Offset

18Racing via Ebay delivered my new wheels yesterday.  15x7.5" 5x114.3 Rota Slipstream.  Advertised and sold as a +40 offset but they are actually boxed, stamped, and stickered as a +35 offset. Backspace measures 5 5/8" or 34.9mm.  Weight 13.45 lbs.

This could be a good thing because front brake caliper clearance is a concern. And depending on ride height, camber, and tire size, the lower offset could also cause problems with outer fender clearance.

Test fit without tires or any suspension modifications and all is good with plenty of clearance everywhere.  Just about a quarter inch clearance at the front brake caliper.  Due to the curve of the spokes it is difficult to tell if the +40 offset wheel would hit the caliper or not.  With a planned moderate drop in ride height and a much shorter tire than stock I do not anticipate any tire to fender rubbing with the +35 offset, although if needed fender lip rolling is allowed.