Q You wrote about needing to replace a bike chain due to ‘stretch’ . Is there anything I can do to prevent this ?
A All moving surfaces wear over time, so the short answer is No, but there are things you can do to slow the wear down.
Most of the moving parts on a bike use ball bearings, packed with grease and need little attention for thousands of miles.
Your bike chain, however, is outside the bike, in the open, exposed to dirt, dust, and rain on a daily basis. It will either look dirty and greasy, or rusty and stiff, neither of which is good for durability.
The answer is to clean it regularly, more often if you ride through mud and snow, and to get oil deep inside where it can smooth out the movements and incidentally make the riding a little bit easier.
Cleaning: if the chain is really filthy wrap an old cloth round the lower part and turn the pedals backwards to draw the whole chain through the cloth a couple of times.
Then you need to degrease the whole chain. This can be done with a container of degreasing fluid. Special fluids have been developed, but people have used Diesel, Petrol, or paraffin, and an old toothbrush to dip into and work the fluid into the links of the chain one at a time. Very effective, but there is a quicker way, using a manufactured chain cleaner which is a narrow tank with rotary brushes that the chain goes round while still on the bike. You just half fill the little tank, put the lid on which presses the chain against the brushes, and turn the pedals backwards a couple of times. This gets deep into each link of the chain and washes out the old oil (if any) and grit. After wiping down, it is a good idea to use soapy water and a sponge to wash the degreaser off, otherwise it can dilute the oil that is the next step.
Oiling: Dry the chain and then oil it by gently dripping oil into each link. If you rest the spout of the oil bottle down onto the top of the link then you can wind the chain backwards again, but very slowly so that at each bump of the chain passing drops a little oil into the joint.
Remember to wipe off any excess oil. You want it inside the chain, not dripping onto the tyres, and not waiting to catch any passing dust.
This explanation probably takes longer to read than to do the actual job. Five or ten minutes once you have got the kit and done it once or twice.
I won’t recommend any make of chain cleaner, they vary in price from the professional ones to the less durable ones that will still do the job many times for a casual user.
Cleaning and oiling your chain will make it last longer, and save wear on your gears as well.