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    Bicycle Aerodynamics

    • Bicycle is responsible for 20-35% of drag.
    • Loose Clothing increases drag by up to 30%.
    Bicycle Aerodynamics - Position
    • Positions
      • Goals: reduce frontal area & reduce drag coefficient

     

    CD
    Frontal Area
    CDA
    Power  to Overcome Drag
    Tops
    1.15
    .55 m2
    .632 m2
    345 W
    Hoods
    1.0
    .40 m2
    .40 m2
    220 W
    Drops
    .88
    .36 m2
    .32 m2
    176 W
    • Rearward vs. Forward position (23.57 – 22.28 N drag)
      • Forward seat position decreases drag at the expense of comfort and pedaling mechanics
      • Union Cycliste Internationale limits the fore-aft position of the saddle requiring it be at least
        5 cm behind the bottom bracket spindle
      • Injury preventive measure
    • Drafting
      • Traveling close behind another rider
      • Broken up air vortices propel second rider
      • Offers advantage to both front and rear rider
      • Riders in group expend 40% less energy than solo riders
    aero12

    aero13

    Drag coefficients of two circular cylinders, one placed behind the other.

    • No advantage to side by side drafting

    aero14

    Aerodynamic interference of two side by side struts.

    Bicycle Aerodynamics -Crosswinds

    • Aerodynamic drag is usually calculated assuming calm weather
    • Crosswinds create aerodynamic moments and instability
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    • CP (point of action of aerodynamic forces) should be behind the CG for maximum stability