The last time I replaced my chain I made it too short by about an inch. I don't remember exactly why -- I probably just forgot to add the extra inch in when I wrapped the chain around the big ring and the big cog because I was busy messing with a camera also.
The result is a chain that's too short. This can be bad, but you're never supposed to "cross the chain" -- that is, you shouldn't ever shift to the big ring and the big cog at the same time. I figured I was safe because I don't cross the chain.
Well, guess what I did last night? Yep, I crossed the chain and pulled my rear derailleur pulley to its limit until it cried "uncle" and refused to budge anymore after that. I broke the chain with my chain breaker tool and managed to get going again, but I now need a replacement chain because it's too short by two inches now.
Be sure your chain is the right length. Too long, by the way, results in poor shifting.
Determining chain length isn't rocket science -- just wrap the chain around big and big and add an inch. Park Tool describes this process in detail along with a couple of other methods.
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An inch= a link pair (one set inner and outer plates with attendant roller.
Use SRAM or Wipperman chains so you can adjust length without trashing the whole chain. Actually SRAM 10-speed connecting links aren't reusable, but you can get replacement links. Much less stressful than getting Shi-no's "special pin" just right.
Ned Overend legitimized the full cross gear a few years ago. That's when I named it The Ned Gear. So it's cool now. At least According to Ned.
I used to go a link short on my mountain bike to reduce chain slap. I just had to remember not to go cross chain. Every once and a while, I wouldn't pay enough attention and would. It seems the derailleur springs on stiffer now so there's not quite as much slap.
Chainlength = Big chainring + big Cog + 1 inch of chain, not through the derailleurs. How hard is this? All chain is 1/2" pitch, so 1" = 3 contiguous pins. Look it up, use m-w.com If on a dual suspension bicycle, fully extend rear end, of the bike, to greatest distance from center of BB, big/big + 1" is the proper length of chain, in that position. You have to be able to shift Ned gear, no way to prevent it, and a certain companies derailleurs must have that tension to work properly. Guess whose!
Like UltraRob, I like my chain a tad bit short. I don't cross chain from the big chainring to the big cog, so I do not feel the need to set my chain length to work in that gear combination. I think staying out of those combinations is second nature to me, but it can be bad news if you forget.
when my RB-1 cracked, I transferred all my parts to the '82 Bianchi road that I had as a spare frame. Thus, one night after work I learned that "the Mouse" has slightly longer chainstays than "Mama Bee" does when I jammed the drivetrain irrevocably.
All I had to do was loosen the wheel, shift it further forward in the dropout, and manually move the chain to a smaller cog -- though the dumpstered Tiagra derailleur never worked the same since.
One of my favorite things about working on bikes is learning all the little secrets.