QUESTION: It’s time to replace my chain. My Ultegra cassette has 10,000 miles on it, so should I replace it, too? Of course, the shop says to put on a new cassette. They say worn cogs will wear out a new chain quickly. The teeth have no visible wear, but I want the drivetrain to function as efficiently as possible. What to do? — Bill M.
RBR REPLIES: If you’d been changing your chain each time it started to show stretch, then your cassette would probably still work fine with a new chain.
But it sounds like you’ve been using your chain for a ton of miles. If so, it’s probably badly stretched and the cassette will have to go into the wind chime bin. Worn cogs don’t always look worn, so here’s how to tell.
Put on a new chain with the current cassette and then very carefully take a test ride.
Do it in a place where you don’t have to worry about traffic or plate-glass windows. Stay seated and pedal hard in each cog from the small chainring, with the brakes dragging for extra resistance. Be ready for skipping when you get to the smaller cogs because they’re usually the most worn.
If the chain jumps and slips on any cogs, replace the cassette. Then replace the chain more often to give the new cogs maximum life.
Rohloff and Park Tool both make a cog-wear checking device, but the test ride will let you know what’s up in real-world conditions.
Remember, stay seated and be careful or you could also get a chance to check your helmet’s MIPS rating.
Putting on a new chain whenever there is any measurable stretch is cheap drivetrain insurance and makes for a happy cassette.