As you mentioned, one of the primary differences between a Presta and Schrader valves are the diameters--with Schrader valves being slightly larger--and therefore the valve holes on bicycle rims are drilled to suit one size or another.
Your foremost concern with using a Presta valve in a rim drilled for a Shrader valve shouldn't be 'movement' of the valve stem, as geoffc suggested, but rather a 'hernia' of the tube through the excess space at high pressure, leading to a blowout.
Most mountain bike tires sit at a low pressure, therefore you will probably get away with it, however, there is a very inexpensive adapter, sometimes called a 'valve grommet', which is made out of rubber or metal and serves to make the valve hole small enough for a Presta valve to fit snugly.
It will also not come loose under high pressure, unlike geoffc's 'old tire' solution.
bicycles.stackexchange.com/users/23/Dustin Ingram
Yes you can.
Many presta tubes come with a grommet to allow you to use presta valve tubes in a wheel drilled for schraeder valves.
bicycles.stackexchange.com/users/11/kkeilman
I do this all the time, basically use the presta nut on the inner side to avoid the tube getting "pinched" in the extra space, then if you can find another presta nut, screw that one to the outside where it's supposed to be.
Works like a charm.
bicycles.stackexchange.com/users/4838/Jesse Stacey
I have not tried it, but consider, once the tube is inflated, the pressure will hold the valve stem pretty much in place.
The concern would be if the edge is rough enough that it would cut into the tube that protrudes.
Consider cutting an old tire and wrap the base of the stem with some old tube material and you would probably be fine.
bicycles.stackexchange.com/users/19/geoffc
As others have mentioned, there's ways to do it.
I'd just recommend not doing it.
I have more pressure loss problems with my Presta bikes than I do the Schrader equipped ones.
Strikes me as a downgrade rather than an upgrade.
The only advantage I find to the Presta is the size, which will let you run narrower wheels/tires.
bicycles.stackexchange.com/users/349/Brian Knoblauch
It should work fine if the Presta tube is meant to inflate as large as a MTB tire is supposed to be.
I'd tape the valve to increase it's size.
bicycles.stackexchange.com/users/30/curtismchale
I have done it and it worked fine.
Another alternative is to drill the correct size hole in the opposite side of the wheel - thus you can run presta or schrader in the same rim.
I inherited the wheels set up this way.
The person explained his reasoning that he preferred to just pump up the tire after a flat rather than changing tubes or patching.
My questions about puncturing the newly inflated tires immediately after got me a dim look since it sounded like he didn't bother to do any triage to remove the cause of the flats...
bicycles.stackexchange.com/users/37/Tim
Back when I rode a road bike hybrid, I always used presta tubes with schraeder rims.
I can't say it worked 100% of the time, but I only had an issue once.
And that was across a couple years.
bicycles.stackexchange.com/users/56/LoganGoesPlaces
On my hybrid I have a schrader valve on the front wheel (the tube hasn't had a flat yet
so I've not changed the inner) and a presta valve on the back.
The nut that holds the presta valve to the rim seems to prevent any "hernia" from occurring, although occasionally I burst a rear tube when pumping it up too vigorously (it appears to "hernia" through the hole slightly and causes a burst around the base of the valve).
I always tighten the nut after inflation.
The reason for the presta valve on the back is that the size of inner tube I use only comes in presta valve versions at Halfords which is where, through pure force of habit, I end up buying replacement inner tubes.
bicycles.stackexchange.com/users/79/Amos
I've been using a Presta valve in my front schrader rim since I picked up tubes last, because they were out of schraders in my rim size.
Haven't had any problems yet, knock on wood.
bicycles.stackexchange.com/users/163/Kibbee
I have used both types of valves in tubes.
In my view the presta is strictly for narrow rims.
I prefer schrader valves my self for several reasons: the schrader valve tubes will hold high pressure the same as the presta.
They are easier to fill
they are easier to check the pressure using standard pressure guages found anywhere.
I say this based on more than fourty years of repairing and riding bicycles.
However, if you prefer presta then I can say that a presta valve in a schrader rim is usually no problem.
bicycles.stackexchange.com/users/5483/J. A. SAFFAS
I keep losing pressure in my tires, and among other things, I'm looking at the valves in the tubes. It's an old mountain bike with 26 inch tires. Can I use Presta tubes on rims drilled for Schrader valves ? I know the valve will be smaller than the hole and could cause issues there, but has anyone had success (or failures) with this?
Can I use a Presta tube in a Schrader rim?
bicycles.stackexchange.com
<mountain-bike><innertube><presta><schrader>
bicycles.stackexchange.com/questions/1
bicycles.stackexchange.com/users/7/Brock Boland
Apparently there is no problem when using Presta tubes with Schrader rims. Many people do it and have no problems. However, some people advise against it as they say the loss of pressure using Presta tubes is more noticeable. In most cases it is safe to use a Presta tube in Schrader rims, especially in mountain bikes that run on low pressure. However, it might not be recommended, as Presta may be optimal for narrow rims, but has more pressure losses, is more difficult to fill and cannot be checked with standard gauges.
In most cases it is safe to use a Presta tube in Schrader rims, especially in mountain bikes that run on low pressure. It might not be recommended, as Presta may be optimal for narrow rims, but has more pressure losses, is ,ore difficult to fill and cannot be checked with standard gauges.