Junior Member
Join Date: Oct 2017
Location: Ottawa, ON, Canada
Posts: 151
Bikes: 1974 PX-10E sold, 1977 Witcomb stolen, 1980 Roberts 1 speed, 1987 Cyclops 3 x 6 friction triple crank, 2010 Masi Commuter 1 speed, 2017 Ribble 525 2 x 10 with Ergos
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CliffordK has identified the issue correctly, I believe.
I just "doublized" a 50-40-30 triple to 46-30. It went well, but it did depend on finding a 10-speed compatible, ramped and pinned 46T middle ring to deal with the counterbore issue. Mine is a 135 BCD ring from Specialities TA, and meets all the requirements plus is beautifully machined and finished. A quick check suggests that they do offer 46T middle rings in 110 and 130 BCD, but not 48T. The other place to look, if only to drool over the amazing choices, is Spa Cycles. Not sure if they have resumed shipping to Canada/States.
oldschoolbike