Reader Bill Rosenfeld asked a frequent and timely question, which is the subject of today’s column. He wrote:
“I’ve heard varying advice about whether you need to change the cassette (rear gears) whenever it’s time to replace a worn-out chain. Do you have an opinion? I believe this is of interest to many as they get their spring tune-ups in preparation for the season.”
Publisher John Marsh and I both replied to Bill.
“No. A cassette should last through the life of multiple chains. It’s made of tougher materials and should go way, way beyond the life of one chain.
“Maybe Jim can provide a sort of ‘timeline’ guideline for it. But it really comes down to recognizing the wear on a cassette — which is going to vary from rider to rider based on style, conditions, mileage, etc.”
To which I added
“John’s right, Bill. It’s a common myth that you have to replace the cassette when you replace the chain. This has never been true. Unfortunately, some mechanics believe this and do this — and say you have to do this because another mechanic told them, and they believe it. But, it’s not true.
“You only need to replace a cassette if it is worn out. And typically, if you shift a lot, you would get about 3 chains out of 1 cassette. Of course, as John said, that varies with how and where you ride, and the conditions, but it’s a ballpark estimate that works for many riders.”
Tip: With the way chain and cassette prices have skyrocketed in recent years, you can save a bundle keeping that cassette until it’s truly worn out. Keeping your chain clean and lubed will extend the life of both.
The cassette test
There’s a surefire way to determine if you need a new cassette when you replace a chain. It’s by testing the cassette with the new chain on a short ride. First make absolutely certain that the new chain is installed correctly and there are no stiff links (because stiff links cause “skipping”).
Then go for a ride on a safe road or in a parking lot with little traffic because this test ride requires concentration and careful control of your bike. What you’re going to do is test to make sure that the chain does not “skip” on any of your cassette cogs.
When a chain skips, it means the cog is worn out and the teeth can’t hold the chain in place under strong pedaling pressure. Instead, the chain rides up and skips forward. This can make a loud “pop” or “bang,” and cause a loss of control as the pedal moves abruptly forward, surprising you. You might even crash. So, do the test holding onto the bars securely and with your weight back so you can’t go over the bars.
All you have to do is shift onto each cog and carefully apply strong/standing/sprinting power pressure on each cog on the cassette to make sure none is worn out. As long as the cassette passes this test, you do not need a new one.
It’s easier to do the test on the small chainring, but you can do it on the large, too, if you prefer. If you have a cassette with large cogs for climbing, they usually have enough teeth that they don’t wear out. But, if you use them almost constantly, you can wear them out. So test them, too. You might do it on a hill where it will be easier to apply enough pedal power to make sure they won’t skip.
Tip: Like worn-out cogs, worn-out chainrings can skip, too, but that’s much rarer.
Rohloff’s cassette gauge
The reason this riding test is used is because it’s almost impossible to see cassette wear. But, there is at least one tool designed to help. It’s the Rohloff Cassette Checker. It wraps around each cog and gives you a way to gauge wear. I’ve tried it but still rely on test rides to ensure my cassettes are not worn out.
Explaining all this to your mechanic
After the exchange we had with Bill, he raised another interesting point. As a longtime shop mechanic, I gave him some more advice.
“Thanks to you both for the rapid and grounded response. It’s hard to argue with the guy in the bike shop, but this is good ammunition.”
“Your mechanic surely thinks he’s doing the right/best thing, Bill, because it sort of makes sense, or is logical that the chain and gears wear at the same rate. But, if you think about that concept, it doesn’t actually make sense. Because every rider uses their gears differently.
“A rider in Florida where it’s so flat only uses a few cogs versus someone in Colorado who has to face the tough, long climbs using all their gears. That rider who only uses one or two gears or maybe a few more is more likely to wear out individual cogs than the person shifting all the time. Yes, the chain is taking a beating but each cog not so much when you use most of your gears.
“Maybe if you explain this to the mechanic he’ll appreciate it, but maybe he will stick to what his mentor taught him. But, it’s wrong and can be proved by testing the cassette when you replace the chain. Unless you use a few cogs a whole lot the way you ride, the cassette will usually keep right on going. You could argue it’s not perfect anymore, but it doesn’t have to be perfect to shift and perform for a lot more miles.”
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.