I just recently got Falken Azenis put on my car and at high speeds the car was rather shaky which was unusual cause' i have never had this problem with my other set of tires so i take the car back to discount for them to check the balance and one of the tires was off balance by .75 whatever that meant but than i drive home and same thing occurs i was wondering what else could cause this? i recently had an alignment done and was wondering if driving on the spare tire for 15 miles to discount tire if that could have contributed to the affect of my car shaking?

 

I would have your tires checked for being out of round. (yes that does happen). and make sure that you don't have a greasy peice of crud keeping one of your rims from sitting flush to the hub and causeing a slight wobble. Since it started after you got the new tires those would be the two most likely causes in my mind. Besides a tire defect. I have have nearly new tires with belt problems when fairly new, but those were Bridgestones.

 

Possibilities:
Wheels (still)not properly balanced, or properly installed.
Need an alignment, but this would not just happen after installing new tires.
And the tires may have manufacturing defects, this does happen.