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New tires blowing tubes as soon as up to PSI.(9 posts)

New tires blowing tubes as soon as up to PSI.sj
Jul 20, 2001 2:47 AM
Mich Carbon 700x23 clinchers on standard rims. I guess they're clinchers they got a bead on them but the package is all in french. I usualy run specialized or contis. The tires where extremely difficult to mount-understatment. i was careful to tuck the tube in and around finishing at the stem and rolling the bead before inflation. I cant even get the tubes up to pressure before the tube blows. At seven bucks a tube its getting expensive. Im sure the tube is being pinched but where, why? Why does one kevlar 23 go on w/ ease and another nearly impossible to get on? I had the same problem w/ Hutchinson Golds i had to sell them and loose money, they where 23's as well. Are my rims just cheap? Ive noticed on my mtbs that the more expensive wheels tires mounts easier.
Rim strips?Mike Prince
Jul 20, 2001 3:11 AM
Has your rim strip shifted allowing a spoke socket (or something else sharp) to be exposed to the tube? A new tire often does fit rather tightly on the rim and does stretch a bit over time. Is the tire bead blowing off or is the tube just puncturing? I have Axial Carbons as well and have had no problems with them on Open Pro rims. What rims do you have?

If the tire bead is blowing off of the rim, try this. Mount the tire/tube without any tire irons - all by hand. Push up the valve stem and make sure the bead is seated at the valve hole. Squeeze the beads together all the way around and make sure no tube shows and is completely encased within the tire. Pump up to about 60-80 psi. Check EVERYTHING at this point and ensure that the tire is firmly seated on the rim. If not then let some air out and re-seat the tire. When all looks good, inflate to full pressure (116 psi for the Carbons).

If you are getting tube punctures, I would:
- check the tire for debris (glass. thorn or wire,...) that could protrude through the casing
- check your rimstrip to make sure it hasn't shifted, exposing a spoke hole or weld seam
- replace the rim strip with Velox cotton tape
re: New tires blowing tubes as soon as up to PSI.DrD
Jul 20, 2001 3:12 AM
I have found some tires to be more difficult than others to mount as well - I have used Michelin Axial Pro's which were a little tight (on Mavic CXP-33 rims) and currently have a set of Conti Ultra 2000's which I can put on/take off easily without using levers... I have also noticed that new tires are harder to get on than ones which have been ridden a couple hundred miles.

Anyway - for the flatting - try coating the tube with talcum powder (so that it doesn't tend to get stuck under the tire bead) then pump the tire up to 30psi or so, and rock the tire back and forth on the rim, working all around the diameter (sort of like you are trying to roll the tire off the rim to one side, then the other) - that wil make sure the tube isn't stuck under the bead. Pump it up to running pressure, and you should be good to go.

Another thing - make sure the rim tape is on there properly, and that there aren't any sharp edges inside the rim.
Can you find the hole in the tube?Len J
Jul 20, 2001 3:44 AM
If so this may allow you to figure out wether it's a problem with the tire, a problem with something on the rim side or a pinch.

I had the same problem during a ride, 4 flats in about 5 miles. What happened was that I had a piece of glass that was embedded in the rubber that was not apparent by running my hand over both the inside & the outside of the tire. I had to look for cracks in the tire, and for each one flex the tire to make sure that there was nothing in the crack. I couldn't believe the size piece of glass that could "hide" in the tire. What was happening was that under pressure & rolling I was pushing this glass into the tube.

Once you know where the hole is (On the tube) you can begin to figure out where the problem is. I would mark a chalk line on the tire Tube & rim (Before I seperate them) so I had some way to line them up once you get them apart and you find the hole so you can figure exactly where the problem is.

Good luck.
yet another advantage for tubulars! nmRusty McNasty
Jul 20, 2001 5:15 AM
Only one reason for a blowout like this...Jofa
Jul 20, 2001 5:39 AM
...presuming that you mean the tube blows explosively.

What happens is the tyre leaves the rim first, which allows the tube to escape through the gap created; the now unsupported tube will blow out violently. This all happens in a fraction of a second, and inspection may lead to the erroneous conclusion that the tube is at fault. It isn't- the problem is that the bead isn't being clinched by the rim properly.

The usual reason for this is that the tyre was mounted carelessly; however you say you've made an effort to ensure this isn't the case... and given some attention, it shouldn't be too difficult to fit a tyre to a rim. Also, you don't say at what pressure the blowout occurs: these tyres are recommended up to about 115 psi, I think. The safety margin for tyre pressure is actually fairly small- most tyres will blow off with only 20% more pressure than the maximum rating, as evidenced by tures blowing off on long steep descents where constant braking has heated up rims enough to cause this pressure increase. So of course, make sure your guage is accurate by cross-referencing it with another.

If you're sure the tyre is mounted properly, and also that the guage is accurate, then the problem can only be the tyre or the rim... and most likely the rim. You don't say what rims you have, but some rims don't have a good enough lip to clinch the tyre, either by design or a happenchance worn extrusion die. Try your tyre on a friend's wheel, and see if it still happens.

No offence to other people, but if I've correctly understood the problem to be these explosive blow-outs, then rim-tape, talcum powder and so on have nothing to do with it.
Jofa
Yep. Rim tape (strips).shmoo
Jul 20, 2001 6:46 AM
It's not the tires (I'm assuming you've already checked the inside of the tire casing for sharp foreign objects). Check your rim tape and your blown tubes to see where the leaks are. I'll bet they're on the inside (hub side) of your tube. You probably have some nipple holes showing - either your rim tape is wondering off center, or it's not wide enough to begin with, or you may have inadvertently scraped the rim tape aside with a tire lever. With a hole showing (and it doesn't have to be more than an eyelash), as soon as your tube approaches psi, it herniates into the hole and blows. If so, pull the narrow stuff off and use the wider (mountain bike) stuff. It will just fit, and will definitely cover the whole of each nipple hole.
re: New tires blowing tubes as soon as up to PSI.4bykn
Jul 20, 2001 6:59 AM
I had a similar problem a few years back, and found the problem to be the bead was actually broken and allowing the tube to blow out the side. Was not visible on the outside, but there were a few threads showing at the bead.
re: thanks everyone..sj
Jul 20, 2001 9:37 AM
New rim strips. Giant TCR Pro wheels w/ carbon spokes, 98'. I'll try the powder and see if that works. Ive even blown them at 80psi. Arrghh!