Vehicle Aerodynamics: Motorcycle vs Truck

[khalid00]

why is a motorcycle more aerodynamically affected than a truck??, I have been lead to believe it is because of the lower density, is that true?? and how can i justify it??

Thanks

 

[mgb_phys]

Drag is proportional to cross sectional area.
An unfaired motorbike make have a higher draw coefficient than a truck (ie is less streamlined) but a truck has a lot more cross sectional area so more overall drag.