OldCoals

My chain snapped and I have orserd a replacement

I picked up the old chain from the road.

The new chain has arrived but it is longer than the old one but I can be sure part of the old one isn't missing.
The is the replacement chain I have ordered.

Shimano XTR CN-M9100 XTR chain, with quick link, 12-speed, 126L, SIL-TEC

Do I need tonremove a few links and adjust the length or is it just that part of the old chain is missing?

alcjphil

New chains have to be cut to the correct length

terrymorse 

Size you new chain to the bike, not the old chain. Yes, you will need to remove some links.

See: Shimano - Checking the Chain length

Koyote

It's almost impossible to believe that your chain broke in TWO spots, and even more difficult to believe that you would not have seen a second length of chain on the road after this happened. In other words, just lay the old chain out on your garage floor, lay the new one next to it, and cut the new one down to the same size. (That assumes your bike shifted properly before the old chain broke.)

Otherwise, there is plenty of info on the web about sizing chains properly. Simply follow one of the tutorials.

Troul 

Probably a 116L stock.
measure old & depin the new to match.

bblair

Yea, lots of info out there. Some You Tube tutorials too.

But a more interesting question: How did you get home after your chain broke?

DaveSSS 

Use the chain length formula. I tried one online calculator and it was wrong. For my 46/30 crank, 10-36 cassette and 415mm chain stays : 46+36= 82. 82/4=20.5. 415/25.4=16.34. 16.34x2=32.68. 20.5+32.68+1 = 54.18

I would use a 55 inch chain because the total is over 54. The online calculator said 54 was OK and 53 was shortest possible - wrong.

Never count links. Measure the length between pin holes center to center, then add the half inch for the quick link. My chains measure 54-1/2, plus the quick link.

choddo

Well, that is certainly accurate but I always count links. Hasn’t let me down yet.

DaveSSS 

I have a rigid tape measure with a fixed pin at one end layed out on a work bench. Place one end over the pin and read the length at the other. Quick and absolutely full-proof. It's aldo the perfect tool to measure chain elongation.

Dave Mayer

Never assume the old chain on any bike is the correct length. At our shop, if we had done this, there would have been untold catastrophes where rear derailleurs get torn off of the frame.

Wrap the new chain on the big chainring and the biggest cassette cog without going through the derailleurs. It has to be long enough to cover this combination, plus one inch (2 links) minimum. Some home hobby customers come in with triple cranksets and a retrofitted pie-plate rear cassette, resulting in no chain that will fit. The chain is too long in the small cogs, and it drags on the ground. The chain is too short in the big cogs, and they protest that: "I never use this gear combination". But inevitably they will, leading potentially to hundreds of dollars of damage.

BTW: Dura-Ace and XTR chains are massively counterfeited; assume every one of these you buy online overseas at a discount is a substandard fake. Buyer beware.

ScottCommutes

Hopefully, you ordered the correct chain.

Might be a good idea to buy another chain - they don't last forever

Replacing your own chain is easy. If your old chain worked fine, shorter your new chain to the exact same number of links.

It might be a good idea to carry at least a new quick link and chain tools with you when you ride. Sometimes a carry a new chain already cut to length.

JohnDThompson 

It's unlikely bordering on inconceivable that your chain broke in two places simultaneously; trim the new chain to match the old one.

bblair

I did this last time and it was perfect.

However, I am running a pretty conventional compact 50-34 and 11-32 cassette. I never use the 11, but the 32 gets plenty of use.

Dave Mayer

At our high-volume big-city bike Co-op, we never assume any of the following:

• That the contents of a box matches the description on the box,
• That any replacement part that a customer brings in will fit as described,
• That the labelling on the parts bin is correct,
• That anything inventoried is sized correctly, such as spokes. Always remeasure - twice, and
• That the previous chain was sized correctly. About a third of the time, the customers previous chain is just plain wrong which includes length and the number of 'speeds'.

Not paranoid, just practical.

Yan 

Speaking of chain length determination and snapping derailleurs off the frame, where is that fool from the other recent thread who insisted that chains should be sized by placing it on the small chainring + small cog? You should post that idiocy here again so we can all take a dump on you a second time.

I think his username name was kcjc.