Valve stem core

Trouble shooting a slow air leak in new rear tire.   I just installed the tire and have about 20 miles on it.  I don't see anything puncture related.  I run beads for balancing.  Could my problem be a faulty valve stem core?   All else seems good.  

If you suspect the valve core it is very easy to check.  I'm kind of an Old School guy, I put a bit of spit on the end of my finger and dab it on the end of the valve stem and look for bubbles.  A more sanitary approach would probably be soapy water, but it's not as handy!

Mike

Soap and water in a spray bottle will help you find leaks.  I've been fighting a leaking car tire, and the spray finds the leak source quickly.  Fixing the leak, on the other hand, isn't so simple...

Assuming it's tubed, your more likely to have nicked the tube when tyre fitting than to have an issue with the valve. Valves are pretty simple and mostly fool proof these days. 

If it’s a tubeless tire you can replace the whole stem without removing the wheel from the bike. But if you suspect the valve you can unscrew it and install a new one. If it’s the tube… this is why I don’t have bikes with tubes.