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I'm primarily a mtn biker, but I was looking to get something to ride on roads. I rode a 2015 Diamondback Interval carbon flatbar road bike - I really liked it and the price was very good. The problem is the gearing, it has 50/34 in front and 11-28 (I think) cassette w/Shamano 105 derailleur in back. I live in western PA, where we have a lot of short, but very steep hills, and I don't think I'm going to get up some of them in that combination. Shamano says 105 is limited to 30T cassette, but Shamano's mtn derailleurs say they are limited to 36T, and people use 40T and 42T with no problem. Does anyone have any experience mating a 105 derailleur to a larger big ring in their cassette (32T, 34T, 36T)?
 

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A lot depends on the specifics of the hanger on your bike. Really no way to say and what someone else has been able to use wouldn't mean you could, or couldn't.
 

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'brifter' is f'ing stupid
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I'm primarily a mtn biker, but I was looking to get something to ride on roads. I rode a 2015 Diamondback Interval carbon flatbar road bike - I really liked it and the price was very good. The problem is the gearing, it has 50/34 in front and 11-28 (I think) cassette w/Shimano 105 derailleur in back. I live in western PA, where we have a lot of short, but very steep hills, and I don't think I'm going to get up some of them in that combination. Shimano says 105 is limited to 30T cassette, but Shimano's mtn derailleurs say they are limited to 36T, and people use 40T and 42T with no problem. Does anyone have any experience mating a 105 derailleur to a larger big cog in their cassette (32T, 34T, 36T)?
The cable pull ratio of the Shimano 10 and 11 speed mountain bike derailleurs is different than the 10 and 11 speed road stuff. You need to use a 9 speed or earlier derailleur if you want to use one w/ road shifters. I'm having a brain fart right now and can't remember if this even works w/ road 11 speed...it does w/ road 10 speed shifters and 8/9 speed mountain bike derailleurs.
Also to clarify terminology, cassettes have cogs and cranks have chainrings. Cogs in back, chainrings in front. And of course is ShImano not ShAmano.
 

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I'm having a brain fart right now and can't remember if this even works w/ road 11 speed...it does w/ road 10 speed shifters and 8/9 speed mountain bike derailleurs.
Nope, only way to put real mtb gearing on an 11sp road setup is with a converter of some type. I Just got back from the Grinduro this weekend where I 'borrowed' my 11sp XT rear end and made it work with a TanPan from Wolftooth/Lindarets on my gravel bike. 46/34 up front with 11-42 out back. It was nice for the event, but will not be a long term thing. Me+bike+gear was approaching 260lbs, and the last 3k feet of climbing was pretty brutal, better than last year, but still rough.
 

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There's a medium cage version of the 5800 rear derailler which easily takes 32T

That is to spec, it may well accept bigger, but you will likely get up nearly any short hill on a light bike with 34 front and 32 rear

New RD and cassette is about GBP 40 here and probably cheaper in USA.
 
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