How to tell when a wheel is worn out
 

I have been wondering how you tell when an aluminum wheel is worn out. Is there a measurement or is it just by looks? I got some used wheels, 700c road wheels, and they have very light grooving on the braking surface, but they spin true.

Light grooves are usually no big deal. Make sure the grooves are not manufatured-in to act as brake-surface wear indicators. If the grooves occurred while on your bike I would suggest checking and cleaning or replacing your brake pads to ensure debris is not causing further damage.

I would say that as long as the rim sidewalls feel pretty flat they are OK. When rims get worn out they generally have a concave profile that you can feel with your hand.

"very light grooving" sounds like you're looking at a machined braking surface. All aluminum wheels that are meant to be used with rim brakes should have that.

Thanks for the info. I'll give them a close look when I get home.