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 |
|
