Do cassettes and chains need to be replaced at the same time?

Question

Someone recently told me that if I replace my cassette I need to replace my chain (and vice versa) so that they wear evenly.

Is this true? And, can anyone elaborate on the reasoning for this a bit more? Why is it important for them to wear evenly?

Why does this not apply to the front chainring? Or does it?

Answer 1

You may need to change your cassette with your chain due to damage, but only if your bike has missed out on some previous maintenance. If you ride one chain beyond the point of wear, it will damage both cassette and chain rings to different degrees.

Your chain is a consumable component on your bike.

For most people, 1200-1500 kilometers on a chain is a safe distance to ride it before it stretches enough to damage the cassette or chain rings.

If you treat changing your chain like changing the oil in your car, and just do it based on mileage, regardless of the actual wear on the chain, then you can continue to use the same cassette through (on average) 5 chain swaps.

The chain rings, at least a good quality set, are thicker metal, with a larger diameter, so they don't wear as quickly. Usually, I get 10 chain swaps before I need to change the chain rings. But they will eventually need to be changed as well.

I hope that helps.

Answer 2

A previous answer from mine to a similar question can be seen here:

https://bicycles.stackexchange.com/a/7880/2355

But the essence is this:

• The chain wears faster, and it causes the wear of the other components (cog and chainring);
• The chain wears because there is friction between pins and inner plates, so the actual distance between pins increases due to lost material in the contact zone. Thus, the longer chain starts to climb the teeth on the gears, so that their tooth becomes ramped ("shark tooth");
• Slightly worn chainrings rarely skip with new chains, and they end up "matching" the pitch of the new chain again. Slightly worn cogs might sometimes skip to the point it is very difficult to get mileage on them (pedalling very lightly) so that they recover. Also, currently most rings are aluminum, which is softer than the steel in the cogs.

Hope this helps.

Answer 3

You should always install a new chain (or have one that's pretty new already) when you install a new cassette. But you can go through 5 or so chains on a single cassette.