I would recommend using the square setup like with they use in Spec Boxster, I run a 17x8.5 square setup (same size wheels and tires in front and rear)with 255 tires, this allows you to rotate your tires and prolong the tire life, cause tires ain't cheap.
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2001 Boxster S
RUF front bumper, Techart side skirts, Gemballa rear bumper, PSS9s, Cargraphic 18" racing wheels, RUF exhaust, GT3 seats
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