tyre blowing off rim...

neeb
neeb Posts: 4,470
edited August 2009 in Workshop
I had a scary experience the other day when a nearly brand new Pro3 Race tyre (ridden 2-3 times) blew off the rim of my front wheel (Ksyrium Elite). I'd just pulled over at the time and was stationary. First I knew of it was the almighty bang of the tube blowing catastrophically. The scary thing is that a minute previously I'd been doing about 25mph across a bridge with a bus 10ft behind me...

Tyre pressure was at about 110psi, i.e. within specs (assuming my pump dial is correct).

Now I'm scared it's going to happen again when I'm moving...

I thought that I was always careful to put tyres on properly and check that they are properly seated. Wondering if it is something to do with the tyre being new, as they are flat when they are folded.

Comments

  • maddog 2
    maddog 2 Posts: 8,114
    tyre could have been incorrectly seated, tyre could have been a dodgy tyre..where did it blow? near the valve? Check you rim bead for any damage/splitting.

    Did you fit with levers or by hand? Levers can sometime stretch the bead and generally speaking you shouldn't used them to fit tyres. If you have the right technique then you don't need them. Only VERY tight tyres need a lever.

    If we assume the rim is straight and round then just clean the tyre and rim bead, fit and inflate to half-pressure, check it's seated and round with no humping (?) and then go full pressure.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • Monty Dog
    Monty Dog Posts: 20,614
    Incorrect tyre installation IMO - inner was probably pinched / stretched at one point and the stress caused it to rupture. After installing the tyre, check all around the bead to ensure that the inner isn't trapped anywhere and then inflate the tyre.
    Make mine an Italian, with Campagnolo on the side..
  • neeb
    neeb Posts: 4,470
    Tyre was fitted by hand, at least initially. I do often have problems with the tube getting pinched between the bead and the rim though, especially when getting the last bit of the bead over the rim. Although I always check all round and "unpinch" any bits where it is trapped, this can be tricky. Sometimes I have used a tyre lever to try to coax the bead over the pinched bit of the tube (once the tyre is already on the rim). I am guessing that perhaps in doing this I have stretched/crinkled the tube unevenly and this is what has caused the tyre to blow off. I have fitted a lot of tyres in my time and have never had this happen before, but I think I will now stop using tyre levers to help "unpinch" tubes...

    What's the best way to persuade a small section of tube that is pinched between the tyre and the rim to get under the bead (or prevent it being pinched in the first place)? It's a real irritation!
  • maddog 2
    maddog 2 Posts: 8,114
    sounds like your tubes are too big.....? The tube shouldn't be between the tyre and the rim unless it's inflated too much or just too big. They should just tuck out of the way.
    Facts are meaningless, you can use facts to prove anything that's remotely true! - Homer
  • neeb
    neeb Posts: 4,470
    sounds like your tubes are too big.....? The tube shouldn't be between the tyre and the rim unless it's inflated too much or just too big. They should just tuck out of the way.

    When I say between the tyre and the rim, I mean that a small section of tube is often trapped under the bead of the tyre, against the internal base of the of the rim. This is only apparent if you squeeze the tyre to reveal the inside of the rim. It's certainly not supposed to be too big for the tyre or wheel according to its specification.
  • bobtravers
    bobtravers Posts: 115
    Don't forget to put a bit of air in your tube before inserting it in your tyre...
  • ride_whenever
    ride_whenever Posts: 13,279
    ^^^ i've found with the smallest tyres, not pre-pumping the tubes is easier...
  • neeb
    neeb Posts: 4,470
    Don't forget to put a bit of air in your tube before inserting it in your tyre...
    ^^^ i've found with the smallest tyres, not pre-pumping the tubes is easier...
    Happens to me whichever I do.... a bit of air certainly helps with getting the tube positioned properly in the first place and preventing it being pinched while putting most of the tyre on, but for getting the last bit on you can't have too much air or else it is too difficult, and whether it's none or just a little doesn't seem to make any difference.

    I use continental race supersonic tubes which are quite thin. Maybe that's the problem.
  • sturmey
    sturmey Posts: 964
    This is pretty basic stuff.
    The last bit of tyre you pop on the rim should be the bit near the valve. As you push it on you should push the valve stem into the well of the tyre which will then allow that last bit of tyre to be pulled down and seat properly on the rim.
    Then look all the way round the circumference of the tyre once it's fitted and make sure that there is a uniform gap all the way round between the edge of the rim and the sidewall of the tyre(near to the bead) They usually put a line all the way round the tyre to help with this.. Any obvious deviations in this gap mean the tyre is not seated correctly and/or tube is pinched.
  • neeb
    neeb Posts: 4,470
    This is pretty basic stuff.
    The last bit of tyre you pop on the rim should be the bit near the valve. As you push it on you should push the valve stem into the well of the tyre which will then allow that last bit of tyre to be pulled down and seat properly on the rim.
    That makes sense, thanks. I'd heard of doing the bit beside the valve last, but as a method of making the tyre easier to get over the rim, not to prevent pinching. I'd never bothered as I never have problems getting the tyre on.

    It may be basic to some, but although I must have changed 100s of tyres and have built bikes from scratch it's news to me. You live and learn... :D
  • sturmey
    sturmey Posts: 964
    No problem. Also remember to leave the tyre levers in the tool box at all times when fitting tyres. If the last bit is stubborn then maybe you could use a tiny amount of soap solution under the carcase of the tyre at that point to persuade it on.
    But generally, you shouldn't need to.
  • Wappygixer
    Wappygixer Posts: 1,396
    neeb wrote:
    [quoteI use continental race supersonic tubes which are quite thin. Maybe that's the problem.

    I used to use these tubes but they are too unreliable and as you say very thin.
    I stopped paying silly amounts for these innertubes a while ago.
    I now find that Michelin ultra lights are far better and only about 20 grams more, plus they are half the price