“How many miles will my road bike’s chain and cassette last?”
That is an excellent question, but it’s also a question without a universal answer. The lifespan of those two wearable drivetrain components will vary drastically based on a number of factors, such as:
Riding environment. Rain, sweat, snow, dust, dirt, mud… these contaminants are all hard on drivetrain components. If your bike is frequently exposed to some, or all, of these conditions, you can expect reduced chain and cassette service life.
Riding style. Shifting under load, cross-chaining, climbing and high amounts of torque/power stress the chain and cassette far more than just casually pedaling around.
Drivetrain maintenance. Keeping your chain clean and lubed will greatly increase its life. If you don’t properly maintain your drivetrain, the components will wear out much faster than they otherwise would.
Personally I thoroughly wipe my chain down after every single ride, I lube my chain every 100-150 miles (my chain lube of choice is Rock N Roll Gold) and I clean my chain once per week. To clean my chain I use the Finish Line Shop Quality Bicycle Chain Cleaner along with Simple Green. I also clean my cassette once per week using Simple Green and Muc-Off brushes. I don’t always remove the cogs from the freehub to clean them, but usually every 2-3 weeks I’ll take that extra step.
Riding on a worn chain. Continuing to ride on a chain that is stretched past its intended service life will damage your cassette.
Quality of drivetrain components. A cheap chain will stretch faster than a quality chain. I am a big fan of KMC chains, and I use the KMC X10SL on my road bike. My cassette of choice is the Shimano CS-6700 Ultegra (11-28).
Okay, so now that we’ve covered some of the variables, let’s talk specifics.
A properly maintained quality chain ridden primary in moderate conditions should last anywhere from 1,500-3,000 miles, or even more. Yeah, that’s a big range, but as we just discussed there are a lot of factors at play here.
The best way to determine if your chain is worn is to use the simple and inexpensive Park Tool Chainwear indicator. For a 10 or 11 speed cassette, you’ll want to replace the chain when the chainwear tool drops at 0.50%. I check my chain once per week.
As an aside, I went through a brief period during which I was replacing the chain every 2,000 miles, even if my chainwear tool indicated the chain was still good. I adopted that practice as a knee-jerk reaction to a wreck that was caused by my chain popping off the chainring (see Thoughts on XFL Training Ride #4 crash). I now believe that the chain came off due to a damaged rear derailleur (since replaced), and not due to the chain itself. I’ve since resumed using the chainwear indicator tool as my guide for chain replacement. I generally get about 3,000 miles out of my chains.
As mentioned above, cassette life is directly affected by the condition of the chain. If you ride a stretched chain, that will damage the teeth on the cogs. You should always replace your cassette with the chain. As for how often you should replace your cassette, some say you should do it at every chain replacement, while others say you can get away with replacing it every 4th chain or more. I guess I fall somewhere in the middle of that range. I’ve always replaced my cassette every second chain, which is about 4,000-6,000 miles. I’ve never had any problems with chain skipping or bad shifts, so I’m actually trying an experiment right now to to see if I can get away with 3 chains. I’ll be putting my third chain on my current cassette sometime this month, so I’ll know pretty soon. I suspect it won’t be a problem.