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Self-detaching Prestas(4 posts)

Self-detaching PrestasAJO
Aug 30, 2003 10:00 AM
I've got a brand new Tomasso bike with about only 54 miles on it. As I was riding two days ago, my rear tube blew out. (As an aside it scared the snot out of me. It was super loud!)

On inspection of the problem I found the Presta valve was completely separated from the tube. (By the by the tubes that came on the bike are Cheng Shins.)

So I went to ride this morning and the front tube was flat. The Presta on this one was not yet severed but has a leak at the base of the valve where it intersects with the tube. This is, I assume, how the rear one started, without my noticing.

Is this normal? Have I under, or over-tightened my Presta retaining nuts?

I put a Bontrager tube on the back, and a Salsa on the front (a little scientific experiementation to determine if I have a preference and which lasts longer).

Can I expect the same of these? What do I need to do to avoid this in the future?
re: Self-detaching PrestasAndy M-S
Aug 31, 2003 4:52 AM
What kind of pump do you use? A few years ago, when I was getting back into cycling, I didn't have a presta-style floor pump, so I used a frame pump. The stress it put on the valve/tube interface cost me several tubes before I wised up. The same thing can happen if you are careless with a floorpump's hose as well...
re: Self-detaching Prestasdivve
Aug 31, 2003 8:19 AM
I don't think it's common....in my opinion those Cheng Shin (aka Maxxis) tubes are junk. Even brand new tubes have valves looking like they dug them up from some prehistoric dinosaur burial ground. They look that bad.
Lose the stem nuts and get decent tubesKerry Irons
Aug 31, 2003 6:06 PM
My favorite tubes are Michelin light weights (around 70 gm) and the valve stems are not threaded, which saves a lot of wear on the pump gasket/grommet. This points out that the nuts are not required (except perhaps when running Presta valves in a Schraeder drilled rim). You or whoever installed the tubes in the first place over tightened the stem nuts or put way to much force on the stem while pumping.