The importance of replacing worn chainrings cannot be overstated.
“I know someone who nearly died as the result of riding on an excessively worn chainring,” says Andy, before producing the ring shown in the picture below. “He was thrown off the bike while riding in front of a lorry.” Miraculously, the lorry stopped in time and the rider escaped unharmed, but Andy has kept the chainring as a warning to others. “He’s lucky to be alive.”
Assessing wear is a simple matter. With just two tasks to perform – carrying the chain, and, to a far lesser degree, aiding its transfer to a second ring – the chainring need only maintain a healthy profile to its teeth. Those that become narrowed, flattened, bent over, or curved in the opposite direction of the chain travel, can become ineffective. Slippage, or the sudden unshipping of a chain, can have unsettling consequences, as described above.
A chainring should outlast a cassette, Andy says, but he highlights the fact that chainrings are typically made of soft alloy and not the hardened steel of a cassette sprocket. Persisting with a worn chain is likely to accelerate wear on the chainring. Greater wear occurs on the outer ring in Andy’s experience, and the load can be shared to some extent by resisting the temptation to climb on the big ring and larger sprockets. By doing so, not only will wear be spread more evenly between the two chainrings, but wear on the chain will be reduced by avoiding the sometimes excessive torque placed on the chain by running ‘big and big’ ratios.
The 3:1 to ratio of chain to cassette replacement is not entirely applicable to chainrings, Andy addsd, but the benefits of a new chain and chainring he believes can be easily gauged. “You can physically feel how much better a new chainring performs if you fit a new one with a new chain after riding on a worn chainring,” he adds. “It rolls so much better.”