anyone have a trick to get chain length right the first time?
 

I am just about to install a new Sram 11 speed chain. My usual method is to guess the length ,assemble it, realize it is too long, cut, test, cut again, etc. Any other way?

Have a chain on already?

Remove it. Lay it across your garage floor...lay new chain next to it...measure twice. Break new chain once.

Alternatively, you can hang chains by their open link with a string off a shop shelf, to keep them and your floor clean.

Some options. I do big/big +2

Javascript Bicycle Chain Length Calculator

Park Tool Co. » ParkTool Blog » Chain Length Sizing

Brand new build , New Sram Force group, 11 sp, The rigorous equation is a bit more than I would like, there must be a Gump way to do it.

I just noticed spoons reply "big,big plus two"

Sounds like a good start.

1. Google "chain length"
2. Pick one.

Using the old chain as a length gauge assumes the old chain is the correct length. Maybe it is and maybe not.

The safest way is to wrap the chain around the largest cog and the largest chainring without threading it through the rear derailleur. Overlap the ends and add two "half links" (1") and cut it at that point. Just be sure the ends are cut to mate, two male ends if using a master link, one male and one female if using a joining pin. Round off upward in case you need to add a 1/2 link to get a match

That technique gives the shortest chain that assures you can shift into big-big, which is essential for safety. Remember, if you later add a larger big cog or larger chainring, you will have to resize.

this is the easiest way:

shift to the smallest ring in the front, and smallest ring in the back. the correct length chain is the longest chain that will have tension in that gearing combo. unless you have a 32 cog in the back and a small cage rear derailleur, the big gears won't be an issue. It will just tax the derailleur spring more if you choose 53/28 (or whatever the biggest cog in the back is). you should never be in that gearing anyway. nor should you be in the 39/11 (small small).

I thread it through the rear derailleur, and size it for big-big. No guess work, and gauranteed to work in big big.

I use Big/Big +1 and have never had a problem.

There are so many easy ways of doing this, that I can't see it being hard.

The real question is whether you want the minimum length chain, big/big + 1" (Sram method)
or the maximum length chain, small small, and the RD just beginning to rake up slack (Campagnolo method)
or something in between, (Shimano method).

Whichever you prefer, thread the chain accordingly, pull it up, cut and splice. (for Sram method, if measured without threading in the RD, you have to thread it before splicing)

BTW - I prefer leaving the chain as long as possible, or at least close. This allows changing to a larger cassette without worry. Handy for race bikes where people may use a donated wheel in a pinch.

It's the small small combo that is the limiter in chain length, not the big big. It's the Campagnolo method in @FBinNY 's post. You want the chain to be just long enough that when in the small small, the rear derailleur still puts tension on the chain. If the chain is too long, you'll have slack here, which is no good. If it's too short (look through some of the Hot R Not pics!), your rear derailleur will be stretched to the max. probably also no good.

Even though I use the small/small method to get the longest chain, we have to keep in mind a major difference between this and the more popular big/big method.

The shortest chain is an absolute minimum with no fudge room down. use a chain that's too short and you can kiss your drive train goodby one day. OTOH there is fudge room with maximum length. The chain will sag like a possum belly in small/small combinations, but it's of little consequence since you rarely, if ever ride these combinations, and no harm will come if you accidentally shift into one.

On bikes with RD capacity in excess of what the gear combination needs, it's of little consequence since either method, or one in between work fine. But on wide gear range touring bikes mechanics often get situations where the long method produces a chain shorter than the short method, and that's where they have to stop and check.

This doesn't help, but the manual for my derailleur says something different than mentioned above. They say put the bike in the big/small combination (big chainring/small cog) the "right" chain length will result in a straight line perpendicular to the ground through both pulleys and the skewer. Sure, that doesn't help you decide how long to make the chain, but it helps you quickly decide if the chain is too short or too long!

http://www.shimano.com/media/techdoc...9830606897.PDF

Bring more than one powerlink to the sizing party and don't tell your friends if you screwed up. Haha

Yes, that's what I called the Shimano (or baby bear) method, and it yields a chain between the longest and shortest IF the RD capacity is adequate.

Small chainring, small cog, run through your derailleur and size it so you can run two fingers between the cage and the chain.

This.

BIB BIG, but a tool like this really helpshttp://www.bikemanforu.com/product_i...65726_zoom.jpg

Fancy ... I just bend up an old spoke to do that.

Me too but I used a length of coat-hanger wire. Both work at no cost.

I like big-big + 2" or so and then put it in the small small through the derailleurs and see if it touches between derailleur pulley and chain on small cog. If it does, I take a link at a time off until it doesn't. If it doesn't touch, it's good. Using KMC chains with their master link makes it easy to make changes.

I am not clear on this.
Can you elaborate?
TIA.

I suspect that he's talking about when the cage rotates so far that the chain is sort of doubled on itself with the lower pulley so high in back that the lower loop touches the chain winding around the upper pulley.

I disagree VERY STRONGLY with his approach, because if he's starting with big/big +2", he has only one inch to remove before hitting the ABSOLUTE minimum length. If a 2nd inch is removed to improve the small/small situation the chain will be too short, and accidentally shifting to the big/big combination will either bend the axle, tear off the derailleur, bend or collapse a chainring, or some combination of the above. (chains are much stronger than the rest of the DT components). (see post no.12 above)

I'm not good at explaining.
http://www.parktool.com/uploads/imag...hain-long3.gif
In the above picture which I stole from Park's website on chain sizing, you can see that after the chain leaves the top pulley of the derailleur and it goes to the bottom pulley, it contacts the chain that is wrapped around the small cog of the cassette. When that happens, you know the chain is too long.
So far, I've never had to remove more than would leave me Big/Big+1". I may do more than big/big+2". It's actually more like 3". I'm cheap so I'm leary of cutting off too much, so I was trying to say that I leave it longer than needed and then cut it back until it's no longer too long (checking before each cut that I still have the Big/Big + 1").

Like I've said I'm not good at explaining. I was just trying to say that I prefer leaving it long and then trimming if needed rather than going straight to the minimum provided by big/big+1" and using a master link made that easy. That was in response to the OP who wanted to make sure they got it right in the first cut. I'm not quite as concerned with getting it done immediately as long as I can get it to the right length. I tend to use triples and fairly wide cassettes so I'm often at or near the derailleur capacity, so there's not a whole lot of distance between too long and too short.

I've had my tool so long I have no idea where I got it and I can't find a photo of it on the web. It's pretty handy though, and I keep it next to my other chain tools so it's always right there. It looks like it might've been made from a spoke, but it's coiled a couple times in the middle to get the spring effect instead of that donut looking thing on the one I posted a photo of. Took me a long time to find that photo too - it doesn't seem to have a universal tool name - some places called it a "chain hook" though.

Edit - here it is... possibly made by Minoura.

http://www.cheapbikeparts360.com/images/b/7848.jpg