Why are motorbikes so fuel inefficient if they weigh so little and have comparably small engine capacity?
A 600 cc bike with 30 hp and fairing should get pretty good mileage. If you want 100 hp from the same engine you need to have the very high degree cams with heavy overlap which keeps the air/fuel mixture momentum high but you lose some unburned fuel through the exhaust pipe. Second thing is the coefficient of drag. It is around 0.28 – 0.35 for cars and 0.90-1.00 for bikes. Even bricks are more efficient than bikes because they have smooth surfaces. Every part of the bike and the human body in sitting position designed to create maximum turbulence, so our bikes can get the worst mileage they can.
