# spoilers on cars, effective? **URL:** \ **Category:** Factual Questions\ **Created:** [September 18, 2006, 9:50pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235 "2006-09-18T21:50:05Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 19, 2006, 5:24pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/21 "2006-09-19T17:24:22Z")
[QUOTE=CookingWithGas] Why do they call it a “spoiler”? What does it spoil (besides the looks and performance of a car, I mean)? [/QUOTE] There should be made a distinction between spoilers and wings. The two terms are frequently conflated in common parlance, but they the perform manifestly different fucntions. Strictly speaking, a _spoiler_ is intended to interfere with (spoil) laminar air flow at the tail of the vehicle that either results in increased drag or instability (from vortex shedding). In this guise, it actually contributes to _reducing_ drag and improving performance. The little pop-up spoilers you see on the back of some 911-type cars and the Porsche Boxster S is a designed for this purpose (because of the teardrop shape of the cars contributing to this condition.) Ditto for the trunk spoilers on stock cars. The flat-laying spoilers, like those on the Saturn Ion perform a similar task but with less drag at commuter speeds, though it’s questionable that it provides real service for the typical suburban driver. A _wing_ is primarily intended to create a downforce to combat lift and increase traction on the drive wheels, which occurs when the air flows easily over the top of the vehicle, resulting in lower pressure above rather than below. Wings also perform the same function as a spoiler, but that’s pretty much incidental to the primary purpose, and an improperly designed wing can contribute to greater instability. You see wings on F1-type cars, for instance, where (owing to the lift these cars develop from their wedge shaped profiles) they perform a critical function and are usually found on the front and rear, often integrated into the body. They’re also often found on rally cars, though just in back. Ironically, the ricers who stick them on the rear of front wheel drive Hondas and Acuras are actually reducing traction over their drive wheels. (Most also appear to be bolted to the rear deck with little structural reinforcement, suggesting that they neither can nor do take much loading.) Stranger ---
**Author:** ![Uvula\_Donor](https://avatars.discourse-cdn.com/v4/letter/u/e19adc/32.png) [@Uvula\_Donor](https://boards.straightdope.com/u/Uvula_Donor)\ **Post date:** [September 19, 2006, 5:32pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/22 "2006-09-19T17:32:37Z")
On most of the cars I’ve seen them on, spoilers make conveniently elevated handles for pushing the pieces of shit off the road when they break down. ---
**Author:** ![crazyjoe](https://avatars.discourse-cdn.com/v4/letter/c/f14d63/32.png) [@crazyjoe](https://boards.straightdope.com/u/crazyjoe)\ **Post date:** [September 19, 2006, 5:36pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/23 "2006-09-19T17:36:05Z")
[QUOTE=ScoobyTX] Always entertaining are inverted-wing spoilers on the rear of front-wheel drive cars. If they are effective (questionable), they act to increase the downforce on the rear wheels (which don’t do anything but support the rear half of the car) and act to lift the front wheels (small moment around the rear wheels). :dubious: If it was much of an effect at all, it would be counter-productive to both handling and power. [/QUOTE] Not at all. If you were to actually attain speeds while racing which utilized the downforce created by the spoiler, you would see there is definitely a point to increasing the downforce on the rear end of a front-heavy vehicle. Your car is not a teeter-totter, you can increase downforce on the rear without adversely affecting the dynamics of the front of the car, especially if your suspension is tuned for it. ---
**Author:** ![Chez\_Guevara](https://avatars.discourse-cdn.com/v4/letter/c/aeb1de/32.png) [@Chez\_Guevara](https://boards.straightdope.com/u/Chez_Guevara)\ **Post date:** [September 19, 2006, 5:47pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/24 "2006-09-19T17:47:38Z")
No. ---
**Author:** ![StinkyBurrito](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@StinkyBurrito](https://boards.straightdope.com/u/StinkyBurrito)\ **Post date:** [September 19, 2006, 7:57pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/25 "2006-09-19T19:57:37Z")
Like **Stranger On A Train** I was under the impression that a spoiler (as opposed to a wing) was to spoil the air flow and reduce the vacuum that is created behind the rear of the car. This reduces the drag and increases the fuel efficiency. The same effect as putting dimples on a golf ball. ---
**Author:** ![Mycroft\_H](https://avatars.discourse-cdn.com/v4/letter/m/898d66/32.png) [@Mycroft\_H](https://boards.straightdope.com/u/Mycroft_H)\ **Post date:** [September 19, 2006, 8:26pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/26 "2006-09-19T20:26:55Z")
I once saw a car with a home-made wing made of wood 2x4s bolted together. :rolleyes: I couldn’t understand it. It looked like something an 8-year old would add to their bike. But, I suppose, that was the mental age of the driver. And **Chez** , good one! ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [September 19, 2006, 9:13pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/27 "2006-09-19T21:13:08Z")
And since we are talking about spoilers we should not forget cars like the [Audi Quattro](http://www.fourtitude.com/gallery/generated/Motorsport/Rally-Hill%20Climb/Pikes%20Peak%20S1/004__scaled_600.jpg) and the [Peugeot 405 T16](http://www.motorsportblog.it/uploads/Peugeot26609.jpg) specially made for the Pikes Peak hill climb. The air is so thin up there that a normal sized spoiler cannot generate enough downforce. And here is the famous Climb Dance featuring Ari Vatanen and his 405! The slide at 3:51 is the best scene of this video IMO. [http://www.youtube.com/watch?v=ib3Q0C07dVo](http://www.youtube.com/watch?v=ib3Q0C07dVo) ---
**Author:** ![BubbaDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bubbadog/32/333_2.png) [@BubbaDog](https://boards.straightdope.com/u/BubbaDog)\ **Post date:** [September 19, 2006, 9:45pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/28 "2006-09-19T21:45:58Z")
[QUOTE=Stranger On A Train] …Strictly speaking, a _spoiler_ is intended to interfere with (spoil) laminar air flow at the tail of the vehicle [/QUOTE] That makes sense. But I remember as a young kid somebody telling me that it “spoils” the attempts of other race car drivers to draft a leading vehicle. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 20, 2006, 1:20am UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/29 "2006-09-20T01:20:35Z")
[QUOTE=mazinger\_z] Is there a general statement that I can make about the effectiveness (or usefulness) of a spoiler? [/QUOTE] How about (to your friend): “Sorry, you were right, I was wrong?” 🙂 ---
**Author:** ![mazinger\_z](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@mazinger\_z](https://boards.straightdope.com/u/mazinger_z)\ **Post date:** [September 21, 2006, 1:30am UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/30 "2006-09-21T01:30:50Z")
[QUOTE=Princhester] How about (to your friend): “Sorry, you were right, I was wrong?” 🙂 [/QUOTE] Well, it seems like for the most part spoilers are ineffective, but, I would like to know hard numbers on when it is effective. Apparently, car shape has a large factor to do with it. I was thinking about speeds. Exactly, on average, how fast are we talking about? I apologize if its in one of the links, the connection I’m on is iffy at best, and I don’t want to stress it out with more browsers. Thanks. ---
**Author:** ![Tully\_Mars](https://avatars.discourse-cdn.com/v4/letter/t/7ab992/32.png) [@Tully\_Mars](https://boards.straightdope.com/u/Tully_Mars)\ **Post date:** [September 21, 2006, 4:43pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/31 "2006-09-21T16:43:22Z")
A question for any aerodynamics types: If you have a car with a really squared-off back end, you have a low pressure area behind the car and below the trailing airstream. I undertood that this low pressure area creates ‘drag’. If you position a spoiler to re-direct the trailing air stream down into that area, can you decrease that drag? If so, is the reduction in drag way less than the increase in drag that the frontal area of the spoiler adds. ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [September 21, 2006, 5:54pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/32 "2006-09-21T17:54:13Z")
[QUOTE=Tully Mars] If you position a spoiler to re-direct the trailing air stream down into that area, can you decrease that drag? [/quote] First, since a spoiler is just an angled attachment to the rear deck, it can only deflect air upwards. You’d need something raised above the surface (like a wing) with air flowing under it that could be directed downwards. Second, If there’s a low-pressure area behind the car, air would be naturally drawn in to the partial vacuum anyway. The real solution would be to reshape the back end of the car to allow that airflow (probably from underneath the car via a rear diffuser). Third, deflecting air downward off the trunk lid would have the effect of lifting the back end of the car. This would decrease the traction available to the rear wheels, with the effect getting worse at higher speeds. (I read an article years ago about someone trying to break a speed record for a class of modified production vehicles. At high speed, the traction was so reduced that the car flipped around like a badminton shuttlecock.) > [@](#): > > If so, is the reduction in drag way less than the increase in drag that the frontal area of the spoiler adds. There’s more to drag than frontal area. It’s one of those you-can’t-get-something-for-nothing things that happens in physics. Even with a perfectly frictionless surface, the mere fact that you are altering the airflow in a usable way carries a penalty. Pilots learn about parasitic drag (from exposed rivet heads and such) and induced drag (an unavoidable cost of staying in the air). I suspect that actively forcing air into the low-pressure area behind a car would make the overall performance worse and not better. ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [September 21, 2006, 6:44pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/33 "2006-09-21T18:44:11Z")
[QUOTE=Dog80] On most cars they are just for cosmetic reasons. On supercars like a Ferrari or Porsche, the whole body is designed so it generates downforce without the need of a spoiler (eg. ground effects). [/QUOTE] Which has been causing some problems as the cars get faster and faster. The problem is that spoilers and wings work all the time, while ground effects only work while the car is close to the ground. There have been more than few accidents where a Ferrari has caught a little bit of air going over a bump at high speed, lost downforce (and therefore traction) because the ground effects were no longer effective, spun out of control, and crashed. There is a bit of a debate going on in Ferrari owner’s groups about whether ground effects are safe on road-going cars, for that reason. ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [September 21, 2006, 7:47pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/34 "2006-09-21T19:47:42Z")
[QUOTE=Robot Arm] There’s more to drag than frontal area. It’s one of those you-can’t-get-something-for-nothing things that happens in physics. Even with a perfectly frictionless surface, the mere fact that you are altering the airflow in a usable way carries a penalty. Pilots learn about parasitic drag (from exposed rivet heads and such) and induced drag (an unavoidable cost of staying in the air). [/QUOTE] Yeah, drag is a fun subject in piloting classes (at least, the class I took). We found that not only does an increase in thrust cause an increase in drag, but that an increase in drag often causes an increase in lift (in particular circumstancse anyways). It was explained to us that flaps increase lift by increasing drag and goofing with the airflow, creating a vacuum that causes airflow over the wing to get sucked downward, pushing the plane up. If the wing is close enough to the ground for the airflow to push against the ground, you get a air cushioning effect called “Ground Effect” that can force a plane off the ground. Sometimes handy, sometimes very dangerous, like if a pilot interprets his plane lifting off the runway as a sign that it’s safe to pull up, only to have the plane leave the ground effect below flight speed and drop tail-down into the pavement (something most planes aren’t designed to do very gracefully). Actually, airflow in general is a really fun and screwy thing that does all sorts of neat (and oftentimes dangerous) stuff to moving objects (Cars, planes, bicycles, reindeer, etc.) ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [September 21, 2006, 10:11pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/35 "2006-09-21T22:11:11Z")
[QUOTE=Absolute] Which has been causing some problems as the cars get faster and faster. The problem is that spoilers and wings work all the time, while ground effects only work while the car is close to the ground. There have been more than few accidents where a Ferrari has caught a little bit of air going over a bump at high speed, lost downforce (and therefore traction) because the ground effects were no longer effective, spun out of control, and crashed. There is a bit of a debate going on in Ferrari owner’s groups about whether ground effects are safe on road-going cars, for that reason. [/QUOTE] I wonder how the new Clio RS 197 is going to handle then. Although the marketing department at Renault wanted a wing (apparently to appeal to the Fast & Furious types) the engineers wanted a diffuser. Eventually the engineers won and here’s the car: [http://forum.softpedia.com/index.php?act=Attach&type=post&id=95111](http://forum.softpedia.com/index.php?act=Attach&type=post&id=95111) What is not evident from this ghost image is that the exhaust pipe tips are angled so they do not interfere with the air flow. According to [PistonHeads](http://www.pistonheads.com/news/default.asp?storyId=13843): > [@](#): > > F1 cross-over technology includes an air diffuser incorporated into the rear bumper – never before seen in this segment – to improve stability by reducing rear-end lift and, at high speeds, channels air flow to increase suction. The radius of the diffuser’s curve is engineered to create a zone of low pressure beneath the car which sucks the car to the ground. > > It reduces lift by a factor of three and produces the equivalent of up to 40kg of rear downforce without detracting from the car’s overall aerodynamics. This means that the rear air diffuser generates such downforce that it eliminates the need for a rear spoiler which would normally counter the lift. > > The location of the twin exhausts is critical to the car’s performance, as the flush-fitted dual pipes are housed within the outer channels of the diffuser so as not to interfere with the aerodynamics, maximising its effectiveness. > > The front of the car gets Renaultsport extended front wings with integrated side air extractors, plus extended rear wings and sills. The extractors have an aerodynamic function, reducing turbulence to reduce drag. The hot air and flow from under the bonnet of the car is facilitated by the extractor vents, while directing air flow along the sides of the car to enhance performance. > > The car gets the Mégane Renaultsport 225’s braking system – which in PistonHeads’ test of that car, we found needed constant heat to work efficiently which is fine for track use but not the A408. The system comprises 312mm-diameter ventilated front discs with Brembo four-pot callipers and 300mm diameter discs at the rear. ---
**Author:** ![groman](https://avatars.discourse-cdn.com/v4/letter/g/73ab20/32.png) [@groman](https://boards.straightdope.com/u/groman)\ **Post date:** [September 21, 2006, 10:43pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/36 "2006-09-21T22:43:17Z")
[QUOTE=Dog80] On the other hand, there are cars like the Subaru Impreza or Mitsubishi Lancer that are almost as fast as a supercar but are based on the body of a compact/mid-size sedan. Those cars really need a spoiler. [/QUOTE] There is really very few possible wing arrangements that would work for a FWD car. The cars you listead are both AWD so they can benefit from a wing at a really high speed (at a low speed the wing is always going to be detrimental due to weight and drag). However, most production cars that I see with aftermarket wings are FWD. You can theoretically use a lift wing to shift traction to the front, but that is not the arrangment of most of these snowboard-style wings people pay so much money for. Sometimes I just want to tell one of these kids to stop wasting their money because they are not going to make their Civic into a racecar without strapping pulsejets to the back. ---
**Author:** ![Raguleader](https://avatars.discourse-cdn.com/v4/letter/r/258eb7/32.png) [@Raguleader](https://boards.straightdope.com/u/Raguleader)\ **Post date:** [September 21, 2006, 11:07pm UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/37 "2006-09-21T23:07:07Z")
[QUOTE=groman] There is really very few possible wing arrangements that would work for a FWD car. The cars you listead are both AWD so they can benefit from a wing at a really high speed (at a low speed the wing is always going to be detrimental due to weight and drag). However, most production cars that I see with aftermarket wings are FWD. You can theoretically use a lift wing to shift traction to the front, but that is not the arrangment of most of these snowboard-style wings people pay so much money for. Sometimes I just want to tell one of these kids to stop wasting their money because they are not going to make their Civic into a racecar without strapping pulsejets to the back. [/QUOTE] Heh, a guy from Australia told me a story where he was driving some well-aged not-so-impressive-looking V8 car of his, towing another car behind it. Some ricer was giving him crap for driving the speed limit on some section of road where passing wasn’t possible, and when the road expanded to two lanes, the ricer pulled up next to him at the stop light and started talking crap. To which the driver of the old car replied with “Keep up.” 🆒 Light turns green, driver smoothy accelerates while the other guy burns the tires on his way through the intersection, passes the speed camera (designed to catch people doing racing starts from stoplights, apparantly) under the speed limit, then pours on the coal and easily passes the Ricer and cruises away. Funny thing is, the Ricer apparantly had a probationary license (I think there’s some sort of tag on the car that identifies them as such) and probably lost it after burning past the speed camera just to get passed a few seconds later by a beat up old car TOWING another car. :smack: 😃 There’s also a comic the guy who does [www.vgcats.com](http://www.vgcats.com) did making fun of guys in riced up Civics. 😛 ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 22, 2006, 12:13am UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/38 "2006-09-22T00:13:58Z")
[QUOTE=groman] Sometimes I just want to tell one of these kids to stop wasting their money because they are not going to make their Civic into a racecar without strapping pulsejets to the back. [/QUOTE] They’re not wasting their money: what they want is a car that looks fast to people who know as little about the subject as they do. And that’s what they get. ---
**Author:** ![GiantRat](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@GiantRat](https://boards.straightdope.com/u/GiantRat)\ **Post date:** [September 22, 2006, 4:38am UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/39 "2006-09-22T04:38:48Z")
[QUOTE=mazinger\_z] My friend and I were arguing on whether it was worth it to have a spoiler on a car. Eventually, I agreed with him that the cost of a spoiler might make the whole thing not worth it, particularly in the general sense. However, I disagree with him wholeheartedly when he says that spoilers have no effect at all. Who is right? [/QUOTE] In addition to what others have said, notice how many cars out there with “spoilers” have “spoilers” with no apparent angle. Many, if not most, “stock” spoilers appear to be flat or nearly flat. Translation: no effort to increase downward force, just cosmetic attempts to make the car look like it must go really fast (my hatred of CRXs is coming back now). Although, if memory serves, when the Porsche 911 became a Boxster, the spoiler came out at 70mph, which seemed to indicate to me that I wouldn’t want to drive that car at its top speed, if it’s prone to start “losing it” at 70." Don’t get me started on Corvettes with Tractrion Control . . . ---
**Author:** ![GiantRat](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@GiantRat](https://boards.straightdope.com/u/GiantRat)\ **Post date:** [September 22, 2006, 4:38am UTC](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235/40 "2006-09-22T04:38:59Z")
[QUOTE=mazinger\_z] My friend and I were arguing on whether it was worth it to have a spoiler on a car. Eventually, I agreed with him that the cost of a spoiler might make the whole thing not worth it, particularly in the general sense. However, I disagree with him wholeheartedly when he says that spoilers have no effect at all. Who is right? [/QUOTE] In addition to what others have said, notice how many cars out there with “spoilers” have “spoilers” with no apparent angle. Many, if not most, “stock” spoilers appear to be flat or nearly flat. Translation: no effort to increase downward force, just cosmetic attempts to make the car look like it must go really fast (my hatred of CRXs is coming back now). Although, if memory serves, when the Porsche 911 became a Boxster, the spoiler came out at 70mph, which seemed to indicate to me that I wouldn’t want to drive that car at its top speed, if it’s prone to start “losing it” at 70." Don’t get me started on Corvettes with Traction Control . . . [Previous page](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235.md?page=1) [Next page](https://boards.straightdope.com/t/spoilers-on-cars-effective/373235.md?page=3)