Less Roof, No Goof; Ford builds a better Mustang.

Byline: MARK VAUGHN

Why is the new Mustang convertible better than the old Mustang convertible, better in fact, than any Mustang convertible ever? There are a lot of answers to that, but it all comes down to architecture.

"This is the first time that we had an all-new platform that didn't require compromises for our use,'' said Mustang vehicle engineering manager Bob Johnston.

That's a polite way of saying Ford finally built a Mustang to be a Mustang, instead of forcing a Mustang on something else. As you'll recall, the previous pony car traced its roots all the way back to the Fox platform of 1978, and even then it had to perform other duties, including but not limited to holding up those "icons'' of style and speed, the Fairmont and Granada. It was like asking your weed whacker to function also as a Flowbee hair trimmer, Waring blender and a snowblower. Sure, with enough engineering it could probably carry it all off, but not as well as any of those should, and you always wound up with hair in your daiquiri.

The new Mustang platform doesn't have to be anything but a Mustang (so far, anyway), and when engineers started to build it, they started with the assumption that it would also be a convertible.

That meant the basic structure of the car was designed to work with a minimum of reinforcement to keep it structurally sound even without a roof.

Ripping the top off a car generally sucks out about 70 percent of its torsional rigidity. That can be replaced with weight-bogging reinforcements to the floor pan, rear structure, A-pillars and windshield frames, but that's like adding the plumbing after you've put in the drywall.