Originally Posted by
whatwolf
I am considering both of these tires. I want to go wider than 38mm if possible, and I wonder if you could tell me what you think of my clearance measurements. I know you have a lot of experience with this... is my bike too tight for a Hertre? This is a late 70s(?) Colner road racing frame, measured at 320mm from axle centers:
Fork: 46mm, Seatstays: ~65mm, Chainstays: 44mm if axle is set back in drop outs. Maybe 45mm if all the way back.
Whatwolf, I think you would be best off targeting a 650x32c tire for your conversion, based on your 45 mm max internal chainstay clearance and your fork clearance. You are exactly on-target performing that measurement at 320mm from the planned axle center, at least for a Hetre. It might be a little shorter (315?) for a 32 mm tire. The seatstays are wide enough for a Hetre, FWIW.
On second thought, I guess 38s would not be bad, but the margin is getting lower.