semi-dumb valve stem question

Doug Smith W9WI said:

I have three spare tubes in the saddlebags right now.  If I recall
properly no two have valve stems of the same length.  The rear tube on teh
bike right now, the stem is something like 5cm (2"😉 long, while the one of
the front is more like half that.

Why?  Why aren't all valve stems more or less the same length?  Why would
one need a valve stem 5cm long?

Depends on rim depth. Single wall rims require the shortest valve of
course, while something like a Velocity Deep V requires an extra-long
valve. I carry a presta long 700x23 tube in my utility bike's
saddlebag, even though it uses wider schrader tubes. I figure it'll
work in a pinch, and if I need to help out a stranger, I can pretty
much stuff it into most tire/rim combos for a limp home.

Doug Smith W9WI said:

I have three spare tubes in the saddlebags right now.  If I recall
properly no two have valve stems of the same length.  The rear tube on teh
bike right now, the stem is something like 5cm (2"😉 long, while the one of
the front is more like half that.

Why?  Why aren't all valve stems more or less the same length?  Why would
one need a valve stem 5cm long?

Deep rims need long valves:

http://www.onetri.com/images/Products/Xlab/2007/xlabAero20Frontlg.jpg

As available rims have grown in depth, so to have available valve
stems, with what is considered long growing all the time.

Joseph

On Fri, 04 Apr 2008 10:55:17 -0500, Doug Smith W9WI

may have said:

I have three spare tubes in the saddlebags right now. If I recall
properly no two have valve stems of the same length. The rear tube on teh
bike right now, the stem is something like 5cm (2"😉 long, while the one of
the front is more like half that.

Why? Why aren't all valve stems more or less the same length? Why would
one need a valve stem 5cm long?

One reason would be owning a Spinergy wheel, on which the 5cm stems
will just barely protrude through far enough for a Silca chuck to grab
them. Different aero wheels have different cross-sectional depths;
where a non-aero rim will typically need no more than a 25mm stem at
most, severe aero designs can require much, much more.

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