Different methods for knowing when you need to change the chain, cassette and chainring on your bike.
A worn chain gives risk of lost power transfer and also wearing your rear cassette more quickly. With a commuting bike I don’t worry so much. I usually just ‘ride it into the ground’ i.e. ride until the chain starts slipping. But, for racing bikes with more expensive cassettes and groupsets, it is worth checking and changing the chain more frequently. Optimal changes of chain can:
- Save money (in particular prolong life of cassettes)
- Protect power transfer of drivetrain – lose less power to stretched chains and bigger gaps in cassette teeth.
How to check whether chain needs changing.
1. Finger test
- A simple test is to use your finger and try to lift the chain away from the chainring. If the chain can be pushed quite a bit away from the chainring (like above), this is a sign that the chain needs changing.
- For this test, I put it biggest gear (biggest front chain ring, smallest rear cassette, e.g. 53*13)
If the chain is badly worn, you will probably need to change the cassette block at the same time. (and possibly front chain ring)
2. Chain measuring tool
You can also buy a chain measuring tool which will tell you how worn a chain is. Such as this Lifeline Chain measuring tool for £6.00 from wiggle
3. Measure with rule
Put a tape measure a the centre of a chain pin. At 12 inches, a new chain will be exactly at the centre of a pin. If the centre of that pin is 1/8 past the 12inches, the chain needs changing.
- If the centre of the rivet is less than 1/16? past the mark, your chain is ok.
- If it’s between 1/16? and 1/8? past the mark you’ll likely need a new chain, but your cassette should be ok.
- If it’s more than 1/8? past the mark, you’ll probably have to replace both the chain and cassette.
4. 1,000 miles
Another less scientific test is simply to change the chain every 800–1,000 miles. This means you can use a couple of chains per cassette block. I do this for my racing bikes. It is said that a chain takes a couple of hours to ‘bed in’, after putting in. So you shouldn’t use a new chain for a race without training on it first – though only 1 watt loss is suggested. (Efficiency of chains)
Note: I would prefer to replace with a cheaper chain (e.g. Ultegra) frequently – than replace with Dura Ace infrequently. Also when replacing the block I tend to go for Shimano Ultegra. The price is about 50% of Dura Ace and only a slight difference in performance.
I try to keep a record of when you change a chain and note the mileage. This will give you a guide to when you need to change the chain. Sometimes, I just change it after one month’s worth of riding.
Chain on my commuting bike
With my commuting bike, I usually wait until the chain starts to slip and then change the chain, cassette block (and sometimes front chainring all together). It means that it can be 12 months between changing the chain. Towards the end of the chain cycle, it is probably becoming inefficient. But, the hassle of changing it is greater than the decrease in inefficiency. However, if it starts slipping off, it is definitely a sign it needs to be changed.
After leaving it for a long time, when I do change the chain and cassette on my commuting bike – you can really notice the difference.
- Take a new chain and put it in the largest front chainring (e.g the 50 or 52 tooth outer chain ring.
- Then put it on the largest cassette sprocket at the back, nearest wheel. This will be a 25 or 27 tooth sprocket.
- Don’t put chain through rear derailleur at this point.
- Pull the chain tight and see where it meets; to this then add an extra two links. This chain length including the two links is the ideal size of a chain.
(Note when riding, you wouldn’t use this combination of biggest chain ring and lowest cassette sprocket (highest number of teeth). This is because such a combination gives a bad angle for the chain – and can be a big cause for loss of efficiency in the drivetrain. It is more likely to grate against derailleur’s e.t.c. You should be going down into the lower chainring.)
When threaded through the rear derailleur, the chain should be workable in all the gear combinations that you are likely to use.
The chain should be tight, without putting too much pressure on the rear derailleur. If the rear derailleur is pulled so it is almost vertical pointing down, this is a sign the chain is too short.
With this chain length, if you had to shorten chain on a ride (because it snapped) you could ride on it. But, you would have to be more careful when using big chain ring and make sure you didn’t use combination of big chainring and low cassette.Once you have the correct chain length, you can just use that chain length to copy any new chain you put on.
A worn cassette, teeth have become a bit pointed. If you put a new chain on this cassette. The chain would slip.
If a cassette is ‘mid worn’ sometimes there is a mild slip, but after a 50 miles, the chain beds down and you can get another chain’s worth out of the cassette. It depends whether you want the hassle of a slipping chain for a short while.
A new cassette.
The worn chainring is on the top. The teeth look like Shark fins. They are more pointed. The new chain rings is behind and the teeth are more rounded.
Chain rings generally survive longer than cassettes. Even if you need to change chain and rear cassette, it may be fine to keep your existing chain-rings.
To test whether you need to change your chain ring, it is the same as for cassette.
- Is there slippage when riding?
- Do the teeth look more like hooks, with bigger gaps?
It is not always easy to know whether chain rings and cassettes need changing. I often end up looking at different bikes and trying to compare the shape of the cassette teeth. There isn’t an easy scientific test. It’s also more difficult because even if it doesn’t slip, I still don’t want to be losing power on my racing bikes.
Personally, I often find it difficult to spot a mildly worn cassette. I’ve often spent quite a while looking at cassettes trying to work out if they are worn / partially worn or not. I have about 3-4 cassettes lying around my garage in a state of partial wear. Not being used, but not being thrown away….
- Changing regularly will help prolong life of your cassettes and chain-rings. It is better to buy several cheaper chains then try make your Dura Ace chain last a long time.
- Have a look at shape of teeth. When they start to become like hooks, they will need changing.
- Chainrings need changing less frequently. Also, the more teeth they have the less they will get worn. THerefore an inner 36 ring is more likely to need changing than an outer 53.
- If you ride with worn chain rings and cassettes, you will lose power transfer and could even start slipping on the pedals.