Vibration on car up to 120kmph

[Don]

I have a 1988 M5, it's got 17' mag wheels. I get a vibration from 100-120, it then goes away.

Also I'm getting petrol fumes in the car.

Please help

[DON]

I HAVE AN 88 M5 AND I CHANGED THE RIMS AND TIRES TO A SET OF RONELL, 17 AND HAD THE SAME PROBLEM.....WHAT I FOUND WAS THAT I NEEDED A HUB CENTRIC FITTING I DONT KNOW IF SOME PEOPLE CALL IT A SPACER HOWEVER IT TAPPED INTO RIM AND I T CURED ALL MY PROBLEMS....GOOD LUCK

[Tony VA]

DO you have after market wheels on it? If so check the hub-centric measurements. E28 is 72.6, most after market for BMW are 74.1... it will make a difference at that speed!

[Snake Pliskin]

Well im certainly no expert, but i know a lot about physics for cars.

Is mag wheels "magnesium"?

Anyways, obviously its vibration as you have said, and when i had this problem on my 1989 mazda mx-6, the wheel are tire wasnt PERFECTLY balanced. That didnt fix the problem, but it made a lot go away, especially when i hit over 140 MPH.
Different amount of unbalanced weights vibrate at different revolutions, dont ask me why, but it does and it will go away if at higher speeds.
A spacer may help as DON said, but im not familiar with that, but i am not familiar with rear wheel drives at all. In fact ill be getting my BMW 528e 1988 tomorrow...
I dont know what it has on it (your car) but if its fully independent suspension, then the CV shaft may not be balanced, thats all i can think of, BTW did you have this "vibration" before you changed wheels? If so then gearing could be the problem.
I just thought i would offer some insight to other problems perhaps but im no expert.

As to fumes in the car. I had that problem with my mazda before it finally was sent to the junk yard. If you have your windows up does it still come in? If so, close your vents and see if they still do. Just some speculation.