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Thread: Worn rims

  1. #1
    Stuart, mmm cheese on toast...
    The tricky bit is deciding how worn is too worn though, all v-brake rims go concave with use. I've had one blow up when I was doing just one more ride" on it as the top of the rim was slightly flared outwards and I reckonned it would go soon. Another two have failed the b-s test at a similar stage. So as soon as the two braking surfaces stop being parallel like this ~~~~~ <-- knobbles\___/ <-- tyre

  2. #2
    Quite simply, how do I know if my rims are worn out? It feels like there's a groove worn along the breaking surface, but I don't know how much is too much...Is it likely to be life-threatening on my next ride? What should I be looking for?

  3. #3
    i found that my rims were too worn when after 5 mins of a weird banging noise (actually the sidewall folding outwards and knocking on the brake blocks!) i was hurled over the bars at 30mph downhill whilst half asleep on my way to work at 6am on a wet dark morning. the general rule now is to stick my finger on the rim sidewall and if it feels more than a bit concave" go buy a new one. believe me, it is not an experience that i would like repeated as it scraped off half my fur and left me looking like roadkill on the cycletrack. "

  4. #4
    Well, Hung Squirrel an incident like that is exactly what I was trying to avoid... You have my sympathy - I once snapped the chain on my way to work. I was almost there and feeling relatively awake when it happened - I'd just had a go at some pedestrians for walking along the cyclepath and jumped onto the road when it broke and sent me knackers-first into the top tube and skidding along on my shoes at 25mph. Said pedestrians thought that I had just lost control and laughed at my pain. B****rds!Like Anthony's potentially dodgy handlebars, I guess it would be better to get out my credit card than be constantly worried about my wheel collapsing and scarring my shiny metal ass.

  5. #5
    Senior Member steve riley's Avatar
    Join Date
    Jul 2004
    Put some long pants on. Maybe ear plugs too.Pump your tyre up to 80-100psi. If the rim explodes you should replace it.

  6. #6
    Stuart, mmm cheese on toast...
    It ain't called the bang-shit test for nothing. Do it outside as well.Other big clues are the wheel going out of true or spokes breaking a lot more often than you'd expect, or the sidewalls starting to bow outwards when the tyre is inflated.

  7. #7
    Baron Von Weissterscheister of Ashby de la Goat
    Steves right. Definetely wear ear defenders and stout shoes, and probably some eye protection and do it outside. I did a pressure test on my rear rim, at 75-80 psi it ripped 90 degrees of braking surface off at the speed of sound (for this is the speed of catastrophic crack propagation). I did it in my garage and I couldn't hear properly for five minutes afterwards, and my neighbours came running out to see if I was OK (they probably thought that I had shot myself!).

  8. #8
    Dave Whittle
    hold a straight edge to the rim, like a steel rule. If the rims' worn it will be concave (is this what you mean by grooved?) and you will be able to see daylight between the rim wall and the rule.Not quite as spectacular as the tyre pumping method I'll grant you...

  9. #9
    Dave Whittle
    yeah but my point is if you can clearly see (rather than just feel) the concavity then its sufficiently worn to be junked.

  10. #10
    Anthony Lee
    After you know that the rim is worn, replace with one with a ceramic coating.

  11. #11
    If you chaps would care to look in the latest CTC magazine their technical person tell you how to make a simple slip gauge using a 2mm spoke so you can measure the thicknessof the rim using a vernier. He advises changing the rim when 1mm thick as they normally fail when they are 0.5-07mm thick

  12. #12
    I'll be sure to use my mini pump when I try the b-s test. That way I'll get a little aerobic workout at the same time.

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