Getting life out of your chain and cogs is important whether you are using the bike in the city or on a long trip. But on a long trip it helps to know what spares to carry and to know the points where you might want to rotate or replace something.
People refer to chain “stretch” but chains don't actually stretch. The metal is not elongating under tension. Chains do lengthen but this is the result of grit wearing the hinge pins and sleeves of the chain. This grit initially adheres to the outside of the chain but does little harm there. It is when the grit reaches the inside of the chain that wearing occurs. Oiling a dirty chain virtually guarantees that wear will increase. It is the elongated chain that cuts into the teeth on cogs and causes them to wear to the point where the chain eventually starts to slip. Then all the cogs and the chain need to be replaced. So it is wise to thoroughly wash a chain with solvents occasionally. Oil it lightly only when it is clean. If the chain looks wet you have put too much on. Just wipe it off.
Keep Your Chain Dry
If you have been riding in rain the drying out of the chain will be more rapid so have some lube handy. Overall though, keep the chain a little on the dry side.
Cog Tooth Wear
For long trips in the ‘old’ world, where getting a good quality 3/32” chain is generally impossible, we want chains that last as long as possible. This is similar to the interest in tyre and rim longevity. In the case of chains, their wearing out (manifested as getting longer) cuts into the sides of teeth on the cogs. These cogs are even harder to get and changing rear cogs requires special tools. On trips over 8,000km it is common to carry a spare middle front chainwheel and a spare chain.
Approaches to Chain Wear
There are different approaches to chain wear on derailleur bikes that work
- Regularly replace the chain before its elongation cuts into the teeth of the cogs. With the quality of chain on VWR bikes this would be 3-4,000km. (frequent renewal system)
- Carry a spare chain on a long trip starting with a new one and swapping them at 4,000 km, recording it on the bag the chain is in so you know where you are up to and then swapping back to the first chain after the next 4,000, etc. (rotation system)
- Ride one good chain, keeping it clean, through to the point where it starts to slip and then replace all the cogs and the chain. On VWR’s that is at least 7,000km and the lighter you are the further out that is.