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I have an Opus Spark 2 which has a Tiagra cassette 12-28 (10 speed). I would like to change for a 11-34. The cassette exists in, a guess, the same series (http://bike.shimano.com/content/sac-bike/en/home/components11/road/Tiagra4700/cs-hg500-10.html).

Is there something else I should check to be sure it is compatible? Will I have space problem with the derailleur and the jockey wheel?

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You are sort-of correct in the assumption that there is a 11-34 cassette in the Tiagra range means it is compatible with a Tiagra rear derailleur, but it's actually only the long cage (GS) version that will take a cassette of that size.

Shimano has a nice set of pages that detail compatibility within a groupset, here's the Tiagra page.

The Opus web page for the Spark 2 shows it has a Tiagra 4700 series rear derailleur. It's not specified which cage length but the picture clearly shows a long cage (GS) version.

You can also check the RD-4700-GS spec page and see it is compatible with a 11-34 cassette.

You also need to check that the derailleur works with the FSA crank chainring sizes, which are 48-32 assuming you have a size S frame or larger.

  • Maximum front difference is 16 teeth - you are good there

  • Total capacity (the difference between the numbers of teeth on the largest front ring and rear sprocket, and the smallest front ring and rear sprocket) is 39 teeth - you need 39 (34+48-11-32), so again you are good.

If decide to fit the bigger cassette you will need a new chain as the required chain length will be longer (chains should be replaced when cassettes are changes anyway). You will probably also need to adjust the derailleur b-screw which controls how close the upper jockey wheel rides to the cassette sprockets.

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  • Thank you for your detailed answer! When I will buy this cassette, is the model number (CS-HG500-10 11-34) guarantees that the cassette is from the Tiagra 4700 series? I saw a CS-HG500-10 11-34 cassette here: mec.ca/en/product/5051-044/CS-HG500-10-Speed-11-34T-Cassette but the series is not specified. Is there more than one type of CS-HG500-10 11-34? – Vinni Dec 13 '17 at 15:06
  • Yep CS-HG500-10 is the 'Tiagra level' cassette (check the link to the Shimano Tiagra groupset line in my second paragragh). BTW, you don't have to use the Tiagra cassette, any Shimano/SRAM 10 speed cassette will work (except possibly some high end ones), same with chains. – Argenti Apparatus Dec 13 '17 at 16:31

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