How much clearance do I need?

Those are slicks or radial tires? Kind of look like slicks in the pic. My current slicks have slightly more clearance than that. Going down the track is no problem as they stand up and get narrower with rpm..... but around the pits and when (infrequent) I drive them on the street they rub on every corner.

The next pair I buy will be 1/2 or 1" narrower....