FYI,,,as far as i know,,and this has been backed up by the feedback from past convertees,,,it hasn't affected the ABS,,
your speedometer/odometer will read a bit different,,,in some cases believe it or not taking the erroneous reading experienced with the 21'' wheel and being on the money with the 19[ktm 950/990 s if i remember correctly??]
on my r1200gs BWOE,,i've gone down to 17 front and up to 21'' from the stock 19''er and 150/70x17 rear to 14/080x18 ,,,,ABS still works
so fret not!!!