What size BB when converting from triple to double?
I've got an old 1983 Trek 614 which has a Sugino AT triple crankset on it. I've pulled the BB & the spindle measures 125mm. Sheldon says the BB is either "127.5 + 2 mm spacer" or "122.5 Asym". Hm..
Anyway, probably doesn't matter. What I want to do is convert this thing to a SS, so I've removed the inner chainring. Now it looks like a double (no extra stuff in the way due to the triple ring). I will also remove the outer 50t chainring & put the middle 45t ring in the outer position. Any idea what size BB I should buy? I'm not too concerned with the chainline at this point, because I can use spacers in the back between the hub & ss freewheel to get the chainline straight (did that on the last SS & it worked perfectly). Though I suppose getting the correct bb will maybe solve this problem for me.
I'd just measure how much clearance you have between each crank arm and chainstay and work backward from there. Example: if you've got 10mm of clearance between each chainstay and crank arm, you'd be able to safely subtract 5mm from each end of the spindle to end up with 115mm. Keep in mind going too far inboard with the right arm will limit how large of a chainring you can run.