# Why Audi put a spoiler on the TT - the definative answer!



## sttu80 (Jan 28, 2004)

Some might have read a previous post where I announced that I was buying an original spoiler-free rear hatch for my baby (mint Â£140). 'Dangerous reptile' asked if it was there for a reason -good question- so I did some digging and came up with loads of information. I've summarised it and I thought I'd share it with you  .

Theres a lot of information so grab a cuppa if your interested 

When the TT was introduced to the market in 1998 it was praised for its clean design, the rounded profile made it a very graceful car. The press argued that the rear end of the car showed signs that the Porsche 911 had been a source of inspiration in the design process. The handling issues were first discovered in Germany when driving at high speeds on the Autobahn. The problems were especially significant when the drivers began to slow down and at the same time started turning to get onto the exit ramp. The rounded design of the rear of the TT did not give the air a fixed release point, instead the release point wandered. This gave the TT a certain degree of instability, which caused the rear of the car to wobble. When this wobble was combined with high speed braking (which gives a dynamic shift of the gravity centre towards the front axle and thus decreasing the load on the rear axle) and also cornering, the TT could no longer sustain sufficient rear wheel grip.

This resulted in 22 severe accidents were the TT spun around and ended lying upside down at the side of Autobahn. That may sound like a lot, but more than 40,000 TTs had been sold worldwide, the ratio of accidents was fully in line with that of other sports cars. As mentioned, the TT's stability issue was primarily a Germany-only problem, because it's the only country in Europe with open speed limits. One TT driver was killed on a notorious high-speed autobahn curve. A second fatality occurred to an unbelted rear-seat passenger. Audi engineers continued to defend the car's original chassis settings, while quietly acknowledging that they recommended a rear spoiler to reduce lift at the rear axle, the prime source of the handling problems. Stylists resisted the spoiler.

"There was a lot of discussion during development, and we all decided not to include a spoiler," admits Dr. Bernd Heissing, Audi's head of chassis development. "Now, we've changed our minds."

Audi quickly realized that they had to do something about the problem because of all the negative press, which could affect the sales of the TT like the elk-test had done to the Mercedes A-class.
Audi said the main aim of the changes was to increase under steer, reduce lift-off over steer, and improve high-speed stability. The TT coupe and roadster got modified front control arms with altered compliance in the mounting bushings. The front shocks were made stiffer in compression and softer in rebound to reduce the pitch motion and weight transfer from rear to front when braking. The front anti-roll bar was made 1mm thicker, and the rear was made 1mm thinner in diameter. On the 2WD version Audi installed an extra 60kg in the luggage space to increase the load on the rear axle. This was not considered necessary on the 4WD version, since it already had a higher rear axle load because of the 4WD-system Audi also offered an ESP installation.

All TTs also got the rear spoiler mounted to the hatch (unless specifically requested by the customer not to have it) in a move aimed at reducing lift on the rear axle at high speeds. The TT has 70kg of lift at the rear axle at 125 mph without the spoiler, and 25kg lift when the spoiler is fitted. By comparison, the BMW Z3 coupe generates 29kg of lift at 125 mph; the Mercedes-Benz SLK, 47kg of lift; and the Porsche Boxster, 30kg of lift. The chassis engineers claim they could have solved the problem without the spoiler, but this would have meant a significant increase in under steer at normal speeds, a trait they wanted to avoid. All TTs also got a version of VW's switchable Electronic Stability Program (ESP).

The changes are noticed, most obviously when you swap lanes and brake at speeds above 100 mph. Stability is much improved. At less exciting speeds, it's the steering that gives the modifications away. The suspension changes have the effect of slowing the steering, so turn-in is more gradual, and any given corner demands more lock.

So, why does the TT lift at high speed? Its down to the basic design of the rear of the car. The sloping shape begins almost at the top of the front windshield and thus causes low pressure over the top of the car. The car is sucked off the road. The TT has a static rear axle load of 620 kg.

What can we do? It is possible to improve the stability of then TT by reducing its centre of gravity (lowering). This reduces the static moment about the front axle (the car is trying to rotate around its front axle when you hit the brakes). Stiffening the springs reduces the pitch motion and weight transfer whilst braking, this in turn helps to reduce the unwanted counter lever effect of the mass (engine) fwd of the rotation point (front axle).


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## L7 (Aug 27, 2004)

So what are you going to do then with or without :?


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## sttu80 (Jan 28, 2004)

Without    I've bought it already  

I guess that anyone who brakes on a bend at +200kph can expect the back to overtake the front.

When its all done I'll post on the results - if it really is totally unstable I can always put the current one back on.


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## davidg (Sep 14, 2002)

sttu80 said:


> Without    I've bought it already
> 
> I guess that anyone who brakes on a bend at +200kph can expect the back to overtake the front.
> 
> When its all done I'll post on the results - if it really is totally unstable I can always put the current one back on.


Let us know , i would say you will not feel any difference


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## Wak (May 6, 2002)

Nice info, can I copy it into a page?


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## clived (May 6, 2002)

Wouldn't you need to ask the original copyright owner Wak?


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## original_tt (Mar 11, 2003)

I've had my original car since oct 99 and i'll never have a spoiler on my car - (they screwed up the handling totally on the recall) it does go a little tail light above 130 mph,but how often do you drive at that speed?
I also think that the car looks a lot better without it.


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## sttu80 (Jan 28, 2004)

Wak said:


> Nice info, can I copy it into a page?


Sorry about the delay to respond, I've been without the use of the PC for a couple of days, makes you a bit crazy [smiley=rolleyes5.gif]

The info was gathered from several sources freely available on the web. I just put it together. I cant see any harm in reproducing the information for the benifit of others. I certainly don't mind!


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## maxy (Apr 30, 2003)

I think the FWD 180 TT (which was the first released?) is more at risk from the rear lift because all the weight is at the front of the car. The Quattro has the Haldex unit and bits at the back to give it extra weight and more evenly balanced car.

I actually reckon most of the fixing they did was in the suspension and the spoiler doesn't have much effect.

BigJon on his training course told me, there was nothing wrong with the original TT setup. He did loads of track testing with it and couldn't find any handling problems with it.


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