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I've got a Boardman Road Sport which I use for commuting and doing reasonable length rides during the week etc. I have Shimano Claris as my rear derailleur and so is some of my groupset. I would like to upgrade my cassette to an either 9 or 10 speed to give me a greater variety of gears. To do this do I need to change my rear derailleur from 8 speed to Shimano 105 or something similar? Or can I just change my cassette? Do I also need to change my shifters as well?

  • I thought this was asking about a replacement cassette with a larger diameter, ie lower gearing. So I edited that into the title. If its not right please use revert, or used edit to clarify further. – Criggie Jul 12 '16 at 20:49
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If you want to change your cassette to something with more gears, then you will need to replace the rear shifter and possibly the rear derailleur. A cheaper option would be to get a wider range cassette which still has 8 gears. You'll have bigger jumps between the gears, but you'll have a bigger range of gears. With a wider range cassette, you may need a new rear derailleur with a longer cage.

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    Seconded: Most modern "road" bikes have a ridiculous amount of gears for a range which isn't actually all that wide: Even a good old 10-speed can have a similar range to that of many modern 20-22-speeds. – errantlinguist Jul 13 '16 at 21:28
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You can upgrade to as much as 1 speed up from what you have, as long as the rear derailler supports it. To see what your derailler supports, you could have a look at velobase and search after your derailler model. For extra speeds, usually, the most important part is the rear derailler. It does all of the heavy lifting when changing gears. That means that if your derailler's max stretch is not able to encompass the extra cog, you won't be able to shift to that gear and you'll have a dead cog. Also, the length of the shifting cable will possibly need to be changed too.

  • It would be more useful to include a link to "velobase", assuming it's online. I would have thought how much cable the shifter pulls would also be important - perhaps you could also explain why it's not? – Móż Jul 29 '16 at 1:00
  • First off, what's with the attitude? Secondly, google velobase, I'm sure it will pop up. Thirdly, looks like i was off, velobase is for vintage gear, at least as much as i saw. Lastly, I never mentioned cable was not important. In fact, reading through my comment reveals that right on the last sentence. Too bad you didn't bother reading. – lorddarq Jul 30 '16 at 16:38
  • Requesting a link is perfectly reasonable: it makes much more sense for you to spend ten seconds editing your post than to have everybody who reads your post spend ten seconds finding the website you're talking about. And the issue isn't the length of the cable but, rather, the amount of cable movement that the derailleur translates into shifting one cog. The cable itself isn't an issue (you don't buy "ten-speed gear cables" or "eleven-speed gear cables"; heck, you don't even buy front or rear -- you just buy a gear cable). The big issue is the indexed shifter. – David Richerby Jul 9 at 8:34

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