I'm lowered and have 18x10's in the back 25 offset 285 tire and I rub the inside of the tire with the inside roof in the wheel well on full compression. There's a few mm room to the outside. I have 18x9 on the front with a 30 mm offset and it's perfect. No room to the inside or outside with a 245 tire. In my opinion with an 8.5" rim 30 to 32 is the offset you want without spacers. On the rear, with a 10" rim I'd stay real close to 25 offset. If your lowered you may have to put up with a little rubbing.

Les