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Spoilers on cars

  1. Jan 5, 2004 #1
    firstly, i am not an enginneer or a physicist, so if i write something foolish, have that in mind.

    i have heard that the reason why some cars have spoilers is to counter the upward lift that the air gives to the underbody of the car as it accelerates forward. this stabilizes the car at high speeds. i have three questions about this.

    #1: is this correct, and if not, what is the correct explanation?

    #2: if the above explanation is correct, will a normal car that needs a spoiler take flight at high speeds if it doesnt have one? (since this is how a plane works, i think, by producing more upward lift on the underbody of the wing than lift on top of the wing)

    #3: if a spoiler is installed, assuming that it is installed correctly, does it in any way decrease the acceleration or speed of a car?
  2. jcsd
  3. Jan 5, 2004 #2
    All this stuff could be terribly wrong so don't quote me.

    I believe the reason spoilers exist on everyday cars is just for style. You (should never) go fast enough to even have the spoiler take effect.

    1. Correct

    2. The car will not "take flight" but it will lose some traction and thus control.

    3. Because the spoiler creates some drag it will slow down a car, but not significantly.

    Again... don't quote me
  4. Jan 5, 2004 #3


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    Spoilers are put onto cars for three reasons -
    1. For looks
    2. To provide downforce
    3. To reduce drag

    If a car 'needs' a spoiler, then removing the spoiler will limit the high speed cornering and acceleration ability of the car.

    What a spoiler does depends on the type of spoiler and the speed of a car.
  5. Jan 6, 2004 #4


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    The "crane hooks" that people put on their civics do absolutely nothing, except look stupid.

    Spoilers are used in race cars to provide downforce to the rear wheels, increasing traction at high speeds. Note that only works for rear wheel drive cars.

    Civics, etc. are not rear wheel drive.
  6. Jan 6, 2004 #5
    NateTG was in error on the drag part. Spoilers ADD drag, thus also increase fuel consumption. For typical streetcar usage, thats the only effect they have.

    In racing, there is always compromise between downforce and drag (think of F1) that slows car down.

    Enigma, I belive they work okay for fwd cars aswell. Critical event is hard deceleration, when rear end becomes awfully light and prone to loose traction. At high speed, rear spoilers add stability during braking, no matter what drive scheme. This could draw a line between stopping quickly and finding oneself in the weeds.

    Many cars are very "nose-heavy" and their normal weight balance already makes rear end relatively unstable. To a degree, spoilers could help with that issue.
  7. Jan 6, 2004 #6


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    Technically, F1 cars have wings, not spoilers.

    A correctly designed spoiler reduces drag. A primary mechanism for drag is to shed vortices. Spoilers can prevent the formation of, or reduce the size of these vortices. At freeway speeds, a spoiler can improve the fuel efficiency of cars by more than 1%. However, if you spend $300 on the spoiler, then you'd have to spend $30,000 on gasoline -- that corresponds to about 600,000 miles in passenger cars -- in order to make it economically viable.

    A popular example of a spoiler is the ridges on aerodynamic helmets worn by bycicle racer.

    This is also incorrect. There are methods of producing downforce that do not require any drag at all, but they're illegal in car racing.

    In 1970 or so Jim Hall built the Chapparal 2J which used snowmobile motors for downforce instead of wings. The increase in drag was minimal, and the car was promptly banned.
  8. Jan 6, 2004 #7


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    The ridges you put on helmets are vortex generators (or possibly fences or other flow control devices), not spoilers. You are right about what they do though. To elaborate, various flow control devices essentially act to keep the air where you want it - keep it attached to the proper surface. Vortex generators create small vortices on the top of a wing, making the flow turbulent (instead of laminar) in a controlled fashion, increasing stall angle of attack and (somewhat counterintuitively) keeping the flow attached to the wing. Keeping the flow better attached also reduces drag (which would be the purpose on a helmet).

    A spoiler, as the name implies, spoils lift. On a wing, this massively increases drag, on a street car, it only increases drag by a little (since cars aren't that aerodynamic to begin with).

    The distinction between a spoiler and a wing though (as you implied) is that a spoiler acts to reduce the lift of the car and a wing creates its own lift (downward) separate from what the car body is doing. NASCAR stock cars have spoilers, Indy cars have wings.
    Ground effects for example. Not illegal, but there are specific restrictions on it. In any case, a wing specifically will always produce a combination of lift and drag and a spolier will always increase drag.

    And one clarification for mark1, the vast majority of lift on a wing is generated by the top surface of the wing, not the bottom. In the caption for THIS GRAPH it says this particular wing has slightly positive overall pressure (producing lift), but some can have an overall negative pressure (sucking the wing down).

    If the underbody of a car is flat, it will produce no suction or lift, but because of the small space between the underbody and the ground, there is almost always some kind of ground effect going on.
    Last edited: Jan 6, 2004
  9. Jan 14, 2004 #8
  10. Jan 24, 2004 #9


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    Hi folks!

    I think spoiles on cars have the mission of providing more friction force between wheels and road. Then, the traction torque is less limited by adherence.

    About drag and lifting:
    i) I don't believe of a usual car fligthing above our heads without a spoiler (except it was a ferrari one). The lift force at 100 km/h is negligible.

    ii) The drag coefficient could be increased by installing a spoiler,
    but i think it depends on the height and in fact, on structure of the flow near of the spoiler. This is a very particular feature of the layout.
    Anyway, it is sure that anybody who puts a spoiler on his car is thinking about the boundary layer flow, but about picking up some girls with his new toy (except in F1).

    Ah! Congratulations to E.S.A. (European Space Agency), Where was the N.A.S.A when was published in all europe mars water photos? Ja,Ja,Ja!
  11. Jan 24, 2004 #10
    spoiler dilemma...

    From where i come from, spoilers are just part of the cool design of a car... The mechanics here do not calculate the aerodynamics of spoilers. Personally i think that for the normal car-user, spoilers arent really necessary (unless you want the style which comes from using one).

    The main purpose of spoilers are to reduce the drag...and unless you're prepared to invest a lot of money to make sure the spoiler really works for your car, it is not really worth the buzz and hassle. Its a totally different story for a street racer though.

    However, through my own personal observations, street racers rarely put any emphasis on the aerodynamics of the spoilers but instead put a lot of energy into modifying and enhancing the engine's performance...

    Are you planning on installing a spoiler yourself mark?:wink:
  12. Jan 25, 2004 #11
    Most high performance sports cars dont have spoilers, how often do you see a ferrari with a spoiler, working for mercedes i know that none of the fast mercedes have spoilers, the SL55 AMG doesnt. But the Design of these cars provides downforce anyway because they are wedge shaped. The new Porsche carrera 4 (i think) has a spoiler that automatically raise from the boot when the car reaches a certain speed.

    Have u ever seen an F1 car loose one if its wings as its going down a fast straight? The drivers are very very lucky if they can avoid smashing into a barrier, the reason F1 cars have Wings is because they are so light and powerful, the power to weight ratio is huge.

    Does anybody follow the Le mans 24 hour race? I have seen one of those cars flip all the way over as it was hurtling down the long straight (cant remember what its called) at speeds in excess of 200mph, and i beleive that was due to a fault with the Aerodynamics of the car, think it was the front scoopdown spoiler, air got underneath and lifted it up, very nasty.
  13. Jan 30, 2004 #12
    high performance cars in Malaysia do...

    Well,in Malaysia, there are plenty of high performance sports cars. In which i mean those which are modified and not those which are the 'original' sports car...

    I'll give you a few examples...the Nissan Skyline is one such car.
    I went to a drag race held at an old airport strip here last year...These cars came in bunches and it was so beautifully modified!

    all of them had one similarity...all had spoilers and bodykits....
    obviously, they went for the style...

    so i can only say them as i see them....

    as for the 'original' high performance cars, who would bring a grand prix vehicle or an F1 car for a ride in the city??? so once again, spoilers aren't necessary for the normal street car...but if you're thinking of joining a drag race once in a while, or bring a car into the circuit, then install one...

    Porsches and Ferraris dont come with one cos they know you dont need them unless you're a serious racer. Like porsches, if you are a serious racer, then the spoilers come into action...
    if not.. then, it just stays in place..
  14. Jan 30, 2004 #13
    nope, im just curious about their affect

    i dont follow le manz, but i saw a clip of that on sportscenter. it was a mercedes. it was probably the scariest racing crash i ever saw.

    thanks to all who replied to my questions.
  15. Jan 30, 2004 #14


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    A similar flaw existed in NASCAR cars until a few years ago - if the car turned sideways or backwards, aerodynamic forces would push air under it, making it fly. Now if the car's attitude gets upset at all, spoiler panels pop up on the roof to keep it on the ground.
  16. Feb 2, 2004 #15


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    First of all, nearly every street car generates lift, not downforce. There are cars which will become dangerously unstable before top speed is reached, although most modern cars undergo extensive testing to avoid this. That means less lift, not actual downforce (except in the case of the Ferrari 360).

    It becomes an issue if (1) you want to race, (2) have a beefed up engine, or (3) like classic cars that had more power than they could safely deal with .

    Spoilers are a simple method for reducing lift, although adding them randomly can make things worse. Aerodynamics is not a very intuitive field. A properly designed spoiler (not a wing) can decrease drag, but it will increase it if its designed more for all out downforce. Its all the engineer's choice. A wing almost always generates a lot of drag though, but it will also generate a lot more downforce.

    Ferraris and such don't have big wings on them because they're ugly. End of story. You will find subtle spoilers though. Exotic car companies spend ridiculous sums of money to improve the aerodynamics of their cars while still keeping a clean look. If they didn't care what things looked like, cars with real downforce would be common. Racing versions of those cars always have wings if the rules allow it.

    As a side note, 911's often have much larger spoilers than other cars because their basic shape is aerodynamically very poor. The car sells well, so Porsche keeps it around. They have to add the big spoilers as a band-aid.
  17. Apr 15, 2004 #16
    Yeah, sorry to dig up an old topic, but I figured that this is the best place to put this litle idea. I forget which issue of Racecar Engineering (Im not even sure if that is actualy the title); there was an editorial from someone who proposed that all aerodynamic downforce (i.e. spoilers and wings) should be banned.

    I know that even your common Joe on the street would think that such a statement would be madness. "Duuh dont spoilers make the car go faster?" :biggrin:

    However he did state an interesting scenario to illustrate his point. In a race, if the car is going near the speed in which the spoilers downforce would take effect, there is a change in tire grip. We all know that it is to be a positive effect on the traction. That very effect is what spoilers are for. However, if a racecar goes into a turn, the vehicle starts to slow down. This starts to limit the effects of the spoiler. The person in the editorial stated that when the downforce disapears, there can be a critical loss in traction. In a race where a drivers life is dependant on the traction that is available to him/her, at times the slightest change can be the diffrence between controll, or crash.

    So, my querry is this; do you think that the person is exagerating? Or do you think that he raises a valid point?

    I personaly am not that sure. I think that it would depend on other variables, and balances in the design of the car. Also, a drivers job is to know his car. A driver, idealy should know the mannerisms of the vehicle that they drive. On the other hand, if the total downforce effect is unreliable enough, or just plain unnecisary, then that should be considered as well.

    I am no where in the league of the proffesionals. However I would like to know the opinions of those who post here. What do you all think?
  18. Apr 16, 2004 #17


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    While the downforce will drop significantly with a drop in speed, the job of the racecar driver is to know and understand their car. Only an extreme event (like happened to Aryton Senna in 1994 when a suspension link broke) would put the driver in a situation where they would have a sudden drop in traction that could be critical.

    Leaving racing aside, why does the new Enzo Ferrari have no wing on a car designed to go 200MPH+? Because the underbody of the car is the downforce generator and it generates enough downforce that it is actively controlled to roll back the downforce generated at high-speeds so the car can be setup with a softer more street-worthy suspension and avoid some of the drag penalty at those high speeds. So if you do away with wings and spoilers, how do you regulate the underbody of a car?

    As Smokey Yunick used to say, "...it ain't cheating if you don't ge caught..." and that is why there are some many rules to control the level of competition. If you compare just Indy/CART/F1 for open wheel racing, the Indy/CART camp have desiginated manufacturers and the teams buy from them, and in Formula 1 you have all the manufacturers complying with rules regarding dimensions and equipment. In both, assuming you ignore Ferrari's recent domination in F1, the racing ends up quite closely matched even though very different approaches have been used to make the competitive field near equal.

    For real downforce, look at F1's history with fans used to create active downforce, and the exclusive McLaren F1 road car used this same technology during its short production run. Those wouldn't drop off with speed. :) But lack of ability to regulate and to reduce costs through reduced complexity such devices were banned along with active suspension and other electronic gadgets.

    Besides that sounds like an editorial from a NASCAR fan who is bitter from the late 60's competition called the Aero-Wars between the Torino Talladega/Cyclone Spoiler and the Superbird/Charger Daytona and the safety issues that arose. Most of those issues had to due with the increase in speed and inability of the tires to support such speeds, not with shifting downforce levels causing lack of control.

    While we're at it, why don't we ban the flaps on the roof of the current crop of NASCAR cars. You know, the ones that lift up to spoil the lift when a car is going sideways? If we're gonna ban all devices, we might as well take out the ones for safety too so we can see spectacular flips and crashes.

    IMHO anyways.

  19. Apr 16, 2004 #18
    Downforce could also be created on cars by having a curved tube whose intake is
    horizontal relative to the ground but with an exhaust end that points skywards.
    As a car turns on a bend in the road it would open a flap which allows air to rush into the tube and shoot up vertically.The reaction to this movement of air would push the car harder onto the road surface.Would make a hell of a noise though!
  20. Apr 17, 2004 #19
    Just in case anyone wanted to know, the article was in "Racecar Engineering" magazine. It was November '03 Volume 13, No. 11. Its a U.K. Magazine and I got it in Barnes & Noble.


    The article in question is called "Drag act" and the author is Paul Van Valkenburgh. Ironicaly enough Cliff J, this guy was one of the people that exploited aerodynamic downforce back in the 60s. However like I stated before, he proposes that the life of a driver is based on the predictability of traction. He also says that in a superspeedway situation, drafting (following the car in front of you so that you gain acceleration from their car blocking the wind) can be dangerous because the rear downforce is affected. Most drivers avoid this trick on "Gentlemen's agreement" and avoid doing so. I have to work on some math homework, and Ill go over anything I left out later on. But once again, he brings up an interesting idea.
  21. Apr 19, 2004 #20


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    Yeah I did a little more research into this as well, mostly NASCAR stuff with the 'pack' effect and how to split up the field for spectators and safety.

    I follow F1 and CART mostly, only sometimes the old-school <80's NASCAR or them on a road course (I like to see drivers drive, not run circles) so my current knowledge of their issues is a bit rusty.

    Anyways, I think their lack of updated safety regarding track design, car design, and safety testing has put them in a more delicate situation than aerodynamics. How many 18-19 year old kids died of basilar skull fracture before Earnhardt without any safety updates that would have ironically saved his life?

    And their aerodynamic problem isn't so much a speed differential, its the giant 3000lb race car messing up the air. How much lead time is given to each aircraft for takeoff at a runway based on tonage (a bunch as dictated by the FAA) and yet wasn't it 2-3 years ago that an Airbus plane went down on Long Island after the tail broke off and the initial likely culprit was turbulence from the preceding plane?

    Personally I think they should change it to be a stock car race again if they want it competitive. Cars that would look like a real street car like the Speed Channel challenge with factory sheet metal over a full cage and not 45 Ford Taruses with only stickers to tell you what brand of car it is suppossed to be. Earnhardt Jr out there with a FWD V6 and 7 inch wide tires isn't going to be able to go too fast to be unsafe! IMO anyways. :)

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