Classic Peanut Fuel Tank First appearing on a Harley-Davidson® motorcycle back in 1948—and providing the inspiration for the Forty-Eight® model name—the small 2.1 gallon tapered peanut fuel tank holds strong today with its traditional styling and modern attitude. A low, powerful bulldog look that gives way for showcasing more engine, the peanut fuel tank is attitude and looks all balled up into one.