Cant remember is it 8mm?

I think it is.

just hold one up against the valve?

Yep, 8mm.

8.5mm

Cheers guys.

Why would you want to do this? Presta works so nicely.

I realised I needed to do this the other week when I got two flats and realised my new rim was only for small valves and I had only packed the car-type… Oops.
8.5mm makes it a comfortable fit for the rubber-surrounded valves.
Use a vacuum while you drill to try to stop aluminum shards going into the rim cavity.

Pack Presta spares only; will always work.

pdV6 – Member
Pack Presta spares only; will always work.

POSTED 22 SECONDS AGO # REPORT-POST

Oh how I laughed when I pulled a presta core from my last tube on the Selirk Merida, only to be told that I “should have drilled your rims mate, I could have gave you a tube”

as paulosaxo said. I was given about £15 in euros and Swiss Francs once when I donated a handy Presta I was carrying. The lucky recipients had Presta rims and a spare Schraeder tube. Ooops.

i wouldn’t rush to enlarge the hole on any of my rims….

a larger hole means the rim is weaker.

+1 for presta. you can even get an adapter that allows you to use the pump at the petrol station on presta valves. costs naff all.

i wouldn’t rush to enlarge the hole on any of my rims….

a larger hole means the rim is weaker.

What like they do in the factory?

20 Euros for a Presta inner tube and use of track pump in Morzine was my best.

However if you would rather not have the option…..

It’s for a non ‘biker’ friends bike and they struggle to use the fiddly presta, trying to make life a bit easier for them.

I much prefer Schralder valves but as I do own various different types of rim (mostly run tubeless) I now always carry presta spares with a little adapter sleeve on each so it can fit in a schralder hole without any slop if required…

I wouldn’t tend ot drill my rims out, while it’s unlikely to damage them, theres alwys the chance…

i wouldn’t rush to enlarge the hole on any of my rims….

a larger hole means the rim is weaker

Do you have ANY idea how much metal is removed when drilling out a rim? It’s tiny shavings, virtually nothing. I’d bet it’s under 0.5g of alloy. I’ve been doing it for 20+ years with every presta rim I’ve ever bought. It is no problem at all, believe me! 🙂

Why anyone uses Presta valves on an MTB is beyond me anyway. weak, fiddly things that they are…..

Why anyone uses Presta valves on an MTB is beyond me anyway. weak, fiddly things that they are…..

While I agree I will still carry Presta spare tubes; Fortune favours the prepared as they say:

I can replace a Schralder tube with a presta tube, I can replace a presta tube with a presta tube, I can fix a karked UST setup on a presta drilled rim with a presta tube and I can fix a karked Schalder valved tubeless setup with a Presta tube, it covers all bases when out riding or on a group ride…

I’m with PP on this one, have done this on my mavic rims for ages, no problem with weakening them 🙄

The only ones I haven’t is my 355s…….well not yet anyway just in case I do go tubeless eventually and the presta valves are more fiddly to pump up.

While I agree I will still carry Presta spare tubes; Fortune favours the prepared as they say:
I can replace a Schralder tube with a presta tube, I can replace a presta tube with a presta tube, I can fix a karked UST setup on a presta drilled rim with a presta tube and I can fix a karked Schalder valved tubeless setup with a Presta tube, it covers all bases when out riding or on a group ride…

I can replace ALL our 7 bikes worth of wheels with a 26in schraeder tube because that’s all I use. 🙂 if that won’t fit someone else’s bike then they should be better prepared! 🙂