I recently purchased a Zipp 808 rear wheel with a CycleOps Power Meter. One of the first things I found out was that the presta valves on my inner tube would not be long enough to pass through the rim of the 808. Zipp sells presta valve extenders just for this purpose. The extender is basically a long steel tube. One on end are threads that thread onto the presta valve. On the other end is a nipple of sorts, onto which you put your pump. The first thing you have to do is open the presta valve by unscrewing it as if you were going to pump it up. The next step is to wrap teflon tape (sometimes called plumber’s tape) around the threads of the presta valve. Next, you screw the extender onto the wrapped threads. The presta valve remains open all the time. I was a bit confused as to how this would really work, but in the end, I realized that the presta vale shouldn’t leak because there is no downward pressure on the valve core. When inlfating, the air pressure from the pump is enough, as usual, to open the valve and let the air into the tube. Zipp recommends putting presta valve extenders on all of your spare tubes as well.
So, now I have my tube and extender, and I put the tube into the tire and inflated the tube using my pump. It was weird placing the pump over the end of the extender because I guess there is no concept of a valve core at the end of the extender. It works great, it’s just visually confusing to me.
Now here comes the really bizarre part. Because there is no valve core on the extender, how the heck do I deflate the tire? Well, I came up with my own solution, which was to open up a paper clip until it was long enough to slide down into the extender until it pushed the valve core open on the presta valve. Low tech at its best. Zipp does not really give you any instructions on deflating the tube with extender in place.
Overall, I haven’t really had any problems using the extenders or pumping up the tire with the extender on it. I did have an issue where the tube almost completely deflated on its own during a trip to Miami. The bike was on the car rack and it wasn’t particularly hot or anything, but I did discover that the extender had partially unthreaded itself. My guess is that the vibration of the drive loosened it and maybe caused the presta valve core to open as well. The tube was fine and pumping it back up fixed the problem.
Topeak also makes valve extenders, but theirs have an inner core that allows you to open and close the Presta valve core. I now use the Topeak valve extender. Sometimes it is a pain to get the core opened as the extender core is not always engaged with the presta valve core, but this extender allows me to deflate the tube without using the paper clip, not that I really ever want to deflate it.
Here is a picture of my wheel with the valve extender in place.
And here is the extender with my “deflation tool” in place, ready to deflate the tube.
This is a picture of the Topeak extender that I now use.