We see customers all the time who ride their bikes until the chain is completely worn out. When these bikes come in for service or to replace the chain it is often too late, and the cassette and chainrings also need to be replaced.
Luckily this can be avoided by keeping a close eye on drivetrain wear. If the chain is replaced in time, the rest of the drivetrain will not be worn yet. You should only have to replace the cassette and chainrings after you have replaced the chain for the 2nd or 3rd time or so, saving you money and keeping parts out of dumpsters.
Here are some info to help you understand drivetrain wear:
What is a drivetrain, and why does it wear out?
Drivetrain on a bicycle consists of a sprocket which drives another sprocket by means of a chain. The driving sprocket is the chainring/s at your crank, and the driven sprocket is the cassette on your rear wheel. These parts are very strong and made to handle forces much greater than a human can pedal. If it were possible for the system to operate well lubricated and free from external contaminants, like in a closed oil bath, it would probably never wear out and last forever. The problem is that on a bicycle, the system is exposed which means it doesn’t stay well lubricated and it gets contaminated by sand, mud, water, dust etc
The chain consists of inner plates and outer plates, and then rollers which move around pins. The wear that is relevant here is the pins which wear out because of the force exerted by the rollers, when engaged with the sprocket. When the pins wear out, the rollers move around freely on the pins, which essentially changes the pitch of the chain (distance between rollers).
Why do the sprockets wear out?
When the chain is worn, the distance between the rollers are longer. This means that when the chain engages with the sprocket, fewer of the rollers engage with the teeth on the sprocket properly. So, the same force exerted now has to be divided by less teeth on the sprocket, which means more load on each tooth. This wears out the sprockets.
Can worn sprockets wear out a chain?
No. The chain always wears first, and sprockets only wear if the chain used on them is worn. If sprockets are already worn and a new chain is installed, it will not engage properly and “jump” or slip on the sprocket. If you install a new chain and it engages properly with no slipping, the cassette and chainrings are still fine to use.
How can I avoid unnecessary wear? Most important is to keep your chain lubricated. Here is how to lube your chain:
- Clean your chain properly with a degreaser
- Let it dry completely
- Apply lube to the inside of the chain while rotating the cranks
- Keep rotating the cranks after applying the lube so that the lube can get in between the roller and pin, as this is where it is needed most
- Wipe off excess lube on the outside of the chain
There are many different types of lube, and even different “philosophies” regarding what type of lube is best. You can always ask one of the guys at the shop for real world info, as we know what works best for particular conditions.
The next thing that is crucial is monitoring chain wear. Buy a chain wear indicator, it is an inexpensive tool that will save you a lot of money. Every now and then after washing your bike, measure the chain wear. 8 – 10 speed chains should be replaced before they reach 0.75% of “stretch”, while 11 and 12 speed chains need to be replaced when they reach 0.5%.
By Andre Bezuidenhout 9 April 2020