Firstly how do you spot if you need a new chain or freewheel on your bicycle?
If you chain is slipping under pressure it is mostly likely due to a worn chain and freewheel.Check out
http://bicycletutor.com/chain-wear/
Measure the Chain
With your chain still on the bike, place the ruler’s ‘0′ inch mark directly above the center of one of your chain pins. Now count 12 complete links. A complete link equals 1 inner and 1 outer. A rivet on a new chain should line up exactly with the 12 inch mark using this method.If the rivet is less than 1/16″ past the mark, your chain is ok. If it’s between 1/16″ and 1/8″ past the mark you’ll likely need a new chain, but your sprockets should be ok. If it’s more than 1/8″ past the mark, you’ll have to replace both the chain and rear sprockets.I’ve just discoved mine is 1/4″!
Cassettes & Freewheels
The reason you’d have to replace the rear sprockets is because they generally wear with the chain. While the chain is ’stretching’, the gap between the teeth on your sprockets also gets wider and wider. This causes the chain to ride up over the teeth and slip while pedaling under pressure. If you install a new chain on an old sprocket, you’ll probably be able to see gaps of light through the teeth as shown. Check out http://bicycletutor.com/replace-freewheel/ which explains how to change a freewheel.
Front Chainrings
Your front chainrings generally won’t need replacing. Because of the larger diameter, the front chainrings usually take twice as long to wear. If worn they are very easy to spot, as they’ll start looking like shark teeth
