Determining New Chain Length

[Splash]

Best way to determine number of chain links when fitted to a new rear cassette and chain ring setup?


Splash

[Joachim]

http://forums.thepaceline.net/showthread.php?t=169332&highlight=chain+length


http://forums.thepaceline.net/showthread.php?t=166356&highlight=chain+length

[katematt]

This will be correctedby someone more technical here, but I route the chain through and have the D'rs on the smallest back and front. Then based on that gear, I determine how many links need to be removed for the Rear D'r to have a little tension on it so it tightens the chain. usually about 4 links.

Hasn't let me down yet and those times when I cross the chain big to big by accident the rear d'r is not too stretched.

[rePhil]

Park tool video: https://www.youtube.com/watch?v=LC8_ndnXJUY

[Tony T]

I use the Park calculation method, and for me it's the same as big-big

[Ralph]

You could just lay in down lengthwise along side the old one. If you are going to a much larger cassette, you could just make it two links longer.

If not above.....just install chain little to little, being generous with links. Check big to big. If too long after that, take more links out. Better than getting it too short to begin with. It's simple to take extra links out, usually have to use another additional quick link to put them in if I get it too short to begin with (or want to use that chain on a set up that requires more links).

[Vinci]

I used to go by what would be needed to accomodate the big/big combo, but now I use the small/small combo and make the chain as long as it can be without losing tension in that combo. That gives a little more room to move to a larger cassette later on at the cost of carrying an extra link or two.

[MagicHour]

If Shimano I use specs from dealer manual (28T or greater method). Works for me.

[Mark McM]

There are two commonly suggested methods to select the length of the chain, often called "big-big" and "small-small" (you can find explanations of each elsewhere). While both methods can give usable results, I will go on the record as saying that small-small is the actually the correct method, and that big-big could be described as wrong. Here's why:

The rear derailleur has a pulley cage that takes up chain slack, so there is actually a range of chain lengths that can give workable results. The two chain methods actually find the limits of usable chain length - the big-big method produces the shortest usable length, and the small-small method produces the longest usable length. While anything between these two will work, there are several reasons why the longer chain is actually the best.

1) It gives more possibility for changing cassette/chainring sizes. Cassettes can range widely in size, but most of that variation is on the large end - the variation in the smallest sprocket size is only a few teeth (typically only 11, 12 or 13 teeth), whereas the variation in the largest sprocket size can be quite a bit larger (can range from 21 to 34 or more teeth). This means that it is far more likely that a cassette size change will require a longer chain than for it to require a smaller chain. This can be important if one change wheels/cassettes frequently. In the odd cases that a shorter chain length is required, it is easy to simply remove a few links; conversely, you can not add links to a used chain, because the new & old links will have different amounts of wear, and can result in drivetrain vibrations.

2) Chains do occasionally break in use. A broken chain can be fixed on the road by removing the damaged link(s) and re-joining the (now shorter) chain with a removable chain link. If the chain already has a few extra links in it, then removing a few links won't affect operation. But if the chain is sized to be as short as possible, than removing broken links may result in a chain that is too short to be fully usable.

3) A longer chain will wear more slowly. Chain wear will be proportional to how frequently the links are loaded/unloaded as they rotate through the drivetrain. For the same gear ratio & cadence, each link on a longer chain will cycle through the drivetrain less frequently than the links on a short chain, and so wear more slowly. Since cassette wear is accelerated by using a worn chain, the longer chain will also improve cassette life.

4) A longer chain will result in lower energy loss in the drivetrain. Energy is lost as the chain articulates through the pulley cage. The higher the tension on the chain as it articulates, the higher the losses. A longer chain will extend the pulley cage less, reducing the spring force, and thus the chain tension on the lower run of chain and pulleys. The resultant energy saved may be only a fraction of a percent, but over the life of the chain it could represent a substantial amount.



Is the longest possible chain always best? Not always. There are a few situations where a slightly shorter chain may be better:

1) If the B-tension adjustment is not sufficient to keep the jockey (upper) pulley away holding the chain directly against the big sprocket. In these cases, removing a few links of the chain may be necessary to open up the chain gap (distance between sprocket and pulley).

2) If the bike is to ridden over very rough terrain, it may be better to have more derailleur cage spring tension to keep the chain from slapping. On very rough terrain the chain can bounce around so much as to slap against the chainstays, and in some cases it may even bounce off the chainrings. In these case have a little extra derailleur cage tension may help keep the chain in place.