Tires to maximize 15" wheels are difficult if you require speed-rated tires and/or matching fronts & rears. Hoosier makes a couple, Avon of England makes some and a few Pantera vendors have some Pirellis in stock; none that I know of are 285-50 x 15, though. The slightly wider 295-50s are sometimes available as are slightly narrower 275-55 x 15". Expect to pay upwards of $400 per rear tire at best, and there may be a waiting period. Tire mfg is spotty ate best for performance 15". Try calling around- I know PPC-Carson City, NV (www.panteraparts.com) has some sources, as this comes up constantly. But its a very small market so the mfgrs do nothing.