I am almost buying a bike equipped with a Shimano Claris group, and I am particularly fond of big hills. So I found lying around my place a new cassette HG41, 11-34 teeth, which is allegedly for MTB. Will the big cog adapt ok with the short road derraileur? Both are 8 speed.

I know Shimano has some compatibility charts around, but I couldn't really figure it out by myself. Maybe something related to too much caffeine right now.

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    You need the derailleur to have enough capacity and maximum cog size. You can look for a code (SS,GS,SGS) on the derailleur and find the model to see the cage type (short, medium, long) and look up these things. However, with 8 speed its not really too much of a problem since you can always throw on a Shimano 8 speed mountain derailleur for ~20 USD (e.g. from the Acera line). – Batman Mar 18 '17 at 15:28
  • @batman that's an answer, not a comment. – ojs Mar 18 '17 at 15:48
  • If it is a short road derailleur then it probably will not take 11-34. If you look up the derailleur on the Shimano site it will list the capacity. – paparazzo Mar 18 '17 at 16:05
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    well, I found it and it says 32t. but being just 2 teeth bigger, I wonder how hard it would be to make it work, or what would be the dangers... – Emílio Dolgener Cantú Mar 18 '17 at 20:54
  • There is no danger. It works or not. You give up on the cassette or acquire a long cage derailleur. You might be able to just not use 30+ when you are on the large front chainring. – paparazzo Mar 19 '17 at 2:29

In short: Yes.

I bought said bike, and tried the new cassete. It works on both big and small front rings, but the derailleur arm gets very very stretched on the big one. My opinion on this is that the 32 teeth maximum limit has a bit of a safety margin, so if in the next 100 km something bad happens, I'll update the answer. Otherwise, problem solved.

And I will try to avoid using that low gear, unless necessary.

Also, here is the resulting derailleur position on the worst possible scenario, which I avoid: enter image description here

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  • You should avoid big-big gearing. It puts incredible stress on your derailleur. Always shift to the smaller front chainring before moving up to the largest rear sprocket – RoboKaren Jun 6 '17 at 20:31
  • @RoboKaren of course. I only wanted to highlight the worst case scenario in the picture. In the small chainring everything works fine, even if 34t is above the limit stipulated by shimano. – Emílio Dolgener Cantú Jun 6 '17 at 20:43

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