Bicycle Mechanics - Adding links to a chain

I know this has been discussed but I couldn't find the answer in a search. I just bought a bike from my LBS. I asked about swapping the 12-25 cassette to an 11-28 (it's a Dura-Ace bike). They said they could do that but a quick check showed they didn't have an 11-28 in stock, so there would be an up-charge for pulling it off an existing bike. I told them no, I could buy one and take care of it myself.

I bought the cassette and can swap it, but I forgot about chain length. The chain is a KMC X10SL. I don't have any Missing Links yet, so I have two questions.

1. Is there a way to test if the chain is long enough without breaking the chain? I know the big/big +2 method but can I test it with the derailluer on? I saw one suggestion of slowly shifting it in the big chainring and stepping back to the bigger cogs. But with indexed shifting I don't see that working, you don't know until it's too late.

2. When I buy a new chain and have to shorten it I keep the extra links in case I have to lengthen it later. In this case, however, I don't have the links. If I have to lengthen it can I just install 2-3 KMC Missing Links in a row? Or do I go to the shop and see if I can bum a section of KMC 10 speed chain?

If the chain length was set with the little/little method, to the longest length it could be without hanging loose or rubbing on the RD cage, then the length should be good. If it was set with the big/big method, it might be 1 inch shorter.

Shift the bike into the big/big with the 25T and see how much movement remains in the RD cage. If it's stretched out so much that there's almost no movement left, then it won't work with the 28T and you need to add 1 inch of chain. If it's really too short it should not even shift into the 28T. If you try to make the shift with the bike on the workstand, it should try to climb over the cog, but stop before any damage is done. Drivetrain damage is only likely if you're riding the bike and try this shift under load, without doing the workstand test first.

Adding 1 inch of chain with replacment pins isn't a great idea. More missing links won't do the job alone, since you need one more inner link, too.

This is a great example of why the little/little method is what I prefer.

If the chain length was set with the little/little method, to the longest length it could be without hanging loose or rubbing on the RD cage, then the length should be good. If it was set with the big/big method, it might be 1 inch shorter.

Shift the bike into the big/big with the 25T and see how much movement remains in the RD cage. If it's stretched out so much that there's almost no movement left, then it won't work with the 28T and you need to add 1 inch of chain. If it's really too short it should not even shift into the 28T. If you try to make the shift with the bike on the workstand, it should try to climb over the cog, but stop before any damage is done. Drivetrain damage is only likely if you're riding the bike and try this shift under load, without doing the workstand test first.

Adding 1 inch of chain with replacment pins isn't a great idea. More missing links won't do the job alone, since you need one more inner link, too.

This is a great example of why the little/little method is what I prefer.

So if it's too short I pretty much just need to buy a new chain, right?

So if it's too short I pretty much just need to buy a new chain, right?

That's the best thing to do, but save the chain for future use. If you always set the chain length for the 28T cog, you can use any other road cassette and have no problems.

1. Yes. See Park Tool's article on sizing a chain: http://www.parktool.com/repair/readhowto.asp?id=26. The sections "Chain Sizing-Existing Chain Method " describes how to tell if an installed chain is sized properly.

If you get a length of the same kind of chain, you can add more with A) chain tool, B more connecting links..

My , Old Long chainstay Stumpjumper, always needs a couple more links than a new chain has ,
so I get a few from the spare bits from the bin at the bike shop, they save them from installations that don't
require the whole length.

If you get a length of the same kind of chain, you can add more with A) chain tool, B more connecting links..

My , Old Long chainstay Stumpjumper, always needs a couple more links than a new chain has ,
so I get a few from the spare bits from the bin at the bike shop, they save them from installations that don't
require the whole length.

Awesome, I was wondering about that. Seems like I'd have to attach two Missing Links but I imagine that's not that big of a deal.