dirtbikedude

This post is a bit of a rant but I also have a question. I have been riding mtb for a long time. Luckly I rarely get flats. In the past year I have had two flats but they were caused by my own neglect not checking tire pressure. A few months ago I purchased my first real road bike. In the first two weeks I had 3 flats. Checked out the rim, no problems. Checked out the road I was riding, no problem. I even went out one day and road slowly to see if there was anything I was going over. Nothing there. Upon checking the tubes I found that the valve stem was ripping off the tube. Tried different tubes and the same thing. Now it happens about every 2 rides.
Then 2 months ago I got new wheels, Spinergy Rev-X tubulars. The first week had no problem. Then it started again. It has droped to once a week but still the valve stem is tearing. I have proper pressure and the tubulars are mounted and glued properly. The only thing I can think of is because of my weigh and the fact that I ride a lot of hills and decend some what fast, could it be over heating the tires?
Any thought on this would be appreciated.
Slainte

p.s. It is always is the front tire

mrfix

You could be damaging the valve stem area when removing the air pump chuck, Don't pull it off, give it a sharp hit to get it off, and don't push it all the way of the large part of the valve stem. And one more thing, take the stem nut off and throw it away.

pokey

Have you checked the rim for sharp edges where the stem goes through? How about pump head removal technique? Rider weight, downhills, and heat as the cause would seem to be a bit of a reach.

dirtbikedude

I take the pump off very carefuly just to be sure that it does not tear the stem. There are no sharp edges either. The stems are tearing at the base away from where it contacts the rim. When they are not on the rim the only way to get them to leak is if they are at an angle. So because of this, the lastfew times I made sure that the tubulars were glued well and that the tire was not slipping. Just had a thought :confused: Since I was riding at a time that the murcury was 110+, could that cause the glue to soften and allow the tire to slip?

Slainte

lotek 

Dirtbikedude,
That does sound plausible. I've heard where during extremely
hot days the glue can soften and cause both slipping and rolling
of tires. That said, I'm in texas, its hotter n hell (and I rode that
one), ride tubulars and haven't had problems.
when you look at your wheel, is the valve stem perpendicular
to the wheel? is it angled? if so thats a good indication of slipping.
I'd think that slippage in rear wheel
would be more prevelant due to torque from drivetrain.
what type of tires are you using?
number one caveat here (and a few would agree)
DON'T RIDE CHEAP TUBULARS.
Are you putting enough glue around the valve stem when
mounting the tires so that area doesn't move?
how are you gluing? what technique?
also what glue? different one's work better in high heat.
I know this isn't alot of help but maybe its a start?
Marty

added content:
Dirtbikedude, I found this at Rec.Bicycles Faq
Marty

dirtbikedude

The reason I belive, if it is slipping, is the fact that I brake hard at the bottom of my decents which I all ways try to do as fast as possible. As for tubulars, I have tried all the brands that were recomended to me and used their best racing/training tubulars. As for glues, I have used Continentals and two others but they are down stairs right now and I am not sure the brand. One of them is that white stuff that I was told is not very good.
I will have to check the stem next time it happens. For now I just cary 2 spares.
Thanks for the advice all. If any one can think of any other reason I like to here them.

Slainte

MichaelW

These days, there are 2 kinds of road inner tube. Ones with longer threadless valves for deep section V rims, and standard short threaded ones for box section rims. use the appropriate kind. Long valves can get damaged more easily on box section rims.
Try changing your rim tape; Velox cloth tape is the best.
When you put the tube in, take care that the valve is not skewed. The valve nut may be useful for keeping the correct angle whilst you are putting the tyre on. You do have to reseat the tyre under the valve before inflation, so loosten the nut, push the valve into the rim, and squeeze the tyre.
You can discard the nut if you like, but I tend to keep mine in place.

dirtbikedude

I run tubulars not clinchers so there is no rim tape.
Slainte

mechBgon

If you haven't tried Continental glue, try that. And it should be very hard to get the tires off, or you're not using enough. I think I mentioned my personal approach (coat base tape with glue, coat rim with glue, let it get tacky, glue rim again, apply tire and pressurize to full pressure or beyond).

Astra

I definitely remember something about professional downhillers back in the day having similar problems. At the bottom of a 60mph+ descent or when coasting the brakes their rims would get exceedingly hot and the valve neck in the inner tube would literally melt and shoot off causing a near instant blow out .

pat5319

Here are some suggestions that may help, and the reasons why:

For the "valve stem " problem
If your valve stems have threads on them USE the "dopey" looking little nuts that thread onto them to hold them in place, if they don't have them, deflate your tires COMPLETELY, especially the sew-ups/tubulars before you add air to them.

Reason- If you add air to a "loose" valve it flexes/moves in the tire and the air pressure resists the movement resulting in stress on the rubber in the tube around the stem eventually causing tearing and loss/ripping loose of the valve.

Expect to have more flats on the road tires:

Wipe your tires off after going through glass or debris, and rebulary during each ride. Have someone show you the technique or E-mail me and I will explain, it may save you nasty crash.

Inspect your tires often, at rest breaks and after rides for any cut, no matter how tiny and probe them with a pointed instrumenet for glass particles and other contaminants.

Reason- Road tires pick up glass particles and other hazards thay may not cause a puncture immediately but can get imbedded in the tires and work their way through the tire and into the tube over a period of time.

I was taught these things early on when I first started riding and I've had far fewer flats because of them.

Ride Smooth
Pat

dirtbikedude

Thanks for the advice. I have Spinergy Rev-x wheels and they require an extension on the valve so it can be accesible so there is no way to put a lock nut on. As for punctures, I have only had one and that was on my fisrt ride. Since, all the flats are do to the valve stem. I am going on a ride with a local club today so I am going to ask if any there has an idea or recomendation.

Slainte