Well I never.
When I visited a bike shop to ask how much it would cost me for them to sort out my gears as they were jumping and not changing correctly (yes, I still haven’t gotten around to learning how to do it myself. It’s on my list of things to do in 2012!), the look on one of the shopkeepers face when he saw my chain on both top cogs was one of dismay. “You shouldn’t be doing that” he said. “It stretches your chain and I can see it is putting stress on your derailleur.” He then began to reel off a list of new things I would need for my bike. Due to my lack of knowledge on this subject and my distrust of this shopkeeper simply because of his approach, I said thank you and left.
I went to another bike shop and asked for them to sort out my gears and they noted that my chain had stretched (such is their keen eyes) and the back cogs and derailleur needed changing due to wear and tear. I enquired about this concept of cycling on the top cogs and they agreed that this is not a good idea as it wears out the chain and cogs quicker.
The rule is as I understand it; the chain should always be in a straight line. So for example, I have a 28 speed gear system. I previously have only really ever used the last 8 gears. Now I am changing my gear changing habits to only use the last four gears on cog 3. When I need to go higher, I move to the middle big cog, which means my chain is kept as much in a straight line as possible.
This has in fact improved some of my performance as well. Before I didn’t mind using extra muscle to climb, but now, I can use that extra muscle more efficiently as the cogs aren’t as difficult to turn. Obvious you may say, but having been used to using the top 8, going lower was never a mental decision for me.
So there you have it, something that every enthusiast expects us leisure/commuters to be aware of and yet, we aren’t; well I certainly wasn’t anyway and I am betting a lot of leisure/commuting cyclists aren’t aware of it either.