Testing the improvised presta adapter.

     By now everyone has seen the make shift presta adapter video on YouTube. If not Here it is. It looks like a good trick, but I needed to check it out and see how well it works.
     First is the obvious downside that you need to have a knife handy, or really strong teeth. It would be easier to leave an adaptor in your bikes seat bag. Another trick is to leave the adaptor on the valve stem in place of a cap.

I like to turn them up side down after I have inflated the tire, that way I know the valve has been screwed closed.
     On with the experiment. Using a box cutter I sliced thru the valve cap right where the knurling ends. The video is not real clear about how the remaining piece is installed. I tried installing it the normal direction.

This left the cap very loose and it was easy to screw it down to far and expose to much of the valve head(Like in the picture above) You could not use a air chuck with the valve protruding this much.
    Getting the cap level with the valve head allowed me to pump the tire with compressed air but there was a lot of leakage. It would be OK for the gas station quick fix.
     Next I tried installing the cap reversed. It was a little tougher to get started but that turned out to be fine because the seal between the cap and valve was much better.

Again you want to screw down the cap until the valve is just flush with the  top of the cap. Using an air chuck and compressor worked great, no leakage. Then I tried the real test, a hand pump. It worked! I as a little surprised that the seal was good enough but I was able to get around 100psi before the pump started having trouble gripping the cap and popped off. This is a solid work around if you need to get a presta tube up and only have a schrader chuck available.

Life time supply of presta adapters.