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The King of Spa

Floors and Diffusers ? The basics explained

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An F1 car is a complex vehicle, a lot of emphasis is placed on the things we can see, the wings and bodywork. Sometimes we can talk about less visible items such as engine, gearboxes, suspension or even electronics. But perhaps the least visible and detailed part of the car is the underbody. The floor and diffuser, that together create nearly half the cars downforce, for almost no drag. Underbody aerodynamics have been the key to F1 car?s ever faster laptimes. All we ever see of the underbody is the exit of the diffuser and sometimes, if seen from a low angle, the step under the cars floor. To aid explanations in my other articles on underbodies, I have summarised and simplified what the underbody consists of.


Reference plane



Reference plane: Red


This is the datum for the cars dimensions and is effectively the lowest part of the cars floor. When the old flat bottom regulations, dating back to the banning of ground effects in 1983 were revised in the wake of Senna?s 1994 crash, the floor has had to have a step along its length. So we see the stepped shape of the car in frontal profile, with the reference plane sitting lowest in the middle of the car. This step cannot be wider than 50cm or narrower than 30cm, the reference plane must by flat and run continuously from behind the front wheels to the rear axle line. The Reference planes leading portion, also forms the splitter, also known as the T-Tray or Bib.


Step plane



Step Plane: Yellow


Above the reference plane is the step plane, this is effectively the underside of the sidepods. This must sit 5cm above the reference plane. Again the surface must be flat and run from the complex regulated bodywork zone around the front of the sidepods to the rear axle line. A large clearance is mandated around the rear wheel to prevent teams sealing off the floor against the rear tyres.


Step or Transition



Step: Orange


In between the reference plane and step plane, is the step itself or transition. Simplistically there must be a vertical surface in between these two planes. Any intersections of these surfaces are allowed to have a simple radius to be applied, with a 2.5cm radius on the step plane and a 5cm radius on the reference plane.





Plank: Brown


Not considered part of the floor for measurement purposes, the plank is a strip of wood placed under the car to enforce a minimum ride height. The FIA technical term for this part is the skid block, although this term is rarely applied. Holes in the plank allow the cars reference plane to sit directly on the FIA scrutineering jig, for legality checks over the course of a GP weekend. Titanium skid blocks are allowed to be fitted in certain places in the plank and their wear is measured to ensure a car is not grounding from excessively low ride heights.

The plank can be made in two parts to make removing the floor easier, bit the front section must be at least 1m long. This must be made of a material with a specific density, to prevent excessivley heavy or hard planks producing a performance benefit. Typically the plank is wood based, eiterh jabroc a laminate of beechwood, although more exotic blends of woods and resins not unlike MDF have been used. The plank is 30cm and 5mm thick, any holes made into it must conform to a FIA template.





Diffuser: Yellow


A purely flat floor would probably produce lift rather downforce, so the rules have allowed a diffuser to be fitted to the rear of the underbody since 1983. Before that date there were no rules demanding floor dimensions and diffusers were the full length ground effect tunnels that typified the wing cars of the late seventies and early eighties.

A diffuser creates downforce by creating a pressure differential, with low pressure beneath and higher pressure above. The larger a diffuser is, the more expansion ratio is has, thus more potential to create downforce. Diffusers were limited to a simple 100cm width, 35cm length and 17.5cm height from 2009. Then for this year the height further reduced to just 12.5cm. This massively reduces the potential of the diffuser to create downforce compared to the previous rules. Diffusers are allowed to have fences, but the fences and the diffuser itself must not form undercuts when viewed from below. Which is why we see the simple vertical fences and jelly mould curvature.


Other rules around floors

Overriding all of the above rules are broader regulations covering holes and flexibility. No unsprung part of the car can be visible from below the floor. Typically this means anything, but the suspension and additionally the wing mirrors. This means that no holes can be made into the floor to let flow in or out. The underbodies surfaces are termed bodywork within the rules, there is no term ?diffuser? or ?wing? mentioned in the rules. Just as with any bodywork in the rules, these parts are not allowed to move or flex. For the floor in comparison the wings, there are few deflection tests commonly carried out, the main one being the splitter deflection test.





Double Diffuser


Over the past two year these rules have been exploited by teams. Firstly the interpretation of holes in the floor and continuous surfaces. This lead to the openings that allowed double diffuser. Effectively the step formed two separate, but individually continuous surfaces, allowing airflow to pass up above the step plane into the upper deck of the diffuser. This rule has been clarified for this year and a single continuous surface must be formed under the floor.

Additionally the flexibility of the splitter has been brought into question, teams were believed to be flexing the splitter upwards, new more stringent tests were introduced in 2010 to stop this.

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Trends 2011 ? Exhausts and Diffusers


This year the technical talk has largely been about exhausts. How teams have adapted to the ban on double diffusers and the added restriction on Exhaust blown diffusers. Just to aid understanding going into the new season, I have explained how these solutions work and how they look from beneath.


Double Diffusers



Force India 2010 Double Deck Diffuser (DDD)


Since 2009 the regulations regarding the floor have been interpreted in a literal sense to allow the double deck diffuser (DDD). Indeed the very same rules were exploited to a lesser extent under the previous rules, but this only produced small extra channels in between the outer and middle diffuser tunnels. With the major cut in aerodynamic aids for 2009, several teams sought to find a way to gain more expansion ratio from the smaller diffusers. In essence the loophole exploited the definition of surfaces formed between the step and reference planes. Multiple surfaces allowed fully enclosed holes, which fed the upper diffuser deck that sat above the 175mm lower diffuser. This allowed diffuser to be significantly larger in order to create more downforce. Notably Brawn, Williams and Toyota launched 2009 cars with DDDs. Other teams soon followed suit in 2009 and last year every car exploited the same loophole. Over the winter the FIA acted to close the loophole, by enforcing a single continuous surface across a 90cm span under the floor. In a stroke this banned the double diffuser, there being no scope to create any openings in the floor to feed the upper deck.



Single Diffuser



Double Diffuser




Exhaust Blown Diffusers

Another approach to regain lost downforce was the re-invention in 2010 of the exhaust blown diffuser (EBD). This used high energy exhaust gasses to blow the diffuser, the faster throughput of flow under the floor increased downforce. Two methods of EBDs were used in 2010, one blowing over the diffuser and the second blowing inside the diffuser. This latter solution was more effective at driving flow through the diffuser and created more downforce. However this necessitated a hole made into the diffuser to allow the exhaust gas to enter, I?ve termed this method an ?open fronted diffuser?.



2011: No openings allowed in the yellow 90cm zone, outside certain holes are permitted


A by product of the 2011 rules intended to ban the DDD, also stopped this open fronted diffuser solution. However the rules enforced the continuous surface only across a 90cm width of floor and the diffuser is allowed to be 100cm wide. Thus a 5cm window was allowed each side of the diffuser.


Outer Blown Diffuser ? Solution



Red Bull Diffuser: Flow passes under the outer 5cm of floor into the diffuser


Red Bull and Ferrari appear to have found this loophole simultaneously. Recently Sam Michael pointed out this was probably the most efficient way to blow the diffuser under the new rules. As Red Bull appeared with this set up first, its often termed the Red Bull Blown diffuser.




What these teams have done is to open up the floor 5cm either side of the diffuser, then route the exhaust towards this opening. The exhaust gas gets collected by the coved section of floor and this directs the high energy gasses under the diffuser, to recover some of the losses from the more open diffuser allowed last year.


Front Exit Exhaust



Renault Front Exit Exhaust: Flow passes wide around the floor before entering the diffuser


Renault meanwhile turned the problem on its head. As the aim of the EBD is to increase flow under the car, they pointed their exhaust at the front of the floor. I?ve had it confirmed to me by two ex-Renault sources that the exhaust does indeed mainly flow under the floor.




The exhaust pipe outlet sits above the step plane just ahead of the leading edge of the floor. This is not simply blowing out horizontally and across the floor, but is ducted slightly to blow downwards and backwards, this is roughly in line the with the flow trailing off the ?V? shape above the splitter. Along with the strong vortices set up by the splitter, vanes and bargeboards, this makes the floor appear wider than it is. The flow will go out beyond the floor and then curl back in and under the floor. Some flow will inevitably pass over the floor, but the most of the energy will be driving more flow under the floor to the diffuser.


McLarens Slit Exhaust



The slit above the floor is visible. Copyright: Liubomir Asenov


No conversation about exhausts this year, would be complete without some speculation about McLaren. Amongst the several exhaust systems run by McLaren over the pre-season tests was a ?slit? exhaust. This appeared at the first Barcelona test, but did not seem to appear for the second Catalu?a test. The exhaust collector could be seen to duct towards a double thickness section of floor ahead of the rear wheels. This section was also interesting for its longitudinal slot, this slot was not large enough to be the actual exhaust outlet, This might be a cooling slot, or to improve the flow from above to beneath the floor. I beleive the Exhaust is actually below the floor. As when the car ran the same floor with a conventional exhaust outlet, there appeared to be a removable section of floor ahead of the rear wheels. Being just outside of the 90mm opening rule, the floor ?could? be opened to allow an exhaust to blow through to underneath. If sculpted correctly, the exhaust could be ducted back inboard and blow towards the diffuser from under the floor. It?s possible that this could be in interpretation of a legal opening, assuming it met the maximum fillet radius rules.

I?d expect the resulting exhaust outlets to be a long wide slot, this wider outlet would be needed to meet the maximum radius rules and also reduce the back pressure from the tight curve of the exhaust outlet. As the exhaust would have a tortuous bend, to curl back under itself to direct the flow inboard, rather than out wide around the rear tyre.



Mac Slit: The exhaust might exit beneath the floor in a long narrow outlet

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Grazie mille x il materiale. Nn sapevo dell'ewistenza di qiesto blog

Staasrra appena ho un p? di tempo mi metto a leggerr con calma:)

Conosci altristi o blog che trattano argomenti tecnici?

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come questo non ne conosco.

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come questo non ne conosco.



Spero che qualcuno mi aiuti....

non riesco a capire i limiti di intervento nello split e attorno....

Per esempio: Si puo' allungare lo split oltre il limite della tavola?? fino all'asse centrale ruote anteriori??

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cosa ? lo split, non sono tecnico, leggo per capirne di pi?. :)

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cosa ? lo split, non sono tecnico, leggo per capirne di pi?. :)



Scusa, ho sbagliato a scrivere... SPLITTER .


Allego immagine per capirsi.


e io tutto potrei diventare meno che tecnico...


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ah adesso ho capito, credo di no perch? credo che quella zona sia regolamentata da date dimensioni, non potendo allungare il fondo piatto in avanti lo splitter per forza di cose non pu? uscire dalle stesse dimensioni.


magari ? possibile creare un unico divisore, come si vede accennato sotto, ma oltre la zona del fondo piatto non credo si possa andare.




vedremo con le future regole che impongono il muso pi? basso se questa zona rester? ancora influente nello stesso modo di oggi.

Edited by The King of Spa

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ho provato a dare una occhiata al regolamento FIA:



ma per ora non ho trovato il divieto di allungare lo splitter...ho trovato solo il fatto che non puo' essere flessibile.


Mi piacerebbe trovare un buco regolamentare in questa parte.

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Explore The Secret Underside Of A Modern Formula One Car




The machine you see here is Nico Rosberg's 2012 Mercedes AMG F1 W03, a carbon-fiber monster with a naturally aspirated 18,000-rpm V-8 producing over 700 bhp. Amazingly, that engine isn't the W03's most impressive feature. Like all modern F1 cars, the Mercedes is both defined and dominated by its aerodynamic aids.


Topside, Rosberg's car uses multi-element wings to produce downforce, but peer underneath and you'll find a cocktail of mind-bending vortex generators and what F1 designer Nick Wirth calls a "horrific assortment of [interconnected] parts and pieces."


Wirth, 46, began his career as an aerodynamicist at March and later served as technical director for Benetton and Virgin Racing. Because the bottom of an F1 car is almost never seen, we asked Wirth to parse it out.


"A Formula 1 car produces much of its downforce from [its underside]," he says. "Think of each component as a link in a long chain. Change one without altering the rest and everything is then out of alignment-the car's aerodynamics simply won't work as intended."


  2. Mercedes' "Double DRS" system uses channels in the body to route air from the rear wing to the car's nose. When the car's DRS system is activated, the flap's motion exposes holes in the rear wing's endplates. Air enters these holes and is then routed forward to the front wing, where it exits on the bottom side to stall the wing, decrease front downforce and boost top speed.
  3. The forward barge board acts solely as a vortex generator. "The rotational direction of that vortex will be counterclockwise," Wirth says, "and because the vortex is traveling downward, it sends down-wash approaching the underbody, which is very favorable. It essentially generates more downforce."
  4. The ornate, sculpted sidepod turning vanes play a vital role in routing the dirty, turbulent wake of air coming off the front tires. "They delay how long it takes before that front-wheel wake starts disappearing under the floor and taking downforce away," Wirth says.
  5. The reference plane, the bottom-most section of the chassis, must be 300?500 mm wide. It creates airflow channels capped and fed by the interior barge boards.
  6. Known as the reference plank, this chamfered skidplate is made from a resin-infused, wood-based composite called Jabroc. It's replaced between track sessions. The holes in the plank's surface allow technical inspectors to measure its thickness, ensuring it stays within the mandated 10-mm (plus or minus one millimeter) tolerance. "The leading edge of the floor will be generating vortices that will then spin down underneath the floor, along the edge of the reference plane," says Wirth. "All of that vortical action reduces the total pressure under the floor and gives you more downforce."
  7. Barge boards produce vortices and increase downforce. "They're cambered like a wing," Wirth says. "Any reduction in pressure there basically torques the floor and reduces pressure all underneath the car."
  8. The car's keel gently moves the column of incoming air underneath the monocoque sideways and out of the way. "It's shaped very carefully and [designed with] the barge boards to generate higher airspeed and thus low pressure."
  9. This small wing sits in what's known as the squish vortex zone. "You have a seal between the rotating tire and the ground," Wirth says, "and the air that hits the tire can't get underneath it, so it forms two very strange jets-they come out at an almost-45-degree angle on each side. This wing is inverted...it has nothing to do with generating lift."
  10. Aperture for the front laser ride-height sensor. It can be set to sample ride height as often as 1000 times per second.
  11. Carbon-fiber front A-arms, with key sections rotated to match the airflow off the front wings and minimize turbulence and drag. Every time the front wing is modified during the season, the car gets a new set of A-arms with a revised, matching angle of twist.
  12. Carbon-fiber backing-plate extensions clean up air coming off the inside of the tire, aiding brake cooling and airflow.
  13. Aluminum tape, 0.05-mm thick. Durable, thin, seals holes and keeps airflow disturbance to a minimum.



This story originally appeared on Road & Track on October 16, 2012, and was republished with permission.


Incidentally, two former Jalopnik staffers now work there, and they, along with an all-star cast of dedicated oddballs, are currently working on a full-scale redesign of R&T's magazine and website. If you like this, you'll love what they have in store. Also, you should send this guy some candy by mail. He will love you forever.


Photo Credit: Paul-Henri Cahier

Edited by The King of Spa

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