Drafting or slipstreaming is an aerodynamic technique where two moving objects are aligning in a close group to exploit the lead object's slipstream and thus reduce the overall effect of drag. Especially when high speeds are involved, as in motor racing and cycling, drafting can significantly reduce the paceline's average energy expenditure and can even slightly reduce the energy expenditure of the lead vehicle.
Drafting is used to reduce wind resistance and is seen most commonly in bicycle racing, motorcycle racing, car racing, and speedskating, though drafting is occasionally used even in cross-country skiing, downhill skateboarding, and running. Some forms of triathlon allow drafting. Drafting occurs in swimming as well: both in open-water races (occurring in natural bodies of water) and in traditional races in competition pools. In a competition pool a swimmer may hug the lane line that separates them from the swimmer they are abaft of thereby taking advantage of the liquid slipstream in the other swimmer's wake. Drafting also occurs in competitive longboarding.
It is believed, but not yet conclusively proven, that thoroughbred racing horses draft each other, especially in longer races. [1]
In cycling, any time one bicyclist is riding behind another, energy is conserved, especially at higher speeds.
In road bicycle racing, the main (largest) group of tightly packed cyclists in a race is called a peloton where cyclists ride in a long formation with each (but not the first rider) drafting behind the others before them.
When cyclists ride fast they form a paceline . Each cyclist, except the first, is drafting behind another one. In order to ride very fast, a team of some skilled cyclists may form the "Belgian tourniquet". Successively, each cyclist leads the group. Drafting can be cooperative: several competitors take turns in the lead position (which requires the most effort and energy consumption). It can also be competitive or tactical: one competitor will try to stay closely behind another, leaving the follower with more energy for a break-away push to the finish line.
Drafting behind another runner can conserve energy when facing a headwind. Generally the effect is much less pronounced than in cycling due to lower speeds.
Nike worked with the aerodynamics expert Robby Ketchell at the University of New Hampshire to experiment with and select a formation of pacemakers that would best minimize drag on the professionals it sponsored in the project it termed Breaking2. A Wired magazine report that interviewed various experts affiliated and unaffiliated with Nike found they universally expected more coordinated pacing efforts to occur in running after Breaking2, with two of the quoted experts predicting that behavior like "cooperative drafting", or races that incentivize cycling-peloton-like behavior could improve running times. [2]
In single seater, open wheel racing series such as Formula One and the IndyCar Series, as well as to a lesser extent in sports car racing, a technique known as slipstreaming is used. Along a long straight a car following close behind another uses the slipstream created by the lead car to close the gap between them, hoping to be able to overtake the leader under braking for the next corner, or if they have a straightline speed advantage, to pass on the straight. However it is very difficult for cars to follow each other close together in fast corners as the "dirty" (turbulent) air that comes off the lead car unbalances the trailing car as its aerodynamic devices provide less grip.
On the faster speedways and superspeedways used by NASCAR and ARCA, two or more vehicles can race faster when lined up front-to-rear than a single car can race alone. The low-pressure wake behind a group's leading car reduces the aerodynamic resistance on the front of the trailing car, allowing the second car to pull closer. As the second car nears the first, it pushes high-pressure air forward so less fast-moving air hits the lead car's spoiler. The result is less drag for both cars, allowing faster speeds. [3]
Handling in corners is affected by balance changes caused by the draft: the leading car has normal front downforce but less rear downforce. The trailing car has less front downforce but normal rear downforce. A car with drafting partners both ahead and behind will lose downforce at both ends. [3]
Similar to the "Belgian tourniquet" in cycling, the "slingshot pass" is the most dramatic and widely noted maneuver associated with drafting. A trailing car (perhaps pushed by a line of drafting cars) uses the lead car's wake to pull up with maximum momentum at the end of a straightaway, enters a turn high, and turns down across the lead car's wake. The combination of running downhill and running across the zone of lowest aerodynamic drag allows the trailing car to carry extra speed and pass on the inside of the leader. [3]
Drafting was discovered by stock car racers in the 1960 Daytona 500, when Junior Johnson found that he could use drafting as a strategy that helped him overcome the fact that his Chevrolet could not keep up with other cars, allowing him to win the race. [4] Like Johnson, other drivers found they picked up speed running closely behind other cars, and as they experimented, they found that a line of cars could sustain higher speeds and/or use less fuel (resulting in fewer pit-stops) than a single car running by itself. [3]
In recent years, as aerodynamics have become increasingly critical to the performance of stock cars on "intermediate" oval tracks (between 1.33 and 2 mi) and superspeedways not requiring restrictor plates (such as the Indianapolis Motor Speedway), the effect of turbulent, or "dirty", air when following closely behind another car has become much more akin to that described above in open-wheel racing (a situation described in NASCAR circles as aero push), and is often cited as a main reason for a decrease in the amount of overtakes. [5]
Drafting is most important at NASCAR's restrictor plate tracks, Talladega Superspeedway and Daytona International Speedway, where the plates mean that much less power is available to push the large bodies through the air. Race cars reach their highest speeds on these superspeedways, so the aerodynamic forces are highest and the effects of drafting are strongest. Since restrictor plates were first used as a safety device, their effect has changed the nature of drafting. Vehicles no longer have sufficient horsepower or throttle response to maintain their drafting speeds upon exiting the draft; they can pull out and squeeze ahead but lack the response to clear the car being passed. This negates the slingshot maneuver. As a result, passing is often the result of cooperation between two or more drivers or is achieved by sucking air off the side of the car being passed, a technique called side-drafting. [6]
Bump drafting is a tactic used at Talladega and Daytona. The technique was initially popularized by the Archer Brothers in the SCCA Sportruck series during the late 1980s. [7] It begins as normal drafting, but the following car pulls up behind the lead car and bumps into the rear of it, pushing the lead car ahead, to maintain momentum.
If done roughly or in the wrong position (e.g. close to the entry of the turn), this tactic can destabilize the handling of the lead car, sometimes causing a crash. Use of the tactic in this manner is known as slam drafting. Due to the danger, NASCAR has attempted to limit the bracing on bumpers on cars, disallowed bump drafting in turns, introduced "no bump zones" on certain portions of speedways where this practice is prevalent, and penalized drivers who are too rough in bump drafting. The 2010 NASCAR season allowed drivers more freedom; bump drafting was allowed anywhere, including turns.
Kyle Busch is largely responsible for a different type of bump drafting, which is now referred to as "two-car drafting"[ citation needed ] and "tandem drafting". [8] At a 2007 test session in Talladega, he asked Ryan Newman to push him from behind, and was stunned to realize he was two seconds faster with Newman's help. At the newly paved Daytona International Speedway in 2011, Busch was the first to realize that the corners were smooth enough to allow a two-car draft for the complete length of the track. During test sessions on the track, when Busch was pushed by his brother Kurt's Penske Racing teammate Brad Keselowski, they ran 15 mph faster than single cars. Other drivers quickly picked up on Busch's strategy, and the two-car draft dominated the 2011 Daytona 500 and Budweiser Shootout. [9] This strategy had also been very prominent at Talladega. In 2011, two-car tandem drafting was used for the extent of the Aaron's 499, with many drivers drafting their own teammates (e.g., Jimmie Johnson and Dale Earnhardt Jr. drafted together, as did Jeff Gordon and Mark Martin). For the 2012 season, the Sprint Cup series cars were modified in a way that made the tandem impossible, in order to return to pack racing. In 2014, bump drafting was banned by NASCAR in the Nationwide Series and Camping World Truck Series. Tandem Drafting made a return when NASCAR removed the restrictor plate and replaced them with Tapered Spacers, and with the flat noses and bumpers of the modern Gen 6 cars, drivers could more easily tandem and gain speed, much like the early 2010s. After Ryan Newman's scary crash in the 2020 Daytona 500, NASCAR made efforts to change drafting at superspeedways, where less horsepower was used: the removal of aero ducts to eliminate tandem drafting and decrease closing rates, and a smaller throttle body to lower the amount of air into a racecar. [8]
Some drivers have been known to draft behind other vehicles, particularly tailgating larger vehicles, to save fuel. For example, hypermilers using this technique can achieve 75 mpg or more (a 10% increase in efficiency of certain hybrid vehicles). [10] Some sources say that the most common tailgating does not save gasoline even at freeway speeds because one is likely to accelerate and brake so frequently that any aerodynamic savings are lost through the brakes. [11]
On the show MythBusters , drafting behind an 18-wheeler truck was tested and results showed that traveling 100 feet (30 m) behind the truck increased overall mpg efficiency by 11%. [12] Traveling 10 feet (3.0 m) behind the truck produced a 39% gain in efficiency. Additionally, on the same episode, MythBusters demonstrated that it can be very dangerous for the following car if one of the truck's tires (or their recaps) delaminate, as the chunks of ejected rubber can be large enough to cause serious harm, even death, to a driver following too closely. [13]
Drafters also face the danger that, if the vehicle in front stops suddenly, there is little time to react. Platooning is under study as a means to get the benefit while also increasing safety.
Computer simulation (computational fluid dynamics or CFD) is increasingly being used to analyse drafting. It is important to understand the aerodynamic behaviour of a motor vehicle when drafting, for example if the rear car is too close to the front car, the air supply to its radiator will be reduced and there is a possibility of the engine overheating. Most motor sport aerodynamic analysis is performed using wind tunnel testing. This becomes difficult for drafting cases, if only because a very large wind tunnel is needed. CFD, a kind of virtual wind tunnel, is used by race teams to understand the car's performance while drafting.
Racing games, such as most in the Mario Kart series, simulate drafting by giving the player a speed boost.
Animals have been observed to use true drafting behavior reminiscent of auto racing or cycling. Caribbean spiny lobsters for example are known to migrate in close single-file formation "lobster trains". [14] [15]
Vortex surfing is a related phenomenon that is currently being investigated by the US Air Force to save fuel on long-distance flights. The idea is to fly aircraft in the upward part of the wingtip vortex of a leading aircraft. [16] In 2003, NASA said one of its F/A-18 test aircraft had a 29% fuel savings by flying in the wingtip vortex of a DC-8. The DC-8/F-18 flight was an exploratory investigation of large aircraft vortex-induced performance benefits on a fighter-type aircraft. The aircraft flew at 25,000 feet with a separation of about 200 feet nose-to-tail. The F/A-18 slowly moved in laterally to explore the vortex effects, NASA said at the time. [17] [18] The Air Force has also tested vortex surfing with C-17s using auto pilot in 2012, and indicated a 10% fuel saving. [16] Tests in 2013 produced even greater fuel savings. [19]
Cooperative fluid dynamics techniques like drafting are also found in nature. Flocks of geese and some other birds fly in a V formation because the wingtip vortices generated by the front bird will create up-wash circulations. The birds flying behind will receive lift force from these up-wash vortices. Thus other birds in the flock do not need to work as hard to achieve lift. Studies show that birds in a V formation place themselves roughly at the optimum distance predicted by simple aerodynamic theory. [20]
An open-wheel car is a car with the wheels outside the car's main body, and usually having only one seat. Open-wheel cars contrast with street cars, sports cars, stock cars, and touring cars, which have their wheels below the body or inside fenders. Open-wheel cars are built both for road racing and oval track racing. Street-legal open-wheel cars, such as the Ariel Atom, are scarce as they are often impractical for everyday use.
Stock car racing is a form of automobile racing run on oval tracks and road courses measuring approximately 0.25 to 2.66 miles. It originally used production-model cars, hence the name "stock car", but is now run using cars specifically built for racing. It originated in the southern United States; its largest governing body is NASCAR. Its NASCAR Cup Series is the premier top-level series of professional stock car racing. Australia, Canada, New Zealand, Mexico, Brazil and the United Kingdom also have forms of stock car racing. Top-level races typically range between 200 and 600 miles in length.
Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce downforce to improve traction and thus cornering abilities.
A slipstream is a region behind a moving object in which a wake of fluid is moving at velocities comparable to that of the moving object, relative to the ambient fluid through which the object is moving. The term slipstream also applies to the similar region adjacent to an object with a fluid moving around it. "Slipstreaming" or "drafting" works because of the relative motion of the fluid in the slipstream.
Downforce is a downwards lift force created by the aerodynamic features of a vehicle. If the vehicle is a car, the purpose of downforce is to allow the car to travel faster by increasing the vertical force on the tires, thus creating more grip. If the vehicle is a fixed-wing aircraft, the purpose of the downforce on the horizontal stabilizer is to maintain longitudinal stability and allow the pilot to control the aircraft in pitch.
A Formula One car or F1 car is a single-seat, open-cockpit, open-wheel formula racing car with substantial front and rear wings, and an engine positioned behind the driver, intended to be used in competition at Formula One racing events. The regulations governing the cars are unique to the championship and specify that cars must be constructed by the racing teams themselves, though the design and manufacture can be outsourced. Formula One cars are the fastest cars in the world around a race track, owing to very high cornering speeds achieved through the generation of large amounts of aerodynamic downforce. Due to the amount of braking force and the total cornering envelope of a Formula One car, Formula One drivers experience frequent lateral g-loadings in excess of five g and peak cornering forces of up to seven lateral g.
Talladega Superspeedway, nicknamed "Dega", and formerly named Alabama International Motor Speedway (AIMS) from 1969 to 1989, is a motorsports complex located in Lincoln, Alabama, north of Talladega, Alabama. It is located on the former Anniston Air Force Base. A tri-oval, the track was constructed in 1969 by the International Speedway Corporation, a business controlled by the France Family. As of 2023, the track hosts the NASCAR Cup Series, NASCAR Xfinity Series, NASCAR Craftsman Truck Series, and ARCA Menards Series. Talladega is the longest NASCAR oval, with a length of 2.660 mi (4.281 km), compared to the Daytona International Speedway, which is 2.500 mi (4.023 km) long. The total peak capacity of Talladega is around 175,000 spectators, with the main grandstand capacity being about 80,000. As of 2023, Talladega is one of NASCAR's three drafting tracks, alongside Daytona International Speedway and Atlanta Motor Speedway.
A restrictor plate or air restrictor is a device installed at the intake of an engine to limit its power. This kind of system is occasionally used in road vehicles for insurance purposes, but mainly in automobile racing, to limit top speed to provide equal level of competition, and to lower costs; insurance purposes have also factored in for motorsports.
Oval track racing is a form of motorsport that is contested on an oval-shaped race track. An oval track differs from a road course in that the layout resembles an oval with turns in only one direction, and the direction of traffic is almost universally counter-clockwise. Oval tracks are dedicated motorsport circuits, used predominantly in the United States. They often have banked turns and some, despite the name, are not precisely oval, and the shape of the track can vary.
The Car of Tomorrow was the common name used for the chassis of the NASCAR Cup Series and Xfinity Series race cars. The car was part of a five-year project to create a safer vehicle following several deaths in competition, particularly the crash at the 2001 Daytona 500 that killed Dale Earnhardt.
In car design, ground effect is a series of effects which have been exploited in automotive aerodynamics to create downforce, particularly in racing cars. This has been the successor to the earlier dominant aerodynamic focus on streamlining. The international Formula One series and American racing IndyCars employ ground effects in their engineering and designs. Similarly, they are also employed in other racing series to some extent; however, across Europe, many series employ regulations to limit its effectiveness on safety grounds.
The 2006 Daytona 500 was the first stock car race of the 2006 NASCAR Nextel Cup Series. The 48th Daytona 500 was held on February 19, 2006, at Daytona International Speedway in Daytona Beach, Florida, before 200,000 spectators. Hendrick Motorsports' Jimmie Johnson, won the 203-lap race after starting ninth. Chip Ganassi Racing's Casey Mears and Penske Racing South's Ryan Newman finished second and third, respectively.
The following is a glossary of terminology used in motorsport, along with explanations of their meanings.
Fuel injection in NASCAR was introduced in 2012, having previously been announced for 2011, which was the last season to see the premier NASCAR series use carburetion. Only the Xfinity Series uses carburetors through into 2021, with no announced change to injection.
The 2012 Daytona 500 was the first stock car race of the 2012 NASCAR Sprint Cup Series season. The 54th iteration of the event, it was held between February 27 and 28, 2012 at Daytona International Speedway in Daytona Beach, Florida, before a crowd of 140,000. Matt Kenseth driving for Roush Fenway Racing took the 202-lap race for his first win of the season and his second Daytona 500 victory. Dale Earnhardt Jr. finished second and Greg Biffle was third.
The 2012 Budweiser Shootout was the first exhibition stock car race of the 2012 NASCAR Sprint Cup Series. The 34th annual running of the Budweiser Shootout, it was held on February 18, 2012 at the Daytona International Speedway in Daytona Beach, Florida, before a crowd of 82,000 people. Kyle Busch of the Joe Gibbs Racing team won the 82-lap race. It was Busch's first victory in the event; Stewart-Haas Racing driver Tony Stewart finished second with Richard Petty Motorsports racer Marcos Ambrose third.
The 2003 Budweiser Shootout was the first of two exhibition stock car races of the 2003 NASCAR Winston Cup Series. The 25th Budweiser Shootout, and the first to be held at night to allow for prime time broadcasting, it was held on February 8, 2003, in Daytona Beach, Florida, at Daytona International Speedway, before a crowd of 75,000 spectators. Dale Earnhardt Jr. of Dale Earnhardt, Inc. won the 70-lap race from 19th. Hendrick Motorsports's Jeff Gordon was second, with Roush Racing's Matt Kenseth third. It was Earnhardt's first Budweiser Shootout win, and his first at Daytona International Speedway in the Cup Series since the 2001 Pepsi 400.
The 2020 Daytona 500, the 62nd running of the event, was a NASCAR Cup Series race held on February 16–17, 2020. It was contested over 209 laps—extended from 200 laps due to an overtime finish, on the 2.5-mile (4.0 km) asphalt superspeedway. It was the first race of the 2020 NASCAR Cup Series season.
NASCAR, the highest governing body and top level division for stock car racing in the United States, has used a range of different types of engine configurations and displacements since its inaugural season in 1949. The engines are currently used in the Cup Series, Xfinity Series, Camping World Truck Series, and the Whelen Modified Tour.
The 2023 Daytona 500 was a NASCAR Cup Series race and the 65th running of the event. It was held on Sunday, February 19, 2023, at Daytona International Speedway in Daytona Beach, Florida. It was the first race of the 2023 NASCAR Cup Series. Jimmie Johnson returned to the Cup Series for Legacy Motor Club in this race. This was the longest Daytona 500 in history going 530 miles.
