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My commuter bike (a cheap-ish MTB) is in need of new gears. As I never use the "granny chainring", I was thinking about switching to a 2-piece crankset, to save tome weight. However, I am unable to locate such parts in my favorite on-line bike shop.

Are 2-chainring cranksets direct replacement to a 3-piece ones? Are they affordable or are already some sort of exotic expensive equipment?

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In theory this change is possible (if you can find the correct parts) but you'd have to think about your shifter as well. –  PeteH Jul 24 '13 at 12:16
    
The weight savings would be microscopic. You can, if you wish, remove the granny ring and maybe then adjust the derailer limit screw to handle only two rings. But the screw may not have enough adjustment range for that. –  Daniel R Hicks Jul 24 '13 at 15:49
    
(But most cranksets are fairly standard and not at all "exotic", until you get into things like external bearings.) –  Daniel R Hicks Jul 24 '13 at 15:51
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1 Answer

up vote 3 down vote accepted

On MTB you don't get such thing as 2-chainring cranksets. Cranksets come in parts: cranks, bottom bracket and chainrings.

If you are buying crankset separately, chainrings are not included. This is to provide a better flexibility in chainring selection: different materials, shapes and tooth numbers. On cheap cranksets you can not separate chainrings, and in this case you'll need to replace the whole assembly. So one of your options would be to check if your crankset allows to remove the granny ring. If you have chainring bolts there, you are in luck: take the granny ring off and adjust the front mech.

If your chainrings are moulded into the crankset, you'll have to replace the crankset, and that might be not a simple business. In this case it's quite likely that you have square taper bottom bracket and these days it is not easy to find a descent crankset for square taper. So you'll have to replace the bottom bracket as well... and this can be a world of cash spent just for removing a granny ring. Not really worth it, unless you want a better quality/lighter cranks.

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x2. Any more, the low end "cheapish" MTB/commuter bikes are almost throwaway, it costs almost as much for some of the parts as it does for a whole new ride. –  JohnP Jul 24 '13 at 16:26
    
Hes got "a cheap-ish MTB" with worn out gears, there are heaps of square taper choices that would be more than suitable for that bike. –  mattnz Jul 25 '13 at 1:49
    
My hardtail runs 2x10, Sram –  PeteH Jul 29 '13 at 7:17
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