BikeLite

If drilling out a presta rim on mountain bike to a 21/64" size, would that make schrader tubeless impossible? I ask because the Park Tool video shows them doing 21/64 on the inner wall and 19/64 on the outer wall of the rim for tubeless schrader.

I don't know why they think two widths are necessary for schrader tubeless. If the inner wall is not air tight at 21/64", the outer wall sure won't be since there is nothing to stop air leaking out even though a smaller diameter, unless their valve nut is somehow air tight fit.

joeruge

I've watched the video you posted. I can't see that drilling the larger hole all the way through would make putting the new valve in impossible. It would still work, bit I think they are suggesting a 'best practices.'

They expect the new schrader valve to seal on the inside wall. I don't run tubeless but thats the way all work, no? Sealing tape is used in the bed of the rim to cover the spoke holes.

They want you to make that hole a little bigger to ensure you're on the rubber sealing cone when you tighten the nut.

For the hole in the outer rim wall, I guess they want a close fit around the new valve stem to give it full support so it is less likely to get knocked or pulled sideways, losing the seal.

If you make both holes 21/64ths the stem should still seal on the inner wall. It's just that the slightly larger hole on the outer wall won't quite support the new stem as well. That's my guess anyway.

shelbyfv

Seems as if they drilled the inner wall larger to allow the rubber shoulder on the valve to sit in the hole rather than ride above it (or below, depending on perspective.) Cool video, never knew there was any interest in tubeless Schrader.