Zipp aluminium Valve Extenders are available in appropriate lengths for each Zipp wheel. The new tube-and-extender system puts the removable Presta-valve core at the end of the extension for the most effective air seal. That means you get the same access to the valve top you would have with an ordinary stem. You simply access the top of the Presta valve directly, just as you would on a tube without an extender. Only a small amount of grease is required to seal the threads of the valve extension and valve core.