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I need to replace the chain and cassette on my bike soon but I don't know what teeth to count.

The Shimano Ultegra 6800 11 Speed Road Cassette - has 11 gears on the back so I know to go for the 11- bit but I don't know the second part -

e.g 11-23t 11-25t 11-28t 11-32t

I think its 25 but what am I meant to count ?

https://www.dropbox.com/home/Photos?preview=DSC_0115.JPG

enter image description here

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    No offense, but I'd check that you have 11 gears on the back first. You need to match the number of cogs to the shifters (and most people who own Ultegra level stuff, or 11 speed groups these days wouldn't have this question). – Batman Feb 1 '16 at 16:23
  • thanks batman, yes i saw 11 starting out but didn't know the other part, i counted 25 – Aindriu Feb 1 '16 at 21:20
  • @Mσᶎ The lock ring on the cassette say CS-6800 11 speed only, so it's definitely an 11 speed cassette. – Kibbee Feb 1 '16 at 21:41
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    your cassette doesn't look that worn, though – Nhân Lê Feb 2 '16 at 11:01
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The first is then number of teeth on the smallest and the second is the number of teeth on the largest cog.

If you like the current gearing then stay with that. Or you can adjust. If you stay with the same then match the number of chain links.

The count is also typically also stamped on the cogs. On the bike and dirty it is typically easier to just count them. cassette

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Take the one with 11-28 for instance. It will have 11 teeth on the smallest ring of the cassette, and 28 teeth on the largest ring of the cassette. The 11 speed cassettes will have 11 diffferent cogs on the the cassette. Look at the cassette you have already. Count how many teeth are on the smallest and largest cogs of the cassette. The most popular is probably 11-28 for 11 speed cassettes. Make sure you count the number of cogs as well to ensure you are getting the correct cassette. Also, I think there are some compatibility problems between 11 speed some manufacturers. If your bike currently has Shimano parts, you should probably stick with Shimano parts.

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