Ok so I have presta valves on my bike and I use the shrader adapter piece .

My question is this: after I open the presta valve , screw on the adapter and fill up my tire , do I need to take the adapter back off and close the presta valve , or can I just leave it open ? It holds air when its open obviously since the air inside is pushing it closed , but Im not sure and flat tires are NO good so I need to know .

Can anybody answer my stupid question for me ? Thank you

Yeah, you can leave the valve open with the adapter on it. If the adapter is taken off, it's generally a good idea to screw the valve closed.

I appreciate your help , thanks man !

My thing (since I long ago bought a floor pump that is Schraeder-only) is to remove the adapter after pumping, close the valve, and then thread the adapter back on in case I need it while I'm out. Just because it only takes 12 seconds and why not?

People with deep dish wheels and valve extenders do this all the time.

I'd do this with a metal adapter, but some of the plastic ones feel like they'd fall off after a few miles of vibration.

Only because they have no choice. And yes, 2 out my 3 bikes here have deep dish carbon pizzas.

ps. you're forgiven

p.s. there's these rad new websites like google and youtube that can help most questions like this

not that we don't get off on answering these questions anyway, just sayin'