What Is Drafting? Letting Someone Else Push the Air
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Following closely behind another competitor reduces the effort required by a substantial margin, because the leader has already disturbed the air. That saving dominates tactics in every sport where speeds are high enough for air resistance to matter.
Why it works
Moving through air requires pushing it aside, and the power needed to do so rises with the cube of speed, which means that at racing velocities the overwhelming majority of a competitor's effort goes into overcoming air resistance rather than into anything else. A leading rider displaces the air and leaves behind a region of turbulent, slower-moving air at reduced pressure. A following rider entering that region meets less resistance, and measurements put the saving at roughly a quarter to a third of the power required at the same speed, rising with how close the following position is and falling off quickly with distance. The leader also benefits slightly, since a following rider reduces the low-pressure region behind them that would otherwise pull them backwards, which is a smaller effect and is real.
Where it decides races
The saving is large enough to organise entire sports around:
- •Road cycling, where the peloton exists because of it and where a rider alone against a group is at an overwhelming disadvantage
- •Team time trials, where riders rotate through the lead so no one spends long exposed
- •Track cycling, including events built entirely around the tactics of who leads
- •Motor racing, where the slipstream is used to close and overtake, and where the disturbed air also reduces downforce and makes following difficult in cornering
- •Speed skating and cross-country skiing, where the same physics applies at lower speeds
- •Running, where the saving is smaller and measurable, and pacemakers are used to exploit it in record attempts
The tactics it produces
Because leading costs more than following, every such sport develops conventions about who leads and when, and those conventions are the tactics. Rotating the lead shares the cost and is cooperative, which means a breakaway group only works while everyone contributes and collapses when someone stops. Refusing to lead is a legitimate and much-resented tactic, particularly from a rider who intends to attack at the finish and who has spent less energy getting there. Teams protect a leader by keeping them sheltered until the decisive moment. Attacking requires either a moment when the group is inattentive, a gradient where the advantage of following shrinks, or enough superiority to overcome the deficit. And a lone leader ahead of an organised chasing group will almost always be caught, since the group shares the cost and the individual does not.
The shapes it produces
Groups moving together adopt formations that are visible and are chosen for the physics. A single file line, with each rider directly behind the one ahead, is the standard arrangement and gives the largest saving to those behind. A diagonal echelon forms when the wind comes from the side, since the sheltered position is then offset rather than directly behind, and because a road has limited width an echelon can only hold a certain number, which is why crosswinds split a group and why those caught behind lose time rapidly. Rotating formations, where riders move continuously up one side and back down the other, share the lead in short turns and are the most efficient arrangement for a cooperating group. Swimmers and skaters use comparable positioning. Recognising the formation in a race tells an observer what the conditions are and what the group is trying to do.
Where it is banned
Several sports prohibit the practice specifically because it would otherwise dominate. Triathlon over most distances forbids it, requiring competitors to maintain a specified gap on the bike and penalising those who close it, which preserves the event as an individual test and requires officials on motorcycles to enforce. Individual time trials in cycling forbid it, including from following vehicles, with rules specifying minimum distances. Marathon record attempts have been argued over, with a distinction drawn between pacemakers who are in the race and arrangements considered to fall outside the rules for a record. The general point is that a rule permitting it turns an endurance event into a tactical one and a rule forbidding it turns it into a test of individual output, and neither is more correct, since they are different sports.
The takeaway
Power needed to push air rises with the cube of speed, so most effort at racing pace goes into it, and following closely saves roughly a quarter to a third. That makes leading expensive and following cheap, which is why rotating the lead is cooperative and refusing to lead is a tactic. Sports that want an individual test forbid it and enforce a minimum gap.