I descend on my face
Stupid rims/tubes question
I have an old POS with schrader valves that needs new tires/tubes. Forgive the n00b question, but would the opening of the rim be to big for a presta valve, or would the lock ring take care of that?
Someone makes an adapter. The problem with using a presta in a shraeder valve rim is that if it moves, the valve stem can be nicked and cut. A quick search found these.
If you don't mind home-made, quick fixes I've got two ideas for you(both worked flawlessly over months of NY messengering, 'back-in-the-day' ):
Take an old mtb inner tube & cut out a square of it, approx. 2.5 x 2.5 cm(you can even use the section from around the base of the valve, slightly thickened and pre-shaped for a circular projection!
Make a neat little "x" cut w/an exacto or razor blade or if your handy carefully cut out a circle smaller than the presta valve diam. Slide this over the new presta tube before mounting and it acts like a grommet
in the schrader rim hole. Cushioning and centering.
Head over to your nearest well stocked hardware store(the one w/the little drawers & shelves of widgets & fasteners) and ask for actual small rubber grommets or bushings that will perform the same job.
Since you mentioned, in no uncertain terms, this was your "beater" I don't think this will clash with any fashion/elite-ist, ego-pros you might ride with.
All the best
\why not just get schrader tubes?
You need a new bike
There's no real advantage to using presta tubes in a rim drilled for schrader valves. In fact, if you need 26 or 27 inch tubes, you can get perfectly acceptable cheap tubes from walmart.