I run that same setup - 215/45-17 star specs on 17x7.5 wheels and TSW springs. Mine took about 10k to wear away the fender liner. You'll see strips of plastic on the tire where the tread blocks cut away at it. First they rubbed on every bump, then they rubbed with a passenger over bumps, and now they don't rub. The fender liner has a jagged crescent-shaped cut where the outside edge wore it away. I thought about Dremeling, but procrastination paid off: it doesn't make any more noise and nothing's falling off the car.
BTW, it was just the fender liner that got cut, not the plastic wheel arch trim. You may have a different situation - I'm not sure what seams you're referring to.
I've worn down the liner - completely gone in basically all the area towards the aft of the car. The arches are worn down fine too. Now the bodywork seams are underneath the fender liner where actual metal unibody arch is seamed at.
I'm probably lower than the TSW springs by a bit - my tire tucks into the fender at rest (coilovers down pretty aggressive - not "Rally" low though.
I can tell that the seams used to be pointing down towards the ground, but the areas that the tire hit have taken the paint off and flattened them a tiny bit.
I've had 215/40/17 Star Specs on my 17x7 et38 - those *almost* don't rub anymore except over the nasty bumps. The new 215/45 rubs on pretty much all rinky dink stuff. Smooth sailing on the freeway *almost*
I too am curious about what people have done for the metal contact areas. I have 215/40x18 on 18x7" wheels with JCW springs and about 37mm offset with wheel spacers. I have rubbed through the plastic liners and arches in a few places, so most rubbing has stopped. However I can see a couple places where the tire rubs on metal so I would like to fix those areas. I have no tire damage (just rub marks) but I do not want to push my luck, especially on the track.
