RoadBikeReview.com's Forum Archives - General


Archive Home >> General(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 )


Mysterious Flats(13 posts)

Mysterious FlatsCFBlue
Jun 19, 2002 10:43 AM
posting for a friend.

bike is a new leMond Bueno Ares (I think) with fancy low spoke count wheels, he doesn't have the bike handy to check the brand name on the wheels. Bike is purchased new in March, has about 750 miles on it, original tires.

just the front wheel, an aero design, deep rim, low spoke count, requiring a extended stem, goes flat, while parked. I've replaced at least 4 tubes with this mystery flat, even changing brands of tubes. he can ride for two weeks, topping up pressure as usual, then one day, he goes out and the tire is flat. The stem (seems)obviously at fault, will not hold air. The tires can be filled with air, but the air leaks back out of the stem, screwing it tight does not stop air escaping. There are no punctures on the rubber, its as if the valve will no longer seat and get a good seal.

monday he took it back to the dealer, *they* changed the tube, looked over the wheel very carefully and attributed all his flats to bad luck. He put the wheel in his trunk, finished the work day, got home and found the tire flat, having never left his trunk. He filled it with air, and this time, it still has pressure today.

Anyone have any ideas to help us sort this out

Thanks

mike
find the leakSteveO
Jun 19, 2002 10:57 AM
1. take a tube which has 'gone flat'.
2. Fill with air
3. Place in a tub of water
4. Watch and wait.
5. Go from there.
double check the rim tapetexfan
Jun 19, 2002 11:22 AM
slightly off-center rim tape caused me numerous mystery flats before I figured it out. (OK I didn't figure it out, someone told me to look for the problem, but you get the idea)

Texfan
I second this, with a twistbigdave
Jun 19, 2002 11:52 AM
I actually bought Salsa rim tape once instead of Velox. Never again. It turns out that the weave was not as tight as the Velox and was not providing the same level of protection. I was getting the "mystery" flats too and never in the same spot. So I looked at the tape closely and could actualy see where the weave of the Salsa tape would spread slightly, allowing the tube to contact the rim near the spoke hole.

--Dave
Second the rim tape--drove me crazy with thin tubesSilverback
Jun 19, 2002 12:25 PM
The spoke holes on my rear Bontrager Fairlane rim are offset a little, and when I taped it, I just BARELY missed covering a couple of them--just a fraction of a millimeter of the rim of the hole was exposed. I rode for 1500 miles on standard tubes with no trouble. When I switched to Specialized thin tubes, I flatted three times in 20 miles. From the location of the holes I could tell it was something to do with the rim, but the tiny slice of hole I'd missed was so small I looked right past it. If the holes are on the rim side of the tube, I'd peel the tape up and re-apply it very carefully.
If the holes are on the tread side of the tube, feel around inside the tire for a broken-off thorn or a piece of glass stuck in the tire.
In the longshot category, two wild-ass guesses: Sometimes (not often, but I've seen it happen) air will travel inside the tire and escape at the valve hole in the rim. Doesn't mean the valve or stem is leaking.
And are you using the little nut that goes on the valve, to clamp it to the rim? Opinions differ, but those things have been more trouble than help to me. I've thrown them away for years. If you use it, be sure the valve is straight up in the middle of the hole before you tighten it down.
A couple of ideasDave Hickey
Jun 19, 2002 11:24 AM
Check the hole on the rim where the valve extends. Make sure there are no sharp edges. It could be cutting into the valve stem. Make sure there is not something stuck in the tire that keeps puncturing the tube. As a last resort, change the rim tape. I've found some rim tapes are too narrow for the rim.
A couple of ideasroadmeister
Jun 19, 2002 11:35 AM
I agree...check the valve hole on the rim. I had a new
pair of Mavic rims a few years ago, and a tiny piece
of aluminum shaving (left on the rim after drilling)
would just slightly prick each new tube I put in and
drain the air, sometimes slowly, but sometimes fairly
quickly. Check for slivers imbedded in the rim tape,
also.
My theoryScot_Gore
Jun 19, 2002 11:26 AM
It's the RIM.

There's several possibilities.
1) check the drill hole for the valve stem. See if there's any "flashing" left over from the drill out that is cutting your tube(s) near the valve.

2) check your rim tape. Any spokes coming through.

As the previous poster said. Find the leak. When you find it, put the tube and tire back on the rim the same way you took it off and throughly check the rim and tire in the region of the leak. That said......I bet you already did that.

Good luck

Scot
My theoryCFBlue
Jun 19, 2002 11:37 AM
There's several possibilities.
1) check the drill hole for the valve stem. See if there's any "flashing" left over from the drill out that is cutting your tube(s) near the valve.

******The problem seems to be with the metal parts, not the rubber. I thought, but haven't had time to check it out, since he lives a fair distance away, that maybe the holes from the two surfaces, the part that the tire contacts, and the deep V section, don't line up, causing the stem to distort.

2) check your rim tape. Any spokes coming through.

As the previous poster said. Find the leak. When you find it, put the tube and tire back on the rim the same way you took it off and throughly check the rim and tire in the region of the leak. That said......I bet you already did that.

********* :-) yes, I all ready did the dumb, obvious things, it is definately not coming through the rubber, but some how makes a stem unable to hold air. But, i will look over the rim tape and check the stem holes for flashing left over. The bike shop mechanic, one of the most reputable shops in the area, supposedly gave the rim a thorough looking over, and it still wnet flat, with in 12 hours... A mystery indeed

Thanks for the thoughts

Mike
Are all punctures in the same place?jose_Tex_mex
Jun 19, 2002 11:54 AM
Have you checked all of the tubes to determine if all the flats are in the same place? If they are all around the stem then the problem must be a jagged edge by the hole that needs to be filed down.

Run your hand around all surfaces of the rim. Pay attention to the sidewall (underneath surface as well). Also, make sure you check the rim joint. I had to file one down once upon a time.

Again, if the flat is continually in the same area check that out first. If it's not, you might just be one of those law of averages.

Finally, many people kill the tube just putting in back on. Can you put the tube in without levers? Some Aero rims can be a real pain.
re: Mysterious FlatsChen2
Jun 19, 2002 12:25 PM
I agree with all of the other suggestions but thought of two more.
Have all of the replacement tubes been of the same brand? On three occasions I have had or have seen repeated flats caused by identical new tubes having identical defects.
Long stem tubes are available in several brands.

It's possible to damage the valve seal by overtightening the valve retention nut.
~Al
Mystery flat...Same Tube???biknben
Jun 19, 2002 12:28 PM
Your last paragraph said that a tube that was flat yesterday is still holding air today?

"...got home and found the tire flat, having never left his trunk. He filled it with air, and this time, it still has pressure today."

I might suspect that something is wrong with the valve. If there's a hole in the tube it's not going to seal itself. Maybe a long shot but is he not screwing the valve closed. If the valve is left open it may release air if bumped/depressed by other things in his trunk.

If he is changing tubes and this situation continues than it's not the valve. I'd replace rim strip entirely and make sure there are no sharp edge on the inside of the rim left exposed.

Sounds very strange.
re: Mysterious FlatsJimP
Jun 20, 2002 6:30 AM
This sounds similar to an issue I had last year with Tufo tires. The valve stem in a deep-aero rim is held in place quite firmly by the deep rim section. If the tire/tube is allowed to move at all, the tube will flex where the valve is attached. This repeated flexing caused the valve stem to separate from the tube causing a leak. The tube would hold air as long as the bike wasn't ridden but would flat quickly. My issue with Tufo really was that the tire would not stay "round" after being ridden a while which caused the problem. This could be an issue for clincher tires too if the tire flexes too much causing the tube to flex around the valve stem.