Are bike repair shops averse to changing chainsets?

The chainrings last a long time but are expensive, and a lot of cyclists are surprisingly tight when it comes to servicing.

Worn rings should be replaced when necessary though, otherwise the shop is throwing away good reputation and good income.

The teeth on many modern rings are often quite pointy and shaped, making identifying wear that much less straightforward.

I'm sure there's no one true answer.

In my experience, a chain or cassette cost half what a chainring costs, and an integrated chainset costs much more.

A bike shop's charges vary, but labour is a significant part of the cost. If they spend an hour on a task, that time is charged, and its well above the hourly wage of the mechanic doing the task.

A complex time consuming task plus the part costs do add up, and if the customer chooses not to pay then the bike shop is left with the repaired old bike to sell. This is a lot more work and therefore less profit than selling a new bike.

Example - why would customer pay $500 for a repair when a new MTB is $500 on the LBS floor ? (or a complete new BSO is $200)

The reason is simple, it's due to the properties of the chain drive system.

• A worn driving sprocket engages to both worn and new chains.

• A new driving sprocket engages to only new chains.

So, by having a worn driving sprocket, your bicycle is superior to one that has a new driving sprocket. You aren't limited to using only new chains, you can use worn chains too!

For the driven sprockets, the rules are as follows:

• A worn driven sprocket engages to only worn chains.

• A new driven sprocket engages to both worn and new chains.

So, in the back you want to have a sprocket that isn't too worn. If it's worn, you can't switch to a new chain without switching to a new driven sprocket as well.

Because sprocket wear accelerates quickly with a worn chain, you'll want to replace the chain regularly. If you replace it early enough, you might get several chains worth of wear from your driven sprockets. But eventually you need to change the driven sprockets too because they refuse to work with a new chain.

In contrast, good chainrings last practically forever. You might want to rotate them occasionally to get even better lifetime because they wear according to the pedaling forces that are uneven. Rotation is ideally 90 degrees which is only possible with regular 4-bolt attachments. With 5-bolt attachments, you can only approximate, and with irregular 4-bolt attachments (like the one Shimano is unfortunately using) you can't rotate.