My 21" P15 has a Weinmann 730 in the back and a 650 in the front, both reaching 27" rims. The front brake shoes are at the bottom of the slot. In fact, I had to file one slot a bit to get the pad low enough on 27" rims. A 650 won't work at all on the rear. I never figured out why it was felt that more clearance was desireable in the rear. Perhaps it was because the rear wheel clearance may change as the wheel moves forward in the long Campy dropouts? Or maybe it was to cause more braking force in the front and less in the rear, much the same way some cars did in the past, with disks on the front and drums in the back?
I ordered the bike with 27" rims because I was going on a long tour and I thought that I might have a hard time finding 700c tires enroute. That was not one of my wiser decisions. When I ordered my wife's P15 a year later, I speced sewups and Campy sidepulls. Her bike still has fender clearance with the long-reach calipers, but the spacing is much more to my liking. She doesn't ride the darn thing anyway.
Steve Barner, still accepting photos for the old bicycle mechanics' gallery, http://BikeToss.com, in Bolton, Vermont
Hard to believe, but true. My '74 Paramount has the looong reach Weinman in the back, and still won't reach a 700c rim even with the pads bottomed out, forcing the use of a 27 inch rim. I guess someone at the design table said "let there be fender clearance." A Campy caliper, even with a drop bolt, misses the rim by a bunch.
Oddly enough, the regular length Weinmann front brake will reach a 700c wheel.Someone pointed out before during our discussion of differing brake reach from front to rear that the placement of the rear brake stay is handling neutral, but too long fork blades required by mega brake reach will adversely affect handling. Just have to hope someone keeps making good 27 inch tires when the three pairs I'm hoarding wear out.
Tom Adams, Shrewsbury NJ