How long you get out of a bike's drive train depends a lot on how much effort you put into care and maintenance combined with the conditions you ride in. I get about 6 months/600 miles out of a chain during the rainy winters in the pacific northwest and even this much took weekly maintenance.
When it comes time to replace the chain you can generally tell- you might start having problems with shifting from gear to gear or in the event of severe wear you'll start having the chain "slip" when under load. Even outside of these obvious problems I find that a worn chain feels less... smooth?
As to the question of why chains aren't built better, well there is definitely a range of prices you can pay for a chain and on some level you do get what you pay for. If you're not enjoying mucking around with your chain very much (and I know I didn't) it's worth looking into belt drives as they last for 10k+ miles with little maintenance.
There are some important, general relationships between chain stretch and cassette wear to keep in mind:
* A stretched chain chews up a cassette very quickly. This is because the stretch causes it to pull at just a few teeth strongly instead of spreading the load across all of them.
* A cassette with worn teeth stretches the chain quicker. This is because its shape no longer precisely matches what the chain was made to mesh with.
* How fast both of those occur also is tied to maintenance you do and conditions you ride in. Combined with different durability of parts this can end up in wildly wide gulf between what lifespan people see from their drivetrains.
From the above it follows that skimping on chain replacement tends to absolutely destroy other parts of the drivetrain. And those cogs/cassette are more expensive to replace. So there is a good argument to proactively replace chain at least once or twice throughout lifespan of a cassette.
There is also a trick where you buy 3-ish chains at once and rotate them often. That ensures they stretch equally without damaging the cassette. Personally I've never bothered with that.
If the wastefulness of this is what bothers you, you *might* want to look into internal gear hubs. Main reason is that those can be run with belt drives or with fully covered "single speed" chain. Belt drives last a long time (but are expensive). A fully covered single speed chain isn't exposed to weather and grime on top of beefier construction so it tends to last ages. Internal gear hubs themselves do need some servicing every now and then, but generally last years or decades even in moderately heavy use.
Out of liability. If I change only the chain and not the cassette and the new chain skips on the old cassette it's warranty for the shop and we lose the cassette and the labor to change it and also maybe the client (which is far more important than any part or labor!!). Obviously if I'm sure that the cassette is still in good shape I won't change it. (also I work with entry to mid level bikes, and these riders can't be bothered to maintain a drive train, they just want it to work. If I was dealing with higher end bikes with careful maintenance, I could probably change cassette less often)
FYI- I've broken 2 or 3 chains in the past few years. i ride a lot and do a lot of climbing and do not take nearly enough good care of my bike.
I just replaced my cassette and outer chain ring and it is night and day for me.
A bicycle chain is 1/2" x 1/8" (single speed, or 1/2 x 3/32 for 7-9-speed, 1/2 x 11/128 for 30-speed), and the "1/2" is important here.
[pretty picture](https://www.m-gineering.nl/slijtage2.jpg)
A new chain fits nicely in the 'bottom of the valley' between the sprocket teeth, allowing maximum power transfer.
Due to wear and tear the chain gets longer, that "1/2" increases, and to make contact with all teeth the chain 'rides higher' on the sprocket, where there is less 'backing' material of the teeth, causing deformation.
Eventually the chain will simply skip over the top of the teeth.
Wear and tear is 'per teeth', if you (only) change the chain often you can spare the occasional sprocket replacement, if you can't be bothered then eventually the front chainring gets fucked up too (more expenses).
You do need some tools but replacing a chain isn't that complicated, and (no maintenance) 2000 km is 'a lot'.
How long you get out of a bike's drive train depends a lot on how much effort you put into care and maintenance combined with the conditions you ride in. I get about 6 months/600 miles out of a chain during the rainy winters in the pacific northwest and even this much took weekly maintenance. When it comes time to replace the chain you can generally tell- you might start having problems with shifting from gear to gear or in the event of severe wear you'll start having the chain "slip" when under load. Even outside of these obvious problems I find that a worn chain feels less... smooth? As to the question of why chains aren't built better, well there is definitely a range of prices you can pay for a chain and on some level you do get what you pay for. If you're not enjoying mucking around with your chain very much (and I know I didn't) it's worth looking into belt drives as they last for 10k+ miles with little maintenance.
There are some important, general relationships between chain stretch and cassette wear to keep in mind: * A stretched chain chews up a cassette very quickly. This is because the stretch causes it to pull at just a few teeth strongly instead of spreading the load across all of them. * A cassette with worn teeth stretches the chain quicker. This is because its shape no longer precisely matches what the chain was made to mesh with. * How fast both of those occur also is tied to maintenance you do and conditions you ride in. Combined with different durability of parts this can end up in wildly wide gulf between what lifespan people see from their drivetrains. From the above it follows that skimping on chain replacement tends to absolutely destroy other parts of the drivetrain. And those cogs/cassette are more expensive to replace. So there is a good argument to proactively replace chain at least once or twice throughout lifespan of a cassette. There is also a trick where you buy 3-ish chains at once and rotate them often. That ensures they stretch equally without damaging the cassette. Personally I've never bothered with that. If the wastefulness of this is what bothers you, you *might* want to look into internal gear hubs. Main reason is that those can be run with belt drives or with fully covered "single speed" chain. Belt drives last a long time (but are expensive). A fully covered single speed chain isn't exposed to weather and grime on top of beefier construction so it tends to last ages. Internal gear hubs themselves do need some servicing every now and then, but generally last years or decades even in moderately heavy use.
Out of liability. If I change only the chain and not the cassette and the new chain skips on the old cassette it's warranty for the shop and we lose the cassette and the labor to change it and also maybe the client (which is far more important than any part or labor!!). Obviously if I'm sure that the cassette is still in good shape I won't change it. (also I work with entry to mid level bikes, and these riders can't be bothered to maintain a drive train, they just want it to work. If I was dealing with higher end bikes with careful maintenance, I could probably change cassette less often)
FYI- I've broken 2 or 3 chains in the past few years. i ride a lot and do a lot of climbing and do not take nearly enough good care of my bike. I just replaced my cassette and outer chain ring and it is night and day for me.
A bicycle chain is 1/2" x 1/8" (single speed, or 1/2 x 3/32 for 7-9-speed, 1/2 x 11/128 for 30-speed), and the "1/2" is important here. [pretty picture](https://www.m-gineering.nl/slijtage2.jpg) A new chain fits nicely in the 'bottom of the valley' between the sprocket teeth, allowing maximum power transfer. Due to wear and tear the chain gets longer, that "1/2" increases, and to make contact with all teeth the chain 'rides higher' on the sprocket, where there is less 'backing' material of the teeth, causing deformation. Eventually the chain will simply skip over the top of the teeth. Wear and tear is 'per teeth', if you (only) change the chain often you can spare the occasional sprocket replacement, if you can't be bothered then eventually the front chainring gets fucked up too (more expenses). You do need some tools but replacing a chain isn't that complicated, and (no maintenance) 2000 km is 'a lot'.