Everyone seems to have overlooked this^^^

That does not sound like a balance or tire wear issue. This could be any number of things that are not safe. Given that you are not able to diagnose it yourself, I'd get someone to look at it soon. Diagnosis is cheap.

 

I agree, check make sure there are no bumps in your tires... how old ARE your tires? You just bought it, have the previous owner have them on there since he bought the car or something? Check make sure irregular bumps in the sidewalls or anywhere on the tires.

 

Here's one people missed. Your rotors will do the samething. Have them turned or resurfaced. That would also cause a shudder or shaking feel in the steering wheel. My wife's G35 does the same and I'm diagnosing it this weekend.

 

i agree with this too, thats why mine was doing it, make sure you check the inner sidewall too, it was scary seeing that and thinking it could have blown out on the highway

 

What wheels and tires are you running? SPecs? I have a booty shake problem at higher speeds...

 

never had that problem, except when i ran my tires down to slicks basically.