HELP! 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!!

The wheel's probably not 'hugging' the hub of your car correctly or if at all. The hub helps to center the wheel on it and to take some of the vehicles weight off the lugs. You might need a new hub ring on the center of the wheel.

Another thought.....after changing to larger wheels than stock, did you do an alignment? Try and have the wheels rebalanced as well.

get z lugs and have your wheels balanced

yeah, it sounds like your wheels needs balancing. You should always get it done when you get new rims or wheels.. or both.