I'm a little confused by this thread.
Do you really want to add DF?? was that increase the point weight on the tyres and therefore the rolling resistance. I would suggest a ballanced approach go for a froint air dam but increase the size of it slowly in steps. chucking a large one at it may result in a the car become twitchy as you've increased front end grip but the back is relatively light in comparison - which brings me the the TT. As stated above the design is a form-over-function golf in drag but it is a very short wheel base car with alot of the weight over the front wheels allowing a huge amount of direct direction change. at Autobahn speeds of 150 MPH (yes MPH not KMH) any golf-size car will get twitchy but I'm stunned they didn't find this out before putting it on sale.
I'm shocked that you car gets wayward at 80! I've had some beaters in my time and all of them have been planted well beyond that ( where legal limits allow
). even my little polo stays glued on 175 tyres at GPS indicated 103 mph (more than book says it can do!!!) and cross winds at 80 don't phase it.
Another suggestion to cure its road manners maybe a new set of struts and lower the ride height, over soft shocks can make it a car raise-up at speed and therefore give a feeling of a lot less control.
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