it to feel "right"
    That's nice dear. But you have to start somewhere and that's where theory and math have their place. But I know this place is allergic to numbers so I'm not surprised.

  11. #11
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    Go as low with pressure as you dare, go out for a ride, if you bottom out either tyre and hit your rim on the ground than the pressure a bit, try again.

  12. #12
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    Different tires and even the same tires with different casings can act different with the same psi. I try to err on the side of having a higher than lower pressure when trying new tires then take a section of gnarly trail.
    Drop the pressure and try the trail section again. Have a pump with you so you can put air in if you let out too much.
    Niner Jet 9 RDO, Scalpel 29, XTC 650b, 04 Stumpjumper FSR Pro, Trek Rigid SS - No suspension, no gears....no problem

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