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I am planning to upgrade my drivetrain and I'm in the process of selecting the various components. My bike currently has a Shimano Tiagra CS-4600 10 Speed Cassette 12-28t. I am looking to upgrade to a Shimano 105 5700 10 Speed Road Cassette. The 105 doesn't have a 12-28t so I was wondering based on the following options (below) what would be the closest to what I am riding now?

  • 11-25t
  • 11-28t
  • 12-25t
  • 12-27t

I am guessing the two in bold would be the closest options. Here's some additional info if it helps:

  • I currently have a compact 50/34t 110mm crank. Plan to upgrade from FSA to Shimano 105 5750 Compact 10sp Chainset (same ratios).
  • I live in a fairly hilly city (Seattle, WA) and ride mixed terrain hills, flats, gravel (short and long rides). Basically everything but steep mountain passes.
  • The existing 12/28t seems to suit me fine.
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    Why do you want to switch from a Tiagra cassette to a 105 cassette? If you like the tiagra's spacing, just put another one on. You won't notice a difference between them. – Batman Jun 12 '16 at 11:54
  • @Batman - perhaps it's in my head, but 105 and Ultegra cassettes gave noticeably crisper shifts than Tiagra 4600. Plus Tiagra seems to develop surface rust pretty easy when ridden in the rain. (I'm roughly 100 km north of the OP - with similar climate. – Rider_X Jun 12 '16 at 17:59
  • @Rider_X - Weird. I'm curious as to why, given that my non-group shimano cassettes are perfectly fine. – Batman Jun 12 '16 at 19:02
  • Good work putting your hilliness in the question,and how you find getting up those hills. I have a 11-24 and I struggle abysmally on the steep grades, even with a 26 front granny triple. So, if hills are no fun now, do not choose a smaller big-cog! – Criggie Jun 13 '16 at 8:29
  • @Batman I just figured while upgrading to other 105 parts (in addition to the posed question I plan to upgrade both front/rear derailleurs & shifters...essentially group set minus brakes). In regards to the existing cassette it dies suit me, however I have little experience with other spacings so why not give 'em a shot? If it matters this is going a steel frame cx bike that I basically use for a great all-around bike (commuter, gravel, light touring, even done several centuries on it). – OtoNoOto Jun 13 '16 at 9:25
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The problem is the Tiagra 12-28 is kind of special as it has a more gradual transition between ratios and less aggressive gearing all the way to the middle of the cassette, where the 105 and Ultegra cassettes with a similar total range have a less gradual change and drop much more quickly into more aggressive ratios.

We can compare the tooth counts to see this:

                 1   2   3   4   5   6   7   8   9  10
-------------------------------------------------------
Tiagra  12-28:  28  25  23  21  19  17  15  14  13  12  
   105  11-28:  28  24  21  19  17  15  14  13  12  11
   105  12-27:  27  24  21  19  17  16  15  14  13  12

I personally found that 2 tooth difference in gears 3/4/5 to be highly noticeable for casual riding, especially gear 3, as I personally use that with the big ring up false flats.

This seems to be true of all of Shimano's higher end road cassettes. I would hazard a guess that these are viewed as being more "race" oriented, where you need to tackle a couple steep sections then you would drop back quickly back into the standard race gearing on the flats.

The closest match to your current 12-28 is a 12-30:

                 1   2   3   4   5   6   7   8   9  10
-------------------------------------------------------
Tiagra   12-28:  28  25  23  21  19  17  15  14  13  12  
Ultegra  12-30:  30  27  24  21  19  17  15  14  13  12

However I am not clear on the max sprocket of the 5700 derailleur. I have seen it listed as 28T in some documentation, more in other. Perhaps this could be separate SE question.

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    +1: Great answer. As far as Derailleur maximums, MTB'ers commonly pushing the limits. Sometimes a longer B screw is needed to get to a bigger cog (or turn the existing one around). You loose a bit of shift precision - some people notice and care, others notice and don't care, others don't notice. but it usually works acceptably. My guess is moving up from Tiagra it would be acceptable, only way to really know is try. – mattnz Jun 12 '16 at 7:06
  • Thanks for the great answer! However, I have not seen the Shimano 105 5700 10 Speed Cassette sold with a 12-30t option. Based on that do you think the 12-27t ratio would be the second closest option? Thanks! – OtoNoOto Jun 12 '16 at 8:11
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    You may also look for SRAM 10 speed cassettes. They are fully compatible with Shimano. – Carel Jun 12 '16 at 8:39

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