overinflated tires ?

Discussion in 'Cycling Equipment' started by ieandro, Oct 2, 2006.

  1. ieandro

    ieandro New Member

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    Hey guys

    While reading these forums it seems like everyone has a different opinion with tire pressures. Some say follow the recommended pressure on the sidewall while others say it's all about weight and performance. Now my tires say inflate to 110psi, but at that pressure it feels numb and mushy. I said forget that and climbed to 135psi front and rear. Feels better and more responsive. I am a 191lb. rider on top of a 2006 size 58 Trek 1000. Am i running it too high? Is anyone riding at higher than normal pressures ?
     
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  2. badkarma

    badkarma New Member

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    I prescribe to the notion that you shouldn't inflate your tires to a pressure higher than what the tire or the rim recommends.

    I'm 185 lbs and I ride at 110 rear, 105 front and I don't have a problem with it. I think your tires are over inflated, but that's just my 0.02
     
  3. garage sale GT

    garage sale GT New Member

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    IMHO, if 110 feels mushy your pressure gauge is messed up. Anyway, it's possible. Of course, I don't know what you're used to.

    Btw, I know through a friend of a friend that it is most definitely possible to blow out the sidewall of a new, quality tire, in case my theory is wrong.
     
  4. marci28

    marci28 New Member

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    I like overinflated tires, faster ride imo :)
     
  5. garage sale GT

    garage sale GT New Member

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    Just thought of something else: When a tire blows out, it's a lot different than a flat. You just hear a loud bang and then you're riding on the rim.

    I had a tube blowout on an older bike without hook edge rims, just running at standard pressure. I managed to stop but I was only doing 12-15 in a straight line. My wire bead, blackwall tire managed to stay on the rim somewhat. If I'd had a kevlar bead it could have ended far differently; I was only a few feet away from 45mph traffic.
     
  6. ieandro

    ieandro New Member

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    it just seems when im riding that rear tires seem to look very flat with my weight on top of it. I am not sure if it's just that I am very heavy and need to compensate. By the way i tested two floor pumps and both seem to give me the same reading (+/- 2psi).
     
  7. badkarma

    badkarma New Member

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    When a tire is properly inflated, you should see the contact patch grow as you apply weight to the bike. So if there's a slight bulge to the tires, then that's normal.
     
  8. ScienceIsCool

    ScienceIsCool New Member

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    But they don't! :) They feel faster, but are actually slower. Also, overinflation can be a big safety hazard. The numbers on the sidewalls are the MAX, not the recommended inflation pressure. Anything more than that and the manufacturer is explicitly telling you that there's a chance the tire will come off the rim. I've never seen anyone roll a clincher during a race and remain upright...

    John Swanson
    www.bikephysics.com
     
  9. sideshow_bob

    sideshow_bob New Member

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    Is the 110psi the max pressure on the tire or the min pressure. Most tires I use say inflate to minimum of Xpsi (100psi in the case of Rubino Pro's) and also have a max rating (145psi).

    I ride at 130psi in clinchers and that feels about right for me (and I'm only 72kg whatever that equates to in pounds). I've also ridden tubulars at much higher pressures than that.

    I agree with the other posters though if the stated max pressure on your tires is 110psi, then it's not a good thing to inflate past this.

    --brett
     
  10. Pendejo

    Pendejo Member

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    I've found that the higher the tire pressure, the more prone it is to flats.
     
  11. dhk2

    dhk2 Active Member

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    Like pendejo, I've found that max pressure got me a lot more cuts and flats, but did nothing for speed. Also found that max rated pressure reduces grip and roadholding when you really need it, like on sharp corners or high-speed descents. It may reduce rolling resistance on a super-smooth road surfaces or track, but on real-world roads, rock-hard tires ruin the ride and grip without adding any speed.

    Most sidewalls give max inflation pressure, not the recommended pressure. Michelin Pro Race is an exception; they list a recommended range of 87-116 psi. The correct pressure depends on rider weight and road conditions, not how much you want to win or how fast you want to go.

    Continental recommends 110 psi for the 4000s, with a max sidewall rating of 120 psi. Believe on their website they rate rolling resistance at 110, and puncture resistance at 95 psi. Somewhere in that range is probably best for most real-world road conditions.
     
  12. unicos

    unicos New Member

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    I wouldnt "overinflate". The tire itself can usually take the pressure. Its the rim that you need to worry about. The bead may not be able to hold the tire to the rim, or the rim may split, and it will usuall blow/slip out down the road when the tires heat up and the pressure goes up too. The rim wont be in warranty if you split it. Manufacturers / LBS's can usually tell a rim split from going beyond the recommended pressure. You may want to try a couple of different pumps and see if your guage is incorrect. If you really want to run higher pressure then switch to tubulars. Some of the tubulars can handle 160psi then you shouldnt have to worry about "overinflating".
     
  13. sig220

    sig220 New Member

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    Inflation pressures and weight determine the contact patch on the road.

    Underinflated tires flex, get hot and can blow out.

    One way to test tires is to check the pressure when the tire is cold, then ride a few miles. Check the pressure again. If the pressure has risen 10% or more, your tires are getting hot to the point where they are raising the pressure. This generally indicates excessive flexing of the sidewalls.
     
  14. ScienceIsCool

    ScienceIsCool New Member

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    This really can't happen. By definition you've described a self-limiting process. The tires would heat and the pressure would rise, but the amount of flexing would decrease... Until a steady state pressure was reached. But this doesn't happen in bicycle tires. Perhaps motorbike tires? Definitely not bicycle tires.

    John Swanson
    www.bikephysics.com
     
  15. bobbyOCR

    bobbyOCR New Member

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    OK. Hopefully this helps

    1) a tyre with a very high pressure (over inflated) will be less prone to flats because it creates a harder, higher tensioned surface, which is harder to break.

    2)overinflating can cause rims to deform and bulge, which is why they shouldn't be over inflated

    3) any pressure over 110psi does not really lose rolling resistance, the safety issue is greater. A high pressure tyre on a bumpy road will lose you speed as it is constantly slowing down when it hits every bump. It has to travel over the bump, it doesn't form to it like a lower pressure tyre does.

    4) Tyre pressure is what gives a bike its comfort. A very high tyre pressure will lead to a HUGE loss in comfort over any less than perfect road.

    5)they generally put the recommended psi on the tyre for a good reason, i suggest following it.

    6) weight will determine what pressure should go into your tyre. For instance, I am under 140lb and only use 80psi in the front, and 90 at the back. (i do increase this depending on road condition and whether it is a race)


    I suggest stick to the recommended pressures. Also, generally, wider tyres have a lower recommended psi, as they provide a greater lever arm against the rim, and can break it with less pressure.
     
  16. Albert 50

    Albert 50 New Member

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    This is wrong. Bocr you usually post good info. But I have to disagree with this statement.
     
  17. nerdag

    nerdag New Member

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    Repetitive flexing of the casing would generate heat, and cause damage to the fibres of the casing holding it together.

    The blow out doesn't occur because of the high pressure - its the weakened casing that gives way causing a blow out.

    Agree that its highly unlikely to happen with a bicycle tyre, however, the idea that it could blow out does hold - I've only ever seen this happen with car tyres. Never heard of it happening with bike tyres, although it is not entirely out of the realm of possibility.

    n
     
  18. sig220

    sig220 New Member

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    You are absolutely correct. And it is more evident in motorcycle tires. However, the steady state may be at a temperature that is not one which is good for the tire compound.

    I agree that recommended pressures are the way to go.
     
  19. bobbyOCR

    bobbyOCR New Member

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    Thanks. I should rephrase it then. The higher tension on the tyre makes it less prone 'flattening' over the contact area. This only creates a puncture protection for pinch flats, not object-punctures.
     
  20. 531Aussie

    531Aussie Well-Known Member

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    mushiness can depend on the tyre and the bike. A flexy bike might feel mushy at 120psi, but a stiffer bike won't; and, IMO, cheaper tyres seem to feel mushier. I'm about the same weight as you, and I have a minimum of 120 rear and 110 front; sometimes 130/120 of my slightly flexier bikes. My pressures are guaged off a Silca floor pump.

    I used to like high pressures as much as anyone (150/160 psi!!!= :)), but I've come to learn that "normal" pressures are better.
     
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