29mm front and 15mm rear. Only factory upgrade is the rear GMBH rs4 17mm which is rare like rocking horse crap ! You best going for Whiteline, Hotchis, H&R, Neuspeed or Eibach antiroll bars. Eibach only do the front though ! Ever other one would need strenghtening brackets for the rear subframe as it's known to break at the mounts, H&R does not have mounts though...