# How much does spoiler really figure in handling?



## ttsteve (Nov 1, 2007)

After a disasterous start culminating with with a number of high speed fatal accidents, Audi modded the TT for better handling. We all know that. Does anyone know how much the spoiler figures in 'taming' the TT, or, is it as I think is likely, it was more of a visual sign to worried buyers that the car was now much safer? I know it comes in to play at speeds over 70mph, but in the overall picture does it play a significant part, or would the car drive pretty much the same without it?


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## paceyjg (Aug 19, 2008)

Didn't they add the spoiler to the old 'widowmaker' as it was known then to help produce down force on the rear of the car?


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## swfblade (Apr 24, 2007)

there was a thread here not long back that had the figures for before and after downforce... I'll see if I can find it...


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## Bikerz (Aug 23, 2008)

paceyjg said:


> Didn't they add the spoiler to the old 'widowmaker' as it was known then to help produce down force on the rear of the car?


What was known as the "widow maker" in car terms? I knew teh Suzuki TL1000S was known as a widow maker. What was the car?


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## Spandex (Feb 20, 2009)

The old 911s, before they worked out how to make them go round corners...


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## drjam (Apr 7, 2006)

As you say, below 60-70mph or so, I'd imagine very little difference.
If you make a habit of going round corners much faster than this, it means more grip at the back, so more likely to understeer than oversteer. IIRC the particular problem they were addressing was to reduce "lift off" oversteer, i.e. people realising they were going too fast, lifting off mid-corner and finding the back overtaking the front...


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## Hark (Aug 23, 2007)

I'm still experimenting, but I actually think it does make a difference. Lower speed hard cornering seems fine, long sweeping ones or motorway bends I'm not entirely sure but I'm beginning to think it does make some difference.


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## Bikerz (Aug 23, 2008)

REember this spoiler doesnt "turn on" at above 70mph, it will always provide downforce as longa syour moving, just the faster you go the more it provides. Hence F1 cars go round corners better at higher speeds


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## hawkeye1972 (Feb 8, 2009)

The spoiler does not produce downforce, it is there to disrupt a Low pressure which was forming over the curve of the boot, and thus lifting the rear end.


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## conlechi (May 6, 2006)

One thing to take into account is that the spoiler was added to the standard car with standard suspension .

A modified car with modified suspension will probably work differently at speed without a spoiler :?

Wind tunnel needed i think 

Mark


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## roddy (Dec 25, 2008)

hawkeye1972 said:


> The spoiler does not produce downforce, it is there to disrupt a Low pressure which was forming over the curve of the boot, and thus lifting the rear end.


i am not disputing this,,, but where did you get this information,,, is this why such a small original one was used....


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## paceyjg (Aug 19, 2008)

Bikerz said:


> paceyjg said:
> 
> 
> > Didn't they add the spoiler to the old 'widowmaker' as it was known then to help produce down force on the rear of the car?
> ...


The early TT picked up that nickname before the improvements - at least that what i was told.


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## chrishTT (May 14, 2006)

does the telson add extra down force then?


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## Dash (Oct 5, 2008)

Bikerz said:


> paceyjg said:
> 
> 
> > Didn't they add the spoiler to the old 'widowmaker' as it was known then to help produce down force on the rear of the car?
> ...


I think all TVR's are in that category too...


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## Spandex (Feb 20, 2009)

I agree with hawkeye1972... From what I've read, the spoiler on the TT is there to add stability (not the same as downforce) by improving the airflow over the rear of the car. I've never seen any mention of increased downforce. The high-profile crashes that triggered the recall were at very high speeds on autobahn type roads, so it's unlikely anyone was negotiating any tight corners at the time.

Oh, and the first 911 turbo (the 930) was called the widow maker due to the snap oversteer from the appalling turbo lag. The whale tail spoiler was introduced in an attempt to stop people parking them backwards into trees. Puts the TT spoiler to shame.


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## peace (May 12, 2008)

surely any spoiler produces down force!?



hawkeye1972 said:


> The spoiler does not produce downforce, it is there to disrupt a Low pressure which was forming over the curve of the boot, and thus lifting the rear end.


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## Spandex (Feb 20, 2009)

peace said:


> surely any spoiler produces down force!?


Why?

You could design one that produced downforce, lift, or exerted no additional force at all. Most road car spoilers are there for stability or aerodynamic efficiency (or looks). This is because the designer knows the chances that you will be cornering at speeds where significant downforce is produced, but on a tight enough bend that you'd actually NEED that downforce, are tiny. The closest you'll come is probably one of those long, sweeping motorway on-ramps, where you can push 60-70 and really take the grip to the limits. These are also the situations where finding that limit might be life-threatening.


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## T3RBO (Dec 9, 2003)

You have to bear in mind that the original TT's didn't have ESP and imo the spoiler was chucked on as extra extra safety

Big thread on the subject with lots of lovely pictures and a table showing newtons of lift

viewtopic.php?p=1349696#p1349696


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## drjam (Apr 7, 2006)

Spandex said:


> peace said:
> 
> 
> > surely any spoiler produces down force!?
> ...


When you say "stability or aerodynamic efficiency", what exactly do you mean? 
As far as I was aware spoilers produce extra drag, which seems the opposite of the second one. 
And I thought the whole point of the stability they gave was by helping keep the car glued to the road (by means of downforce, reduced lift, whatever you want to call it). If not this, what stability _do _they bring?
[Not disagreeing with you, as I don't know much about it, just would appreciate a clearer explanation. cheers.]


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## Spandex (Feb 20, 2009)

drjam said:


> When you say "stability or aerodynamic efficiency", what exactly do you mean?
> As far as I was aware spoilers produce extra drag, which seems the opposite of the second one.
> And I thought the whole point of the stability they gave was by helping keep the car glued to the road (by means of downforce, reduced lift, whatever you want to call it). If not this, what stability _do _they bring?
> [Not disagreeing with you, as I don't know much about it, just would appreciate a clearer explanation. cheers.]


The airflow over the body of a car isn't all smooth and fluid and usually it's most disrupted as it leaves the rear surfaces at the tail. Rounded boots (such as on the TT) are actually worse for this than most other designs as the airflow doesn't detach smoothly. The typical solution to this is a 'lip' type spoiler (the word spoiler comes about because it's designed to 'spoil' the normal airflow around the car. To do this it needs to be as close to the body as possible). The turbulence caused at the rear of the car from messy airflow increases drag and therefore affects the efficiency.

To create downforce, you would use a rear wing, not a spoiler. This works exactly like an inverted plane wing. As you say above, this WILL increase drag, as it's diverting the airflow above the body to provide the downforce


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## Spandex (Feb 20, 2009)

I've just noticed you have an Elise. I remember watching the documentary about the whole design process (well worth tracking down if you can) and the bit where they tell the designer that it will need that boot-lip spoiler is pretty entertaining (he really did throw all his toys out his pram). Anyway, the reason they did it was for aerodynamics, not downforce. The airflow off the back of the car was terrible as originally designed and the wind-tunnel team attached a cardboard spoiler to the boot of the model they were using for testing to show how it improved it.


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## swfblade (Apr 24, 2007)

T3RBO said:


> You have to bear in mind that the original TT's didn't have ESP and imo the spoiler was chucked on as extra extra safety
> 
> Big thread on the subject with lots of lovely pictures and a table showing newtons of lift
> 
> viewtopic.php?p=1349696#p1349696


Thats the fella I was trying to find!


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## ttsteve (Nov 1, 2007)

Spandex said:


> I've just noticed you have an Elise. I remember watching the documentary about the whole design process (well worth tracking down if you can) and the bit where they tell the designer that it will need that boot-lip spoiler is pretty entertaining (he really did throw all his toys out his pram). Anyway, the reason they did it was for aerodynamics, not downforce. The airflow off the back of the car was terrible as originally designed and the wind-tunnel team attached a cardboard spoiler to the boot of the model they were using for testing to show how it improved it.


Thanks Spandex for your valued posts.

So, it all begs the question, was the spoiler added to the TT to:

1) Improve airflow (for extra speed)?
2) As a visual sign to worried buyers that the car was now 'safe and stable' (but it really doesn't do a lot in that respect) ?
3) To genuinely improve the handing of the car at very high speeds?

Maybe it's a combination of those things - if so what are the splits?


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## swfblade (Apr 24, 2007)

There you go.


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## ttsteve (Nov 1, 2007)

So, looking at the top row, middle car with standard spoiler, at 90mph what is it doing differently to the one on the left without spoiler? What are those 'H' values?


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## swfblade (Apr 24, 2007)

Its basically the amount of lift. The more there is, the more the car "lifts" and that wheel, so to speak. That means the rear wheels will have more contact to the road, thus more grip (more or less, in laymans terms).


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## krismc (Apr 4, 2009)

it basically shows the lift from front to rear, and how without spoiler its more tail happy as theres more lift generated at the rear, with spoiler however the lift is reduced at the rear and is therefore more understeer prone due to more lift at the front than the rear as a result of the spoiler


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## Spandex (Feb 20, 2009)

ttsteve said:


> 1) Improve airflow (for extra speed)?
> 2) As a visual sign to worried buyers that the car was now 'safe and stable' (but it really doesn't do a lot in that respect) ?
> 3) To genuinely improve the handing of the car at very high speeds?
> 
> Maybe it's a combination of those things - if so what are the splits?


I'd guess a combination too.

As for the diagram, one thing to bear in mind, there is a difference between decreasing lift and increasing down force (although the end result, as far as stability or grip is concerned may end up the same). Adding a spoiler to clean up airflow separation from the rear of the car will also reduce lift at the rear too. Adding a wing (i.e. an aerofoil, higher up away from the body) will increase down force, but at the cost of increased drag. Typically a lip spoiler is the best way to do it on a road car.

As for the TT, its a pretty terrible shape, aerodynamically speaking as it's fairly short for its height. The boot spoiler probably does help with fuel economy and maybe even keeps the back end stable during very high speed cornering, but realistically you won't be pushing the limits of grip whilst doing tight corners above 70mph (generally accepted as the minimum speed needed to generate any useful aerodynamic effect on a car) so I wouldn't worry about it.

As for most of the 3rd party spoilers, I doubt they have access to the expertise, test facilities and wind tunnels that Audi do so chances are they do nothing useful and probably just slow you down.


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## Phil_LG (Mar 13, 2008)

Any tips on finding that TT design documentary? I'd be very interested to see it.

Cheers,

Phil


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## Spandex (Feb 20, 2009)

Phil_LG said:


> Any tips on finding that TT design documentary? I'd be very interested to see it.
> 
> Cheers,
> 
> Phil


It was a documentary about the Elise, not the TT, sorry.


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## SimonQS (Jul 21, 2008)

drjam said:


> As you say, below 60-70mph or so, I'd imagine very little difference.


I would go further than that, since the fatal acidents were in Germany and were as a result of lift off oversteer when coming off the deristricted roads - I would suggest the rear spolier is fairly useless under 110 - 130mph.


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## RobLE (Mar 20, 2005)

apparently the ESP and spoiler were added partly because of the TT's success as 'the car to have' and too many people buying a car with (depending on which model) 180 - 225bhp at launch who had never driven a high performance car before...hence not knowing how to drive one and ending up in ditches! :roll:


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## l4nche (Jun 19, 2009)

To my understanding the whole issue witht he TT's original design is that it had the rounded tail end which causes lift. I can't even think of a similar car that doesn't have a boxed off end and not require a type of spoiler. Most all cars, high performance or not, need to have a non-rounded tail to keep it from lifting as speeds increase. Even the new body of the TT has been modified to a more boxed off end to eliminate the issue.


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## peace (May 12, 2008)

yet it still has a spoiler!?



l4nche said:


> To my understanding the whole issue witht he TT's original design is that it had the rounded tail end which causes lift. I can't even think of a similar car that doesn't have a boxed off end and not require a type of spoiler. Most all cars, high performance or not, need to have a non-rounded tail to keep it from lifting as speeds increase. Even the new body of the TT has been modified to a more boxed off end to eliminate the issue.


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## peace (May 12, 2008)

or is that a wing?



peace said:


> yet it still has a spoiler!?
> 
> 
> 
> ...


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## swfblade (Apr 24, 2007)

Either way, it still has it. Guess they just wanted to be sure this time! :lol:


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## ttsteve (Nov 1, 2007)

RobLE said:


> apparently the ESP and spoiler were added partly because of the TT's success as 'the car to have' and too many people buying a car with (depending on which model) 180 - 225bhp at launch who had never driven a high performance car before...hence not knowing how to drive one and ending up in ditches! :roll:


Only partly true. What really shook everyone and brought the problem right out into the greater public domain was when a well known German former rally driver (?) was killed in a high speed crash on an autobahn. People started thinking, "well if THIS guy can't control the damned thing, it must be a dangerous car". That's when they introduced ESP, spoiler etc etc.


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## Dash (Oct 5, 2008)

Very interesting thread.

Useful read for anybody thinking of changing their spoiler - or removing it all.


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## roddy (Dec 25, 2008)

ttsteve said:


> RobLE said:
> 
> 
> > apparently the ESP and spoiler were added partly because of the TT's success as 'the car to have' and too many people buying a car with (depending on which model) 180 - 225bhp at launch who had never driven a high performance car before...hence not knowing how to drive one and ending up in ditches! :roll:
> ...


do you remember the "former rally driver " s name ???


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## Spandex (Feb 20, 2009)

roddy said:


> do you remember the "former rally driver " s name ???


It was a former East German rally driver called Peter Hommel. He was 60 at the time of the crash though, so not exactly at the peak of his career...

<edit>Actually, after reading a bit more about it, it seems that the spoiler and suspension changes were made after a number of crashes but this didn't fix the 'problem'. Peter Hommel was actually killed after these initial changes and his death seems to have been the final straw that led Audi to fit ESP as standard.

So, you could take that to mean that the spoiler only really had an effect on handling as part of a package of changes and on it's own it really isn't that significant.


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## Spandex (Feb 20, 2009)

Info above taken from this article (it discusses the changes made prior to the US launch, rather than the recalls in Europe, but it seems relevant):

http://www.nytimes.com/2000/02/20/automobiles/audi-offers-tt-fix-after-5-deaths.html

The last two paragraphs should be of interest to the people looking to return their cars to a pre-recall state in the name of good handling.


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## roddy (Dec 25, 2008)

Spandex said:


> roddy said:
> 
> 
> > do you remember the "former rally driver " s name ???
> ...


thanks mate,,, cant say i have ever heard of him tho, and i used to "know" them all,, maybe before my time !!!


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## hawkeye1972 (Feb 8, 2009)

Very quick lesson in aerodynamics, Very Quick because it's a hell lot more complicated then following explanation, I could go into drag and lift coefficients, but I won't.

Saying the spoiler does not affect the efficiency or lift on the TT until 70,130,140 mph is incorrect, aerodynamic forces do not just appear at speed they start as soon as the car is moving. The nature of aerodynamic force is nearly expediential and not linear until you hit the speed of sound, then a new set of rules apply. For example, say the force on an object at 1mph is 1kg force at 10mph it would be 2kg force, at 20mph it would be 4kg, 30mph - 8kg, 40mph - 16kg, 50mph - 32kg, 60mph - 64kg, 70mph - 128kg, 80mph - 256kg; this is not the exact way works but it will do as an example.

If you apply this to the TT where the aerodynamic forces are higher due to it's shape you would find in a wind tunnel that the effect of the spoiler would be felt at under 1 Mph but the affect would most likely be small. But as you increase speed the affect of the spoiler is expediential.

Lift is caused by speed differences in airflow, the faster the air moving over the surface of an object the lower the pressure. If you take a look at a cross section of an aircraft wing you would see that the top surface is curved where as the lower surface is flat. A wing produces lift because the smooth air flow approaching the wing has to split into two flows as the wing passes through it, now as the air passes over the top curved surface of the wing it accelerates in order to meet the flow passing under the wing. This causes a low pressure above the wing and difference between the low pressure above the wing and normal pressure below causes the wing to be sucked upwards.

Now look at a side cross section of the TT, it is effectively shaped like wing. Except the curved surfaces are more flat, except in 3 places; the bonnet nose, the top of the windscreen, and the rear curve where the spoiler is. As the air passes over these points they effectively act like an aircraft wing, the air speeds up and causes a low pressure to form, which produces lift.

The reason it is such a problem at the rear of the TT is because of two reasons, one is the engine is not there so the is not as much weight to counteract the lift. The other reason is that the TT like all cars creates a low pressure behind it as it passes through the air. What this does is make the air passing over the car rush to fill the gap left behind the vehicle, thus accelerating the air even further.

This Lift then causes the TT's rear to lift up on the rear suspension, allowing the suspension to travel further on any change of direction, and thus unbalancing the car.
Note also that the problem is not actually caused by lack of grip as such, it caused by a shift in the TT's centre of gravity, which act's like a pendulum effect.

The TT's spoiler does exactly what it says on the tin, it spoils the airflow over the curve of the boot and stops the low pressure from forming, and the tail from raising due to lift.

It does not produce Down force. In order to produce down force you would need a well designed rear splitter and/or a high level wing.


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## ttsteve (Nov 1, 2007)

Great stuff. I never thought this thread would generate such good responses from knowledgeable chaps - thanks. Anyway, any thoughts I had of ever removing my spoiler - and it was never a strong idea - are now banished. I think I prefer the rear of the car to be 'unlifted' - at any speed!


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## Spandex (Feb 20, 2009)

hawkeye1972 said:


> Saying the spoiler does not affect the efficiency or lift on the TT until 70,130,140 mph is incorrect, aerodynamic forces do not just appear at speed they start as soon as the car is moving.


I was careful to say that the spoiler wouldn't have any *useful* aerodynamic effect until around 70mph and I'd still stand by that. This is exactly because the effect is exponential rather than linear. Whilst it obviously depends on the car, I'm sure it's an accepted rule of thumb that aerodynamics won't have any significant effect until you get up around 70.

The TTs problem is more that it's shaped like a ball, rather than a wing. The air doesn't detach smoothly from the radiused rear profile and this causes the problematic turbulence. The spoiler is designed to create a clean edge where the air separates from the body (I know this is what you said at the end, but I think the wing analogy is slightly misleading as all cars will force the air to travel further above them than below them).


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## beeyondGTR (Jun 16, 2009)

hawkeye1972 said:


> The spoiler does not produce downforce, it is there to disrupt a Low pressure which was forming over the curve of the boot, and thus lifting the rear end.


they put it there so the car would not lift at the rear end- huh I am confused sounds like downforce just a little :?:

must look into


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## Spandex (Feb 20, 2009)

There is a difference between producing down force and preventing lift. The spoiler does the latter.


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## beeyondGTR (Jun 16, 2009)

But you see plenty of spoilers and wings on everyday cars, like Honda and Toyota sedans. Do those really add an aerodynamic benefit to a car? In some cases, it can add a little high-speed stability. For example, the original Audi TT didn't have a spoiler on its rear decklid, but Audi added one after its rounded body was found to create too much lift and may have been a factor in a few wrecks [source: Edgar].

A wing mounted close to the trunk will not work like a ground-effects item. The proximity of the two surfaces and the fact that they are (possibly, in reality, probably not) increasing the velocity of the passing airflow by reducing the cross-sectional area, will create a downward force on the wing, but will also create an equal and opposite force on the trunk lid (or whatever it is beneath the wing) which will give a resultant of no downforce. Just drag.

The Audi TT's "wing" was a spoiler, not a wing. It is an effective item.

As to the speed at which aerodynamics become effective - it's a little extreme, but there was a Formula Student car a few years ago which had a multi-element wing which began to make "significant downforce" at speeds as low as 30mph. You don't need a rocketship to create downforce. I don't doubt a good front airdam could have a measurable effect on a Miata. Someone needs to do some skidpad testing...

In the original Audi TT's case, Audi added a wing as there were issues with traction in back. The wing(quite small and nice looking IMO) cured this issue.
Spoiler basics: how they work and where they came from

Spoilers were first developed as an ingenious creation appearing on race Ferraris in 1961. These top-end sports cars, born for ridiculous speed, needed some help staying tight in turns without adding weight.
The problem facing these Ferraris continues today with other racers. They must be as light as possible for maximizing acceleration and speed. At these high speeds, though, the back end of the car tends to get "loose" - especially in turns. That's because the car isn't sticking to the track well, thanks to excess lift.
One way to combat lift is to add weight to the car, which creates the extra downforce needed to keep the back end from being too loose. Weight, though, is an enemy of speed. And, in turns, the momentum of the extra weight means the driver must fight against its inertia.
Adding a spoiler to the car was the ideal solution to creating extra downforce on the vehicle without extra weight. A spoiler changes the aerodynamics of a vehicle, disrupting the airflow over the car. The disruption adds more downward pressure to the back end, tightening turns and reducing hazardous lift.
There's a catch to the spoiler design. Disrupting the airflow over the vehicle increases drag, thus reducing speed. Getting the right mix of downforce and reduced drag is an art form, leading to many shape and style changes to race cars. Most top-speed racers have adjustable spoilers for tweaking the balance of lift and drag to an optimum mix that maximizes speed without exceedingly dangerous handling. It's just one of the many adjustments racers of all level make in time trials and practice laps.

Who KNows . All I know is it looks cool. [smiley=dude.gif]


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## hawkeye1972 (Feb 8, 2009)

beeyondGTR said:


> Spoilers were first developed as an ingenious creation appearing on race Ferraris in 1961. These top-end sports cars, born for ridiculous speed, needed some help staying tight in turns without adding weight.
> The problem facing these Ferraris continues today with other racers. They must be as light as possible for maximizing acceleration and speed. At these high speeds, though, the back end of the car tends to get "loose" - especially in turns. That's because the car isn't sticking to the track well, thanks to excess lift.
> One way to combat lift is to add weight to the car, which creates the extra downforce needed to keep the back end from being too loose. Weight, though, is an enemy of speed. And, in turns, the momentum of the extra weight means the driver must fight against its inertia.
> Adding a spoiler to the car was the ideal solution to creating extra downforce on the vehicle without extra weight. A spoiler changes the aerodynamics of a vehicle, disrupting the airflow over the car. The disruption adds more downward pressure to the back end, tightening turns and reducing hazardous lift.
> ...


That's pretty much what i said I think, although the downwards pressure does not exist on the TT as the spoiler is only designed on the TT to disrupt the air, with out creating drag.

I would Like to point out that you can actually create downforce with a spoiler. Basically the low pressure which is at the rear of the car, which usually only causes drag, can be used to suck air out from underneath the car. Usually the bigger the low pressure behind the more air gets removed from under the car droping the air pressure under the car and pulling it towards the ground, thats how side skirts and splitters got invented. The splitters smooth (The front should also be designed to reduce air flow in aswell) the flow of air in and out of the gap under car where as the skirts stop air being sucked in from the sides (This is why you get pulled towards a truck when you pass one which is doing anything over 30). The spoiler can be used to increase size of the low pressure behind the car therefore decreasing the pressure underneath the car even more. But this has the negative effect of sending the cars drag through the roof.


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## Spandex (Feb 20, 2009)

beeyondGTR said:


> it's a little extreme, but there was a Formula Student car a few years ago which had a multi-element wing which began to make "significant downforce" at speeds as low as 30mph. You don't need a rocketship to create downforce.


That's the point though. Down force becomes useful when it is a significant percentage of the mass of the vehicle. On a normal road car this has to be a pretty high value, but on a little ultra-light racing car it's easier to do.

So, creating a 'significant' amount of down force at 30mph is probably feasible on a Formula Student car, but that doesn't mean it's so easy on a ton and a half of Audi TT. Although I'm always amazed that no one on here has bolted an old Porsche 930 whale-tail to the back of theirs...


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## Dash (Oct 5, 2008)

Spandex said:


> Although I'm always amazed that no one on here has bolted an old Porsche 930 whale-tail to the back of theirs...


This should do the job...


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## Dash (Oct 5, 2008)

So - on the subject of tidying up the air and such at the rear of the car, and the fun in the recent F1 season.

How about a rear defuser? And apart from the OSIR defuser stylee valance, has anybody put one on?


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## Spandex (Feb 20, 2009)

Dash said:


> How about a rear defuser?


The way it works as a system is kind of like turning the underside of the car into an inverted wing. The diffusers are there to smoothly decelerate the air that is moving at high velocity under the car which is why they are curved upwards and outwards.

So, for diffusers to have any effect, you need to create these channels of air that you're speeding up as they pass under the car, then slowing down as they leave. To do this you need a smooth underbody and either proper side skirts (hanging lower than the underbody, not the decorative ones that come with body kits) or some sort of curved channel from front to back.


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