THE CORVAIR’S FLAW
The Corvair’s tail-heavy, rear-engine layout had a number of effects on its performance, some good, some less so. With nearly 64% of the car’s static weight on the driving wheels, winter traction was excellent. The rear weight bias aided braking as well, although the early Corvair’s brakes still faded heavily in hard use. On the other side of the ledger, the Corvair was more sensitive to crosswinds than was a typical front-engine car. Also, in fast turns, the Corvair’s rear tires lost their grip first, sending the tail sliding toward the outside of the turn — a condition engineers describe as terminal oversteer.
The Corvair’s oversteer was the product of both its weight distribution and its suspension design. With the engine behind the rear axle, the rear springs had to be quite stiff to support its weight. The rear coils of the early Corvair were more than twice as stiff as the rear springs of a contemporary full-size Chevrolet. As a result, the Corvair had very high rear roll stiffness, something that was exaggerated by the geometry of the rear suspension.
Body roll is in part a function of the distance between the center of gravity and the suspension’s roll center (the axis on which the car’s sprung mass rotates when lateral force is applied to it). Because of its swing axles, the Corvair’s rear suspension had a high static roll center, which effectively increased the rear roll stiffness even further. Roll stiffness reduces body lean in turns, but it also increases the slip angle of the outside wheel (the angle between the direction the tire is pointed and the direction it is actually rolling). Since the Corvair had much higher roll stiffness in the rear than in the front, the rear tires’ slip angles were higher than those of the fronts, resulting in oversteer.
Oversteer is not necessarily any more dangerous than understeer — either can put a car in the weeds. However, few American driver-education programs teach the techniques involved in correcting oversteer and many of an untrained driver’s knee-jerk responses will make the effect worse. For that reason, most automakers try to tune their cars for final understeer, which is easier for the average driver to manage.
The early Corvair’s real Achilles heel was not oversteer per se, but rather another side effect of the swing-axle rear suspension: jacking. In a hard turn, the halfshaft of the outside rear wheel would drop below the pivot point of its universal joint. As cornering forces increased, the halfshaft then acted as a lever, forcing the tail upward. Body roll offered some relief, reducing the magnitude of the forces involved and transferring weight onto the outside wheel, thereby resisting the vertical component of those forces. However, early Corvairs had such high rear roll stiffness that there was little weight transfer.
As the tail rose, the outside rear wheel would “tuck under,” assuming an exaggerated positive camber angle that would weaken and eventually break the tire tread’s already-tenuous grip on the pavement. The result of this progression was a sudden burst of non-linear oversteer. It was not always easy to predict at exactly what point the tail would break loose and catching it was not always easy.
(This behavior was by no means exclusive to the Corvair. Most cars with swing-axle rear suspensions suffered it to one degree or another, the most notorious example being the Mercedes-Benz 300SL “gullwing” coupe. The early (1961–1963) Pontiac Tempest also behaved similarly for the same reasons, since the Tempest shared the Corvair’s suspension.)
Chevrolet engineers were well aware of these tendencies and took several measures to mitigate them. The semi-trailing arms caused some rear steering, changing the toe angles of the rear wheels to induce understeer in turns. The original design also specified a front anti-roll bar to increase front roll stiffness. The anti-roll bar wouldn’t have changed the rear suspension’s behavior, but by increasing the slip angles of the front wheels, it would have caused the front end to wash out well before the rear tires reached their limits of adhesion.
Unfortunately, the anti-roll bar became a casualty of the last-minute cost-cutting program. As a cheaper stopgap, Chevrolet specified unequal tire pressures: 15 psi (1.03 bars) in front, 26 psi (1.79 bars) in back. The lower pressures reduced the grip of the front tires, effectively promoting understeer. It was at best a half-measure and the lower pressures served to reduce the load capacity of the front tires by 40%, which meant that a full load of passengers and luggage would strain the load capacity of the 13-inch tires. In any event, few owners observed the recommended pressures and even Chevrolet dealers offered differing opinions about the best settings.
In normal driving, neither the oversteer nor the jacking was usually an issue. Many owners drove their Corvairs for years without noticing anything unusual about the handling. A sudden maneuver taken at too high a speed on an unfamiliar road, however, could provoke an unexpectedly severe response. Since many Corvair owners had never owned a swing-axle car before, the effect was not unlike a normally docile family dog suddenly going for its owner’s throat. Even knowledgeable drivers could be caught off-guard; John DeLorean later claimed that Chevrolet engineer Frank Winchell actually flipped a Corvair prototype at the GM proving grounds in Milford, Michigan.
Early (1960–1963) Corvairs were involved in a number of serious, occasionally fatal single-car accidents, including the crash that killed comedian Ernie Kovacs in January 1962. Some of those accidents struck very close to home. The Corvair was very popular as a personal car for GM employees and their families, and at least two children of senior executives died in accidents involving Corvairs.
Some owners filed civil lawsuits against General Motors, charging that the Corvair was unsafe. By 1965, there were more than 100 such suits. GM strenuously denied any mechanical fault, blaming the accidents on driver error or road conditions, but Chevrolet, perhaps stung by the accusations, developed an optional handling package to rectify the problem, followed in 1964 by an extensive revamp of the standard suspension (see sidebar below). Nonetheless, the accusations and lawsuits would eventually do serious damage to the Corvair’s reputation.
CORVAIR MK 2
In 1961, Ed Cole was promoted to group vice president of the car and truck group, ceding the management of Chevrolet to Bunkie Knudsen. Under Knudsen’s leadership, Chevrolet began work on the second-generation Corvair, which arrived for the 1965 model year.
The new Corvair, designed by Henry Haga’s Chevrolet 2 studio, under the supervision of Chevrolet chief stylist Ron Hill, was one of the prettiest cars to come out of GM in this era. The new Corvair retained some of the basic themes of the first-generation car, but was sleeker and more curvaceous, with new hardtop roof lines for both two- and four-door models.
Under the skin, the swing axles and semi-trailing arms were gone, replaced by an entirely new three-link rear suspension. Developed by Frank Winchell and Zora Arkus-Duntov, the new layout was based on the rear suspension of the 1963 Corvette Sting Ray. The wheel hubs were now carried on long trailing arms with small lateral links to adjust toe-in. The half-shafts, now pivoted at both ends, acted as upper control arms while two lateral links acted as lower arms. Unlike the Sting Ray, the Corvair used rear coil springs. The 1964 Corvair’s additional transverse leaf spring was deleted as it was no longer necessary.
With the new suspension, the second-generation Corvair’s ride and handling impressed even British critics, who tended to regard the road manners of American cars with dismay. The new Corvair could still be made to oversteer (as could most front-engine domestic sedans of the era), but it had none of its predecessor’s eccentricities. The second-generation Corvair handled and stopped as well as many contemporary sports cars. With the optional 140 hp (104 kW) normally aspirated engine and four-speed gearbox, it could also go from 0-60 mph (97 km/h) in less than 12 seconds and reach a top speed of perhaps 105 mph (169 km/h), while returning better than 20 mpg (11.8 L/100 km). Few cars of the mid-sixties could offer all of those qualities simultaneously, particularly for a price under $3,000.
If the second-generation Corvair had arrived a year earlier, it probably would have been a great hit, but by the time it appeared in the fall of 1964, it faced a formidable new rival: the Ford Mustang.
Even before the new Corvair debuted, it had largely relinquished its economy-car role to the Chevy II. You could still buy a stripped Corvair 500 coupe, but people generally bought Corvairs because they were sporty, not because they were sensible. Most buyers who could afford it generally chose the Monza with the hotter normally aspirated engine. The new Mustang, therefore, was aimed directly at the fattest part of the Corvair’s market.