Originally Posted by Malek
Most likely it's the wheels. They may not be 100% true.
What kind of tires are they? If you could provide this information, I could most probably tell you what your problem may be definitively. I deal with these cars everyday.
Well let me back up a bit. Originally when I installed my AP BBK I had to run 12mm spacers along with the OEM 18" wheels with the stock Pilot Super Sport Michelin's. Was super smooth up until that day. Every since there has been some degree of vibe's. So with a new set of Michelin's installed on my ARC-8 wheels about a year ago and new AP rotors, road force balanced, it was smooth. Then about this last fall started the steering wheel wobble at cruise and increased vibe under braking. Installed new Bridgstone Potenza's, correct size tires now on the ARC-8's (265/35R18F, 285/35R18 Rears) Road Force balanced again. Did some rotor disc cleaning with race pads to clean up the surface of any pad transfered materail build up and now pretty much smooth under braking but at cruise above 78mph, I still have this slight vibe/steering wheel wobble. Its never smooth like at say 50mph for example once I get it up past 78mph and higher.
A while back I had asked APEX about the wheels but the responce was that maybe I hit something or bent the rim(s). Very, very unlikely but I was running tires two sizes smaller for a while. Now with proper size tires, no spacers, I still got the same damn problem. Right nowmy Potenza's are ony about a month new and barely any miles as I don't DD the M3.
I think I have two seperate issues. One is the AP BBK rotors probebly gained some uneven pad material which I think so far is cleared up but I can't be sure with the steering wheel still manifesting a vibe at 78~80+mph.