Bicycle with 1 tire with Presta valve and 1 with Schrader valve One simple question: I have a mountain bike that has 2 tires with schrader valves. I bought a new tube with a presta valve by mistake.

Do you see any issues with replacing one of the tubes that had a schrader valve with a tube which has a presta valve and keeping the bicycle with one of each, or is this not recommended?
I swapped out both tubes on my mountain bike with Presta (less chance of crap getting in to the valve and it means I can carry the same CO2 inflator as I do on my road bike) and got the bushings - once they were in I've had zero issues with the valve stem. I'd definitely recommend putting one in since there's the chance that the valve stem could rub against the edge of the hole or the tube could even prolapse through the hole. 

I have two of the Presta to Schrader adapters, mostly in case my CO2 inflator dies and I need to try and fill from a gas station (it happened once and I didn't have 'em). Just walk into your favorite B&amp;M store and they'll probably have 'em in a container on the counter. I think I paid just over a dollar apiece. If you're really concerned about losing it you can screw it onto the Presta valve and leave it there; just make sure the valve is screwed shut before you thread the adapter on.