Joined: Dec 2004
Posts: 12,547
Likes: 797
From: Middle of da Mitten
Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, Catrike Speed
I thought the purpose of a spoiler was to use airflow to provide more downward force on the wheels for more traction. IOW, reverse lift. They are used in automotive applications (i.e. racing) in spite of their aerodynamic cost, not because of it.
Fairings and diverters, OTOH, are meant to smooth the air flow.