Using portable emissions equipment, a wide sampling of cars and bikes from the 1980s, 1990s and 2000s and with the help of Dr. Kent Johnson of UC Riverside, the Mythbusters team claims they proved motorcycles are dirtier than cars.Doing so meant gathering data in real-world driving conditions along a 75-percent freeway, 25-percent city driving loop in and on the vehicles from different eras. The results of that test proved one thing that everyone should already know: motorcycles use less fuel than cars.They also produce less carbon dioxide than cars, which accounts for 90 percent of a vehicle's emissions. Where cars pull ahead, though, is in the amount of other noxious gases they produce. The Mythbusters found that bikes produce tons more hydrocarbons, which are carcinogenic; nitrogen oxides, which cause acid rain; and carbon monoxide, everyone's favorite odorless deadly gas. Astoundingly, the 'busters claim bikes produce up to 8,000 percent more carbon monoxide than cars. Yes, 8,000 percent.A controlled test on a track using a small displacement, fuel injected modern bike didn't give two wheelers the help the 'busters thought it would.To give bikes another chance, Jamie and Adam built an aerodynamic frame to make the modern bike sip even more gently through the wind. The result, predictably, was that the emissions got a little better, but were still worse than the car's. See the videos for yourself after the break.