Per WD-40 site:
http://www.wd40.com/faqs/#a98
What surfaces or materials are OK to use WD-40 on?
WD-40 can be used on just about everything. It is safe for metal,
rubber, wood and
plastic. WD-40 can be applied to painted metal surfaces without harming the paint. Polycarbonate and clear polystyrene plastic are among the few surfaces on which to avoid using a petroleum-based product like WD-40.
All it does is soften up the rubber which make them grab more. I personally think that it cause the rubber to wear prematurely.
Simple green is different. It acts like a glue that sits on the top which sticks to the ground. But it will not last but 2 laps, it does not penetrate the rubber like WD40.
@ Frank - happened to me to bud, that sucked