Disc brakes for road bikes? They sound like a great idea; massive, predictable and reliable stopping power in any riding conditions with no rim wear to worry about, long pad life instead of rubber blocks that can wear wafer-thin over the course of a day’s riding in really bad conditons and no need to worry about the wheel rim going out of true or receiving a dent that would cause a rim brake to snatch.
All these are real advantages for discs, which is why they are increasingly fitted to machines such as the Aardvark. Lightweight road bikes are a different matter, since disc systems are not only heavy in themselves but require a hefty left-hand fork leg and reinforcement to the left-hand rear stays to cope with the stresses imposed by the location of the caliper.
Where disc operation is a possibility and dropped handlebars a preference, Shimano’s BR-R505 calipers fit the bill as they are specifically designed to work correctly with the cable pull of brake levers made for drop ‘bars.
Front and rear calipers are identical but for the bracket for attachment to the International Standard mount, which is front- or rear-specific. Both front and rear calipers come with a brake cable, sintered metal all-weather pads and a 160mm brake disc to fit Shimano’s CenterLock splined disc mounting system.
Assuming the existence of a suitable frame and fork mounts, caliper fitment is a doddle provided it is done to the correct end. The two bolts securing the bracket to the IS plate are tightened first and the two “radial” bolts securing the caliper to the bracket tightened with the brake applied to centre it on the disc. This means the cable has to have been installed and initial play adjusted using the threaded adjuster on the front of the caliper.
Subsequent adjustment is done using one of the two 3mm Allen screws seen on the sides of the caliper. Both move their respective pads closer to (or away from) the disc, the outer being part of the arcing arm that compresses the pads together. In other words, pad adjustment is independent of the brake cable.
With each pad adjustable separately, excess cable play as a result of pad and disc wear is taken up by moving each pad towards the disc until both are equidistant. Since the inner pad stays put during operation, the disc is distorted sideways by the outer pad until it reaches the inner. Correct adjustment means this is never more than about 0.5mm.
What are the brakes like to use? With but 200 miles on them, they are as described above – massive, predictable and reliable stopping power – but with added feel and power. Update coming with more mileage covered.