Top Speed. The top speed of Fat Boy 114 is 110 mph (166 kmph). It reaches 0-60 mph in just 5.0 seconds. Mileage or MPG. Fat Boy 114 gives a miles per gallon of 47 mpg. With the fuel tank capacity of 5 gals. The bike can go up to 235 miles with a full tank. Fat Boy 114 Colors. Harley Fat Boy 114 is available in 4 colors. Vivid Black – MSRP uTrm5Or.