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Vintage Touring Gearing and Derailleur Recommendation

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Vintage Touring Gearing and Derailleur Recommendation

Old 12-01-23, 09:44 AM
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Originally Posted by cyccommute
Nope. That’s not the right bolt circle diameter. It looks like yours is a 110 but you can measure it by measuring center to center between two adjacent bolts and multiply by 1.70 which will give you the BCD in mm.
Measuring c-t-c and multiplying by 1.7 yields 69.1 x 1.7 = 117.5 mm. Measuring center of the crank to the center of the bolt yields 58.9x2=117.8. While I could break out the gage pins, I’m convinced the BCD is 118, which from feedback here means another smaller chainring is likely unobtanium.

Sakae 118 bcd chainrings 36 & 48

So I live with what I’ve got, find a lower range crankset (possibly combined with new hubs and 11-~28 cassette), or find a triple with a granny.

Thanks for all the inputs! It’s helped me frame the situation at least.
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Old 12-01-23, 12:03 PM
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Originally Posted by cyccommute
4 mph at 90 rpm. Not really an RPM that is “way up there”. At 60 rpm, the speed is just under 3 mph which is still rideable and, on a hill, faster then a walking while pushing a bike. With a 22” gear, you have to work harder to pull up the same hill
Do a direct measurement of your gear inches and then do the math. I don't think it is what you think it is. Gear inches is simply how far you go per revolution, 4 miles is 253,440 inches, divided by your actually measured gear inches tells you how many revolutions you need in an hour. Divide by 60 for RPM.
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Old 12-01-23, 12:23 PM
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Originally Posted by cyccommute
4 mph at 90 rpm. Not really an RPM that is “way up there”. At 60 rpm, the speed is just under 3 mph which is still rideable and, on a hill, faster then a walking while pushing a bike. With a 22” gear, you have to work harder to pull up the same hill
Always prefer pedaling as well. Pushing a loaded bike up an incline is closer to 1 mph.
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Old 12-01-23, 12:28 PM
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For the record I'm not arguing just for the sake of arguing. I just like geeking out about stuff like this. I'm not a high RPM kind of guy so sustaining 100+ RPM is just not in the cards for me but others can pull it off.
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Old 12-01-23, 01:44 PM
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Originally Posted by abdon
Do a direct measurement of your gear inches and then do the math. I don't think it is what you think it is. Gear inches is simply how far you go per revolution, 4 miles is 253,440 inches, divided by your actually measured gear inches tells you how many revolutions you need in an hour. Divide by 60 for RPM.
Dunhem postulate. Someone else has already “dunh ‘em” so there’s no need to do it again. Dirk Feeken’s calculator does it for me to the level of accuracy I need.
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