Tyre Pressures

Discussion in 'Cycling Equipment' started by NSM3, Jul 28, 2005.

  1. NSM3

    NSM3 New Member

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    I have just put some new Mavic rims on my bike with 20c clincher tyres. The Mavic website recommends a tyre pressure of 146psi?

    With my bike mounted pump, I could only get to a pressure which "felt" plenty firm enough to ride on, but the pump kept blowing off the presta valve stem. I borrowed a more robust pump with a crude pressure guage, foot stand and extendable handle and managed to get 120psi (my previous attempt had managed about 85psi). The tyres are now absolutely rock hard and seem almost too hard to take out on the road?

    What pressures do you run on and if these figures of 140+psi are correct, how do you easily inflate your tyres? I may not be Arnold Scwharzenegger but I really can't imagine physically pumping past 120psi.
     
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  2. mark higgins

    mark higgins New Member

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    Are you sure this is not the maximum tyre pressure? I would only run a good tubular at these pressures and then only on good road surfaces. Otherwise it is a very harsh ride!
     
  3. NSM3

    NSM3 New Member

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    Just checked and you are correct, 146psi is the maximum pressure which matches the 150psi maximum on the tyre sidewall (Conti GP3000).

    I have also found that the minimum pressure recommended is 100psi.

    I haven't had chance to ride them yet at the new high pressure, so I may well adjust down to 105-110psi if they rattle my teeth too much!!

    It will be interesting to see if my av. speed improves much as I have been riding around at sub 90 psi for the last 1500 miles.
     
  4. eric_the_red

    eric_the_red New Member

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    I have one set of wheels with 20C tires, and I usually set the pressures at 110-120 rear and around 100 front. I weigh around 185 lbs and find those pressures still have a little give without being too soft.
     
  5. NSM3

    NSM3 New Member

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    Sounds good to me - I weigh 189lbs - I will give it a try - thanks.
     
  6. boudreaux

    boudreaux New Member

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    Get a clue.Depending on your weight 90 to 120 is plenty. If you get pinch flats then you aren't running enough.I'd ditch the 20s too.
     
  7. NSM3

    NSM3 New Member

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    Thank you.
     
  8. tourdelivermore

    tourdelivermore New Member

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    Check out the tire specs on the package. Michelin Pro Race tires have a graph of weight vs tire pressure. I use this as my guide to inflate my wife's bike and my bike accordingly.

    I'm suspect Michelin would like to maintain an optimal contact surface area for the tire, where weight and pressure are the variables.
     
  9. otherworld

    otherworld New Member

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    1 - You need a floor pump.

    2 - 20mm tyres are too narrow for your weight on average roads.

    Get 23mm GP3000s and run 100-110psi in the front and 110-120psi in the rear. If you are not racing get 25mmm tyres and your can run even less pressure say 90 front 100 rear and they will roll much better than narrower tyres particularly on rougher surfaces.

    Narrow tyres like 20mm need higher pressure to achieve the same rolling resistance as wider ones for a given weight load. The sole advantage in using narrower tyres is aerodynamic. If you aren't racing theres no point as the actual advantage is slight compared with rolling resistance issues.

    Take your 20mm tyres off and save them for smooth surface time trials or track racing.

    Jay.
     
  10. dhk

    dhk New Member

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    A second for the good comments from otherworld. I run 23mm GP 3000s around 100 psi front, 105 rear for my 175 pounds. Better ride, grip, and handling, as well as lower rolling resistance on real roads, so it sounds like we're right in agreement.

    Took me many years of riding to learn about tire pressures, as I used to just run whatever max rating was listed on the sidewall. Wasn't until I bought Michelin Pro Race tires, and noticed the sidewall had a "recommended range" of 6-8 bar (87-116 psi) that I started trying lower pressures. That, and a couple of articles I've read convinced me that more isn't better when it comes to tire pressures.
     
  11. 531Aussie

    531Aussie Well-Known Member

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    the 146psi on the Mavic site is only a guide for the maximum load that the rim can handle -- it doesn't mean that the tyres should at thise pressure. The 146psi is only rough guide: they have the same limit for all their clinchers (what a coincidence), and I've proven year after year that they can handle more :)

    While I'm at it, a 20m tyre on the front is bad news :)
    They need higher pressures to "deform" properly, so they're uncomfortable. They're more dangerous for cornering, and every little crack on the road turns into a train line!! It's like riding on a knife's edge. :p As far as lighter weight goes, only the expensive, fast-wearing 20s are noticeably lighter than a good quality 23.

    If you want a 23mm tyre with a higher psi rating, for your weight (it's nice for us "heavies" to have a bit more psi in the rear tyre), perhaps try a Vredestein TriComp, or one of the high-end Vittorias.
     
  12. NSM3

    NSM3 New Member

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    Thanks all for the advice.

    I would say that the test 15 miler I did on the 20's (with the new wheels) at around 90psi seemed fine in terms of comfort and steering control etc, a significant improvement over the 23's on ALX295 rims - but that may have been largely due to better construction of the wheels/spokes etc - the Alex wheels are exceptionally harsh over anything but super smooth tarmac.

    Agreed on the floor pump, that is what I had to borrow to get the higher pressures - looks like the compact bike unit is a "get-u-home" only device from now on.

    I must admit I had assumed that a thinner tyre at higher pressure equals less rolling resistance and therefore higher average speed for a given effort. I may have to re-evaluate that after a few hundred miles - especially if the cornering ability is much reduced!
     
  13. MichaelB

    MichaelB New Member

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    I run most 23 cross section tyres at 6.5 bar up front and 8.5 bar in the rear. In the wet I would lose half a bar front and rear and maybe a bit more from the front.
    A high front tyre pressure is tricky to feel and also makes the bike slide at the front a lot more than the rear. If you struggle to feel the front breaking away from you then a lower front tyre pressure will help as it carcass will deform more under load and it is this that you use to help tell you when the tyre is slipping.
     
  14. ChangMan

    ChangMan New Member

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    Ditto on the 20s comment. I usually run only 100-110 on 23s.
     
  15. coolworx

    coolworx New Member

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    That's what the thread starter was attempting to do by asking the question.

    Sheesh... what a snippy one you are.
     
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