I ordered a KMCX10SL to replace the SRAM PC1071 on my EVO with 2012 (not newest) Red.

Do I simply count the number of links on the current chain and use a chain tool to remove the extra number of links from the KMC one? Then do the master link/ missing link thing?

I know there are guidelines to how to measure the chain length, but it's the first time I'd do it myself so I'm hoping I can just go with the exact same number of links.

Thanks.

Counting links works, given ONE condtion: the previous chain length was correct Ok, two conditions, you have to know how to count.

I count links on bikes I have made sure chain length is right. Its even easier on the single speed...lol Follow the instructions on chain length setting, to see if the current chain is good, then by all means count links. Count (each chain) twice, break chain ONCE...

Just line both chains up on a newspaper and compare. Make sure you don't over compensate for the master link on the old chain and line up the inner plates / outer plates. Should be easy enough.

+1 to checking the length of the original chain first (break it, then measure it on the big ring/big cog while not passing through any pulleys and you should have 2 extra links)

All this is preparatory for telling you why it is you want to choose your chain length with care. Specifically, you want it to be as long as possible. Don't try to shorten the chain in order to save weight. You specifically want to avoid forcing the rear derailleur to work beyond its limit, and that limit is generally considered to have been reached when the lower pulley is directly below the upper. Best if that lower pulley is never in front of the upper.


Source: https://www.slowtwitch.com/Tech/The_c...chain_444.html

If you want the longest possible chain, use the little/little method and shorten just enough to cause the lower pulley to move forward a bit when the ends of the chain are brought together. With this method, the chain is threaded through the RD and positioned on the smallest cog and smallest chainring.

What the cage looks like in the big/big is irrelevant. If by "directly below", the author at slow twitch means directly below along a vertical line, that's wrong. That's often the description for the position when the you're in the big ring and smallest cog, which is not even close to the maximum extension.

Generally, if you have a chain that you're confident was cut correctly, just count links and go for it. But it's so simple to check if you're not sure. What I would do - before removing the old chain is to take 30 seconds to do two things:

Shift to the small/small combination. The RD derailleur will be angled backwards quite a bit. Make sure that the chain coming out of the derailleur that is returning forward to the crank doesn't interfere/touch the derailleur pulleys. If it interferes, the chain is too long and you should make the new chain a link or two shorter. Sure, you probably wont be using this combo, but it will indeed give you the maximum length that will work. Called the "small small" method.

Carefully shift to the large-large combination. The rear derailleur will be angled forward. Do the last rear shift carefully, watching to make sure that the chain makes at least a little S curve from the cassette sprocket and through the two RD pulleys. It shouldn't make a straight line. You're trying to see that the chain isn't trying to pull the RD pulley cage forward beyond it's ability. (if that makes sense). If you think that's happening (no curve to the chain, putting stress on the RD), the chain is too short and the new chain should be a link or two longer. This is a version of the "big big" test and tells you the minimum length of the chain that is safe to use.

When in doubt, it's better to make the chain a link too long than a link too short. You'll get noise in the small-small combination but (1) you probably won't be using it anyway and (2) it's not going to cause catastrophic damage like a too-short chain could do if you use it with the big-big combo.

Just do those two tests, they take a second, and you'll know if it's good enough to just count links or if you should add or subtract.

Thanks everyone! I'm thinking my current/stock chain is too short, basing on the info all of you are telling me. On the 53x25, the lower pulley is way in front of the upper pulley!

As long as it is not parallel to the ground you are ok. Large to large with a short chain can destroy the rear Der.

dude. lemme tell ya a story:

someone asked me to replace a door on their utility shed attached to a garage. they had a solid core replacement door already.
took off the original door, measured verrrrrrrry carefully to get the length exactly the same (using it as a template); marked and notched the hinge places and it hung perfectly.

one problem: the original door was too short and rubbed across the top of the concrete sill instead of being below it. couldn't believe it. a former owner had done the original wrong and i hadn't caught it.

It's normal for the lower pully to be way in front of the upper pulley wheel when you're on big-big. As long as it makes a definite S curve through the pulleys, it's OK. BUT it sure doesn't hurt to make the chain an inch longer - just test it using the small-small combo after you install it and make sure there's no interference. You can always shorten it again, but it's a pain to lengthen it!

Look at this page for illustrations of what I was trying to describe for big-big and small-small. https://www.parktool.com/blog/repair-...-length-sizing

If you were happy with the shifting performance with the old chain, cut the new one to the same length. Otherwise the tried and true method for cutting the proper chain length is to stretch the chain around the big-big and add an inch (one link). Don't run the chain through the derailleur.

This^^^^. Al

While many people advocate the big/big method, it suggests the shortest possible chain. If you later want to change the cassette to get a larger cog, the chain will be too short. Not so, if you use the little/little method. It provides the maximum wrap capacity. If you're deliberately exceeding the RD's wrap capacity, then the big/big method must be used, but the chain will hang loose in the little ring and perhaps several of the smallest cogs, since 1 inch of chain equal 4T of wrap.


Some people here mention shortening the chain by a link or two, but the minimum increment of change to the length is two links or 1 inch of chain. You can't remove an odd number of 1/2 inch links. A link is only 1/2 inch, since they are sold as having 114 links and the length is 57 inches.

Big-big plus 1" is preferable to small-small unless the user has done their homework wrt RD capacity. Lately, I've figured that since I don't save leftover chain to patch together later, I might as well use as much of it as I can. So, I add any leftover RD capacity to big-big+1", and round up. In the end, it may hang a little slack in the small-small, but I try not to use that combo anyway.

OP; How did you manage to make this sound complicated??

Count? I just hang the two chains side by side.

I always make sure big-big works, not really in love with the idea of killing an RD because I misshifted.

[QUOTE=reddog3;15417271]If you were happy with the shifting performance with the old chain, cut the new one to the same length. QUOTE]

Not the same length, the same number of links. The old chain has stretched.

[QUOTE=Al1943;15421175]Having been around the chain maufacturing industry most of my working life (I'm only 67), when discussing chain length it was always number of links, never a linear measurement. Of course we had to be talking the same pitch. Doesn't matter whether of not it wasn't bike chain. Chain is chain. I thought this was common knowledge. Speaking of stretch- It's unlikely you'd run a chain of say, 114 links, and the stretch would be so bad that it would equal 115 links of new chain. Count the links.

If a bike chain is used to 1% stretch, is will be one full link longer than a new having the same number of links, but if you lay a new chain beside it, the ends that match up would not be the same as the old chain and it couldn't be joined. You can easily see the mismatch increase as you get to the end of the chain. The new chain would be 1/2 inch shorter, but have the same number of links and the ends can be joined. Counting the number of links is never needed.

I wouldn't worry about changing the cassette to a larger one since a new cassette almost always requires a new chain and you would size it to match the new cassette. As you noted, sizing the chain based on little-little requires an adequate rear derailleur wrap capacity and exceeding it, as I often do by changing the OEM 30T granny ring for a 26T, can make the chain too short for safe big-big clearance. I always size for big-big and avoid small-small.

I check big big an as I like as short as chain as possible with a MTB triple. If it checks out just hold the chains up and all is good. I have added links back when moving drivetrains to another bike without any issues.