chainring question
07-05-11, 10:58 AM
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chainring question
My friend has an old trek 360 and is starting to ride again after many years without. He is riding in much steeper terrain and with much older knees than before. He would like to gear down a bit by using smaller chainrings. Currently they are 52/42. I believe the FD is a Suntour Alpha 4050. The RD is new Shimano Sora short cage. It can handle 14 tooth difference in chain rings.
How small can we go with the front chainrings without getting a new FD?
How small can we go with the front chainrings without getting a new FD?
07-05-11, 11:00 AM
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If the crank has a 130 mm bolt circle, you can go down to a 38T chainring. If it has a 110 mm bolt circle, a 34T ring will fit.
07-05-11, 11:06 AM
#3
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What is the BCD (is the diameter of the bolt holes for the chainrings)? If it is 110mm, the smallest you can go is 46-34 which is a nice and practical combination. There shouldn't be a problem, but you have to lower the front derailleur clamp on the seat tube.
07-05-11, 11:23 AM
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Thank you! What a fast reply! We'll be riding together later in the week and I will measure the BCD then. 46/34 would be great!
07-05-11, 03:12 PM
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Sedges: The BCD is 1.7 times the center-to-center distance between adjacent bolts.
07-05-11, 05:17 PM
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07-06-11, 11:39 AM
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From the picture of the Trek 360 in the 1988 catalogue on the Vintage Trek site, it looks as if the 360 had a Sugino crank with a 130mm BCD. That would limit the small ring to 38 teeth.
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