Ferrari Italia (W.I.P)

I'm trying to create a Ferrari Italia, but so far the problem is the tyre that I create aren't COMPLETELY CIRCLE at all. So when I test the tyre, the car keeps bouncing...

Can someone help me create a tyre that are 100% circle and can run smoothly? (helper name will be credited )

And I need someone to create a beautiful car sound for me. (Sasha from Russia, will u help me?)

Thanks!
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