1. you have mismatched tires...they will always feel off...the faster you go the more swirly they will get, and dangerous!
2. You bought low performance tires that are softer than the stock tires, they are going to feel less planted.
3. Next time do some research on tirerack.com and spend some money on the right tires (all 4 the same brand/model for your sports car.
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