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My 26" mtb rims support presta sized tube stems, however can I drill the diameter of the holes in the rims bigger in order to support Schrader stemmed tubes? what is the proper way to do this, is there a kit?

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    How come you want to do this? What's wrong with presta?
    – Scott Hillson
    Oct 30, 2012 at 7:39
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    thank you for all the responses. THe only reason i wanted to do this was that I accidentally bought a 10 pack of schrader tubes and am stuck with them. So now I can use them ;)
    – sov
    Aug 14, 2013 at 15:49
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    This reminds me of my question: What's the advantage of Presta valves? They seem to have become popular, but I can't tell whether there's any good reason beyond the idea that the slight weight savings might help -- which is an unreasonable fantasy for many/most of us.
    – keshlam
    Jul 7, 2014 at 2:15
  • Has the material of the rim been mentioned?
    – Daniel Shillcock
    Jun 15, 2017 at 7:04
  • "Why don't you just use another type of valve" when someone says "I'd like to use this valve" is a really poor answer, good intentions aside. Different valves have different strengths: there is no "best valve" in all respects and no, adapters do not magically erase all the differences. I will never use a presta valve: I don't want to carry around an adapter, adapters do not allow me to gauge tyre pressure as easily (or at all) and it's so much simpler and quicker to stop at any gas station and inflate to an exact pressure. If I had a road bike with 15 mm rims, I'd sing a different tune etc.
    – Tomislav Nakic-Alfirevic
    Sep 18, 2020 at 10:29

8 Answers 8

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Drilling out your rims will reduce the strength of the rim and increase the likelihood of cutting the valve stem on your tube. For a few dollars you can buy two of these:

Schrader Valve Adapter

This adapter threads onto a Presta valve and effectively turns it into a Schrader valve. Presta valve tubes are the same price and are as widely available as Schrader valve tubes, so you shouldn't need to drill out your rims. (Also, depending on how deep your rims are, finding Schrader valve tubes with valve stems long enough could be a challenge.)

For a discussion of the virtues of Presta v. Schrader valves, check here.

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    These are also useful when you have deep rims and short valve stems. My LBS was out of tubes with 60 mm valve stems, so I got some tubes with 48mm stems and used these. My pump requires that Presta tubes have quite a bit of the valve protruding from the rim in order to make a proper seal. Also, at my LBS the longer stems are more expensive, so the shorter stems combined with the valve converter was actually cheaper.
    – Kibbee
    Oct 29, 2012 at 19:57
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    Thanks, I was hoping to go the other way around. Turning a presta rim into a schrader rim to fit a schrader tube.
    – sov
    Oct 29, 2012 at 20:15
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    Bad answer, the OP was asking the exact opposite.
    – RoboKaren
    Jul 4, 2014 at 14:52
  • Here's an interesting hack that is very useful at least to know about: youtube.com/watch?v=cZja_8crIEI
    – heltonbiker
    Jul 4, 2014 at 17:00
  • This doesn't answer the question - the OP was wanting to use Schrader tubes in a rim with a presta sized hole, and this doesn't solve that problem.
    – brendan
    Nov 15, 2019 at 14:16
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In case you really want to drill, the only thing you need is a 10mm drill bit, and a sandpaper to give a smooth finish.

It is true that the rim gets weaker, and very narrow rims should not be drilled, but I have performed this enlargement a couple of times and rode the wheels some honest hundreds of km in every kind of terrain, with no problem.

I did this because I like the ease to get at any gas pump to top tire pressure after trails, and also because schraeder tubes are more avaliable and less expensive where I live.

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    The OP specifically mentions MTB tires, so rim weakening really isn't an issue here.
    – RoboKaren
    Jul 4, 2014 at 14:53
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    A Schrader valve is 7.6mm (with threads) so a hole 8mm is needed. 10mm is too wide.
    – bat_cmd
    Nov 9, 2021 at 16:48
  • Some Schrader valves (more after car valves) are covered by gum at the base and wider there.
    – nightrider
    Jan 27, 2022 at 13:24
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With MTB tires, there's really no issue in drilling out the valve hole to a larger size since the rims are so wide to begin with. You can do it yourself with a drill bit (3/8" or 10mm) or have your LBS do it. Sanding or reaming the hole afterwards is important, as well as making sure there aren't any sharp metal bits floating around afterwards that might puncture your tubes.

If you ever want to go back again (after having blown through your 10-pack of schraders), you'll find that you have the opposite problem -- the hole is now too large and the presta valve will fit loosely. You can get "presta schrader rim adapters" that fill in this gap and prevent the tube from bulging through or the valve rattling:

search term: https://www.google.com/search?q=schrader+presta+rim+adapter

Rim adapters Rim adapter on valve

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Actually, correct drill bit size is 21/64", not 3/8"

http://sheldonbrown.com/gloss_sa-o.html - search for Schrader

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  • I have a 3/8" drill bit, but I certainly don't have a 21/64"!
    – rclocher3
    Aug 5, 2016 at 0:07
  • It's a bit of specialty size, but it's not all that uncommon. Not too expensive, though it'll probably cost you only a few dollars off of Amazon from what I've seen.
    – Drizzt321
    Aug 10, 2016 at 22:05
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    Or just buy the correct metric size.
    – Criggie ♦
    Jul 30, 2017 at 22:58
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It depends on the width of the rim, and how it's constructed. If the rim is over about 32mm (about 1.25", measured from inside to inside) then it probably has sufficient "meat" in the rim that drilling will not significantly weaken it.

But of course it would be silly to do this simply because you have a Scharader tube -- tubes are cheap.

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21/64" is the proper size drill bit. I found one of this size at Autozone.

If you drill from the tire-side in toward the hub, most of the sharp edges will end up on the outside of the rim and will never even impact the tube. Just scrape off the worst of it so you don't cut yourself on the edges. In my case, sanding was not even required.

I have ridden on a drilled out rear wheel for the past six months and treated it to some rough cross country sections including small jumps (at most six feet of distance spent airborne), tree roots and steep rock gardens and there is no sign of metal fatigue around the drill site. I am not sure how this sort of modification would impact a bike used for downhill biking.

I am so happy with my results that I just drilled out my brand new set of wheels because I appreciate the convenience of the schrader valve.

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Don’t drill a 10 mm hole for schrader valves , that’s too big, the magic number is 8.5 mm, but start small first. 7 mm, then 8 mm and lastly 8.5 mm, then place valve through the hole and if it’s too tight for you’re liking then no bigger than 9 mm. The rule here is you can go slowly bigger with the hole, but you can never go smaller with the hole once you have drilled.

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Open hole with tapered reamer nice quick no filings to clean up

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    So what do you think happens to the metal fragments and shavings that the reamer removes from the rim? They will go somewhere.
    – Criggie ♦
    Oct 15, 2017 at 8:22
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    Bad idea. The hole size will not be as accurate as using the correct size drill, and the walls of the hole will be tapered leaving sharp edges.
    – mattnz
    Oct 20, 2017 at 2:15

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