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Hello all,

Here's the deal. Right now I have an FSA Gossamer 46/36 crankset on my cross bike. I'm planning on switching to a 50/34 crank. The cassette is 9 speed with a 105 rear and Tiagra front der.

I want to go ahead and replace the chain that's on there. I may need to add 2 links because of the difference in chainrings.

Should I be looking for a 9 speed chain with 2 additional links? What is the difference between a 9 and 10 speed chain?

Thanks,
Erik
 

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When you buy a new chain it will be more than long enough. You will remove links to make it the proper length for your setup. It may be one link longer than what you have, or maybe not.

10-speed chains are narrower, because the cogs on a 10-speed cassette are narrower and closer together.
 

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Did a little more research. The inner width is the same, outer is difinitely different. On 10 speed, a shorter pin changes the overall width. It turns out that at least on Campy, the pulley wheel (cage) width is the same from 9 speed to 11 speed.

But the way that chains drop from on cog/ring drops from one to the requires small changes from one system to another. If I want to put a 10 speed ring on a 9 speed crank, I need a .4 mm spacer. I believe the teeth are actually cut a little off center. Shimano puts a bevel on that is cut off center.

Another example that might happen is that there is more room on the opposite side of the 9 spd fd when used with a 10 speed chain. This would cause less control of an overshift. The chain might skate on the tops of the teeth, possibly even drop.

Short answer is that a 10 speed may work, but be less accurate. Over / undershifts are controlled better with proper chain.
 

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It would be stupid to get a 10 sp chain if you don't need it: they are much more expensive, and generally wear faster. And the thinner chain might drop between the chainrings of an older 9-sp crank.
 

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It would be stupid to get a 10 sp chain if you don't need it: they are much more expensive, and generally wear faster. And the thinner chain might drop between the chainrings of an older 9-sp crank.
Usually, 9 speed chains are cheaper, but often 10 speed chains can be found pretty cheaply on special. Also, they do not wear faster because the length and diameter of the bearing surfaces between the pins and formed surfaces of the inner plates (where wear causes chain elongation) is the same, as are the bushings.
 

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A fascinating discussion, to be sure, but lest the original poster be confused by irrelevancies, all you need to know, partyofone, is that if you have a 9-speed cassette you should get a 9-speed chain.
 

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I actually never knew there was a difference in the thickness of chain. I have a bike that was modified so the front gears were taken off and I believe what is left is a 5 speed bike on the rear gears. for this change should I have swapped the chain for a different one?
I have all kinds of problems with the chain fall off. I ended up taking out a few links until it was much tighter. but if I take any more off it wont switch into the last gear - so I believe the length is just right now. I've tried many things with many different people and everyone always shakes their head in confusion and suggests a front derailer which I'd rather not have to put on.
 
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