Grassroots Motorsports
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COVER STORY: ENGINEERING A SPORTS CAR HOW TO ENGINEER THE PERFECT SPORTS CAR Now we have some parameters for defn- ing a great sports car, but how do we turn them into metal, rubber and glass? Let me start out by saying that a sports car project is the highlight of most any automotive engineer's career. (There are those who aspire to design minivans, but we Vaseline their keyboards when they're exposed.) Designing a sports car allows an engineer to get down to the core of performance in so many areas. The job becomes a labor of love. At last, the mar- keting doofs and accounting geeks are locked in a closet and objectivity rules. Capable engineers, equally informed, seldom disagree–the physics of vehicle dynamics rule the day. The exterior designers (aka stylists) also have more freedom when it comes to sports cars. They're better able to create a passionate shape for these proj- ects than for, say, their mid-priced SUV assignments. Ugly is called out when it's tried–no Aztecs sneaking through the system here. Beauty is the goal. Giving creative and talented people a long leash can lead to brilliance in a prod- uct, provided the management will keep their hands off the fnished work. The automotive world is peppered with some truly remarkable sports cars that were born out of the dreams of gifted men and women. In the best cases–think Porsches, Ferraris, Lotuses, etc.–the DNA for a performance car comes from all offces of the company, including the head offce. The paradigm of sports car design begins with eliminating as much of the unnecessary as possible. Think of an air- craft: Nothing comes on board unless it adds to the goal of getting aloft or staying aloft. Same for a sports car: Everything that is put into the vehicle has to have a purpose that is additive to the goal of taking a curvy road (or race course) at maximum speed. Every component must carry its weight, so to speak. From an engineering standpoint, the priority list for a sports car goes like this: a light and rigid chassis, evenly dis- tributed weight, a low center of gravity, optimal camber patterns, low unsprung weight, a strong engine, and good or great brakes. The particular order of this list may be juggled from project to project, but these are the components that make up a sports car's soul. Step 1: Win the Battle Against Weight So, let's start with weight. You'll remember enough of your high school physics class to conceptualize the tension that would be in a length of fshing line used to hold an object as you spin it over your head. A tennis ball won't break your 20-pound test line no matter how hard you spin, but a brick certainly will. It's harder to get a heavier weight to travel around a circle than a lighter one. Since we want our sports car to be superb around corners, lighter is better. No amount of tuning or shocks or tire tech- nology will overcome sheer weight. This is one reason why the original Austin-Healey Bugeye Sprite was an amazing-handling car despite its average suspension design: It only weighs 1452 pounds. Check out the column to the right to see some weights of representative sports cars, from lightest to heaviest. At the very beginning of a sports car design project, the packaging/layout engineer will start with a driver of some proportion. This is typically a virtual mannequin representing the 92nd- percentile American male: 6-foot-2, 180 pounds, 32-inch inseam, 34-inch waist. For the Corvette, it's probably the 95th percentile given the demographic, and for early Lotus 7s it was more like today's 50th-percentile American male–before all those hormone-laden McDonald's burgers hit the U.K., one can suppose. This is no small point, since the driver is the single largest component that must be packaged, challenged only by the engine. Imagine how small a sports car could be if you didn't need to ft all those pesky legs and torsos inside. Well, you'd end up with two Suzuki GSX-Rs bolted together side by side. Once the engineers have packaged the part that makes the monthly payments– important point, that–they can work on ftting in all the other bits, such as the engine, transmission, driveshaft, rear differential, gas tank, radiator, steering column, and at least a heater core as a nod to comfort. The more tightly he can package all of these components, the smaller the structure that will be needed to support the weight. One task of a car's chassis is to hold all its parts off the ground–to serve as a kitchen table, as it were. Fewer compo- nents means less weight to carry, which means a lighter structure can be used. So for a sports car, options (used to be) limited. Triumph added air conditioning (begrudgingly) to the TR6 toward the end, but it was not pretty. Today, all main- stream sports cars have a/c as an option. We have become comfort divas, I suppose. The limit to making a sports car's structure light is that the chassis has to be as rigid as feasible. All the great suspen- sion geometry in the world won't mean much if the chassis fexes. I had a friend's Morgan over at my garage one day and jacked it up to change the left-front tire. My jacking point was on the frame, just behind the front wheel. As I lifted the front wheel off the ground, I noticed that the rest of the car was still sitting nearly fat; such was the fexibility of the wooden frame. Driving that car was like sledding on top of a chest of drawers, squeaks and all. A lot of brain time goes into optimizing weight versus rigidity, but a sports car will be well served if optimal rigidity is a priority. car lbs. Lotus 7 1300 Austin-Healey Bugeye Sprite 1452 Morgan 4/4 (1967) 1624 Lotus Europa Twin Cam 1700 MG TC 1750 Triumph Spitfre 1750 MGA 2100 Mazda Miata (1.6L) 2138 Porsche 911 (1963) 2200 Fiat 124/2000 2300 Austin-Healey 3000 2300 MGB 2310 Triumph TR6 2390 Porsche 911SC 2500 Alfa Romeo 2000 2548 Jaguar XKE 2700 Cobra 427 2800 BMW Z3 2800 Mazda RX-7 (3rd-gen) 2857 Porsche Boxster (2015) 2888 Nissan 370Z (2015) 3278 Chevrolet Corvette Stingray (2015) 3298 WEIGHTS