When I hit 90-100 the car feels unbalanced
 

Ok so I purchased 2 rear wheels, and I am not sure the bastards balanced the tires. Somthing doesn't feel right.

When ever I hit 90+ I feel like im riding on gel or something. Its weird. Could it be because The tires are different than what was stock? Or did they not balance them? The car is not wobbly at 90,,,,,just feels slippery.

I made an apt at nissan next Sat for oil change, I was gonna have them look at the tires too.

I just got corner balance and alignment done by Darin at West End Alignment. You'll be happy to take your Z there. He works by appointment only.

your problem is most likely because your new Rear tires are different from your front tires.

Breaking In Your Tires




Tires are comprised of many layers of rubber, steel and fabric. Due to these different components, your new tires require a break-in period to ensure that they deliver their normal ride quality and maximum performance. As tires are cured, a release lubricant is applied to prevent them from sticking in their mold.

Some of the lubricant stays on the surface of your tires, reducing traction until it is worn away. Five hundred miles of easy acceleration, cornering and braking will allow the mold release lubricant to wear off, allowing the other tire components to begin working together. It is also important to note that your old tires probably had very little tread depth remaining when you felt it was time to replace them. As any autocrosser or racer who has tread rubber shaved off of his tires will tell you, low tread depth tires respond quicker."Don't be surprised if your new tires are a little slower to respond (even if you use the exact same tire as before). Their new, full depth brings with it a little more tread squirm until they wear down.

NOTE: Be careful whenever you explore the capabilities of your new tires. Remember that every tire requires a break-in period for optimum performance.

Tire Tech Information - Breaking In Your Tires

Thank you for the explanation, it makes sense. I appreciate everyones suggestions and help. I believe what you say is true.

Have you checked the air pressure? What type of types did you replace the rears with? Normally out of balance tire will cause a vibration, and in your case from the rear.

And this Fourm doesn't Condon driving the speeds your claiming on public roads.
So I know your talking about a private Road. :rolleyes:

I got Goodyear eagle 1's. I don't suggest them. They suck actually.

yah, definitely need to wear off the release agent on new tires before they stick well. especially on RWD you want to be careful the first 35-50miles. you can obviously shorten it if you do a quick burn out...