When does the chain need replacement?
When is a chain shot? Here are some major signs:
1. You start seeing tight links. When you turn the rear wheel with the bike on the centerstand, instead of the chain being completely straight between the sprockets, some links stay kinked.
2. Worn chain. If you pull back on a properly-adjusted chain at the rear of the rear sprocket, you can pull it away enough to almost see the top of the sprocket teeth.
3. If you adjust the chain, and then it needs adjusting less than 100 miles later, and then again in another 100 miles.