I a considering aftermarket front and rear sway bars because I would like to keep more rubber on the ground in corners. The rear tires want to ride on the edges in sharp turns.

Is it correct to say that the RX-8 already has sway bars and the aftermarket bars are just stiffer replacements?

 

Yes, and some aftermarket bars even are adjustable.

 

While sway bars are a great addition to the car, they won't keep the rear tire from riding on the edges (if by that you mean the tire is rolling over while cornering). They will reduce body lean. Depending on what you mean by riding on edges, the way to correct for that would be to increase air pressure in the tire. Or changing the alignment settings.

 

So to summarize, the RX-8 already has sway bars, just not as stiff as the aftermarket ones.

What are stabilizer bars?