What would happen to the ride height of an A4 if an S4 suspensions was installed???

Bet it would get lower :) Especially since the rest of the body/frame is the same.

That would NOT be a good idea.

Why? I thought it was a fairly common thing for people to do.

Read this first...
 

<a href="https://forums.audiworld.com/a4/msgs/926303.phtml" target="_blank">S4 suspension on A4 writeup</a>

no. for starters the ride height is no lower than an A4 sport. secondly, the S4 springs/shocks are
 

designed for a heavier front end. The results would be unpredictable.

Well for starters, go here. :)
 

I agree that it could probably be done to a 2.8 with performance benifits because the weight bias is closer to that of the S4. But on a 1.8T, your front suspension is going to be way, WAY to beefy.
But, I still won't install an S4 suspension on a 2.8 (and I have been asked) because the S4 supension was designed for the S4, not the 2.8. IMO, you would be better off dropping a few more bucks for an a/m setup designed for your car.<ul><li><a href="https://forums.audiworld.com/a4/msgs/926303.phtml">https://forums.audiworld.com/a4/msgs/926303.phtml</a</li></ul>