The tank size is advertised as 4.8 gals. 4.8 is more than likely the capacity with sufficient space for air. Putting in about 5 gals, is only a difference of 29 ounces. With an avg speed of 55 mph, you can get very close to 300 miles on a tank (providing riding conditions are optimal, i.e no hills, no wind, no low temps, lightweight rider)