> On Dec 10, 2024, at 11:56 AM, Piaw Na <[email protected]> wrote: > > Ironically I had the opposite problem. When I spec'd my custom Ti touring > bike I asked for 57mm because that's what the spec said. It turned out that > if you have exactly 57mm just because of the vagaries of the process you end > up having to file down the brake slots of the "long" reach brakes. To be safe > you really have to design/build the bike to 55mm reach. >
This is a geometry problem that affects the front much more than the rear. The seat stays, to which the brake is attached, are almost exactly perpendicular to the brake track where it crosses between them (depending on the rear axle location relative to the seat stays, and whether the seat stays are straight). The brake mounting hole, being perpendicular to the seat stays, is parallel to the brake track. But the rim is running away from the brake hole as you get farther from the bridge, so if the hole-rim distance at the bridge is 57, then, yeah, because the brake sticks out from the bridge, at the center of the brake pads the distance will be >57. The front brake is a different story and more problematic, typically. Front brake holes run perpendicular to the steering axis, but the brake track is pretty far from perpendicular to the brake track. By the time you get to the center of the brake pads, the brake track has moved significantly upward, so if you are at 57 at the fork crown, you might have 50 or less at the center of the pads. Which screws you when you try to install fenders. I have yet to encounter a builder who explicitly does the math to figure this out. I’ve suggested to a couple of builders they drill front brake holes at an angle to preserve brake clearance … they’ve politely dismissed me as a crank. Ted Durant Milwaukee, WI USA -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/rbw-owners-bunch/E9DB9D9C-745E-4A17-9641-E48BD2D44B76%40gmail.com.
