I've always been a believer in the old "if some is good, more is better" philosophy, especially when it comes to brakes. I'd already gotten a substantial improvement in stopping power with the big rotor conversion from M.A.P. Engineering, but when I heard on the Airheads mailing list that it was possible to fit the dual piston caliper from a later oilhead BMW I couldn't resist leaving well enough alone. I dug a little bit and found that the left caliper from an R1150GS, part number 34117670391, has the same mounting bolt spacing as the R100GS caliper, and would center over the rotor if about 0.10" of the boss thickness was milled off (several R11XX model BMW motorcycles use this same caliper). I fished around the IBMWR classified page for a used caliper, but some folks have an exadurated sense of worth for their old parts. A fellow lister suggested Cycles Recycled as a possible source, and Fred Rowland quickly answered an email inquiry with a $35 plus shipping offer I couldn't refuse. Two weeks later the part was in hand and I had to figure out how to get it to fit. First thing I did was remove the brake pads and fit the new caliper to the M.A.P. bracket to make sure that the bolt spacing was indeed the same. It was. And just as my fellow listers had said, the caliper didn't center over the rotor very well. It seemed to be about a tenth of an inch too far toward the center of the wheel. That meant that material would have to be removed from the outside of the mounting bosses on the caliper. I figured that wouldn't be a problem for the little milling attachment I have for the ancient South Bend lathe in the corner. I used a telescoping hole guage to measure the gap between the rotor and the inside of the caliper on each side, subtracted the two distances and divided by two to get the distance that the caliper was off center. That came out to 0.109" on my bike, and that's the amount I'd end up taking off the mounting bosses.