My two cents. If I remember correctly, installing the second ATB in my S3 3.0 Roadster Sport didn't just have advantages in terms of the driving experience. I wrote earlier in this thread that the car gained so much control with two ATBs that I even removed the Panhard rod again. (Perhaps the workshop had not installed the retrofitted Panhard rod with the correct geometry, because every time there was a vertical bump in the road, the PR translated the force into a horizontal movement that was extremely uncomfortable for my back. I didn't have this problem with my P4SS, where the PR was factory-fitted).
Now back to the ATB. As has been said here, these ATBs are extremely heavy. And two of them have, in my humble opinion, changed the car in two negative ways. 1. The car became noticeably sluggish and lost some of its fantastic agility. 2. With two ATBs, everything was more controlled, but also less fun and somehow more sluggish. The willingness to turn into corners was less enjoyable in my subjective perception.
What I didn't realise at the time was the possibility of changing the leaf springs, as I have now done with my 4/4 with the 4-seater leaf springs. If I were in the position to optimise a roadster again, I would do without both ATBs (because one is nonsense and my Roadster Sports always drove in a slightly slanted line across the road when accelerating sportily). But I would install reinforced leaf springs. For a while, there were some that were designed asymmetrically to prevent winding, but I have no experience with them... whether they were OK or too flexible overall.
To be honest, one of the reasons I switched to a 4/4 was because it's such a wonderful driving experience with 145 hp and an unladen weight of 800 kg, because none of my optimisations added even 1 kg, and because I don't have to take any measures to harness the power of a roadster with additional linkages and corsets.
So, bottom line, I would leave out the ATBs, never accelerate from a standstill because it rapes the car, and maybe use different leaf springs, or maybe not, if yours aren't sagging after all these years, if they feel strong enough and if you drive sensibly.
Another tip... I would definitely try it out without ATBs, at least on a trial basis, to see how it drives before you spend any money on any parts. You might be positively impressed by the new driving experience when the car really drives straight ahead when accelerating.
By the way, the video above refers to the 270 bhp of the 3.7 Roadster and it's not as dramatic with 220 bhp and less torque.
