Expect around 56mpg for normal riding, which will give you theoretical fuel range of 222 miles from its 18-litre tank - an easy 200 between stops in the real world. Reliability & build quality BMW R 1250GS. Year. 2021. Engine. Four stroke, two cylinder horizontally opposed Boxer, with two overhead spur gear driven camshafts, a counterbalance shaft and variable intake camshaft control system BMW ShiftCam, 4 valves per cylinder, intake 40mm, outlet 34 mm. Capacity. 1254 cc / 76.5 cu-in. Bore x Stroke. Bt8dGx.