That depends entirely on the terrain of the day, I get from 9.8 mpg in the rocks up to almost 20 mpg cruising the desert. I believe the X4 has a 7.7 gallon tank so that's anywhere from 75 to 154 miles per tank. I ride above 7k feet, so my fuel injection 'should be' leaner than lower altitudes.
Check your mileage a few times to get a feel for your (heavier) X4.
