Drafting (racing)
Encyclopedia
Drafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
due to exploiting the lead object's slipstream
Slipstream
A slipstream is a region behind a moving object in which a wake of fluid is moving at velocities comparable to the moving object . The term slipstream also applies to the similar region adjacent to an object with a fluid moving around it...
. Especially when high speeds are involved,as in motor racing and cycling, drafting can significantly reduce the paceline's average energy expenditure required to maintain a certain speed and can also slightly reduce the energy expenditure of the lead vehicle or object.
Drafting in sport
Drafting is used to reduce wind resistance and is seen most commonly in bicycle racingBicycle racing
Bicycle racing is a competition sport in which various types of bicycles are used. There are several categories of bicycle racing including road bicycle racing, cyclo-cross, mountain bike racing, track cycling, BMX, bike trials, and cycle speedway. Bicycle racing is recognised as an Olympic sport...
, car racing, and speedskating, though drafting is occasionally used even in cross-country skiing
Cross-country skiing
Cross-country skiing is a winter sport in which participants propel themselves across snow-covered terrain using skis and poles...
and running
Running
Running is a means of terrestrial locomotion allowing humans and other animals to move rapidly on foot. It is simply defined in athletics terms as a gait in which at regular points during the running cycle both feet are off the ground...
. Some forms of triathlon
Triathlon
A triathlon is a multi-sport event involving the completion of three continuous and sequential endurance events. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances...
allow drafting. Drafting occurs in swimming
Swimming (sport)
Swimming is a sport governed by the Fédération Internationale de Natation .-History: Competitive swimming in Europe began around 1800 BCE, mostly in the form of the freestyle. In 1873 Steve Bowyer introduced the trudgen to Western swimming competitions, after copying the front crawl used by Native...
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 separating 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
Longboarding
Longboarding is the act of riding on a longboard.Longboarding is an offshoot of street skating, but, like all board sports, its roots lie in surfing. Developed as a single sport on the west coast in the 1950s, by the 1990s, Longboards and Skateboards branched off into their respective disciplines...
.
It is believed, but not yet conclusively proven, that Thoroughbred
Thoroughbred
The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
racing horses draft each other, especially in longer races.
Bicycle racing
Road bicycle racing
Road bicycle racing is a bicycle racing sport held on roads, using racing bicycles. The term "road racing" is usually applied to events where competing riders start simultaneously with the winner being the first to the line at the end of the course .Historically, the most...
the main (largest) group of tightly packed cyclists in a race is called a peloton
Peloton
The peloton , field, bunch or pack is the large main group of riders in a road bicycle race. Riders in a group save energy by riding close near other riders...
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
Road bicycle racing
Road bicycle racing is a bicycle racing sport held on roads, using racing bicycles. The term "road racing" is usually applied to events where competing riders start simultaneously with the winner being the first to the line at the end of the course .Historically, the most...
. Each cyclist (but not 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 him or her more energy for a break-away push to the finish line.
Open-wheel racing
In single seater, open wheel racing series such as Formula OneFormula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...
and the IndyCar Series
IndyCar Series
The IZOD IndyCar Series is the premier level of American open wheel racing. The current championship, founded by Indianapolis Motor Speedway owner Tony George, began in 1996 as a competitor to CART known as the Indy Racing League . Citing CART's increasing reliance on expensive machinery and...
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 he has 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
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
) air that comes off the lead car unbalances the trailing car as its aerodynamic devices provide less grip. However, on the straight this effect is much less of a detriment due to the lower levels of grip required.
Stock car racing
NASCAR
The National Association for Stock Car Auto Racing is a family-owned and -operated business venture that sanctions and governs multiple auto racing sports events. It was founded by Bill France Sr. in 1947–48. As of 2009, the CEO for the company is Brian France, grandson of the late Bill France Sr...
, ARCA
Automobile Racing Club of America
Automobile Racing Club of America is an auto racing sanctioning body in the United States, founded in 1953 by John Marcum. The current president of ARCA is Ron Drager. The ARCA RE/MAX Series races stock cars similar to those seen in past years in the NASCAR Sprint Cup Series, and indeed most cars...
, and at one time the IROC
International Race of Champions
International Race of Champions, better known as IROC, was a North American auto racing competition, promoted as an equivalent of an American All-Star Game or The Masters...
series, 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.
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.
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.
Drafting was discovered by stock car racers in the 1959 Daytona 500
Daytona 500
The Daytona 500 is a -long NASCAR Sprint Cup Series race held annually at the Daytona International Speedway in Daytona Beach, Florida. It is one of four restrictor plate races on the Cup schedule....
. 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 than a single car running by itself.
Bump drafting
Drafting is most important at Talladega Superspeedway
Talladega Superspeedway
Talladega Superspeedway is a motorsports complex located north of Talladega, Alabama, United States. It is located on the former Anniston Air Force Base just outside the small city of Lincoln. It was constructed by International Speedway Corporation, a business controlled by the France Family, in...
and Daytona International Speedway
Daytona International Speedway
Daytona International Speedway is a race track in Daytona Beach, Florida, United States. Since opening in 1959, it has been the home of the Daytona 500, one of the most prestigious races in NASCAR. In addition to NASCAR, the track also hosts races of ARCA, AMA Superbike, Grand-Am and Motocross...
where a restrictor plate
Restrictor plate
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 and thus increase safety, to provide equal level of...
is used, making much less power 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.
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. 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
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
.
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
NASCAR
The National Association for Stock Car Auto Racing is a family-owned and -operated business venture that sanctions and governs multiple auto racing sports events. It was founded by Bill France Sr. in 1947–48. As of 2009, the CEO for the company is Brian France, grandson of the late Bill France Sr...
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 allows drivers more freedom. Bump drafting is allowed anywhere, including turns.
Kyle Busch
Kyle Busch
Kyle Thomas Busch, is an American NASCAR driver and team owner. He currently drives the No. 18 Mars/Interstate Batteries Toyota Camry for Joe Gibbs Racing in the Sprint Cup Series, the No. 18 Z-Line Designs/NOS Energy Drink Toyota Camry for Joe Gibbs in the Nationwide Series, and the No...
is largely responsible for the current popularity of bump drafting, which is now referred to as 'two-car drafting'. At a 2007 test session in Talladega, he asked Ryan Newman
Ryan Newman
Ryan Joseph Newman is a driver in the NASCAR Sprint Cup Series. He drives the #39 United States Army/Tornados/Haas Automation Chevrolet Impala for Stewart Haas Racing under crew chief Tony Gibson. Newman graduated from Purdue University in 2001 with a B.S. in vehicle structure engineering...
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
Daytona International Speedway
Daytona International Speedway is a race track in Daytona Beach, Florida, United States. Since opening in 1959, it has been the home of the Daytona 500, one of the most prestigious races in NASCAR. In addition to NASCAR, the track also hosts races of ARCA, AMA Superbike, Grand-Am and Motocross...
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's teammate Brad Keselowski
Brad Keselowski
Bradley Robert Keselowski is an American auto racing driver currently competing in the #2 Miller Lite Dodge Charger in the Sprint Cup Series and the #22 Discount Tire Company/Ruby Tuesday Dodge Challenger in the Nationwide Series for Penske Racing...
, they were running 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
2011 Daytona 500
The 2011 Daytona 500, the 53rd running of the event, was held on February 20, 2011 at Daytona International Speedway in Daytona Beach, Florida over 200 laps on the 2.5 mile asphalt tri-oval. First race of the 2011 Sprint Cup Series season, it was won by the Wood Brothers...
and Budweiser Shootout
2011 Budweiser Shootout
The 2011 Budweiser Shootout was a NASCAR Sprint Cup Series stock car race that was held on February 12, 2011 at Daytona International Speedway in Daytona Beach, Florida. Contested over 75 laps, it was the first exhibition race of the 2011 Sprint Cup Series season. The race was won by Kurt...
.
Drafting in nature
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....
and some other birds fly in a V formation because the wingtip vortices
Wingtip vortices
Wingtip vortices are tubes of circulating air that are left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. The cores of vortices spin at very high speed and are regions of very low pressure...
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. The theory behind this is the same as the one for the wings of an airplane in general. However it does not work quite the same way as drafting in racing. Birds fly in a flock for better lifting force whereas the race cars stay close for less total aerodynamic drag force.
Other 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".
Tailgating and hypermiling
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). Some sources say that the most common tailgatingTailgating
Tailgating is the practice of driving on a road too close to the vehicle in front, at a distance which does not guarantee that stopping to avoid collision is possible...
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. On the show Mythbusters
MythBusters
MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...
, drafting behind an 18-wheeler truck was tested and results showed that traveling 100 feet (30.5 m) behind the truck increased overall mpg efficiency by 11%. Traveling 10 feet (3 m) behind the truck produced a 39% gain in efficiency. Of course, they warn that this type of driving "is insane" because the truck's blindspot is in that area, and if the truck stops quickly there is much less time to react. Truckers are not fond of the extra stress this puts on them, worrying about cars on their tail. Additionally, it can be very dangerous for the following car if one of the truck's tires (or their recaps
Retread
A retread, or "recap," is a previously worn tire which has gone through a remanufacturing process designed to extend its useful service life.Retreading starts with a safety inspection of the tire. The old tread is then buffed away, and a new rubber tread is applied to the bare "casing" using...
) delaminate
Delamination
Delamination is a mode of failure for composite materials. Modes of failure are also known as 'failure mechanisms'. In laminated materials, repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical...
, as the chunks of ejected rubber can be large enough to cause serious harm, even death, to a driver following too closely.
Computer simulation of drafting
Computer simulation (computational fluid dynamicsComputational fluid dynamics
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with...
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.