I looked up the history of cars vs bikes in A.M.E.C. Economy Run competitions. Unfortunately there have only been two motorcycle riders that have entered, but here's how they fared against the cars.
Economy Run I
Ernie Yue entered his 2008 Kawasaki Ninja 250 in our Aug 10th, 2008 Economy Run I event. He weighed in at 580 lbs. and outperformed all of the cars with 73.06 mpg. The best car at that event was Dave Burnham's 1991 Jetta Diesel that came in at 56.36 mpg.
Economy Run III
Shift518.com's Vlad Saakyan entered his 2003 Suzuki Svs650 and was able to get 62.28 mpg from it. However, he was up against some mighty stiff competition from our all time high mpg driver, Chang Ho Kim in his 1989 Honda CRX HF, who scored an amazing 118.18 mpg!
So as it stands, it is a tie:
Cars = 1
Bikes= 1