brucem76 Posted December 5, 2017 Share Looking to get the right derailleur for my 2x10 bike, which currently has 11-42 at back, and 24-38 at front. I see derailleurs that say: max 42t cog, 41 tooth capacity, and max 10 tooth difference on chainring. I get the first 2 specs - but why a max difference on the chainrings? Also, can anyone recommend any Shimano derailleurs for this job? Sent from my Redmi Note 3 using Tapatalk Link to comment Share on other sites More sharing options...
PeterF Posted December 6, 2017 Share Just get an XT long cage rear derailleur and you will be fine. Sepia 1 Link to comment Share on other sites More sharing options...
Edition 507 Posted December 6, 2017 Share If you in the small ring and the smallest cog at the back then it will scrape the big ring if the difference between the two rings is too big. It is not a problem if you don't mind losing out on a gear or two, and besides, it is not recommended that you use your gears in the extreme opposites of the chain rings and cogs, so don’t worry about it. brucem76 1 Link to comment Share on other sites More sharing options...
brucem76 Posted December 6, 2017 Share Just get an XT long cage rear derailleur and you will be fine. All the long cage ones seem to say that the max cog size at the back is 36T? From what I've seen, the long cage can handle a bigger range on front chainrings, but a smaller large back cog? Sepia 1 Link to comment Share on other sites More sharing options...
Fat Boab Posted December 6, 2017 Share Have you tried Google? "why do rear derailleurs have a max chainwheel difference" http://forums.roadbikereview.com/components-wrenching/maximum-front-difference-value-rear-derailleurs-68895.html Link to comment Share on other sites More sharing options...
brucem76 Posted December 6, 2017 Share Have you tried Google? "why do rear derailleurs have a max chainwheel difference" http://forums.roadbikereview.com/components-wrenching/maximum-front-difference-value-rear-derailleurs-68895.htmlThat would be great, except that the link you sent me has sharply disagreeing opinions on the matter. I posted here because others would have tried similar things and would have advice based on experience ... Sent from my Redmi Note 3 using Tapatalk Link to comment Share on other sites More sharing options...
PeterF Posted December 6, 2017 Share All the long cage ones seem to say that the max cog size at the back is 36T? From what I've seen, the long cage can handle a bigger range on front chainrings, but a smaller large back cog?To my knowledge Shimano do not make a 10 speed cassette with more than 36 teeth, hence their rear derailleurs are not designed for a 42 tooth cassette. But for your chainring and cassette combination imho the XT long cage will work best. Link to comment Share on other sites More sharing options...
Odinson Posted December 6, 2017 Share To my knowledge Shimano do not make a 10 speed cassette with more than 36 teeth, hence their rear derailleurs are not designed for a 42 tooth cassette. But for your chainring and cassette combination imho the XT long cage will work best. Au contraire... Shimano CS-HG500-10 Cassette 10-speed - 11-42 Teeth Link to comment Share on other sites More sharing options...
Mr lee Posted December 6, 2017 Share To my knowledge Shimano do not make a 10 speed cassette with more than 36 teeth, hence their rear derailleurs are not designed for a 42 tooth cassette. But for your chainring and cassette combination imho the XT long cage will work best. The new Deore M6000 is 11-42 10 speed! I just compared the differences of the new Deore medium and long cages as well as the SLX M7000 and XT M8000 and I am even more confused than ever as they all differ.... Anyway this is how the new M6000 Deore are specced! Medium cage length: Largest sprocket:42Smallest sprocket:11Max difference in chain ring:10 Long cage length: Largest sprocket:36Smallest sprocket:11Max difference in chain ring:22 EDIT: My bad!!! Can't use M8000 and M7000 as they are 11 speed but there are similarites. There is even a difference between the medium SLX and XT by a few teeth in overall capcity! Edited December 6, 2017 by Mr lee Link to comment Share on other sites More sharing options...
Mr lee Posted December 6, 2017 Share So besides the cassette sprocket differences the longer cage allows you to have a greater difference in chain ring sizes....but the FD would also have to be able to cater for this differnce to change correctly! Link to comment Share on other sites More sharing options...
Mr lee Posted December 6, 2017 Share OP are you upgrading to 2x10 with the specs you mentioned in your original post? Which RD does it currently have? Link to comment Share on other sites More sharing options...
PeterF Posted December 6, 2017 Share Au contraire... Shimano CS-HG500-10 Cassette 10-speed - 11-42 Teeth Thanks for increasing my knowledge Link to comment Share on other sites More sharing options...
brucem76 Posted December 6, 2017 Share Capture.PNGThis says Max Sprocket: 36T Sent from my Redmi Note 3 using Tapatalk Link to comment Share on other sites More sharing options...
brucem76 Posted December 6, 2017 Share So besides the cassette sprocket differences the longer cage allows you to have a greater difference in chain ring sizes....but the FD would also have to be able to cater for this differnce to change correctly!Yes but the longer cage says Max sprocket 36T. Can't find anything that can handle 42T sprocket and 14 tooth FD difference.... Sent from my Redmi Note 3 using Tapatalk Link to comment Share on other sites More sharing options...
brucem76 Posted December 6, 2017 Share OP are you upgrading to 2x10 with the specs you mentioned in your original post? Which RD does it currently have?I already have 11-42 with 24-38 with a Deore M610 SGS long cage, but shifting is horrible.... Sent from my Redmi Note 3 using Tapatalk Link to comment Share on other sites More sharing options...
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