SPRING ARRIVES AT 150 MPH; New Crossfire Roadster offers all this and no roof, too.(News)(Product/Service Evaluation)

Byline: MARK VAUGHN

]] The more Crossfires we drive and the faster we drive them, the more we like them.

Chrysler is very proud of the Crossfire's stiff structure, perhaps too stiff for some, though there are always those who feel any chassis could be stiffer. Chopping off the top of the coupe loosens it up a little and actually makes it more comfortable for everyday driving. The Crossfire goes from a stiffness of 50 hertz as a coupe down to 29.2 hertz as a roadster. It actually works out to be a nice compromise between ride and handling, even with those low-profile tires.

Hertz is a figure everybody quotes, but almost nobody understands. It is the resonate frequency at which a body vibrates. Hang an object on a string then tap it with a hammer and listen. An empty milk carton would have a low hertz figure, a Coke bottle a high hertz. By any measure, if you cut the hertz of a given structure in half, say by chopping off its roof, you soften it up.

We spent a day driving several convertible-topped roadsters and felt just fine by the time we turned in the keys in the late afternoon. The day included time on an autocross course, where the roadster sailed through the corners with aplomb.

The basis for this car is the soon-to-be- former Mercedes SLK, never much of an autocrosser to begin with. Chrysler stiffened that body up, then added a sporty wheel and tire package-225/40ZR-18 fronts, 255/35ZR-19 rears. Those are sports car-sounding tire mea-surements. The treads are summer treads, too. If you want all-season tires you have to go to an optional package of the same dimensions but with better all-season grip.

Suspension is pure Mercedes, upper and lower A-arms in front and a five-link independent rear.