New chain, or new chain and cassette?
Your bike is back on the road and back in use after the winter hibernation. Suddenly, the chain starts to skip on your favourite gear. Darn! Time to replace the chain. Or is it the cassette? Or is it both the chain and cassette? What it the rule for this cycling dilemma? The first general rule is that the bike shop will always say replace both. This is not only because they want to make money—by replacing both the bike shop knows that the problem will certainly go away.
Chains and cassettes wear together, and the amount of wear depends on how clean you keep your drive train and how many kilometres you cycle. If you fail to replace your chain on time, then both will be worn out. And if a gear starts skipping, you do need a new cassette and chain. Most chains last between 3,000km and 5,000km. Most cassettes will last well over 10,000km, if you replace your chain regularly. It’s advisable to keep a log book of repairs to know when you should replace your chain. If that’s too complicated there are a number of ways to test your chain wear or ‘stretch’. Youtube is your friend on this, as well as on how to go about replacing both of them if you have not attempted this before yourself.
So, if you replace your chain regularly, your cassette will last longer. But if you replace your chain with a new one and the gears start skipping then that is a clear signal that should also replace the cassette. In short, replacing the chain regularly will better preserve both your cassette and the (often very expensive) front chainrings. If you leave it too late, a worn-out chain will wear out your cassette and chainrings faster than a new one: costing you a lot more money in the long run. Also, keeping your drive train super-clean also helps the whole system last longer. Never replace your chain the day before a big event or special ride: you may find out too late that your chain is skipping and the cassette needs to be replaced. There is no point in trying to switch a single cog. Even if only one gear skips, you have to replace the whole cassette.