I have had my bike since January and I probably do an average of 20 miles per week. The chain has started slipping on 2 sprockets and reading up on the web it seems this could be down to the sprockets being worn as they are the 2 that probably gets the most use. I took it to a shop near were I work and thats what they think. However I took it to a shop near home to get a price for replacing the sprockets and they think I should try replacing the gear cable first as that is becoming slightly frayed. Does anyone have experience of this and isnt it more likely to be the sprockets?
I presume this isn't a new bike else there wouldn't be this much wear and tear on it in so short a time.
If the cable is frayed you should replace it but I doubt that it will fix the skipping problem. So I'd replace the cassette too. The thing is, usually you can't just replace the cassette and you'll probably have to replace the chain and possibly the front chain rings.
I would not totaly rule out the cable if it is frayed. If the cable is frayed it may be hanging up inside the cable housing. When shifting into a higher gear the spring in the deraileur may not be strong enough to pull the cable through housing. As the rider you may be compensating for this error by over shifting. As you ride along the vibration from riding could ease the cable bind up leading to fanthom shifting that you think is the chain skipping because you are not shifting when this happens. With that said replace your cable and add a little lubrication in your housings. This may solve your problem.
This normally is a sign of a worn chain, but if the chain checks out good, then it probably is the cassette cogs. If you want to check the chain, each link of a new chain should be 1" long between the centers of the pins. Therefore, 12 links should be 12" long. If you have a fairly accurate 12" ruler, you can measure 12 links along the bottom of your chain run. If they measure between 12" and 12-1/8", then the chain is OK. Over 12-1/8", it needs to be replaced.
