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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 05-17-09, 01:06 PM   #1
mint-sauce
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Changing my tyres - its always the simple things

simple enough task i thought, have taken on and off the tyres plenty of times, when changing them at home, to changing a burst inner tube at the road side, but have just walked away from the bike in frustration

basically i have some new tyres in the post, current ones worn, and putting the spare ones back on whilst i wait, spare tyre back on the front rims, pumping it back up and tyre was bulging more so around the valve, never noticed this before, so let all the air back out to make sure no parts of tyre was caught, took of tyre, tube, put back on, put a little air in, still bulging

had a look at my back wheel to see if bulging the same, am yet to change tyre on this one, no obvious bulge, so back to front wheel, off comes tyre again, this time using a new tube, all back on, pumping up gently, got to just under 60psi, and pop

in all my life, never had or noticed this issue before, am i missing something really obvious, or did i just get a dodgy tyre, oh, and its a racing bike if makes any difference

the offending pop

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Old 05-17-09, 01:20 PM   #2
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That looks like a rim tape failure issue.

Either spokes are protruding past the nipples (if the spokes are too long), or the rim tape has failed, either failed completely or just failed in providing adequate protection. Remove the rim tape and visually inspect the ends of the nipples for protruding spokes - if they are protruding you'll need to grind them down. Some types of rim tape are incompatible with high pressure, narrow road tyres (think < 25c).
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Old 05-17-09, 01:31 PM   #3
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That looks like a rim tape failure issue.

Either spokes are protruding past the nipples (if the spokes are too long), or the rim tape has failed, either failed completely or just failed in providing adequate protection. Remove the rim tape and visually inspect the ends of the nipples for protruding spokes - if they are protruding you'll need to grind them down. Some types of rim tape are incompatible with high pressure, narrow road tyres (think < 25c).

if a rim tape failure, why now, have done several hundred milles before taking of tyres today, usually have my wheels up to 80 to 100psi, and this pop happened before wheel was even put back on fork, have done a quick inspection of the rim, taking a closer look around where pop happened in relation to valve, nothing obvious or jagged, could i have just got caught with a bad batch of tyres
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Old 05-17-09, 09:22 PM   #4
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[QUOTE=mint-sauce;8933918]
basically i have some new tyres in the post, current ones worn, and putting the spare ones back on whilst i wait, spare tyre back on the front rims, pumping it back up and tyre was bulging more so around the valve,
QUOTE]

This part sounds as if the tire bead was not seated at the valve, a common problem. Before pumping up the tire/tube if you push the valve into the tire this will insure that the tube is all in the tire and not interfering with the bead. In other words, use the valve stem to push the tube inside the tire, allowing the bead to seat in the rim.
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Old 05-18-09, 12:47 AM   #5
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A pop that looks like that happens when the tube bulges out through a hole. Either a spoke hole not covered by rim tape, or a gash in the tire sidewall, or maybe listing off an unseated tire bead (though the last one usually produces a long straight gash). What kind of rim strip is it? The rubber or plastic ones can get pushed sideways uncovering the spoke holes, and slide back to look like nothing is wrong when you inspect.
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Old 05-18-09, 05:46 AM   #6
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Line up the hole with the rim & tyre and see if there's something in that area that's defective. Such as the rim-strip or the tyre. You did way it was on the road side of the tyre right?
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Old 05-18-09, 12:34 PM   #7
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cheers for all the tips/advice guys, both wheels back on, pumped and ready to go again, think it may have just been a defective tube, or tyre bead not seated, put the original tube back in, checked the rims and inside of the tyres to make sure nothing sharp or jagged, nothing found, good tip about pushing the valve back into the tyre, think its one of those jobs you do more often than others you end up missing the simplist thing, was a bit wary when the tube got to around 40 to 60 psi, was bracing my self for another bang, took her out for a spin, back in business, will do it all again next week when the new tyres arrive

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Old 05-18-09, 12:46 PM   #8
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Yeah, if you don't start and stop at the valve-stem, you have a much lower chance of pinching the tube at that spot. I usually start 90-degrees off to the side of the valve-stem and go over it along the way. Since this way never pinches it, I never need to stuff the valve-stem back in to un-pinch the tube.
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Old 05-18-09, 01:58 PM   #9
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Originally Posted by mint-sauce View Post
if a rim tape failure, why now, have done several hundred milles before taking of tyres today, usually have my wheels up to 80 to 100psi
What size are the tires and how much pressure are that rated for? There is a huge difference between 80 and 100 psi. From the picture it looks as if the flat could be a result of the tube being pinched between the tire and the rim on impact due to insufficient pressure. The tire looks to be a road bike tire that would normally be run in the 100 - 120 psi range. I suggest that you fully inflate your tires before each ride. The pressure that is right for you depends on what the tire is rated for and on the total weight of the bike, rider, and equipment. My body weight is 165# and I run 120 psi in the rear tire and 110# in the front, 700c x 23 tires.
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