Endurance Innovation

59 - Drafting 102

Episode Summary

Andrew and Michael revisit an oldie but a goodie: our first episode on drafting and aerodynamic drag. This time, we add a few new pointers and also cover recent developments in the understanding of running aerodynamics.

Episode Notes

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• 2:30 what is drag?
  • Pressure drag is the difference in pressure that the air in front of an object exerts with the pressure that the air behind the object exerts, where front and back are relative to the direction of travel
  • Surface drag is caused by the shearing or tugging at the air molecules by the surface of the object as it slips by
• 10:15 why drag matters
  • Aero drag is the major contributor to energy loss at typical cycling speeds
  • Drag force scales in proportion to the CUBE of the velocity, so doubling speed requires increasing power by a factor of eight!
• 12:30 some relatively common aero values: a triathlete with a very good aero position (CdA of .215) requires ~240W to travel at 40kph on flats. Of this, 30W is consumed by overcoming rolling resistance. The remaining 210W by aero drag. Assuming an immaculately clean and lubed drivetrain.
• 17:15 what is drafting? The reduction in difference in pressure between the front and rear surface
• 19:45 maximal reduction in drag by drafting at various distances in IDEAL CONDITIONS
  • At 2m: 35% reduction
  • At 5m: 27% reduction
  • At 12m: 11% reduction
  • At 20m: 2% reduction
• 25:00 using legal drafting to your advantage in triathlon
  • each  LEGAL pass (12m draft zone, 20s to pass) with drafting at 40kph can save up to 3s - 3.5s
  • If passing 200 athletes, you may gain UP TO 600s or 10 minutes!
• 34:30 a discussion of Alex Hutchinson’s article on drafting in running
  • Following a runner directly was more advantages than slotting between two runners
  • which runner was followed was not very consequential
  • It is still not very clear how much of a velocity increase can be gained from reducing aerodynamic drag for runners
• 45:45 why are we not making more aerodynamically optimized decisions in running?
• 49:00 drafting helps everyone! Even those being drafted see some reduction in drag.

Read Alex Hutchinson’s article on drafting . And for your fluid dynamics fix, check out FYFD.