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Tyre PSI for TT's.

ma123ma123 Posts: 87
edited April 2009 in Road beginners
Hi proberly another silly question but a couple of days ago while having a good at a 7 mile hilly TT route I punctured which wasnt caused by a thorn or glass, but there was two pinch holes in the innertube, Now is this down to inaddequate air in the tyre while pushing myself on the bike.

my wheels are normal road size 700 by 23 and I ride on Continental gator skinz or Schwalbe stelvio depending on which bike and im 15st, 6ft 2.

Posts

  • It could be - you dont say what pressure you are running.

    For your weight i would run the tires fairly close to the max rated pressure - 120ish psi.

    If the pressure is right and your still getting snakebite punctures, its because your riding isnt smooth enough - a pothole isnt a target.
  • ma123ma123 Posts: 87
    Thanks for the reply I think it was down to not checking the pressure before leaving and it was proberly well below 120.
  • Jeff JonesJeff Jones Posts: 1,865 Editor
    The heavier you are, the more pressure you need. At 15st, you probably want tyres that can take more than 120psi.
    Jeff Jones

    Product manager, Sports
  • Jez monJez mon Posts: 3,809
    Bear in mind that your rims might not be rated to more than 120 psi
    You live and learn. At any rate, you live
  • Jez mon wrote:
    Bear in mind that your rims might not be rated to more than 120 psi
    If that were the case I sure wouldn't want to be a 15st rider on them then :o
  • Jez mon wrote:
    Bear in mind that your rims might not be rated to more than 120 psi
    If that were the case I sure wouldn't want to be a 15st rider on them then :o

    Im just over 14st and I get away running 90psi no problem. My rims are rated at up to 120 and are still true (i do have to re-tension every few months though). The roads I ride are full of potholes and I miss most of them but not all, infact I've hit potholes at 40 in the past without any issues (except it wasnt the most pleasant experience).

    I really don't see why it matters too much about a persons weight, sure I'll shy away from carbon as im too heavy for its rated weight but still, I enjoy cycling, and not going to stop because people think im too big/heavy.
    "War is Peace; Freedom is Slavery; Ignorance is Strength." George Orwell - 1984
  • For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max
  • gtitimgtitim Posts: 225
    For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max

    I agree - whatever you're weight is, for a TT you want your tyres to be pumped to the max - far faster and easier.
  • ma123ma123 Posts: 87
    Thanks all for the replys, I went out this morning and had another bash at the 7 mile TT hilly course and recorded a time of 23.30 which isnt to bad considering I got stopped at a Zebra crossing and the person who won over this course last time out did it in 20.50.
    I would have finished 6th that day with this time.

    Ive never done any TT's or any racing before and plan to start next season.

    P.S I may be 15st but its funny how many smaller blokes I pass on the hills, Magnus Backsted is 94KG/14.8 stone and he won Paris - Roubaix not bad ay.
  • gtitim wrote:
    For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max

    I agree - whatever you're weight is, for a TT you want your tyres to be pumped to the max - far faster and easier.
    Harder is not always faster.
  • Jez monJez mon Posts: 3,809
    gtitim wrote:
    For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max

    I agree - whatever you're weight is, for a TT you want your tyres to be pumped to the max - far faster and easier.
    Harder is not always faster.

    Yep.

    Rock hard tyres just aren't faster over rough surfaces, plus uncomfortable bikes can fatigue you more, which can be a factor in longer TTs.

    However, if you really want a hard tyre but are limited to clinchers, then Tufo do a tubular that hooks on to a clincher rim, which you can inflate to very high pressures with no trouble.
    You live and learn. At any rate, you live
  • To answer the original question: percussion (or snakebite) punctures are caused by the tyre deforming and forcing the tube out between the rim and the tyre bead.

    The liklihood of the the tyre deforming is determined by two things: the force on the tyre and the pressure in the tube.

    The kind of forces needed to caused a snakebite generally only occur when you hit a pothole or encounter some other kind of impact (ride over a ledge, stone). But the heavier you are, the greater the force will be when this happens.

    The greater the pressure in the tube, the more force needed to deform the tyre and therefore the lower risk of puncturing.

    So in summary, heavier riders should run higher pressures, but I would be very surprised if the puncture wasn't preceded by some kind of noticeable impact (unlesss your tyres were really very soft indeed say <60psi).

    As far as the harder=faster debate is concerned, I would say that it's more important to strike a balance based onthe road surface - you don't want a rock solid tyre on a poor surface or you'll keep losing contact with the ground and wasting energy.
  • ma123 wrote:
    Thanks all for the replys, I went out this morning and had another bash at the 7 mile TT hilly course and recorded a time of 23.30 which isnt to bad considering I got stopped at a Zebra crossing and the person who won over this course last time out did it in 20.50.
    I would have finished 6th that day with this time.

    Ive never done any TT's or any racing before and plan to start next season.

    P.S I may be 15st but its funny how many smaller blokes I pass on the hills, Magnus Backsted is 94KG/14.8 stone and he won Paris - Roubaix not bad ay.

    Paris Roubaix aint hilly though :wink: In fact it is a race which suits more powerful riders.
  • sub55sub55 Posts: 1,025
    gtitim wrote:
    For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max

    I agree - whatever you're weight is, for a TT you want your tyres to be pumped to the max - far faster and easier.

    wrong
    constantly reavalueating the situation and altering the perceived parameters accordingly
  • gtitim wrote:
    For TTs - as high a pressure as they can stand.
    I have mine at 170psi (tubs). If clinchers, then 120psi usual max

    I agree - whatever you're weight is, for a TT you want your tyres to be pumped to the max - far faster and easier.

    Please, keep doing this - im a climber, and suck at TTs, if all my competitors are doing something this stupid, it will give me a bit of an advantage.


    If your on a perfectly smooth surface, solid tyres would be the way to go to minimise rolling resistance. Unfortunately, there is no such thing as a perfectly smooth surface on the road - that vibration your getting through your 170psi tubs is you going up and down over lots of tiny hills constantly - so not only will you be hugely less comfortable than me, you will have a higher rolling resistance.

    Clinchers at the proper pressure have the best rolling resistance - proof of this from anywhere that has ever performed a test upon it - me being lazy wont be linking you - but westwoodvelo's forums have some of the best TT specific information around - go look.
  • itboffinitboffin Posts: 20,049
    I pumped my tyres to 120psi today and within 20 bumpy potholed miles I was spent, I dropped 25psi from the front and 20psi from the back after 30 miles and increased my avg by almost 6mph.

    I love Windshire (Wiltshire) but hate the poor quality of the roads.
    Rule #5 // Harden The censored Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
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