XC racing psi?

Discussion in 'Racing and Training' started by fongster, Feb 9, 2014.

  1. fongster

    fongster Active Member

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    Maybe some of you with a similar weight (or possessed knowledge) can help me...what psi should I run for XC racing on typical OC trails? I'm 170 lbs. riding a Kona Hei Hei with a tubeless Bontrager 29-3 x 2.3 up front and a 29-1 x 2.0 on back. I keep it pretty much on the ground. I have 25 psi F and R right now...that was just based on a total guess, I have no idea on how low I could go. Your thoughts? Thanks!
     
  2. Allthatflash

    Allthatflash New Member

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    Normally you take your weight and divide by 7......that should be your front tire pressure and add 2 for the rear. As that notion says that more is faster, that's not actually correct. So at 170lbs the front should be 24.2 and the rear at 26.2 the 25 f and 25 r was close
     
  3. duke777

    duke777 Active Member

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    only you can answer your questions.

    Amount of PSI has direct correlation to grip and rolling resistance. More pressure means less rolling resistance and less grip! Some racers run really high pressure but have great bike handling skills and willing to sacrifice some traction for speed. So go as high as you feel safe for the course, every course is different so you have to adjust for each course and condition of the course. Plus every tire has different sidewall strength so that also effect the PSI.

    You have to do your home work, pre-ride the course and adjust your suspension, tires and tire pressure accordingly.

    Better question would be how and why for other racer's PSI and tire preference.
     
  4. surftime

    surftime New Member

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    i dont race.... But to me try around 33-35 psi, especially fire road climbs higher psi has been faster for me. Lower psi is more comphy and more fun for me though and that is why i ride so i settle around 28 psi on my HT according to my pump. for example on Willow im dragging if my PSI is too low
     
  5. mtnbikej

    mtnbikej Well-Known Member

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    that sounds painful......even at 210 lbs, running 28/29 lbs felt like I was running on concrete tires.
     
  6. leondelmonte

    leondelmonte Member

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    like mentioned previously, it depends on the course you are riding.
    for loose conditions, go as low as you can on the front, anywhere from 20-35 psi in the front, and rear always with a little more cause thats the one that carries the weight.
    but in the end, whatever someone tells you, even if its your brother who has the same bike and weight the same as you, it all goes down to personal preference. play with it and see what you like best.
     
  7. skyungjae

    skyungjae Member

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    I think this is the most sound advice. It's definitely going to be multi-factoral regarding terrain, bike, you, etc. Just make your adjustments based on results rather than feel. Sometimes what feels great isn't faster.
     
  8. XcShane

    XcShane Member

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    Yup, those pretty much sum it up.

    I test a tire by starting at say 35 psi and take it down to basically where it feels like it "sticks" or doesn't want to let loose. Then I lower it an add'l 2 psi and roll with it. Probably would be better to start low and go high but that's just how I've done it. So again, personal preference.
     
  9. wizard

    wizard tradersancho's dad

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    Are you tubeless? When I ran tubes, I felt good traction at 30 psi. When I switched to UST, I couldn't get similar traction until I got down to around 20. Currently I normally run about 20 in the from and 22 in the rear with UST and maybe 22 to 24 with the thinner walled tubeless ready tires. I weigh in at about 165 buck n.
     
  10. duke777

    duke777 Active Member

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    You do have to run a few more PSI so you don't get snake bite but tire pressure solely depends on your weight and tire.


    if you are racing XC you should go max pressure then lower to a point where you feel almost safe.......if you are truly racing XC . Also go with as skinny and bald tire as the course will allow. If you just riding the race then go with what you feel comfortable.
     
  11. fongster

    fongster Active Member

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    Thanks, good intel. I've heard though that lower pressures have better rolling as it allows the tire to mould or "form" over terrain vs bouncing over it...any thoughts on that?
     
  12. strobe

    strobe resident noob

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    Sure. Air up to 40psi and take a run down Rock-It. Then, decrease the air down to 26psi and take another run down Rock-It. You'll have many thoughts about it if you didn't get a concussion from the first run down. Like they say, you really have to test out for yourself. Riding style, tubes, tubeless, terrain, racing, trail riding, tire size, brand of tire, type of tire.... They all make a difference in feel and performance and only you can find your magic numbers.
     
  13. Old School

    Old School Member

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    I've heard that too in recent years. Here's a link to a study that showed higher pressures gave lower rolling resistance on smooth surfaces like paved roads, but lower pressures gave lower rolling resistance off-road.

    http://www.mtbonline.co.za/info/mtb-tyre-rolling-resistance.htm
     
  14. duke777

    duke777 Active Member

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    Again assuming you are racing In earnest, highest pressure with enough traction to be riding safely will give you best rolling resistance/speed. Yes in sandy or very loose situations lower tire pressure will float better and not dig in which gives you better rolling resistance. But not too many XC races will be held in courses with long stretchs of sand and marbles. Again this boil down to tailoring your tire and pressure to the course and condition. Narrowest/lightest/baldest tires with highest pressure permitted by the course is what you should aim for.

    Remember the race is won on the up hill and lost on the down hill so you need to balance your setup for the entire course or at least the majority of it.
     

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