some places i've read they're the same and others i've read they're differant.

i'd rather get other sway bars, but my buddy is offering me his s4 sways if i just pay shipping.

 

well i took my search to google and it appears the s4 sways differ from the a4 sport sways.

a4 sway bars are 16mm
a4 sport sway bars are 18mm
s4 sway bars are 20mm

assuming the above is true, I hope this info will help someone else.

edit: the above is for the rear sway bar.

 

What's the size on the front sways on an A4 sport?
Will an S4 sway fit?
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Not sure if it will, but if it does, chances are it's still a larger diameter than the A4 bar, which means it's going to create more of a tendency to understeer, and the A4 already has that capability in spades. If you're looking to upgrade, get the S4 rear bar and call it a day - stiffening the rear of the car will help it to rotate more readily, thereby dialing out some of the car's natural tendency to understeer. If you go to an upgraded front bar as well, you're going to take away some of the advantage of quicker rotation that the S4 rear bar gives.