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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? – hillsons Oct 30 '12 at 7:39
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 '13 at 15:49
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 '14 at 2:15
up vote 13 down vote accepted

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 '12 at 19:57
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 '12 at 20:15
Bad answer, the OP was asking the exact opposite. – RoboKaren Jul 4 '14 at 14:52
Here's an interesting hack that is very useful at least to know about: – heltonbiker Jul 4 '14 at 17:00

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 '14 at 14:53

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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Tubes may be cheap, but good luck filling a presta valve when you are on the road in the USA. NO gas station has presta chucks. And if you are living in the USA, it's a 3/8 inch drill bit to convert to schrader valve. I have yet to see anyone have a wheel collapse due to converting to schrader valves. The bike shops warn against it because they gotta sell those presta tubes they have in stock. Only reason I can see for NOT converting is there may not be a schrader tube available in your size rim. That's when you use the adapter shown above. Look on YouTube and you will find videos on how to change from presta to schrader valves.

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If you're "on the road" you should be carrying your own pump. – Daniel R Hicks Jul 2 '14 at 19:36

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:

Rim adapters Rim adapter on valve

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