Mazda’s MX-5 is officially certified as the best-selling two-seat roadster in the world, and it’s hard to find a car that better defines affordable performance. When you’ve got that kind of a history and track record, creating something new and exciting for SEMA takes more than a little effort.

Sometimes less is more, and that seems to be the philosophy behind the new Mazda MX-5 Spyder concept. It doesn’t sport a massive turbo, giant rear wing or garish neon paint; instead, the most obvious difference between the Spyder and a production MX-5 is its bikini-style soft top.

Designed by both Mazda and Magna Car Top Systems, the removable top gives the MX-5 Spyder an even lower profile and even cleaner lines. Unlike the production MX-5’s folding soft top, removal of the bikini top takes more that flipping a lever and tossing back the top, but we’ll bet the added effort is rewarded with a fairly substantial weight savings.

Since the MX-5 is already a light car, finding places to shave pounds was a challenge. The MX-5’s battery has been changed from lead acid to lithium ion to reduce weight, and the car’s featherweight stock wheels were swapped for a lighter set of Advan RS wheels fitted with Yokohama tires.

Under the Spyder’s aluminum hood is a conventional 2.0-liter Mazda MZR engine, fueled by isobutanol. Isobutanol is a biofuel that doesn’t negatively impact performance, and is compatible with existing technology and infrastructure, which makes it ideal to represent Mazda’s concept of “Sustainable Zoom Zoom.”

The exterior is finished in a tasteful Stratosphere White with dark red trim to match the bikini top, and black mirrors are used with black wheels and black side skirts to add contrast. Inside, the seats are covered in black leather with dark gray suede inserts, and  bright aluminum (what Mazda calls “Spider Silk Gray Metallic”) trim is used to finish off the look of the interior.

We doubt that Mazda will actually build the Spyder, but we’d be curious to know if the bikini top will be available from the aftermarket. We couldn’t justify it on looks alone, but the potential weight savings (with its associated increased performance) may make it an attractive option for some.

Can't get enough news about SEMA 2011? We've got even more show coverage and breaking news for you here.