Tom -- since you're car is primarily a smooth-pavement autocross purpose-built car, I highly suggest you get bigger TBs (~1.18 at the minimum, as well as eventually try 1.22, 1.24.. don't make quick decisions.... work with them for a few events/or a season or two, as well as perhaps stiffen the rear leafs... stiffer shocks, bigger sway bars, balance the weight at the corners in competition-ready weight.. with the driver and the approximate load (fuel) you'd be typically running.... it becomes a complete package to be the goal. Remember... your car runs on smooth flat surfaces and is autocross competition intended. Your tires are saying "help me stick so stiffen me up.... prevent excessive lift/dive".