Need HELP Please! New rim vibrations

Hi, I have a 1999 Mitsubishi Galant DE, and I wanted a cheap upgrade on the rims, so I researched and found that the 350z stock 17" rims match my lug pattern, and the offset was very little. So I got ahold of the 350z stock rims and put on some new Kumho Ecsta 711 tires size 225/45/17 - per recommendation of tires.com, tirerack.com, and the tire servicers (America's Tires).

After putting them on, I get major vibration going over 50mph. I've narrowed it down to have something to do w/ the lugs. The lugs were tightened by the service technician to about 80lb/foot. I tried tightening them to 90lb/ft and it got better but not good enough. I then went to 100lb/ft and now it is A LOT better but not gone. The vibration doesn't start until 70mph, but it is still significant. I don't want to tighten it any further because I'm scared it might screw the wheel studs (I've broken many wheel studs in the past from overtightening).

I noticed from the old lug nuts that the wheel studs for 350z is thicker. You guys think this is the problem? Or should I torque it even tighter.. say 110lb/ft? Will this cause any issues? Any help would be MUCH appreciated!!

For starters, do not increase the torque! You are stressing the studs and you run the risk of of stud failure. :nono: Not safe! It sounds like your wheels are not hub-centric (don't fit snug on the axle end). Your car does not have the same center bore as a 350z. If it is an aftermarket wheel it would require a center ring to fit safely. It can't just center on the lugs. You need to get back with the shop that sold you the wheels for the correct (safe hardware) if it's available. The stock 350x wheels have an even smaller center bore than your car so I'm at a loss to know how they would even think the wheels are going to fit safely.