bikecommuter13

My old chain is more than 0.75 but less than 1 worn using a chain tool. For the new chain length, I cut it to be less than 1 link shorter than the worn one. It seems fine when I test ride it. But I thought the chain is worn more than 1 link; If I were to cut the chain even shorter, I need to cut out two more links, that might be too short right?

Is there a rule of thumb on new chain length vs worn chain length?

maddog34

unless there was a problem with the old chain... Cut the New Chain to the SAME NUMBER of Links.

oldbobcat

No. You don't know how worn the old chain is or if it was sized correctly.

Follow the manufacturer's directions for sizing the chain, usually included with the chain. There are also dozens of youtube videos on chain sizing and installation. And parktool.com.

Chuck M 

This... There is no way anyone could wear a chain more than a link and not have problems.

veganbikes

Assuming everything was done properly the first time and was checked and verified, then yes you would just break the chain to the same number of links. If not or you are simply unsure do as oldbobcat said and follow manufacturers instructions or look at Park Tool or Sheldon Brown 's website.

djb

number thirteen
look up the Park Tools video series, such a wealth of well made vids , well filmed, well lit, clear and concise wording from the cool Park tool dude, look up any questions you have and going over the vids will help you visualize what you are thinking of doing.
The reason its always best to use one of the sizing techniques is IF someone before you has not put the right length of chain on. A chain that is too short can eff up stuff pretty fast if you mistakenly go into the big-big combo, and you can eff up your derailleur etc , meaning mucho dollars.
I prefer the chain sizing method of putting the new chain on the large front chainring, the largest cog of the cassette, and NOT running the chain through the rear derailleur jockey wheels and doing that "add two links" or whatever it is.
The park tool guy mentions it. To me this is the fastest way to get the right chain length, plus it applies to whatever bike you do it on.

HillRider

+1. If the old chain was sized correctly, cut the new chain the same number of links. As to elongation, assuming typical chain of 112 links (yeah, I know it's "half links") for a chain length of 56". If the elongation is 1% it would be .56" or about 1 half link. You can't shorten a chain by a half link.

Iride01 

Why use a rule of thumb when the manufacturer of your rear DR has a procedure for determining the proper length of your chain. Shimano and SRAM at least make their instructions available with a little bit of looking.

Usually it's wrap the chain around the big/big combo without going through the RD and then add 1 or 2 links. But not always. Shimano has some different procedures for some of their products and sometimes it makes a difference if the bike is 3x vs 2x.

But assuming the original chain was sized correctly, you just use the same number of links. They don't grow more links with use. But it's also possible that your bike will shift fine with one less link. It'd probably also shift fine with one link more than the previous chain.

Big thing to look for is that your chain doesn't have the RD stretched to it's limits when in the Big/Big combo. Nor do you want the chain to droop and be slack when in the Small/Small combo.

smd4

Exactly. No guessing required if you just follow the instructions.

maddog34

"They don't grow more links with use."

Perfecto.

FBinNY 

Some basic knowledge and simple math will answer your question.

The typical guideline for chain replacement is when it has "stretched" close to 1% or 1/8" per foot. Since a chain is roughly 4 feet long a worn chain is about 1/2" longer than a new one.

So, to answer your question. Your new chain will be the same as the original if measured side by side and 1 link or so shorter.

This confirms the OP matched the original correctly.

djb

and yes, its the easy way.

FBinNY 

Why should the OP start from scratch. He has a chain which he knows is right because it's been working all along.

So simply matching, after allowing for the 1/2" stretch is the simplest solution.

djb

I figure if there's any -doubt- about chain length with a used bike or whatever, it's just good to know the basic concept of how to be sure, that's all. I've compared old and new chains side by side on newspaper, it works but seems to me faster doing the on bike thing.

Iride01 

Ahh, another way to look at what the OP might have been saying. I assumed they were asking about number of links from the beginning of both chains.

However you seem to be saying they meant just relative from the end of the chains as they lay next to each other.

Good catch and maybe that's what the OP meant.

FBinNY 

The OP tipped me off when he spoke of 1 or 3 links. That could only mean new vs stretched chain.

SkinGriz

I’d make it the same number of links assuming it worked as intended previously.

Polaris OBark

It is 0.75 % elongation, not 0.75 links. The tool has no way of knowing how long your chain is.

rm -rf

I put a micro screwdriver shaft through both the old and new chain end. Lay them side by side on the floor. pull using the screwdriver to align them together.

You'll see that the old chain links are offset from the new chain, but it's easy to see where to cut the new chain to match. If in doubt, realign the two chains about halfway down. My chains tend to be well less than a single 1/2 inch link difference.

!! use a piece of tape or a marker pen to indicate the hole where it will be shortened. No guesswork or second thoughts this way!!

Quick links: the quick link takes the place of one outer plate 1/2 inch link. If both old and new chains use quick links, you'll see the narrow link on both ends. If a pin is pushed out on the old chain, one end has a plate, then other has a narrow link. A quick link for the new chain takes the place of the orphan outside plate link in this case.