Cassette Wear Questions Answered

One of the misunderstood concepts of regular bicycle maintenance and repair is cassette wear. Typically, you'll go through 5 chains for every quality, name-brand cassette -or about 10,000 miles. But there are stories of Campy Record cassettes lasting a decade and people who live in sandy areas who ride hard might replace a Sunrace cassette every 2 chains.

Here are some common cassette questions that I will try to flush out:

What does it mean that a cassette is worn?
So in normal usage the rollers of a chain rub against the cassette as it rotates around and around while you pedal. Usually there is a lubricant in between such as chain oil, but even so, every time the chain rubs on the cogs of the cassette, wear grooves into the leading edge of the cog's teeth. Sand, grit, and an unlubricated chain increase friction and thus increase wear. In the most extreme cases, the teeth of the cassette will be rubbed down and cause the chain to skip under pressure. In a less extreme case you'll experience quicker chain wear because the space between the teeth has increased and the chain no longer fits perfectly. Also, shifting performance will reduce, especially under pressure because the little pick-up ramps on the sides of each cog wear down and won't be able to help the chain climb up to the next cog.

See how there's a little lip on the side of the tooth? That's wear.

How do you know if a cassette is worn?
The easiest way to see if a cassette is worn is to compare it to a new cassette of the same make and model. They should look identical, but if they don't then one is worn. If you don't have a new cassette on hand there are still methods to determine wear. First, clean the old cassette until it shines, then look at the cogs in the middle of the cassette. These are the ones you use most often and they get the most wear. Look straight down from above (see the pic on the bottom of this post). Does it look like the leading edge of the tooth is mushrooming out a little? That's from the metal being rubbed down and compressed by the chain. Think of it like a roll of cookie dough. If you slap it down on the table, the bottom will spread out but the top will remain intact. The metal of the cassette acts the same way.
Next, look at the pick-up ramps. If they look like they're being rubbed away, that's a clear sign of wear. Lastly, there is a phenomenon called "Shark Finning" where the leading edge of a cog tooth will start to curve inwards, making it resemble a shark's dorsal fin. In time this will erode the top of the tooth and cause the chain to skip.
There exists a tool that measures the gap between teeth and tells you whether a cassette is burnt out. It doesn't work that well, especially for 10-11 speed cassettes, so I'm not going to explain it much more. Just like the Park Tool Chain Checker, it's more of a sales tool then a maintenance tool.

Shark Finning in action

Can I ride a worn cassette? 
Yes. It's not dangerous to ride a worn cassette, but it will lead to premature chain fatigue, which will lead to more cassette wear and chainring wear and bad shifting and occasional skips and loss of efficiency and loss of friends and ugly shoes and bad hair and so on.

How can I make a cassette last longer?
Cleaning and lubricating your chain whenever it's dirty or dry is the best thing you can do for overall drivetrain health. I like to take a rolled up towel and floss between cogs every so ofter too. Besides that, make sure the derailleur is correctly tuned -if there is too much or too little cable tension the chain will want to jump between cogs, creating wear on the tips of the teeth and pick-up ramps. Chains and cassettes are designed in tandem to work together, so it's best to use chains and cassettes made by the same company. Some cheaper KMC chains are a little bit wider than Shimano or Sram and tend to rub on the side of the cassette. This will cause premature wear to the pick-up ramps.  Also, remember to shift. Don't just grind away in the same gear all the time; shift, spin, and be happy.

What cassettes last the longest?
There are a lot of good cassettes out there, but Dura-Ace cassettes make use of different alloys for different cogs. The middle cogs use titanium for better wear resistance. Campagnolo cassettes also last a very long time because of their proprietary alloys and forging methods. Sram cassettes sacrifice longevity for performance and weight savings. Generally you get what you pay for. If you ride a lot you should get the better cassette, it will save you money and head-ache in the long run.

My new cassette is missing teeth. Whaddupwitdat?
Is it a Sram cassette? If so, that's fine. They used to do that to improve shifting or reduce weight or something. They don't do that on the new 11-speed stuff though. Even on Campy and Shimano cassettes some of the teeth will look different, and that's OK. The lesson I want you to take away is that it's OK to look different.


Remember, everything wears and everything breaks. However, if you buy quality and do the right maintenance steps, a cassette will give many miles of problem-free use.

This cassette was owned by a professional road and cyclocross racer. As you can see, the profile of the chain has imbedded itself into the side of the cassette over several thousand miles of hard use. It's possible that her derailleur had too high of tension or the derailleur hanger may have been bent, causing the chain to ride a little too close to the next largest cog. This cassette is totally hosed. 

Here you can see the cogs that the rider liked to use the most. The third and fourth cogs down both have lips, while the second one down doesn't.