Originally Posted by
carpediemracing
Valve extenders are nice. There are two types - the "tube" type which simply extend the reach of the pump but do nothing functionally for the valve, and the other type which is the kind which replaces the top part of the valve with a longer valve, typically on tubulars.
The first type (I'll call it Type 1) which is more common leaves the valve unscrewed. You unscrew the presta tip, screw on the extension, pump up. The extender is simply a threaded tube, one end wider for the valve, the other end narrower for the pump. This leaves you vulnerable to a sudden impact-related deflation - if you hit a bump pretty hard at the right place on the rim, the valve depresses and deflates just a bit. Suddenly you have a slightly under pressure tire that mysteriously doesn't lose any more pressure and has no punctures when you check after the ride/race. That is a disadvantage. Well, for me it was an advantage because it happened to the other guy in the break and he lost.
The second type (Type 2) really is a valve extension. You unscrew the original valve core and replace it with a longer one. Or you unscrew the valve core, screw in an extension tube, and then screw the valve core into the new extension tube. You have a presta screw tip thing at the top, you pump up the tire like normal, you screw the presta tip thing shut like normal. Only thing is that it sticks out of the rim.....
cdr
Type 1 extenders do not seal very well. Zipp recommends using teflon tape on the stem threads for a better seal. If you don't use teflon then you have to pump quickly to ensure that more air gets in than escapes in the process.
Type 2 extenders work best, BUT they only work with tubes that have stems with
removable cores. Not all tubes have cores that are removable.
Bob