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Help! ---Tire blowoffs(8 posts)

Help! ---Tire blowoffsDana C.
Jun 20, 2001 10:07 AM
I am back into road racing after a long layoff and am having problems with tire blow offs. 1st was a Veloflex at 130 psi on a Rolf Sestriere (in a corner), second was a Performance Pro kevlar at 125 PSI on a Velomax acent pro (in a corner), third was a 20 mm Conti Supersonic on the Acent pro inflated to 160 psi just sitting in the basement. Tires and tubes and rims have all been cleaned carefully to remove powder or lubricants. HELP-- I'm getting afraid to corner and I used to love crits!
re: Help! ---Tire blowoffspeloton
Jun 20, 2001 10:25 AM
Leave the talcum powder on the tubes in the future. It lubricates the tube inside the tire. A good idea is to even get a freezer bag full of talcum, and shake your tubes in it before installation. This can help to fight flats.

The frequency of your blow-outs suggest perhaps improper installation (or horrible, horrible luck). Make sure that the tube isn't pinched under the bead of the tire before inflation. Sometimes by looking at the bead on both sides before inflation, you can see parts of the tube trapped by the bead. Carefully with your hands work these sections under the bead so that they will not pinch when air enters the tire. Sometimes the tube will pinch near the valve stem as well. Give the valve a couple of pushes before inflation as well. This can help free up pinched sections near the valve. The tire that had a blow-out in your basement I suspect came from a section of the tube being pinched. This is usually the case in these situations. This could also be the case with your other two blow-outs.

When installing your tubes, make sure you don't use any tools. Use your hands to seat the bead. Don't be tempted to seat a tight bead with a tire lever or a screwdriver. This can be another cause of tube failure. Check your rim tape as well. Make sure that the nipple eyelets are covered, and there are no sharp edges to be seen anywhere. I would also check your rims. Frequent blow-offs can be a sign of a rim defect such as a ding that could cause the bead not to seat properly and be prone to coming off the wheel. This may not be the case as it seems to have happened to you on two wheelsets. Also make sure to check the inside of your tires to see if there is any object lodged in there that could be causing these failures.

Most of the blow-outs that I have seen can be traced back to improper installation of a tube, mostly tubes pinched under the bead and the rim. Take a close look at your set-up, and good luck.
re: Help! ---Tire blowoffsdana.castro
Jun 20, 2001 5:30 PM
Thanks for the long and detailed message. I think that I am doing everything you've said, except for the talc. The Sestrieres are pretty new with no dings, and the Ascent Comps are BRAND new. The join in the rim is a little rough on the Velomaxes, which I tried to smooth out with some fine sandpaper. I find that with all of the tires I have mentioned I can, ALBEIT WITH SOME DIFFICULTY, get the tires both on and off WITHOUT tire irons.(Admittedly, I do have pretty strong fingers.) Is this right or does it mean the tires are too "loose"? (Pardon the question but when I used to race I only used tubulars and so am not fully up on clinchers yet.)

thanks, dc
re: Help! ---Tire blowoffspeloton
Jun 20, 2001 9:41 PM
No, the bead should be able to go on by hand without the aid of tools. A lot of people will resort to using things that they shouldn't to get the bead on the rim instead of fighting a little with their hands. I would just make sure to give the valve a couple of pushes in the direction of the rim, and look in between the bead and the rim for parts of the tube sticking out and therefore getting pinched before inflating the tube. A piece of tube stuck under the bead will blow off. I've done it a couple of times, and had the tire blow off with a gunshot like noise while still on the work stand. Part of the learning process I guess.

A question though. When you say blow-out are you referring to the tire merely going flat suddenly, or the act of the tire actually leaving the rim instantaneously?
re: Help! ---Tire blowoffsJerry Gardner
Jun 20, 2001 11:19 AM
Dana,

What is the max inflation pressure for these tires? If you go too much above the max rated pressure, you will have blow offs.
re: Help! ---Tire blowoffsdana.castro
Jun 20, 2001 5:21 PM
The inflated pressures quoted are all 5-10 PSI below rated maximums, using a Silca Super Pista pump.
Just a thought....Greg Taylor
Jun 21, 2001 9:13 AM
You may want to double check the pressure gauge that you are using. It could be inaccurate - inflate using your usual gauge, then cross-check with a buddy's.
Just a thought....peloton
Jun 21, 2001 10:17 AM
Pressure can be a factor in blow-outs but I don't know if a subtle difference in pressure over the reccomended would cause the number of blow-outs he is talking about. Most tire manufacturers rate their tire's pressure at about half of what would blow the tire off the rim. It would have to be a fairly substanstial inaccuracy in the gauge of his pump to be off by that much. I would suspect that there is another problem contributing to these blow out problems.