Drafting is a technique where a vehicle or athlete tucks in closely behind another to reduce air resistance, allowing them to maintain the same speed with less effort or go faster with the same effort. In cycling, drafting behind another rider cuts drag force by 38% to 42%. In motorsports, the effect is dramatic enough that entire race strategies revolve around it.
The Basic Physics of Drafting
Any object moving at speed has to push air out of the way. That creates a high-pressure zone in front and a low-pressure zone behind. The low-pressure zone behind a moving vehicle is sometimes called “dirty air” or the slipstream, and it’s the key to drafting. When a second car or cyclist slots into that low-pressure pocket, they face far less resistance than they would out in clean air. The lead vehicle has already done the hard work of parting the airstream.
What’s less obvious is that the trailing vehicle also helps the leader. The follower’s presence fills in that low-pressure pocket behind the lead car, raising the pressure at the leader’s rear. This reduces the “suction” effect pulling the lead vehicle backward. The benefit for the leader is smaller than for the follower, but it’s real and measurable. In truck platooning studies, the lead vehicle showed noticeable fuel savings at close spacing, though trailing vehicles saved considerably more.
How Much Speed and Energy It Saves
The numbers vary by sport, but they’re consistently significant. A meta-analysis across multiple disciplines found drag reductions of 38% to 42% in cycling, 23% in speed skating, 25% in cross-country skiing, and 6.5% in running. Even in swimming, passive drag drops by 13% to 26% when trailing another swimmer.
For cyclists, that drag reduction translates directly into power savings. A rider drafting in a two-person line at moderate speed can reduce their power output by roughly 30% to 35% compared to riding solo. At higher speeds around 27 to 28 mph, the savings for a third rider in line sit between 5% and 9% compared to the second position. This is why professional pelotons are so tightly packed: riders deep in the group can cruise at race pace while burning a fraction of the energy of the rider on the front.
In marathon running, where the human body is smaller and less aerodynamic, the savings are proportionally lower but still race-altering. Researchers at the University of Colorado Boulder calculated that for a runner of Eliud Kipchoge’s size and speed, drafting alone could save between 3 minutes 42 seconds and 5 minutes 29 seconds over a full marathon. If pacers could hold on for an additional 10 kilometers beyond where they typically drop off, another minute of savings would be possible.
Drafting in NASCAR and Oval Racing
Drafting is most visibly strategic in stock car racing, particularly at superspeedways like Daytona International Speedway and Talladega. These tracks are so long and fast that NASCAR limits engine power through restrictor plates (or their modern equivalent, tapered spacers), cutting roughly 300 horsepower from the cars. With engines artificially limited, drafting becomes the primary way to gain speed. Cars form long single-file or double-file lines where each vehicle benefits from the reduced drag created by the car ahead.
The forces involved are intense. At superspeedway speeds, the low-pressure zone behind a car is strong enough that it has literally pulled rear windows out of vehicles. A driver named Johns reportedly lost his rear window while drafting because the pressure differential was that severe. This is part of why restrictor plates exist: without them, the combination of raw engine power and drafting effects would push speeds to dangerous levels.
The Slingshot Pass
The most exciting application of drafting is the slingshot maneuver. A trailing car sits in the leader’s slipstream, maintaining pace while its engine works less hard against drag. Because the engine is fighting less air resistance, there’s untapped power available. When the trailing driver pulls out of the slipstream and into clean air, they can briefly accelerate past the leader using that reserve energy. The leader, suddenly without the pressure-filling benefit of the trailing car, feels drag increase at the same moment.
Timing is everything. Pull out too early and you spend too long fighting full air resistance before you reach the finish line. Pull out too late and there’s not enough track to complete the pass. In cycling, the same principle governs sprint finishes: riders sit in the draft conserving energy, then launch past the leader in the final moments. The trailing rider in a cycling draft has been pedaling with roughly a third less effort, saving that energy for a burst when it counts.
Bump Drafting
At superspeedways, drivers sometimes take drafting a step further by literally making bumper-to-bumper contact. The trailing car nudges the lead car’s rear bumper, physically pushing it forward while both vehicles benefit from reduced drag. This technique, called bump drafting, can push paired cars to speeds neither could reach alone.
It’s also dangerous. A slight misalignment during a bump can turn the lead car sideways at 190 mph. NASCAR has repeatedly adjusted rules around bump drafting, sometimes penalizing it and sometimes allowing it depending on the era and the specific track. The physics that make it effective are the same physics that make it risky: at those speeds, even small aerodynamic disruptions can have outsized consequences.
Why Closer Is Better (to a Point)
The drag reduction from drafting increases as the gap between vehicles shrinks. At larger distances, the disturbed air behind the leader has time to partially recover before the trailing vehicle reaches it. Get closer, and you sit in a deeper low-pressure pocket with even less resistance. Computational fluid dynamics studies of NASCAR vehicles show that trailing cars experience noticeably lower pressure across the front fascia, windshield, and spoiler compared to a car running alone, and the effect intensifies at tighter spacing.
There’s a practical limit, though. Following too closely reduces the airflow reaching the trailing vehicle’s radiator and engine bay. With less cool air flowing through the grille, engine temperatures climb. Even partial blockage of radiator airflow can meaningfully reduce cooling capacity. In a long race, overheating can force a driver to back off or risk mechanical failure. Drivers and teams constantly balance the aerodynamic advantage of close drafting against the thermal cost of restricted airflow.
Side Drafting
Drafting isn’t limited to directly behind another vehicle. In side drafting, a car pulls alongside the leader, positioning itself so that its front end disrupts the airflow along the leader’s side. This disturbs the high-pressure zone on the leader’s body panels and can destabilize their aerodynamics, effectively slowing them down. Side drafting is more of an offensive weapon than traditional slipstream drafting. Instead of gaining an advantage for yourself, you’re creating a disadvantage for a competitor, particularly useful when trying to prevent someone from pulling away on a straightaway.