I know a lot of road bikes (perhaps all of them now) used presta valves as they were skinnier..but why do MTB use them? Seems like another pretentious un-needed item for mountain biking like wearing matching lycra outfits..no?
Easy Stans fluid refill location without needing to debead the tire. Thats if you have the two piece presta stems that is.
i dont have proof, but ive heard that presta has a smaller hole and makes for a stronger rim. ive seen older 19mm wide rims where the valve hole goes almost across the entire flat section where the spokes holes are.
You can pull the core out of a schrader valve to do the same. The valve hole area is the weakest point of the entire rim. If the hole was drilled bigger to fit a schrader valve, it would be even weaker. That or it'd be heavier to possibly offset that weakness.
On today's wider rim there is no advantage. Schrader tubes sometimes cost less and you never need to look for an adaptor. I drill all of my rims. Also filling stans through s presta is a pain. For Schrader you can easily remove the core and clean the core with a schrader tool available from abny auto parts store.
Good question, my best answer is science, and a little econ: Force=Pressure x area. Area = pi*r^2. Perimeter = 2*pi*r. The area of the opening being smaller, the force applied to the pump by the air in the tube is maybe 75% less for presta, while the surface area of the o-ring is only 50% less. So all things being equal a pump has an easier time staying sealed to a Presta valve. Non-enthusiast oriented bikes use Schraeder because everyone knows where to get air with a Schraeder for free. Nobody who buys a $59 bike wants to drop $50 on a presta pump too. The larger aperture of a Schraeder makes it better for moving large volumes of low pressure air into a large volume like a truck tire. Your trail pump doesn't need to move quite so much air. That said, why suspension uses Schraeder is a complete mystery, except that someone decided that there were only two types of valve possible in the universe, and they would pick the one with a threaded interface. A very small threaded valve would be a better answer, but then we'd have to learn about another standard.
Though all my bikes are schrader, I do feel that presta valve tubes are easier to service out on the trail. What I mean by easier is that there's less fiddling with the nozzle that has to have that perfect seal. You can actually use your mouth to blow air into it too.
Gabe I never get tired of the random pics.. and BTW we have spent time with Kyle the last couple of sessions in Big Bear but haven't seen you bro, Ryan has been asking about you..
The nut on the presta valve is kind of nice to keep the valve straight in the hole before everything's fully inflated and tire beads seated. Don't have to put pressure on it from behind to jam a pump head on it. They're compatible with extensions and fit in rims drilled for shrader, so you can simply just stock one kind. Presta to schrader adapters are $1-2. It's also much easier to release air from, but that exposed valve core is also its weakness as you can accidentally release air if you bump it with the pump head or while screwing it shut. That and you might need to pull out some pliers to straighten it if it gets bent. Presta makes sense for rims, primarily for the smaller drilled hole so the rim retains strength and secondary for the ease of inflation (due to that nut that holds it in place). I suppose the other weakness is that people, who don't know about presta, that ask to borrow your pump (dual headed) to air up their beach cruiser might mangle the presta side up. That and people probably wouldn't know that they need to unscrew the valve's tip to allow for inflation without being instructed about it, upon their first time encountering it. The gasket on my pump is so mangled that it doesn't create a seal around the presta valve anymore...
25 years ago, they were not ubiquitous, and switching to them was a point of controversy. When I got rid of my '89 Stumpy in '06, I was still running Presta rear, (Mavic rim), Schrader front, (Araya rim.) Back in the day, innovation was all over the place, and folks were looking for any edge, any way to drop weight, any way to make flat repair easier. There is probably a bit of truth to your suspicion that we do it because road bikes do it, but I believe that is less a function of pretense/inferiority, and more a function of bike shop mechanics being aware of Presta and preferring it. I'm not sure what they use in Europe, but that might play into it as well. Presta are lighter, more functional, less fiddly, and arguably cooler looking. I still run Schrader on my BMX bikes, but the big wheel bikes are Presta. With smart tips on the floor pump, I don't think about it much, except when I have to wrangle that pesky Schrader.