Shimano Ultegra Di2 12Speed ST-R8170 + BR-R8170 Hydraulic Shifter Disc Brake Set (Pair) Flat-Mount. ULTEGRA Di2 ST-R8170+BR-R8170 2x12-speed Disc Brake Set. That is "Science of Speed". The hydraulic 2-piston brake caliper BR-R8170 for with Flat-Mount.
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