Bicycle Mechanics - tire blowouts at the stem
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07-17-07, 09:01 PM
Seriously, this is really starting to piss me off...I've never had a problem changing a tube before.
I've had my tires blow out 3 times in a row. It seems that the tubes I am using always give up at the stem (presta). They sit fine for a while, then randomly explode. Checked the tires for thorns and things several times, the rim strip looks alright, and the wheel doesn't have any rough edges near the hole where the stem goes through.
I don't think the tubes are bad because I bought them at different times. The only thing I can think of is that the bead of the tires is really loose. I can change a tire with no effort without tire levers (I don't think that there are too many miles, maybe <1k). When I mount it, it looks fine, however.
Please help me out!
07-17-07, 09:08 PM
If your tighten the nut, too tight on the presta, it can cause
tire to blow out that way.A lot of rider, dont use the nuts
that come with the tires. Also check the hole in the rim, if
you use presta's on rims that take regular Sharader, the
differamce, in hole size can cause the problem also. Good
luck in finding the problem.
07-17-07, 09:10 PM
Nope, this last blowout I made sure I didn't tighten the nut. The rims are presta.
The whole thing is really frustrating because I would ordinarily just replace the tubes, but I ran out of them and I can't patch them either.
07-17-07, 09:22 PM
Your loose beads are most likely your problem. What's happening is when you apply the brakes, the tire moves on the rim, thus stretching the tube at the valve stem. This is actually a relatively common problem. I used to see this all the time when I was a mechanic, especially on mountain bikes. So...you can do a couple of things, either check to make sure your valve stems are still straight, and if not deflate the tires and spin them on the rim to get them straight...or, get some tires that have a tighter bead. One other question is, it's not so much how many miles are on the bike/tires, but how old they are. If the sidewalls are really dried out, this will exacerbate the problem, as the dry sidewalls will slide more easily along the rim.
07-17-07, 10:51 PM
I wrecked about half a dozen tubes at the valve before I found the solution. Take those locknuts and thrown them as far away as you can. Once I stopped using them, I stopped having tubes tear at the valve.
07-17-07, 11:03 PM
Also, check the valve hole on the rim to make sure it doesn't have any sharp points from the machining.
07-18-07, 12:43 AM
used to have this happen a lot until I ran a drill bit around the inside of the valve hole (by hand) to remove any sharp edge, I then put a bit of duct tape over the hole on the inside of the rim and cut a little cross in it to allow the stem thru. Keep the stem nut but dont tighten it too much
07-18-07, 01:36 AM
Use a floor pump. Hand pumps are really only for emergencies on the road.
07-18-07, 09:13 AM
+1 to the floor pump. I've killed lots of tubes with the mini-pump.
Tires slipping on rims is often a sign of underinflation. Road tires need to be pumped up before each ride, larger bike tires at least once a week. +1 for using a floor pump with built-in gauge.
07-18-07, 02:13 PM
Hmm... I think redtires nailed it. The bead is so loose I can literally put my fingers between it and the rim, but it was seating alright, so I never figured that would be the problem. On to a new tire...anybody ever tried the Serfas products? I'm thinking about picking up the SECA road tire. All I know is that I didn't really get much life out of my Kenda Kontender OEM tires, but they left me fairly flat-free.
I always use a floor pump and place the pressure > 110psi everytime before riding unless I have to change a flat on the road when I usually use Co2.
07-18-07, 05:00 PM
A new tire is fine but you need to make sure you are using proper technique when mounting. Once you have mounted the tire and tube completely, push the valve into the rim hole, (this helps make sure the tube is not sitting under the tire bead) and then push the tire down into the rim. Inflate to about 30 lbs, check seating all around and adjust as needed. Then inflate another 20-30, check again and top off.
Also, if you have a blowout don't bother looking for tacks, rough spots, rim strips, etc. Blowouts ONLY occur if the tube escapes the tire, either between rim and bead or through a large slit or sidewall failure in the tire. Blowouts are always either cause by poor mounting technique or tire defect (well, very rarely by overinflation).
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