Hard to measure exactly John but looks about 125mm on my Torq1 with SBF motor; the main 'body' of the motor is about 100-120mm wide with the extra protrusions close to the axle and a 5mm spacer - I'm not sure what the absolute minimum motor width is cos I can't tell which of the extra bits are motor & which are addons, if you get me
.
110mm which others have said sounds about right and the motor width is still 9cm at 4.5cm above centre of axle, so fork spacing at that height must be more than that
.
Stuart.