Wow. What you people are saying to Grizzly makes me wonder what you say about my car behind my back... wait, you can't do that because I read every thread. Never mind.
I have diffusers and side skirts. It doesn't detract from anything and I'd never go back to owning a boxster without side skirts.
The sides of the 986 are just too plain without them. Just be sure to buy polyurethane.
PS - A new front bumper is not required. It's already at the right height for skirts.
PPS - What red blooded man doesn't like staring at a new set of skirts?
