Grassroots Motorsports
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Grassroots Motorsports 53 causes the tires to move away from perfect alignment (camber-wise) to the pavement. Numerous books and Ph.D. papers have been written about this subject, but we can summarize it by saying that a tire likes just a bit of negative camber when it's forced into a turn. Why? Because as the tire is distorted by the variety of forces acting upon it, negative camber keeps its tread portion in optimal contact with the road. Of course, making a suspension perform this feat costs money in the form of special linkages and mounts. It's a lot easier (and cheaper) to throw in a solid rear axle, but the camber is always 0 degrees with one of those–unless you get creative with a torch, which can be done. A semi-trailing arm is a step in the right direction (thanks, BMW, for popularizing this design in the '70s), but they sometimes cannot achieve aggressive enough camber gain to compensate for body roll. Same goes for MacPherson struts, which are chosen for their cheapness and ease of packaging. They're mostly found in the front ends of imports with creative variations, but they, too, mostly have limited camber gain during compression. The fxes for this are to use massive static negative camber at rest and to use stiffer anti-roll bars to reduce the "camber loss" during cornering. But these are mere patches. The clean-sheet-of-paper sports car engineer wants to use uneven A-arms or some variation on that theme to get the camber gain desired without breaking the bank. It would take another article to do this discussion justice. Let's just agree that the suspension needs to be independent at all corners, and has to have aggressive camber gain to keep the tires aligned with the pavement in an optimal fashion during hard cornering. Exceptions abound. We cited the Sprite and Lotus 7 for being excellent sports cars, and both have solid rear axles. See what being lightweight does for you? There are dozens of other criteria for a sports car's suspension to discuss, some of which include low unsprung weight, toe-in and toe-out behavior of each wheel during braking, accelerat- ing, engine braking, etc. The overall goal is to achieve both high cornering limits and a certain seat-of-the-pants feel for the tires' contact patches. It's a complicated formula that car companies don't always apply well. Lots of parts can be assembled and you end up with a Stepford wife-type of car–no passion. Legendary sports cars commu- nicate their own zeal. How a car feels involves many compo- nents: How the steering responds to your input, how the body leans over when thrown into a corner, how the engine revs (or doesn't) when goosed, how the brakes feel, how the brakes upset (or don't upset) the chassis when applied mid-corner, how the vibrations from the suspension telegraph what's going on at the road surface, etc., etc. The car has to ft like a glove and deliver a real connection to the driver. Mazda's oft-repeated "oneness between horse and rider" tagline was not a marketing department concoc- tion for the Miata. It came up at a brainstorming dinner at the beginning of the project, when we were discussing what the perfect sports car would feel like. Great sports cars have an almost telepathic relationship with the driver's will. They nearly anticipate the next move. Soul: The Secret Ingredient A sports car in its fnal form has to be like your favorite song, the one that begs you to reach over and crank up the volume knob every time it comes on. The car has to evoke a passionate response from its driver. How do you make a bucket of bolts do this? It's a combina- tion of purposeful choices, careful development, and uncom- promising stubbornness on some key points we've discussed. Just when does the soul get put into the design? At the very start, my friend. At the frst glimmer in the engineer's eye. Otherwise, all is for naught. No matter how hard you try, you can't fake passion in a project like this. SUGGESTED READING "The Sports Car" by Colin Campbell: ISBN 0-837601-58-4 "All Corvettes Are Red" by James Schefter: ISBN 0-671685-01-5 COVER STORY: ENGINEERING A SPORTS CAR