Sorry guys, I was working very late last night and didnt log on at all when I got home.
S&M will, and pretty much always have, made custom frames however people want um. My guess is that someone wanted a CANTI (not U or Vee) brake on their HAF. No idea why they would, but Ive never seen another one like it. Also, this frame was is a shop with my 18” tt HAF, so they might have been part of the same custom order, even if they did end up in a shop in the UK.
I have spoken to Rory about this frame before and from what we can work out, its designed to run a centre pull Canti brake. There is an inner cable guide / Outer cable stop behind the top tube, which wouldnt work with a Vee brake (although you could still use a Vee if you didnt use the cable stop). Id be sure that the cable leading to a Vee brake would stick out the side and catch your feet, so a nice Low profile Canti, like mi16kie pictured is probably the way to go.
As this was probably a one off then there is every chance that the brake wont clear at all. The early S&Ms with 990s clashed everywhere and you had to cut 990 arms all over the place to get them in there. It might not be as easy as just finding the right brake.
Rory, I have got a few pairs of old shimano cantis kicking about (I used to use them on the front). I will grab a set and get them over to you. No point spending any money if it still might not work. btw, the HAF is lookin great!!!!
Oh, and Rob. I think this is the first time I have seen you make a mistake with your advice, but like you said, S&Ms aint your thing.
