Analytic Cycling Logo Gear Selection, Track Competition

Gear Selection for Points Race 

Let's say a rider needed to select a gear for a points race at the track.  The rider estimates that the event will have several fast laps at say, 55 kph, 15.3 m/s.  The rider knows this by timing several fasts laps at previous events, just to get an estimate. The rider has an effective pedaling range of 90 to 125 cadence.  What gear should the rider use?  The following table suggests a 49x14.

 Recommended Gear 
 
Closest Gear  49x14    
Gear Inch, Closest  92.5  inch 
Rollout, Closest  7.378  m 
Maximum Speed  15.3  m/s 
Wheel Diameter  671  mm 
Desired Gear Inch  92.0  inch 
Desired Rollout  7.344  m 
Frontal Area  0.5  m2 
Coefficient Wind Drag  0.5  dimensionless 
Air Density  1.226  kg/m3 
Weight  75.  kg 
Coefficient of Rolling  0.004  dimensionless 
Effective Stroke  70.  degree 
Grade  0.  decimal 
Wind Resistance  35.9  kg m/s2 
Rolling Resistance  2.9  kg m/s2 
Slope Force  0.0  kg m/s2 
Crank Length  165.  mm 
Maximum Cadence  125.  rev/min 
Pedal Speed  2.2  m/s 
Average Pedal Force  275.  kg m/s2 
Effective Pedal Force  707.  kg m/s2 
Power  594.  watts 
 

Suppose that conditions change, for example Air Density goes to 1.15 kg/m2.  If power stays the same, speed could go to 15.62 m/s (from Speed, Given Power see below).  The table after then suggests a gear of 50x14: 

Speed For Given Power 
 
Speed For These Parameters  15.62  m/s 
Power  594  watts 
Frontal Area  0.5  m2 
Coefficient Wind Drag  0.5  Dimensionless 
Air Density  1.15  kg/m3 
Weight Rider & Bike  75  kg 
Coefficient of Rolling  0.004  Dimensionless 
Slope of Hill  0.  decimal 
 
Recommended Gear 
 
Closest Gear  50x14    
Gear Inch, Closest  94.3  inch 
Rollout, Closest  7.529  m 
Maximum Speed  15.62  m/s 
Wheel Diameter  671  mm 
Desired Gear Inch  94.0  inch 
Desired Rollout  7.498  m 
Frontal Area  0.5  m2 
Coefficient Wind Drag  0.5  dimensionless 
Air Density  1.15  kg/m3 
Weight  75.  kg 
Coefficient of Rolling  0.004  dimensionless 
Effective Stroke  70.  degree 
Grade  0.  decimal 
Wind Resistance  35.1  kg m/s2 
Rolling Resistance  2.9  kg m/s2 
Slope Force  0.0  kg m/s2 
Crank Length  165.  mm 
Maximum Cadence  125.  rev/min 
Pedal Speed  2.2  m/s 
Average Pedal Force  275.  kg m/s2 
Effective Pedal Force  707.  kg m/s2 
Power  594.  watts 
 

©1997 Tom Compton