Presta valve stem - how much beyond the rim?

[nfmisso]

How far should a Presta valve stem extend beyond the rim?

I have noticed that Presta come in lengths of 36mm, 48mm and 60mm - and probably other lengths too. I understand that the different lengths are so that there is enough of the valve stem beyond the rim to be able to attach a pump for standard thru deep aero rims. How much is needed to attach a pump to a Presta valve?

My particular rims are Sun M14A, which from the inside of the rim (where the rim tape goes) to the outside (where the valve stem comes out) is about 10mm.

Thank you.

[JohnV]

I never gave this much thought, but I'm glad someone asked this question. My road bike has the original tubes in it and as a spare, I bought one of the bike manufacture's 700c tubes for the tire. The valve is high enough for the pump head to clamp on to the valve, but even with the lock nut tightened against the rim, the value has a tendency to have lateral movement when I attach the pump.

I had wondered if this was normal in all Presta valves or did I just get a mismatched set of tubes for those rims (Mavic CX22) as both front and rear valves do the same thing. I hope someone here has the answer.

[RobAR]

hi Nigel. You are correct in that you need enough stem exposed to securely attach a pump head. Any extra length is just additional weight and offers more leverage should something happen that tries to break the stem off.
If your rims are 10mm in cross-section, I would expect a 36 would be long enough for most any pump.