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  1. #1
    Commuter JohnBrooking's Avatar
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    A warning (tires) and a tip (practicing VC)

    This morning before leaving I refilled my tires. It was about 60 degrees F. I filled them to near max. Everything was fine when I got to work. When I went out to get lunch, the back was flat. No just flat, the tire was partially off and the tube had a slit it in about 8 inches long. It was probably about 75 F by that time. I figure the air must have heated and expanded during the morning. I can't think of any other explanation. So, a word of warning during this time of year of cool nights and warm days. (In both hemispheres, I would think, eh?) So, always carry a spare tube and the means to inflate it -- a hand pump or CO2 cartridges. I was glad I did!

    It was the tube that came with the used bike, so perhaps it was old and weak anyway, and this just pushed it over the edge. Maybe in the future I should consider just replacing both tubes right away whenever I buy a used bike.

    Anyway, here's the tip. I was on my way to get lunch at the mall food court near my office. I've said this before, and some were skeptical, but I really think that a mall perimeter road (the one that goes around the inside of the parking lot, next to all the entrances) is a great place to practice riding in traffic. The posted speed limit is 10 MPH, and most cars actually do go slowly because the straightaways are all pretty short, they generally aren't going far on it, and they do realize there are blind corners and a car could come out of a parking row at any time. But on a bike, these are great practicing speeds (and I probably slightly break the 10 MPH limit most of the time). You can take the lane the entire time for visibility (both yours and theirs), and most of the time you are keeping up with the cars and not impeding them at all. As always, scan for cars pulling out, and pedestrians to slow down or even stop for if necessary. Obey all the right of way rules, and stop and take your turn at stop signs. With everyone operating at slower speeds, and in a closer space, I've found negotiation and eye contact to be much easier than on the open road. Hence, great practice for it. Sometimes I even ride the complete perimeter once or twice, about a mile each circuit, just for fun. (At least relative to the heavy and faster traffic surrounding the mall and my office, which I would have to go through to get to any better recreational routes! )

    Your experience may vary. People are generally friendly in Maine, even in a mall parking lot (except maybe in late December), so I can't speak for all malls.

  2. #2
    I'm not hardcore
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    Your advice about having a spare tube is well taken. But there's virtually zero chance your blowout was caused by the temperature variation.

    A 15-degree rise in temperature is going to correspond to about a 3% increase in pressure. (If anyone cares for the gas-law proof, just ask.) So even a road bike tire at 120 psi would only increase to 124 psi. That's not enough to cause a blowout, and might not even be within the measurement tolerance of a lot of guages.

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    Your tire slipped off the rim, probably because the tire was old or it had some damage to the bead along the edge of tire that allowed it to stretch too much. I had the same thing happen when I replaced a tube on an old 700x23C tire that had accumulated a lot of holes and cuts (these didn't affect the tube because I use tire liners). Just as I pumped the tire up to the max. of 140 PSI the tire jumped off the rim and the tube failed explosively with the same 8" rip. And I mean explosively! I was between 3-story buildings and I heard the bang echo at least twice (it may have been more but I couldn't hear over the ringing in my ears!).

    Note to self: when replacing a flat, don't pump tires to maximum until you get home again....

  4. #4
    Commuter JohnBrooking's Avatar
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    Quote Originally Posted by aerodave
    Your advice about having a spare tube is well taken. But there's virtually zero chance your blowout was caused by the temperature variation.

    A 15-degree rise in temperature is going to correspond to about a 3% increase in pressure. (If anyone cares for the gas-law proof, just ask.) So even a road bike tire at 120 psi would only increase to 124 psi. That's not enough to cause a blowout, and might not even be within the measurement tolerance of a lot of guages.
    That's what I thought I'd heard before. That's why I hedged about the possibly old and weak tube. But it certainly did blow sometime while it was just sitting there this morning, and the timing of having just filled it this morning seems too significant to be coincidence. I guess it's possible that I simply overfilled it (perhaps my guage, which is built into the pump, has a wide tolerance!), and it was just coincidence that it didn't blow while I was riding.

  5. #5
    Commuter JohnBrooking's Avatar
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    Yes, the tire is old too. I replaced the front a few months ago when it developed a large bump; maybe it's time to do the back now.

  6. #6
    It's true, man.
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    It's possible that the rim strip has slipped to one side, as well. I've had that happen from inflating/deflatating a tube from trail-riding pressure to commuting pressure back and forth a few times, never dismounting the tire at all.

    The strip moved to the side, and the tube blew itself up on the edges of the spoke holes.

  7. #7
    Two H's!!! TWO!!!!! chephy's Avatar
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    Quote Originally Posted by JohnBrooking
    This morning before leaving I refilled my tires. It was about 60 degrees F. I filled them to near max. Everything was fine when I got to work. When I went out to get lunch, the back was flat. No just flat, the tire was partially off and the tube had a slit it in about 8 inches long. It was probably about 75 F by that time. I figure the air must have heated and expanded during the morning. I can't think of any other explanation.
    Same thing happened to somebody I rode with yesterday! He filled the tires the day before to the max, and went out riding in what turned out to be an unusually hot, summer-like day. That gunshot-like blowout scared the crap out of everybody. No idea if it had anything to do with temperature or what.

  8. #8
    Sophomoric Member Roody's Avatar
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    I've gotten flats while I was working too. Usually they are slow leaks, not 8 inch splits, and I can pump it up and make it home before I change the tube. You, on the other hand....

    It sounded like your tube blew so suddenly that it blew the tire partway off the rim! Have you checked the rim for cracks or rough spots? I had a rim crack once, but the tube didn't blow until a few minutes later, when I released the brake.


    "Think Outside the Cage"

  9. #9
    Sumanitu taka owaci LittleBigMan's Avatar
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    Good heads-up, John. I had an older front tire go flat at about 25 mph. on a freeway overpass on a busy, 6-lane street during rush hour. I don't have to remind you that you immediately lose front braking on a front-flat, not to mention maneuvering is very dicey at speed. I was seriously focused in intense concentration until I could pull off into an available driveway.

    The cause: my old tire had a tiny split in the sidewall which I had failed to do an inspection on. Could have been much more serious.
    No worries

  10. #10
    going downhill fast maximusvt's Avatar
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    Yeah, decaying old sidewalls inevitably result in flats, it's just a matter of time. The last two times I've had tubes go out on me they were both due to the old tires, and the sidewalls practically wore thin. Now I know to keep an eye on them before they get that old.
    Both times I heard the blast from inside like "what the hell was that??"
    ...and don't forget to stretch!

  11. #11
    Commuter JohnBrooking's Avatar
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    Yeah, I figure someone in the row of offices by the wall near the bike rack must have heard something, if they were in their offices at the time. Probably wondered what it was. (If they knew, they probably would have told me, as it's a small office and they all know me.)

    Cephy, sounds like your friend's experience could well have been just plain over-filling. I've had that happen before too. In this case, however, it was less clear because it thankfully didn't happen right away and while I riding, it happened sometime after I got here! If it wasn't the temperature, I'm thinking the old tire couldn't take the stress of the increased pressure but it wasn't bad enough to make it happen right away. Maybe it sat there at the rack and just stretched and stretched until... BOOM!!

  12. #12
    Kwisatz Haderach fillthecup's Avatar
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    I stumped my LBS with this last one, at least for an afternoon. My rim looked fine and spun reasonably true, but everytime it was pumped to 90psi or thereabouts the tire would jump the rim and the tube would explode. This happened several times, and it would last a while before popping off the rim. It exploded once at work and scared the hell out of everyone, who thought it was gunfire coming from my office.

    So I bought a new rim and it hasn't happened since. My LBS conjectured that my old rim (1971 original) had many small flat spots that were leading to the tire slipping off at high pressure.

  13. #13
    Dog is my co-pilot 2manybikes's Avatar
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    Quote Originally Posted by JohnBrooking
    That's what I thought I'd heard before. That's why I hedged about the possibly old and weak tube. But it certainly did blow sometime while it was just sitting there this morning, and the timing of having just filled it this morning seems too significant to be coincidence. I guess it's possible that I simply overfilled it (perhaps my guage, which is built into the pump, has a wide tolerance!), and it was just coincidence that it didn't blow while I was riding.
    This happens once in a while, the tire blowing out when you are not there. The most common cause is because the tube is pinched between the tire bead and the flat area of the wheel the bead should sit on. To check for this, after inflating carefully go around the rim with your eyes and look for a place where the edge of the tire, (usually a line running parallel to the rim edge of some kind) is away from the center (raised) , if it is, the tire needs to be deflated and have the tube unpinched. It usually happens after a tire is installed, but I think a flat tire and rolling the bike with a flat tire could possibly do it too.

    If it's an old tire it could well have been a damaged bead that you did not know about. Your gauge could be way off, but it's uncommon. And rarely, tubes do get rubbed or abraded by something on the wheel.

    If it's an old bike with a steel wheel sometimes the wheels just don't grab the bead well enough to hold maximum pressure when they get old. Do you have another bike now?

    You probably read about the one that exploded in the same room I was sleeping in at 3:00 am.
    [SIGPIC][/SIGPIC]

  14. #14
    Happy old man al-wagner's Avatar
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    Quote Originally Posted by chephy
    Same thing happened to somebody I rode with yesterday! He filled the tires the day before to the max, and went out riding in what turned out to be an unusually hot, summer-like day. That gunshot-like blowout scared the crap out of everybody. No idea if it had anything to do with temperature or what.
    Why would you fill your tires to the MAX air pressure? That is asking for trouble.
    http://www.thegmbc.com/
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    In New England we have nine months of winter and three months of damned poor sledding.

  15. #15
    Senior Member ollo_ollo's Avatar
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    This happened a few years ago on my commuter bike. It was a 25F day & I pumped up prior to my commute in. I park indoors by my cubicle. They were 25c tires & it happened about 2 hrs after arrival, KABAM! Sounded like a gunshot & freaked out everyone in my end of the office. We all thought something had exploded in the old HVAC system & were looking for problems in the furnace room. Took a while until I noticed the flat/over rim condition of my tire. I got a lot of kidding when I fessed up & took the blame. Tires weren't old, just about 50% worn & I hadn't had a flat on that tire for months. I had gone with the heat = higher pressure theory but apparently something else caused it. Anyway, put a new tube in & had no further trouble with that tire which wore out a thousand or so miles later. Don
    visit my homebuilding blog: www.monoplanar.blogspot.com

  16. #16
    Two H's!!! TWO!!!!! chephy's Avatar
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    Quote Originally Posted by awagner109
    Why would you fill your tires to the MAX air pressure? That is asking for trouble.
    Well, I usually don't. However, I don't really think of it as a dangerous thing since there is a pretty wide safety margin that's supposed to be built into those things. And if you blow the tires up to max you are still within the range and the tires should certainly be able to handle this.

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