RoadBikeReview.com's Forum Archives - General
Pinch flats -- worse with certain rim/tire combi's, or(8 posts)
|Pinch flats -- worse with certain rim/tire combi's, or||bill|
Aug 12, 2003 8:14 AM
|solely a function of weight, pressure?
I never used to get pinch flats. I guess I've had a couple, but now I've had a couple in the last week, and I'm starting to wonder what I'm doing wrong.
I always ran my tire pressure up to 115 at least, up to 125 if the tire says it'll take it. Read a post last week said that 110 works as well as higher pressures and more comfy to boot. So, I tried it. Not great results. Comfy, yes. Flats are, however, a pain in the butt.
I'm running Axial Pro's on AC 420's. Pro's are rated to 110 -- I always used to pump them to 115 anyway. Nary a problem. Reduced to 110 -- problem.
Should I try a different, higher psi tire on the same rim? Is it a problem with the rim? The tire? The combi?
I weigh 160 lbs.
|How do you know?||filtersweep|
Aug 12, 2003 8:23 AM
|How do you know they are pinch flats, vs anything else? A rash of them suggests your tires have had enough.
Are your Axial Pros a bit long in tooth? They don't exactly make them anymore, and if they are like Pro Races, they will be fine for a few thousand miles, then it will be flat city. Finally, is your rim tape in good shape?
Realistically, I don't think you should be getting any pinch flats unless you are hitting something hard enough to wreck your rim...
|The tires are pretty new -- I'd say maybe 400 (?) miles on them||bill|
Aug 12, 2003 8:34 AM
|I guess I don't know for sure if they are pinch flats (which does bear double checking), but I've found nothing in the tires and ridden them a few tens of miles between flats, making me think that it's not something stuck in there.
I guess I could check the rim tape, too, but it's pretty new, as well (unless it has shifted around somehow).
Good ideas to check, though. Thanks.
|There's pinch flats and then there's pinch flats ...||Humma Hah|
Aug 12, 2003 8:38 AM
|... a true pinch flat, aka "snakebite", happens when you hit a square-edged bump and mash the tire flat against the rim. It produces a matched pair of small tears, about 1/8" long, on the tube. If you're suddenly getting these with good tire pressure, could be you've just developed a nasty spot on your favorite route that's worse than you thought.
Thinner tubes and skinnier, thinner-sidewalled tires may both be more sensitive to snakebites. Undersized tubes can also be a problem. If the tube has to expand to fit the tire, it is more likely to tear when pinched, and any hole that happens opens up and leaks very fast. A tube sized to fill the tire case with just a puff of air in it will be more resistant to flats.
One thing I've found that seems to help prevent snakebites is a little Slime in the tube. It seems to lubricate the inside of the tube so that it doesn't tear when pinched.
The other way of pinching a tube is if the tube is getting caught under the tire bead during installation. That can be a function of tire/rim/tube combinations ... a technique you have used for years may not work cleanly when you change one component.
Other non-pinch causes that might act like repeated pinch flats ... an imbedded piece of junk in the tire, a burr or other sharp spot on the rim.
|One more thing to check...||retro|
Aug 12, 2003 8:51 AM
|I'm not sure from your description that you're really getting pinch flats, especially at your weight and with the pressures you're using. I've got 70 pounds on you, and I haven't had a pinch on a road bike in years.
The location of the holes is a good clue to what's going on. Somebody else already mentioned the rim tape, but you might want to triple-check that. I had a rash of flats last year that I couldn't figure out, in the same general area of the rim side of the tube but not in exactly the same place. The tape looked good, but eventually I realized I'd gotten it dirty when I installed it so a 6-inch strip hadn't stuck to the rim. Under pressure it was slipping just a hair, less than a millimeter, and that was enough that a little piece of the tube could protrude into the spoke hole and eventually wear through.
|the mystery either has been solved or has deepened considerably||bill|
Aug 12, 2003 4:52 PM
|I was taking off the tire, and out of nowhere a stupid little valve cap appears. Really from nowhere, alhough the only place it could have come from, it seems, is from inside the tire. Now, I have no idea how such a thing could have happened, but somehow it seems as if maybe, just maybe, that cap could have been rolling around inside the tire even as I rotated it to clean it out. Could have happened, I suppose.
|LOL! Looks for a screwdriver too! OTOH, latex tubes...||Spunout|
Aug 13, 2003 4:04 AM
|could stop pinches, being a softer compound. They will bend around the pinch, expand, but will not rupture.
And, everyone should get Velox cloth rim tapes.
|No way will 5 psi less cause pinch flats!! (nm)||Kerry Irons|
Aug 12, 2003 5:42 PM