Argthtjtr

I'm always a little weary of people telling me I should replace things on my bicycle that aren't broken. Because of this, I'd like to know details and symptoms about what happens if I ride my bike with an older, worn cogset? Do I lose efficiency? How much? Is there higher potential for breakage? Do my gears skip?

FYI, the answer to this question should be about the same as answering these similar questions:

• "What are the benefits of replacing an older, worn cogset?"


• "What
  symptoms will my bike exhibit that means I have to replace my
  cogset/casset/sprocket?"

As a chain wears out, the distance between links gets bigger (this is what chain wear tools measure). As this is happening, the chain will grind the cogs to match the worn chain (distance between teeth increases). This is why your gears might not feel so bad, but then they get much worse when you put on a new chain. The new chain's links do not line up with the teeth on the cogs. This will be noticeable in a few ways depending on how worn the cogs are.

First is the noise coming the drivetrain and no amount of lube will silence it. The next one will be shifting performance as you find the chain getting stuck on a cog more often. If the cogs are extremely worn, you'll then get slippage as the chain slides forward over the cog (staying on the same cog, not shifting) when you put pressure on the pedals. This last one can actually be a safety hazard as you might fall if you are out of the saddle pushing, then suddenly the drivetrain lets go (it feels similar to a broken chain when it happens).

Based on this, you might think that it's a good idea to keep the worn chain on for as long as possible, but that will lead to much faster wear on other components as well. Chainrings and jockey wheels rarely need replacing on a well-maintained drivetrain, but if the chain is too worn, then it will grind into these just like the cogs, making it a much more expensive replacement. Many people replace their cassette and chain at the same time once the chain length is 1% longer than when new. This ensures that you won't put excessive wear on the chainrings and jockey wheels.

I prefer to replace my chain at 0.75% which allows me to keep the cassette for about 5-6 chains. This is cheaper for me since I use Dura Ace and Ultegra cassettes, but if you're using more entry level gear, then it's usuallly cheaper to wear them out together and replace them both at once.

I've done the opposite to a lot of riders - I had a chainset of unknown mileage and rather than guess, I simply rode the whole thing into the ground.

Shifting got progressively worse over time, but it wasn't linear. There were certain gear combinations that slipped more under normal load, and others that slipped under heavy load.

Climbing a grade became risky, a good steep ramp could see me slip. So I learned that climbing seated (or very close to the saddle) was a wise plan.

Toward the end, the gears could slip when taking off from stopped, or when putting in some power to accelerate.

At this time I changed everything, chain, cassette, chainring, inner/outer cables, and both jockey wheels. Even though the old cassette was ultegra and other parts were 105, replacing with the lowest cost (tiagra?) components was a phenomenal upgrade in shifting accuracy and snappiness.

I also changed brake pads and cables, and bartape because the old stuff was a bit thin and didn't survive removal.

There's no gain to replacing only the chain if its already significantly elongated. The cassette will be worn to suit, so all you do is get worse shifting and drastically accelerate the wear of your new chain.

So in summary - wear is a gradual degradation process that you might not notice over time.

If your sprockets are worn your chain is probably worn too. A worn drivetrain will suffer from poor shift shifting and with advanced wear, the chain skipping over the sprockets. A worn chain is also more likely to break.

A worn drivetrain will definitely be less efficient although I can't point you to anything that quantifies how much. How worn you can let the drivetrain really depends on what kind of riding you are doing. If you are riding casually and don't care how fast you go you will be able to tolerate more wear.

Sloppier shifting, faster chain wear. In extreme cases you'll get chain skipping.

it's a drag to replace things that are just old, but being an old dog myself, keeping things up to date makes riding easier and more fun, no skipping of the chain which is so annoying. I live in a city where the rain and grit are murder on my chain and cassettes. My whole bike really. The filth on my bike every week is amazing. I find getting my bike tuned each spring and fall just part of the small cost of keeping my bike shops going. I also replace pieces like the chain and the cassette which I can't do (am no good at this) but it makes my girl run so much better. I don't see it as a cost, but as an investment for both of us.