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Newbie looking for FC 7800 Crankset guidance

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Newbie looking for FC 7800 Crankset guidance

Old 07-05-18, 12:22 PM
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Newbie looking for FC 7800 Crankset guidance

I'm climbing the learning curve and need a little guidance from anyone that's willing.


I bought a 12 year old Trek with dura ace components and have come to learn that the ten speed, 11-25 cassette and 54-39 chain rings will not get me up the steep hills where I live. So, I'm buying a 11-28 cassette which I think is straight forward but changing the chain rings to 50-34 which is the norm around here has posed some questions that have me puzzled.


My existing set up is FC 7800/7803 , 130mm BCD with 175mm cranks and on the large ring the letters SG X B are visible.


I've read on some site that 50 34T rings in dura ace quality cannot be found in 130mm BCD yet I see some new ones (just the 50 not the 34) on eBay. So, my questions are:


Can 50-34 dura ace chain rings compatible with my crank set be found or must I buy a complete crankset? If not what's the deal with those 50 34, 130 BCD rings being offered?


Does the SG X B label limit me in any way or is the FC 7800 all I need to search?


Am I restricted in my search to just FC 7800 rings or are others suitable.


Thanks and any related observations other than about my ignorance will be appreciated.
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Old 07-05-18, 08:40 PM
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The smallest chainring that will fit a 130mm BCD crank is 38 teeth. Good luck finding one they are almost impossible to find. It is physically impossible to fit a 34 tooth chainring on a 130mm BCD crank
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Old 07-06-18, 07:18 AM
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Originally Posted by prmbrown
Can 50-34 dura ace chain rings compatible with my crank set be found or must I buy a complete crankset? If not what's the deal with those 50 34, 130 BCD rings being offered?

Am I restricted in my search to just FC 7800 rings or are others suitable.
A 50/34 chainring set requires a 110 mm bolt circle and is incompatible with your current crank. Those "50 34 130 BCD rings being offered" are in error and offered by someone who doesn't know better.

You are not restricted to FC 7800 series chainrings but any 130 mm chainring will fit. Shimano does sell their chainrings in matched pairs to properly align the shift enhancements but any similar Ultegra or 105 set will work just as well.
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