Measure chain wear. Place a 12 inch ruler along the bottom chain run, align the 0 mark with the center of a chain rivet. Note where the 12 inch mark aligns on a rivet. If the center or the rivet is at 12 inches the chain is new or nearly new. Off by less than 1/16" and the chain is showing some wear but is still serviceable. If it misses the 12 inch mark by more than 1/16" the chain requires replacement and the rear cogs should be closely inspected. Worn cogs on a new chain will typically cause the chain to jump or skip in the worn out cogs.
