My R100GS was doing well to return 40 mpg- there are ways to improve things, though. With a set of 38 mm flatslides mounted, mt buddy's R100GS's mileage jumped almost 5mpg and made more power. If you add high compression pistons, dual plug the heads, and install a freer flowing exhaust, things will only improve. My Dad's R75/7 had dual plug heads, electronic ignition, 900cc Venola pistons(10.5:1) and an RS fairing and it regularly sipped it's fuel to the tune of 60 mpg at a steady 70 mph. Grab those wrenches and get busy!