Need input on wheel/tire set up for track

[MikenOH]

I've been looking for a R compund tire I can drive to the track and found out that Nitto makes a R compund tire that would work for the 987 tire OD set up--2 sizes that are at least the same front and rear--245/45/17 and 275/40/17. The MPSC sizes are a lot smaller in 17".

To use these sizes, I'd need to have at least a 7.5" on the front and 9" wheel on the rear. I have a set of 986 boxster style wheels with the rear width at 8.5" and offset of 50. I could buy a couple of the 9" widths --55 offset--of the same style off a 911 for probably $150/wheel.

Assuming these sizes would actually fit in the wheel wells, my concern is the change to the car's footprint and what it might do to handling at high speed. My std front wheel has a width of 8" and offset of 57. Going with the 8.5" 986 wheel would extend the outside edge of the front wheel +13mm out from the car. Using the 9" wheel with the 55 offset in place of the stock 9" rear wheel with a 43 offset, brings the rear outside wheel edge in 12mm closer to the car. the overall change is 25mm or nearly and inch.

Significant change or not? thanks for any help.