Bicycle Mechanics - How tight should a chain be??

Yesterday I was out riding, and I started off quickly, I heard a pop, I think it was because my bike wasn't in gear properly, but I was wondering how tight should a chain be? I hold the chain by the sides and I can move it up and down.

This is not so straightforward, Crazy C. especially now that triple c'rings and ten cog clusters are common. Here's a routine I use: Put the chain on the largest c'ring and the largest rear cog you are ever likely to use. (probably not the biggest cog on the cluster, please note) The power-train should turn relatively easily and the rear deraileur pulleys should have some room for more flex. Now, the more important part is this: put the chain on the smallest c'ring and the smallest cog you are ever likely to use. (again, probably not the smallest cog on the cluster) Look at the bottom run of the chain as it enters the jockey pulleys on the rear deraileur. There should be 3 to 5 mm of clearance between the bottom run of the chain and the chain right above it as it snakes through the jockey pulleys. More than 5mm and the chain is probably going to be too tight at the other extreme. (big ring - big sprocket) Less than 3mm, or even worse the chain rubs, and you need to shorten the chain.

I wish I could send you a picture of what I'm trying to say. Anyway, hope this helps. Ride on!:)

See
http://www.parktool.com/repair_help/FAQchainlength.shtml

Originally posted by Crazy Cyclist
Yesterday I was out riding, and I started off quickly, I heard a pop, I think it was because my bike wasn't in gear properly, but I was wondering how tight should a chain be? I hold the chain by the sides and I can move it up and down.

Depends on what you're riding....

- single speed / fixed gear / multi-speed hub: a little bit of play (1/4 - 1/2") up and down.

- a bike with a rear derailleur / multiple front chain rings: The chain should be long enough to wrap around your largest chainring (e.g., 53t road or 44t MTB front ring) and largest cog (e.g., 25t road or 34t MTB cog at the top of your cassette). The chain should be running is what almost looks like a straight line from the bottom of the rear cog through the pulleys and down to the bottom of the chain ring with a 1/4" - 1/2" of play.

I concur with everyone else, but note that you may have to compromise chain length a bit for some combinations of derailleurs and gear sizes. Avoiding cross-chaining will simplify your life considerably, but a chain should generally be just long enough to shift into the large-large combination, in case you go there accidentally.

I agree with John E - I often like to start off from traffic lights a 39/19 or 39/17 combo, and will sometimes will forget to change the Front DR to low before I stop. Also on the odd occasion I have forgotten to change the front DR on a hill climb - i was half way up thinking I was in 39/25 but I was in 52/25 - therefore to avoid damage in these situations you need enough chain length to accomodate.

Brendon
:beer:

Having a too-short chain can be VERY inconvenient. A couple of years ago I stuck on a cassette with larger cogs than my usual one. It didn't occur to me to check the chain length. Although I avoid cross-chaining I occasionally do it momentarily. A rear shift is just quicker and cleaner than a front shift so if I just need a slightly lower gear for just a second I will go to the big/big combination rather than go to the small ring, downshift 3-4 cogs in back then have to reverse it almost immediately. When I did this after putting on the larger cogs the drive train locked up! The chain shifted up to the large cog without a hitch, but it was so tight the wheel wouldn't even turn. It was also too tight to shift back to a smaller cog. I had to stop, loosen the wheel, move the chain, then put the wheel back on. And, the quick release is not so quick when there is that much tension on the chain. It was VERY difficult to get open. I may have even had to pry it with something. By that time I was so aggrevated I didn't care if it broke.

The way I measure chain length is the length of the chain wrapped around the largest chainring and the largest cog, then lace it through the derraileur.