Lowering a Spider

I'm thinking of lowing my Spider purely for cosmetic, currently fitted with OZ wheels, am i right in thinking you can lower a Spider 20mm on the standard suspension?
If so, as anyone got first hand experience of lowering a Spider, any issues, the one thing which worries me is the underbody clearance with speed humps etc, Any thoughts would be appreciated.
Thanks, Steve.

Personally, I wouldn't lower my Spider. Although there's some space to do it at the front of the car, it already bottoms out on pretty much all speed bumps and several country lanes. At the rear, I don't know about your OZ wheels, but with my stock wheels and tyres I don't think there's even 20mm between the tyres and the body, so I don't think it would even be possible. Just my thoughts though