How to check rear cogs condition
I'm preparing to replace the rear derailleur (by SRAM 9.0) along with the chain and the shifters. Since I'll be dismantling the rear wheel + gears, I thought perhaps it worth also to remove the cogs at least for a good cleaning. But then, another thought comes to mind: how to check cogs wear ? Perhaps it would be better to replace it instead of just cleaning and putting back ?
So, how to assess cogs wear level ?
One way is to measure your old chain. If it is stretched, then you might need another cassette. Another way is to look at the cassette and if the teeth on the cogs (especially the bigger ones) are very "pointy" then you might need another cassette. Still another way is to put the new chain on the old cassette, head to a steep hill, to see if the chain skips.
Originally Posted by alexzabr
Drivetrains are pretty flimsy these days, so it is a good idea to check before you head out on a big ride. Also, don't forget about your front chainrings. They wear out too. If they are worn out, they will be pointy and cause chainsuck, or they might outright reject the chain upon torque.
First of all, consider that while riding with a stretched (worn) chain will greatly increase sprocket wear the opposite isn't true.
Riding with a worn cassette will not have any adverse impact on the chain or other parts, so, there's no preventative maintenance reason to replace a cassette. You can ride the old cassette until chains begin to skip.
That said, you can make a judgment call on the condition of your cassette by a careful eyeball examination. Look for chipped, bent, or otherwise damaged teeth, and if possible dress them back to profile with a file or grinder.
Also look for the characteristic hook shape caused by chain wear on the back side of the teeth. This used to be easier, but these days many cassettes have asymmetrical tooth profiles, so they look worn when new.
All in all, my advice is not to bother worrying about the condition of your cassette, unless you're embarking on a long . Clean and re-install it and if the chain runs fine, count your blessings, having put off the replacement cost a bit longer.
The key to solving any problem is to understand and address the underlying cause.
I would look at this page from Sheldon Brown...it has excellent pictures to show worn cassettes and/or worn chains look like together
I've had multiple different experiences. What happened in my case, and I'm sure I'm not alone, is that cassettes starting to wear out have wider teeth than can screw up a new chain.
Originally Posted by FBinNY
As you can see, the teeth was "widened" by wear. with a new chain that didn't wear out with the cassette, this wider portion will spread plates and cause a stiff link or literally break your brand new chain. What I do is sand down the rough edges of worn teeth of the cassette when I change chains with the following result.
I've used this technique often and proved it to be valid by "salvaging" a chain/cassette that had been damaged as previously described.