McLaren Aerodynamics: The Evolution of Airflow, Airbrakes, Underfloors and Ground Effect

Aerodynamics on a McLaren is not simply about fitting a large rear wing to generate downforce.

The underlying philosophy is considerably more sophisticated.

Air travelling towards the car has to be divided, accelerated, slowed, redirected and ultimately released while performing several different jobs. Some airflow is used to create aerodynamic load. Some is directed towards radiators, brakes and the powertrain for cooling. Some is deliberately guided around the rotating wheels, while other airflow is accelerated underneath the vehicle before being expanded through the rear diffuser.

The challenge for McLaren's aerodynamic engineers is therefore not merely to create downforce.

It is to manage the energy of the airflow throughout the entire vehicle.

Over successive generations of McLaren road cars, this philosophy has evolved from carefully managed passive airflow and active airbrakes into increasingly sophisticated integrated aerodynamic systems.

The latest McLaren W1 represents perhaps the clearest expression of this development: McLaren officially describes the car as using ground-effect aerodynamics with an active front splitter and McLaren Active Long Tail.

Understanding how McLaren reached that point requires understanding what actually happens to the air as it passes through, over and beneath a supercar.

The Fundamental Physics Behind McLaren Aerodynamics

At speed, a car has to push through a mass of air.

That interaction creates pressure differences around the body.

A simplified aerodynamic force relationship is:

F = ½ × ρ × V² × A × C

where:

ρ = air densityV = vehicle speedA = reference areaC = aerodynamic coefficient

One of the most important consequences is that aerodynamic forces increase approximately with the square of vehicle speed.

Double the vehicle speed and, under otherwise comparable conditions, aerodynamic forces become approximately four times greater.

This is why aerodynamic control becomes increasingly important as speed rises.

For a road-going supercar, however, producing maximum downforce is not automatically the best solution.

Increasing aerodynamic load frequently increases drag.

The real engineering objective is therefore aerodynamic efficiency: producing the required stability and tyre loading while minimising unnecessary resistance.

Downforce Is Only Part of the Equation

A high-performance vehicle has several competing aerodynamic requirements:

Low drag for acceleration and maximum speed.

Front downforce for steering authority.

Rear downforce for stability and traction.

Cooling airflow for radiators and heat exchangers.

Brake cooling.

Engine or powertrain intake airflow.

Control of turbulence generated by rotating wheels.

Stable aerodynamic balance during braking.

Acceptable behaviour in yaw when the car is cornering or exposed to crosswinds.

Road-car ground clearance and suspension movement.

The airflow required for one function may disturb another.

For example, opening a large cooling inlet can improve thermal performance but increase drag.

Increasing rear-wing angle may create additional rear downforce but alter the aerodynamic balance of the entire vehicle.

Aerodynamic development is therefore fundamentally about managing compromises.

How Air Moves Around a McLaren

When a McLaren travels through the atmosphere, the air approaching the vehicle separates into several primary flow paths.

Airflow Over the Car

Some air travels across the bonnet, windscreen, roof and rear bodywork.

The objective is generally to maintain attached, predictable airflow for as long as practical.

Abrupt geometry changes can create flow separation.

Once the boundary layer separates from the body, large turbulent wake structures can develop. These typically increase pressure drag and can reduce the effectiveness of downstream aerodynamic devices.

Consequently, seemingly aesthetic surfaces on a modern McLaren may also perform aerodynamic work by controlling pressure gradients and maintaining useful airflow.

Airflow Around the Car

Another major portion of the airflow travels around the vehicle's sides.

One particularly difficult region is the front wheel.

A rotating exposed road-car tyre produces a highly disturbed, energetic wake. Engineers therefore try to prevent this turbulent air from contaminating aerodynamic devices farther downstream.

Body sculpting, wheel-arch treatment, turning surfaces and carefully positioned outlets can all help manage this region.

Airflow Through the Car

Modern McLarens increasingly allow air to travel through body structures rather than simply around them.

This approach can provide cooling while also reducing the aerodynamic penalty normally associated with forcing cooling air into the vehicle.

The Artura, for example, uses hidden door inlet ducts and rear buttresses as part of its airflow-management strategy. McLaren describes the body as directing air over, under and through the car.

This is an important distinction.

An aerodynamic opening is not necessarily there only to create downforce.

It may be supplying:

radiators,

engine cooling,

charge-air heat exchangers,

brakes,

or another thermal-management component.

The location where that air exits can be almost as important as where it enters.

McLaren Underfloor Aerodynamics

The underside of a performance car is one of the most valuable aerodynamic regions available to the engineer.

Unlike a conventional wing mounted high on the body, useful aerodynamic load can be generated underneath the car without requiring a visually dominant external aerodynamic device.

Why the Underfloor Matters

Air approaching the underside can be guided through carefully controlled passages.

Where the geometry causes airflow to accelerate, static pressure can fall.

A properly designed underbody can therefore create a lower average pressure beneath sections of the vehicle relative to the pressure acting above them.

The resulting pressure differential contributes to aerodynamic load.

This does not, however, mean that every flat-bottomed McLaren should automatically be called a “ground-effect car”.

There is an important technical distinction between:

general underbody aerodynamic management,

flat floors,

diffusers,

venturi-shaped channels,

and a vehicle explicitly designed around ground-effect tunnels.

Those terms should not be used interchangeably.

How a Rear Diffuser Works

At the rear of the vehicle, the underfloor typically has to transition back towards ambient external conditions.

A diffuser does this by gradually increasing the cross-sectional area available to the airflow.

The objective is to decelerate the underbody airflow progressively and recover pressure without causing excessive separation.

If the expansion angle or pressure gradient becomes too aggressive, airflow may detach from the diffuser surface.

When that occurs, diffuser performance can deteriorate significantly.

The diffuser therefore forms part of an interconnected system involving:

the front of the floor,

vehicle ride height,

floor geometry,

air leakage from the sides,

rear body pressure,

and external wake structure.

It should never be considered an isolated component.

Ride Height, Pitch and Aerodynamic Performance

Underfloor systems are particularly sensitive to the distance between the vehicle and the road.

Reducing ride height can strengthen certain underfloor aerodynamic effects, but only to a point.

If the floor becomes excessively close to the surface, the airflow can become restricted or unstable.

Pitch is equally important.

During braking the front suspension compresses and the rear may rise.

During acceleration the opposite occurs.

Consequently, the shape of the aerodynamic passage beneath the vehicle is continuously changing.

An advanced supercar therefore requires the aerodynamic package and suspension behaviour to be developed together.

This interaction becomes increasingly important as a greater percentage of total aerodynamic load is generated underneath the vehicle.

McLaren Air Ducts: Not Every Hole Is an Air Intake

Perhaps one of the most misunderstood aspects of supercar aerodynamics is the duct.

A duct may perform several completely different functions.

Cooling Ducts

Cooling ducts collect high-pressure external air and direct it towards a component that needs thermal management.

Possible destinations include:

radiators,

engine heat exchangers,

brake discs,

brake callipers,

turbocharger-related cooling systems,

and powertrain components.

After absorbing heat, this airflow must be discharged.

Poorly located outlets can create aerodynamic penalties, so cooling exits must also be integrated into the external airflow.

Brake Cooling Ducts

Braking from very high speed transforms enormous amounts of kinetic energy into heat.

Brake ducts therefore have to deliver sufficient air towards the discs and associated components without introducing excessive aerodynamic drag.

For a road-and-track supercar this is particularly challenging because brake cooling requirements differ enormously between normal road use and repeated heavy circuit braking.

Aerodynamic Ducts

Some openings exist principally to manipulate airflow rather than cool a component.

They may:

redirect high-energy airflow,

control wheel wake,

energise another aerodynamic surface,

extract high-pressure air,

reduce separation,

or feed another part of the underbody system.

The distinction becomes particularly interesting on the McLaren W1.

McLaren states that structures resembling brake ducts do considerably more than cool the discs and callipers. They also work with the Aerocell architecture to manage airflow around the tyres, contribute to aerodynamic load and provide cleaner airflow towards the rear radiators and diffuser.

That is a good example of modern aerodynamic integration: one airflow path performing several jobs simultaneously.

The McLaren 12C and the Modern McLaren Aero Philosophy

The 12C marked McLaren Automotive's return to series-production road cars and established many principles that would become familiar on later models.

McLaren states that hundreds of hours of computational fluid dynamics and extensive wind-tunnel work went into shaping the 12C.

Rather than treating aerodynamics as an accessory added after the basic body had been designed, airflow became part of the vehicle architecture.

One particularly recognisable McLaren solution was the active rear aerodynamic surface, commonly associated with the company's modern Airbrake concept.

How a McLaren Airbrake Works

An airbrake differs from a conventional fixed rear spoiler because its position can change.

When positioned at a comparatively low angle, an active rear aerodynamic surface can operate as part of the normal aerodynamic package.

When commanded towards a more aggressive position, the aerodynamic effect changes substantially.

Airbrake Mode During Heavy Braking

Raising the rear surface increases its aerodynamic resistance and changes the aerodynamic load acting on the rear axle.

The aerodynamic drag contributes to vehicle deceleration, although it does not replace the mechanical braking system.

Arguably more important is the ability to influence rear aerodynamic loading during a braking event.

Under heavy braking, longitudinal weight transfer shifts mechanical load towards the front tyres.

An appropriately controlled active rear aerodynamic surface can help maintain useful aerodynamic loading at the rear and contribute to high-speed stability.

The system is therefore much more sophisticated than simply acting as an aeroplane-style drag flap.

The McLaren P1: Active Aerodynamics Become Central to the Vehicle

The McLaren P1 represented a major development in McLaren's road-car aerodynamic philosophy.

Its body was tightly packaged around the mechanical components to minimise unnecessary frontal area and direct airflow towards the vehicle's cooling and aerodynamic systems.

More importantly, active aerodynamic control was central to the car.

McLaren states that the P1 uses moveable front and rear aerodynamic devices and that the system can generate a peak of 600 kg of downforce.

The important engineering lesson is not simply the figure.

The significance of active aerodynamics is the ability to change the aerodynamic configuration according to operating conditions.

Instead of accepting one permanent compromise between drag and downforce, the vehicle can alter its aerodynamic state.

McLaren 720S: Airflow Through the Body

The 720S introduced another important step.

At first glance, parts of the car appear surprisingly free of the enormous side air intakes traditionally associated with mid-engined supercars.

Instead, airflow management became increasingly integrated into the body architecture.

The famous double-skin door construction and surrounding surfaces allowed McLaren's designers to manage cooling airflow while maintaining a very clean external profile.

The rear aerodynamic surface remained active; McLaren's official specification classifies the 720S aerodynamics as Active Rear.

The broader development philosophy was increasingly clear:

rather than simply attaching aerodynamic devices to the body, the body itself became the aerodynamic device.

McLaren Senna: Downforce Takes Priority

Where the 720S had to combine enormous performance with everyday usability and relatively elegant aerodynamic integration, the McLaren Senna had a different objective.

Track performance took priority.

The result was a much more visibly aerodynamic vehicle.

Large openings, aerodynamic blades, an aggressive diffuser and substantial active rear wing were justified by function rather than styling convention.

The related Senna GTR pushed the idea even further.

McLaren describes the GTR's active rear wing as incorporating both airbrake and drag-reduction functionality and operating in conjunction with front aero blades. The GTR produces up to 1,000 kg of downforce, according to McLaren.

This illustrates another important concept: aerodynamic balance.

Generating huge rear downforce is not sufficient.

Front and rear aerodynamic load must remain appropriately balanced so that steering response and rear stability develop predictably as speed increases.

Drag Reduction Versus Maximum Downforce

A wing configured for maximum aerodynamic loading normally also creates significant induced and profile drag.

At very high speed, this resistance can limit acceleration.

Active systems can therefore reduce the aerodynamic aggressiveness of a wing when maximum downforce is unnecessary.

This is the basic principle behind a drag-reduction configuration.

The reverse can occur under braking or cornering, when additional aerodynamic load is more valuable than minimum drag.

Active aerodynamics therefore gives the control system another variable alongside:

engine torque,

braking,

damping,

differential control,

and stability systems.

The McLaren Speedtail: Aerodynamics for Low Drag

The Speedtail demonstrates the opposite end of McLaren's aerodynamic spectrum.

Rather than maximising circuit downforce, the design priority was extremely efficient airflow for very high speed.

McLaren removed conventional exterior mirrors in favour of cameras and used carbon-fibre front-wheel aerodynamic covers to reduce disturbances around the front wheels.

One of its most unusual features is the use of flexible active rear aerodynamic surfaces integrated directly into the rear bodywork.

McLaren describes the Speedtail concept as generating additional aerodynamic load when necessary while reducing drag when it is not required.

The significance of the Speedtail is important.

Aerodynamic sophistication does not necessarily mean producing the maximum possible downforce.

Sometimes the objective is precisely the opposite:

maintaining stability while disturbing the air as little as possible.

McLaren Artura: Integrated Passive Aerodynamics

The Artura demonstrates another branch of McLaren aerodynamic development.

Unlike cars that depend heavily upon a prominent active rear aerodynamic device, McLaren lists the standard Artura's aerodynamics as static.

Its body instead uses carefully integrated passive airflow management.

McLaren specifically identifies hidden door inlet ducts and rear buttresses as devices that channel airflow over, underneath and through the vehicle.

This illustrates how passive aerodynamic engineering can still be extremely sophisticated.

Active aero is a tool — not automatically a superior solution for every vehicle.

McLaren 750S: Refining the 720S Formula

The 750S continues the aerodynamic architecture developed around the 720S while refining the complete vehicle package.

McLaren officially lists the 750S as using active rear aerodynamics.

The distinction is worth noting because McLaren's aerodynamic development does not follow a simple progression where every new model receives increasingly aggressive active devices.

Each vehicle uses the aerodynamic strategy appropriate to its performance target.

A GT-oriented car, road-biased supercar and track-focused Ultimate Series model have very different requirements.

McLaren W1: Ground Effect Becomes the Centre of the Car

The W1 marks the most fundamental change in McLaren road-car aerodynamics discussed here.

Rather than primarily developing rear downforce from a conventional high-mounted rear wing, McLaren says the W1 was designed as a fully ground-effect car.

This is not merely an enthusiast description.

It is McLaren's own terminology.

The carbon-fibre Aerocell architecture itself was shaped around the aerodynamic requirement.

McLaren explains that the footbox was raised, the central portion of the vehicle narrowed and the door hinges relocated to create the physical space required for the underbody airflow architecture.

This demonstrates the extent to which aerodynamics has progressed.

The chassis is no longer simply carrying aerodynamic bodywork.

The chassis architecture itself is influenced by the airflow requirements.

The W1 Underfloor and Ground-Effect System

McLaren states that the majority of the W1's aerodynamic load is derived from its ground-effect system.

The principle involves using carefully controlled underbody airflow and pressure distribution to generate aerodynamic load efficiently.

The advantage is potentially substantial.

Producing a greater proportion of downforce underneath the vehicle can reduce dependence upon extremely large external wings.

However, ground-effect aerodynamics creates difficult engineering problems.

The system must remain predictable through:

ride-height changes,

pitch,

roll,

steering input,

yaw,

braking,

acceleration,

kerb strikes,

and changing road surfaces.

A road car must also operate across a much wider range of ride conditions than a Formula 1 car.

This makes producing controllable road-car ground effect considerably more complicated than simply designing an aggressive diffuser.

Active Front Aerodynamics on the McLaren W1

A powerful underfloor system also requires control at the front of the vehicle.

The W1 therefore incorporates an active front aerodynamic system.

McLaren explains that the moveable front surface regulates airflow entering the underfloor and helps control aerodynamic balance.

This is crucial.

If rear aerodynamic loading changes substantially without a corresponding change at the front, the aerodynamic centre of pressure shifts.

That can alter the vehicle's handling characteristics.

Modern active aerodynamics therefore increasingly concerns aero balance, not merely maximum downforce.

McLaren Active Long Tail

At the rear of the W1 is one of McLaren's most interesting active aerodynamic developments: the McLaren Active Long Tail.

In Race mode, McLaren says the structure extends rearwards by 300 mm.

McLaren further states that this effectively increases the functional length of the diffuser/underbody by around 20 per cent.

Together with the car lowering itself in Race mode and other aerodynamic changes, McLaren says the W1 can produce five times the downforce it generates in Road mode.

This is fundamentally different from simply fitting a bigger conventional rear wing.

The Active Long Tail interacts with the underbody airflow and diffuser system.

In other words, the rear body geometry becomes part of the floor's aerodynamic expansion process.

Why Wheel Aerodynamics Matter

Wheels are one of the most difficult parts of any road car to manage aerodynamically.

They rotate.

They steer.

They are partially exposed.

They sit inside complex wheel arches.

And the tyre itself continuously moves relative to the road surface.

The resulting airflow is highly three-dimensional and turbulent.

If uncontrolled, this wheel wake can contaminate cleaner airflow intended for:

the floor,

side bodywork,

cooling ducts,

or rear aerodynamic surfaces.

The W1 demonstrates the increasing importance McLaren places on this region.

McLaren specifically says airflow around the tyres is controlled using the aerodynamic structures around the Aerocell and compares part of the concept to the outwash-management philosophy of an F1 turning vane.

High Pressure, Low Pressure and Air Extraction

A useful aerodynamic principle is that the designer is often not simply asking:

“Where can we collect air?”

The equally important question is:

“Where should we release it?”

Cooling air entering a radiator loses energy as it passes through the heat exchanger.

If that air is released into an unfavourable pressure region, aerodynamic drag can increase.

Strategically positioned outlets can exploit lower-pressure regions of the external flow to encourage extraction.

This is why vents behind radiators, wheel arches or engine compartments are often carefully positioned and shaped.

They are not simply holes for hot air to escape.

Their performance depends upon the pressure field surrounding the vehicle.

Airflow Separation and Boundary Layers

Air directly touching the surface of the vehicle forms a boundary layer.

Within this thin region, airflow velocity changes from effectively zero at the solid surface to the velocity of the external airflow.

As air moves across a body surface it encounters changing pressure gradients.

If the airflow loses too much momentum while moving into an increasing-pressure region, the boundary layer can separate.

Flow separation creates turbulence and often increases drag.

This explains why apparently small details such as:

surface curvature,

spoiler edges,

duct lips,

diffuser angles,

wheel-arch outlets,

and trailing edges

can have disproportionately large aerodynamic effects.

Vortices: Sometimes the Enemy, Sometimes Useful

Vortices are rotating structures within the airflow.

Uncontrolled vortices generally represent energy being placed into airflow that may not contribute usefully to vehicle performance.

But deliberately generated vortices can also be useful.

Aerodynamicists can use controlled vortical structures to energise a boundary layer, influence flow separation or help control leakage between regions of different pressure.

The objective is therefore not simply to eliminate turbulence.

It is to make the airflow behave predictably.

Why Cooling and Aerodynamics Cannot Be Separated

A high-performance McLaren generates enormous quantities of heat.

The engine, turbochargers, transmission, brakes, hybrid systems and associated electronics may all require thermal management.

But every kilogram of air routed through a heat exchanger has aerodynamic consequences.

Cooling airflow therefore becomes part of the overall aerodynamic calculation.

An ideal system directs sufficient air through the required heat exchanger while minimising:

inlet drag,

internal pressure losses,

flow separation,

and inefficient discharge of heated air.

McLaren's development of the W1 provides a particularly clear example of this integration. During hot-weather validation, McLaren stated that the vehicle achieved the required balance between aerodynamic performance and cooling rather than treating the two objectives independently.

Active Aerodynamics Versus Passive Aerodynamics

Neither system is automatically better.

Passive Aerodynamics

Passive devices include:

splitters,

diffusers,

fixed wings,

floor channels,

body sculpting,

ducts,

vents,

air curtains,

and carefully designed trailing edges.

Their advantages include simplicity, low mass and immediate operation without actuators.

Active Aerodynamics

Active devices can alter their position according to operating conditions.

Potential advantages include:

higher downforce during cornering,

greater rear stability during braking,

lower drag on straights,

different aerodynamic balance for different driving modes,

and adaptation to vehicle speed and dynamic state.

Their disadvantages include additional actuators, software, sensors, mass and mechanical complexity.

McLaren has used both philosophies according to the objectives of each vehicle.

The Evolution of McLaren Aerodynamics

Looking across McLaren's modern road-car development, a clear engineering progression can be seen.

The 12C established aerodynamic integration and the modern McLaren active-rear-aero philosophy.

The P1 made active aerodynamic control central to an Ultimate Series hypercar and combined moving aerodynamic devices with very high downforce.

The 720S demonstrated how cooling airflow could increasingly be routed through the physical architecture of the body.

The Senna prioritised track performance, downforce and active aerodynamic control.

The Speedtail approached the problem from the opposite direction, prioritising aerodynamic efficiency and extremely low drag.

The Artura showed that sophisticated static aerodynamics and internal airflow management remain entirely relevant.

The 750S continued to refine the active-aero Super Series formula.

And the W1 moved the aerodynamic centre of the car dramatically towards an integrated ground-effect concept, active front airflow control and an Active Long Tail that interacts directly with the underfloor and diffuser system.

This is perhaps the most important evolution of all.

McLaren has moved progressively from designing aerodynamic components for the car towards designing the entire car around the airflow.

Why McLaren Aerodynamics Matter on the Road and Track

The benefit is not simply faster lap times.

Good aerodynamic engineering can improve:

high-speed stability,

braking confidence,

cornering performance,

thermal management,

tyre utilisation,

straight-line efficiency,

and overall vehicle predictability.

For a driver, the ideal result is not necessarily dramatic.

The car simply becomes more stable and more consistent as speed increases.

That consistency is particularly important on track, where aerodynamic load increasingly influences vehicle behaviour as velocity rises.

Aerodynamic Modifications Must Be Treated as a Complete System

One important lesson from McLaren's approach is particularly relevant when modifying high-performance road cars.

Aerodynamic components should never be considered independently.

Installing a larger rear wing does not simply “add grip”.

It changes rear aerodynamic load and therefore the overall aerodynamic balance.

Likewise, changing:

ride height,

front splitter geometry,

diffuser geometry,

underfloor panels,

cooling exits,

wheel design,

canards,

or rear-wing configuration

can affect other areas of the vehicle.

A component that looks more aggressive is not automatically aerodynamically superior.

For a correctly engineered track setup, the objective should always be aerodynamic balance rather than maximum isolated downforce.

Conclusion: McLaren's Real Aerodynamic Advantage

McLaren's aerodynamic development is much more sophisticated than the visible wings and airbrakes that attract most of the attention.

The important engineering occurs throughout the entire airflow path.

Air is managed before it reaches the front wheels.

It is divided between the upper body, cooling systems and underfloor.

It is redirected around rotating tyres.

It is accelerated and pressure-managed beneath the vehicle.

It is used for cooling.

It interacts with active aerodynamic surfaces.

And finally, it must be released into the wake as efficiently and predictably as possible.

The development from the 12C through P1, 720S, Senna, Speedtail, Artura and 750S to the W1 shows how deeply aerodynamic engineering has become integrated into McLaren vehicle architecture.

The W1 represents the logical extreme of that philosophy.

The carbon-fibre structure, suspension position, cooling strategy, active front aerodynamics, underfloor and Active Long Tail are no longer separate engineering systems.

They form parts of one controlled airflow system.

And that is perhaps the best way to understand modern McLaren aerodynamics:

the aim is not merely to push the car onto the road — it is to control where every useful stream of air goes, what work it performs on the way, and how cleanly it leaves the vehicle.

Frequently Asked Questions About McLaren Aerodynamics

What is the McLaren Airbrake?

A McLaren Airbrake is an active rear aerodynamic surface capable of changing position according to the vehicle's operating condition. During heavy braking, the surface can adopt a more aggressive angle, increasing aerodynamic drag and altering rear aerodynamic loading to contribute to high-speed stability.

Does a McLaren airbrake actually stop the car?

It contributes aerodynamic drag, but the vehicle's friction brakes remain responsible for the majority of braking force. An important additional benefit of an airbrake is its influence on aerodynamic balance and rear-axle loading during high-speed deceleration.

Does every McLaren use active aerodynamics?

No. McLaren chooses different aerodynamic strategies according to each vehicle's purpose. For example, McLaren officially classifies the Artura's aerodynamic system as static, while the 720S and 750S use active rear aerodynamics.

What is McLaren ground effect?

Ground effect refers to using the interaction between a vehicle's underbody airflow and the road surface to create useful pressure differences and aerodynamic load. McLaren explicitly describes the W1 as a fully ground-effect car.

Is a diffuser the same as ground effect?

No. A diffuser is one component used to manage and expand underbody airflow. Having a rear diffuser does not automatically make a vehicle a true ground-effect car.

Why does the W1 have active front aerodynamics?

McLaren uses an active front aerodynamic surface to regulate airflow towards the underfloor and help maintain the desired front-to-rear aerodynamic balance as the vehicle's aerodynamic configuration changes.

What does the McLaren W1 Active Long Tail do?

In Race mode the Active Long Tail extends rearwards. McLaren states that it effectively increases the functional length of the diffuser and underbody while working with the car's ground-effect aerodynamic system.