What wheel specs (width / ET) were you using for the 255 / 285 F/R setup ?
Also any other suspension mods, maybe aggressive camber ?
Z06Jerry and Chiraoka, sorry for the delay. I purchased OZ Ultraleggera's wheels with the fronts at 8.5x19 with 54mm offset. Stock is 57mm offset. For the rears 10x19 with 40mm offset, stock is 45mm offset. The 718 has limited camber adjustment. I was able to get about 1.1 degrees of negative camber in the front. This was maxed out, so we set the rear at 1.5 degrees of negative camber. There are no other suspension changes and no wheel spacers. Realize that the offset is measured from the center of the wheel, so the higher the offset, the more the wheel is tucked into the wheel well. The lower the offset the wheel sticks out from the wheel well further, thus with the lower offset from stock, I do not want to include any spacers.
Racing autocross there is a slight bit of overstreer with this setup. The car rotates very well, however I would like to get the rear a little more planted when rolling on the power, so I am going to 305/30/19 in the rear. The tires are supposed to arrive this week and there is a PCA race this Saturday, so I will post my impressions next week. I do have to note, the current 255/285 setup, worked very well with new tires and it was only later that the car started loosing traction in the rear coming out of corners due to the tires having quite a few runs on them.
A racing friend with a base 718 Cayman changed his front sway bar to a GT3 bar and really likes the results. I am thinking about this as well, but am a little concerned about increasing the understeer.