Michelin is introducing a new Pilot Sport Cup Series tire end of this month.

It's a 325/30-19.

They have been making this as a private label for Goodyear for the Z06 Corvette, and due to incredible demand they are now introducing it under their own label.

Use this calculator: http://www.miata.net/garage/tirecalc.html

You can see exactly how a tire size change affects everything.

With proper offsets (see: https://www.rsracing.com/tech-wheel.html ) and in some cases with the aide of spacers you can get almost any tire/wheel combination to work.

As far as 20" rims, it seems we are going back to bicycle tires! It's getting a bit ridiculous. There is no sidewall remaining!