Road rear Derailleur on a MTB



easyrusset

New Member
Aug 12, 2004
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I'm currently trying to max out an old Kona Cro-mo frame for commuting, and wondered whether Road Derailleurs (Ultegra, Dura-ace) are compatible, and would work more efficiently? Do road derailleurs work with MTB shifters?

Has anyone had any experience of these set ups?

I'm running a single 44 at the front, and currently 8sp cassette (altough I only tend to use 3)

Also what are peoples experience of smallest possible slicks to mount on rims? i.e. What is considered a minimum (or maximum) safe width for rims when fitting a 1" or 1.25" slick?
 

endcat

New Member
Feb 5, 2005
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There's no point in changing to a road rear derailleur at all. In fact, unless you are running a closely spaced cogset like on a road bike, then you will create serious shifting problems - a road derailleur is not set up to handle a 32 or 34 tooth cog and has less chain-wrap capacity (ability to take up slack in different gear combos). For comparison, an XT can handle a 34 tooth cog and has a chain-wrap capacity of 45 while an Ultegra can only handle a 27 tooth cog with a chain-wrap capacity of 37.

To get the best of both worlds, swap out the crankset and front derailleur to road bike triple and replace the granny gear with a 24 - This is what I've done with my touring bike and now it has an XT rear derailleur, 11-32 cogset, Ultegra front derailleur, and 52/39/24 front sprockets. Shifts smoooooth and has amazing range. Only drawback is if you try to run the big/big combo it will self-destruct, but then you shouldn't be doing that anyway.
 

endcat

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Feb 5, 2005
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Heck, I guess I didn't read your post that well - if you're running a single front sprocket then a road derailleur would work unless your biggest cog is more than 27 teeth. But again, why bother? A Deore XT works fine. But if you only use 3 gears anyway, you oughtta consider getting a fixed gear or single-speed...:D
 

easyrusset

New Member
Aug 12, 2004
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I'm seriously thinking about the SS option at the mo.

I do have a few hills to negotiate on my way to work though, and although not adversed to getting out the saddle and sweating blood, I'm not sure I'd be happy with a gear to cover those killer hills, to lose the 44x11 burn down the other side. Although the arrival of my geax 26x1.25 tyres, with presta tubes next week, may make me change my mind.
I'm also looking into running a bigger front end 46/48 with a road cassette 11/12-23. Which would suit the road type derailleur, but if you guys reckon I'll gain nothing by switching derailleur it hardly seems worth it.

I know this is going of the thread a bit, but what in your experience is the best all round SS ratio? ie reasonably hill climb vs decent coast and acceleration, I won't be going off road.
 

endcat

New Member
Feb 5, 2005
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Here in the hilly city of San Francisco, it seems like 42x16 is a pretty popular gear amongst the fixed gear crowd. That's what I run on my Surly Steamroller and it works pretty well. I can't climb the steepest hills (they are mega-steep), but on the more moderate grades it just takes getting out of the saddle and cranking. 32x16 is standard mountain single-speed, I run 32x18 on mine -- too much spinning on pavement but perfect off road. On a mountain bike with slicks, you could probably spin a bigger gear than 42x16 since the overall diameter of the wheel will be smaller so in that case 44x16 would probably do it.