Obviously sprockets need to be changed when they are worn, but when you purchase a used bike and don't know how many miles have been on the sprocket, how can you tell if your sprockets are worn out? I have a couple pics of my sprockets. Are they worn out and in need of replacing? Any help is appreciated. Thank you!

 

How many miles are on the bike itself? That may be the original sprocket. It looks good to me.

 

Your sprocket looks fine, the teeth will begin to get more pointed as the sprocket wears, if you wait to long eventually you may notice your actually missing teeth. yours looks nearly new.

 

Thats a stocker which is a very hard steel, it will last forever. You know they are worn when the teeth don't have that flat spot on the tops anymore, they are just a sharp point. Thats not going to happen before your stock chain gives out so change them when you change the chain.