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Dr. David’s bike chain FAQ

Having suffered a broken chain at the start of a recent ride (and dashed home to quickly replace the chain), Dr. David uses his hands-on home bike repair knowledge to share some tips on how to keep the chain in tip top condition – especially important in Winter:

David’s Chain FAQ:

The chain is an important part of the bike delivering the power from you to the back wheel. There are lots available for the different chainsets and number of gears. Ensure you purchase the correct chain for your bike and look after it.

Q. Aren’t chains getting skinny now we have 11 speed. Won’t they stretch?
A. Chains have got slightly narrower over the years from 8 speed (7.1mm) to 10 speed (6.2mm). They do not stretch but the bearing surfaces do wear over time and will need replacement.

Q. I’ve been doing a lot of weights in the gym and worried I may break my chain!
A. Chains have been around for years and are a mature technology. Quoted tensile strengths are in the regions of 8-10KN (1 tonne). You will not break it. If a chain is damaged it may fail. Are you training to take on Cav!

Q. I’ve been told that Brand X is much longer lasting than my Shimano chain. Is this true?
A. Some bands of chain do wear better than others. Connex and Campag seemed better than SRAM in a Wipperman test in 2010. Try different chains and judge for yourself.

Q. I always use a Brand X because it is faster than Brand Y. Am I kidding myself?
A. Yes! We are talking miniscule percentages. All chains are >90% efficient even without lubrication or special coatings!

Q. I was told by my mate to use Castrol GTX on my chain as his local garage said it is synthetic so must be better. Is it?
A. Don’t use car engine oil on your chain/bike. It contains additives including detergents that will harm your chain and bearings.

Q. Isn’t a good idea to clean your chain in eco-friendly detergent and then re-lube it after every ride?
A. Chains are assembled with a coating of very thick grease to all internal bearing surfaces during manufacture. This is the best possible lubrication. It will wear out. Don’t wash it away prematurely with solvents.

Q. Are sprays better than liquids for lubrication?
A. Sprays tend to have the lubricant mixed with the propellant or other carrier liquid/solvent. These can harm the internal grease. It is better to use a good quality liquid and put it where it is required and not sprayed over the tyre and braking surfaces!

Q. How do I clean my chain?
A. As above it is best not to use harsh solvents and chemicals. You can get fancy cleaning baths which work well. Also a brush and a rag work well to get off the surface grime and grit. I find an old sock works well to get of the outer layer of crud! Also using oil to clean it avoids damaging the internal lubrication.

Q. How can I tell when my chain needs replacing?
A. Chains wear as the internal bearing surfaces wear (see diagram below). They are considered worn out when there is 1% wear. Buy a chain wear gauge and use it often.

Q. My bike shop says I need to replace my cassette when I replace my chain. That is expensive! Is it necessary?
A. When a cassette and chain are new the chain sits snugly in the teeth and valleys of the sprocket. The pressure is spread evenly across all the teeth. As the chain wears it tries to ride up the teeth and exerts more force in the teeth nearest the large chain ring (pedals). This causes wear and it elongates the valley and the teeth get slimmer. Over time the chain will start to cause the teeth to become hooked. Eventually the chain will jump. If you replace a chain before it causes damage then you may not need to replace the cassette as well. Ultimately the cassette sprockets do wear and need replacing. In my experience I get 3 chains to 1 cassette.

Q. Does oiling my chain make me go faster?
A. No! Chain drive is 90-98% efficient. Different oils and greases have miniscule effects on performance. (See below). Thick, sticky winter oils tend to attract the dirt but resist the winter wet and muck. Dry lubes are probably better reserved for the summer. Tests show that the different lubricants have no significant effect on performance. A “dry” chain has the same efficiency and one soaked in snake oil!

Q. Spinning along in the small front chain ring is more efficient isn’t it?
A. You are wasting energy. Studies have shown that using larger sprockets is more efficient. There is a 3% difference between an 11 and 21 tooth in favour of the 21. There is also an increase in efficiency with increased tension of the chain (3% improvement from 100 to 175watts). So you are better off powering along using the large chain ring!

Q. My Dad said never to ride with a large chain offset. Does it waste power?
A. Being in the large front chain ring and large rear gear would appear to put a strain on the chain. It may cause more wear. Studies have shown no loss of efficiency though.

Q. How do I lubricate the internal joints of a chain?
A. The manufactures do it while it is being assembled. Oils will find their way in due to capillary action. Silicone/PTFE in dry lubes (that come out wet!) will be carried in by the volatile carrier which then evaporates. In some circles people boil their chains in wax. I can remember my mate heating his motorbike chain in a pot on the cooker. The theory is that the heat expands any air in the joints and as it cools it contracts and sucks the oil/grease/wax in. I have not tried it with my cycle chains.

Chain construction Below you can see the construction of a cycle chain. The pin(3) goes through the inner plate(1) which has “shoulders” that form a bearing surface with the pin(3) on the inside and the roller(4) outside. The force is transmitted through the roller(4) and to the pin (3) via the inner plate (1) “shoulders”. The pin(3) is fixed to the outer plate(2) . The inner plate is the one that mainly wears.


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