From the December 1987 issue of Car and Driver.
Few technical innovations have captured the imagination of the car industry as quickly as four-wheel steering. Although the concept of steering the wheels at both ends of a vehicle is nothing new, its development for production cars gained no real momentum until 1983, when Mazda unveiled its MX-02 show car. Since then, such dream machines as the Corvette Indy, the Pontiac Pursuit, and the Peugeot Proxima—indeed, most show cars that have been more than mere styling exercises—have also employed four-wheel steering.
What's more, in comparison with such other modern developments as turbocharging, four-wheel drive, and anti-lock brakes, four-wheel steering has advanced virtually overnight from show-car curiosity to mass-production reality. Honda won the race to market last summer when it introduced the 1988 Prelude Si, on which 4ws is optional. Mazda followed suit almost immediately with optional 4ws for the new 626 Turbo. More all-wheel-steer models are on the way from Nissan and Mitsubishi, and several other manufacturers, in the United States and Europe as well as in Japan, are working on their own 4ws systems.
The manufacturers' rush to 4ws is surprising in view of the fact that, until the Prelude was introduced, their customers had demonstrated little interest in the prospect of steering all four wheels. And why should they have? Unlike turbocharging, 4wd, and ABS, the benefits of which are easy to understand, four-wheel steering is not obviously a technological breakthrough. Mention 4ws to most people and you'll get blank stares, if not laughter, followed by sarcastic questions about whether it will make their cars go down the road sideways.
In fact, as the manufacturers know well, four-wheel steering has several important potential benefits. Every 4ws system that we've seen so far turns a car's front and rear wheels in opposite directions under some conditions and in the same direction at other times. Opposite-direction steering makes a car turn more sharply, improving its low-speed maneuverability and tightening its turning circle. Same-direction steering, in theory, improves handling at higher speeds. To understand why, consider that the front tires of a conventionally steered car develop cornering forces immediately when they are steered, but the rears develop cornering forces only when the body of the car has begun to turn. On a 4ws car in contrast, all four tires develop their cornering forces at the same time. The result is more responsive handling in transient maneuvers, such as entering and exiting corners. Furthermore, since the rear tires of a 4ws car do not depend solely on the car's drift angle to produce their cornering forces, the car's tail doesn't swing out as far in corners or wag as much in quick lane changes. These advantages are particularly pronounced on slippery surfaces, say the advocates of 4ws.
Both Honda and Mazda claim these benefits for their 4ws systems, though they have come up with distinctly different means of adding rear steering to their cars. The Honda system, the simpler of the two, is entirely mechanical. A shaft from the front rack-and-pinion linkage drives a rear steering gearbox, which steers the rear wheels in the same direction as the fronts when the steering wheel is turned less than 246 degrees from straight ahead, and in the opposite direction beyond that point. Since turning the steering wheel more than 246 degrees from center is likely only at very low speeds, the countersteer mode typically comes into play only in parking-lot maneuvers. In neither mode do the rear wheels steer very much. Their maximum same-direction steering angle is 1.5 degrees, and their maximum counter-steering angle is 5.3 degrees.
The Mazda system operates along similar principles but is much more complex in design, employing mechanical, hydraulic, and electronic elements to produce an elaborate tailoring of front and rear steering angles. With the help of speed sensors and a control unit, the system adjusts its operation not to steering-wheel angle but to car speed. At speeds below 22 mph, the rear wheels steer opposite to the fronts, up to a maximum angle of five degrees. Above 22 mph, they steer in the same direction as the front wheels. The relative steering angles and the transition from countersteering to same-direction steering are regulated by the system's control unit. The resulting steering characteristics are similar to the Honda system's, with one major exception: while the Prelude's steering wheel must be wound considerably before countersteering begins, the 626 countersteers at low speeds whenever its steering wheel is moved from center, no matter how small the angle. Mazda's system thus promises superior low-speed maneuverability.
Of course, the design principles of the two systems tell us little about how they work on the road. The only unquestionable benefit of 4ws is improved parking lot maneuverability. The Prelude's system reduces its turning circle from 34.8 to 31.4 feet; the corresponding figures for the 626 are 38.0 and 36.1 feet.
To examine the effects of 4ws on higher-speed maneuvers, we ordered two-wheel-steer and four-wheel-steer examples of both the Honda Prelude Si and the Mazda 626 Turbo and mapped out a series of handling tests. In addition to track testing in the controlled confines of Chrysler's proving grounds in Chelsea, Michigan, we would drive the four cars on the road and note any subjective handling differences. Our purpose was not a direct comparison of the sporty Prelude and the four-door 626. Rather, we would seek to discover the effects of four-wheel steering by pitting Honda versus Honda and Mazda versus Mazda. In the process, the relative merits of the two makers' approaches to 4ws would also become apparent.
It was important for our testing that the 2ws and 4ws versions of each model be as similar as possible. The only difference between the two Preludes we ordered was that one had the 4ws package, which includes alloy wheels, power door locks, and bronze-tinted glass. Both cars were equipped with the same springs, shocks, anti-roll bars, and tires, though Honda specifies 28 psi of tire pressure all around for the 4ws Prelude and two pounds less for the rear tires of the 2ws model.
Unfortunately for our purposes, Mazda doesn't offer 2ws and 4ws 626s that are as equal as the two Preludes we ordered. Mazda's 4ws option is available only on the turbocharged, automatic-transmission, four-door 626. The same basic car is available with 2ws, but all 2ws 626 Turbos are equipped with Mazda's Auto Adjusting Suspension. The AAS system employs three-position shocks, and none of the damping settings corresponds to the fixed calibration used on the 4ws car. Moreover, the springs and anti-roll bars that come with AAS are softer than the hardware fitted to the 4ws car. To compensate for these softer components as much as we could, we set the AAS system of our 2ws Mazda in its Sport Auto setting, which yields substantially stiffer damping than the 4ws car's shocks. At least the wheels and tires of the two cars we ordered were identical.
Our testing concentrated on handling in transient maneuvers, since 4ws should have no effect on straight-line driving or steady-state cornering. The most useful transient-handling tests are the slalom and the double lane change. The slalom test requires driving a serpentine path as quickly as possible through a line of evenly spaced cones. Other things being equal, cars with a tight grip on the road and consistent steering response perform best in this test. Our double-lane-change test requires switching rapidly from one twelvefoot-wide lane to another, then back again, at points marked by cones. Good performance in this test requires controllability and quick and accurate steering response during the two sharp cuts. For both tests, we varied the dimensions of the courses to study the effects of 4ws on different speed ranges. And, because 4ws is said to be especially helpful on slippery surfaces, we conducted most of our tests both on dry pavement and in the wet.
Dry Performance
Although 4ws theoretically has no effect on steady-state handling, we began our testing on Chrysler's 300-foot skidpad to see how the cars would compare in roadholding. The Hondas were close, with the 4ws car having the edge, 0.78 to 0.77 g. The Mazdas were spread a bit further, with the 4ws car at 0.76 g and the 2ws model at 0.74 g. Given the 4ws Mazda's more favorable weight distribution (contributed by the rear-steering hardware) and its generally firmer suspension, its skidpad advantage was not surprising.
Our first transient test was a very slow slalom, formed by eleven cones spaced only 25 feet apart. Our intention was to force the cars' speeds low enough to bring out the effects of countersteering in the 4ws models. With speeds in the 12-to-13-mph range, we certainly succeeded; however, we had to wind the steering wheels so vigorously that none of the four cars' power-steering systems could keep up. As a result, this slalom turned out to be little more than a test of our upper-body strength. The minor speed difference between the two Hondas (see chart) indicates nothing more than the relative abilities of their power-steering pumps.
Honda Prelude Si, 2WS/4WS
Roadholding, 300-ft-dia skidpad: 0.77/0.78 g
25-ft cone spacing: 12.5/12.0 mph
50-ft cone spacing: 31.5/31.5 mph
100-ft cone spacing: 62.0/62.0 mph
Lane change, low speed: 30.5/34.0 mph
Lane change, high speed: 57.5/61.0 mph
When we increased the cone spacing to 50 feet to study the effects of same-direction 4ws, the power-steering problems disappeared and our testing began to indicate the handling abilities of the cars. The two Hondas turned in the same speed, 31.5 mph. Both turned sharply and exhibited good control, though the 4ws car required a bit more steering effort.
The two Mazdas were much less alike. The 2ws car turned in nicely and kept its tail well controlled, while negotiating the course at 32.0 mph. The 4ws car required a bit less steering motion than its mate, but it suffered from a slight two-step effect in its steering response when switching from one direction to another. Its speed through the cones was only 30.0 mph.
With the cones spaced 100 feet apart, the two Hondas no longer felt similar. The 4ws Prelude turned in beautifully and seemed to have tremendous grip at both ends of the car. The 2ws model exhibited much greater tail swinging and required considerably more steering correction. The two bottom lines, however, were identical: both Preludes negotiated the course at 62.0 mph.
The two Mazdas reversed their positions in the 100-foot slalom. Although the 4ws car still had a twitch in its steering, it ran the course at 58.0 mph, 1 mph faster than the 2ws car. The front-steerer felt better at the wheel, but its softer suspension limited its speed.
Summing up our dry-slalom results, the 4ws Honda was more controllable than its 2ws counterpart, but no faster. The two Mazdas were also roughly equal in speed, the 2ws car's more linear steering compensating for its softer suspension.
Mazda 626 Turbo, 2WS/4WS
Roadholding, 300-ft-dia skidpad: 0.74/0.76 g
25-ft cone spacing: 13.0/13.0 mph
50-ft cone spacing: 32.0/30.0 mph
100-ft cone spacing: 57.0/58.0 mph
Lane change, low speed: 32.5/32.5 mph
Lane change, high speed: 61.5/61.5 mph
In the double-lane-change test, we again started at the low end of the speed spectrum. Our first course consisted of a 25-foot segment for the first lane change, followed by a 50-foot straight run, and then another 25-foot slot for the return to the original lane.
The 4ws Prelude was substantially quicker through this course than the 2ws model, beating it 34.0 to 30.5 mph. The two did not feel very different at the limit, however. The 4ws car required more steering effort and felt somewhat more stable, but both Preludes displayed consistent understeer and kept their tails under tight control.
In contrast, the two Mazdas turned in the same speed, 32.5 mph, but they felt markedly different from each other. The 2ws car understeered steadily and was easy to drive. The 4ws car also understeered, but its steering was much less smooth. Its power-steering pump again could not keep up with the sudden steering motions required by the course, causing a major spike in the steering effort required during the lane changes.
For our higher-speed lane change, we doubled the lengths of all three segments of the course, increasing the length of each crossover section to 50 feet and that of the straight stretch to 100 feet. The 4ws Honda maintained its solid advantage in this test with a 61.0-mph docking, compared with 57.5 mph for the 2ws version. Not only was the 4ws Honda faster, but it negotiated the course with much less fish-tailing as well. The 2ws car's wagging tail was not particularly difficult to control, but it did make us work harder at the steering wheel.
The two Mazdas again turned in the same speed, this time 61.5 mph. However, as was the case with the Hondas, the 4ws model was the easier car to drive. It fishtailed less than the 2ws 626 and was generally more benign, despite a bit of power-steering lag.
Our lane-change results speak better for 4ws than our slalom findings, at least in the case of the Honda system. The 4ws Prelude was both faster and more controllable than the 2ws model. Indeed, the speed difference was so large that driving the 4ws Prelude through the double lane change at the 2ws car's limits was virtually effortless. In contrast, the Mazda 4ws system was a mixed blessing. Although the 4ws 626 felt better than the 2ws car in the high-speed switches, its lagging power-steering system made it harder to steer. More important, 4ws did not improve the Mazda's speed through the courses.
Wet Performance
We thought it likely that the claimed stability advantage of 4ws would be more apparent in our wet testing, since any such advantage should be exaggerated on slippery pavement. Chrysler's low-friction Jennite surface, thoroughly wetted by a sprinkler system, was perfect for our purposes, and we repeated most of our dry tests on it. We didn't repeat the 25-foot slalom, because that exercise had tested the cars' power-steering systems more than their handling. And since Chrysler's Jennite surface isn't large enough for a 300-foot skidpad, we ran our wet-roadholding test on the circle we normally use, with the help of a hard rain.
Our wet-skidpad results were surprising. Four-wheel steering should make no difference on the skidpad, since only steady-state cornering is involved, but both 4ws cars in fact lost ground to their 2ws siblings in moving from the dry to the wet test. The 4ws Honda went from a 0.01-g advantage in the dry to a 0.03-g disadvantage in the wet. The 4ws Mazda lost its 0.02-g advantage, tying the 2ws model. We have no explanation for this shift, but it immediately called into question the supposed slippery-surface benefits of 4ws.
Honda Prelude Si, 2WS/4WS
Roadholding, 300-ft-dia skidpad: 0.76/0.73 g
50-ft cone spacing: 24.0/24.0 mph
100-ft cone spacing: 44.5/44.5 mph
Lane change, low speed: 28.0/27.0 mph
Lane change, high speed: 49.5/47.5 mph
When we moved to the 50-foot-interval slalom course on the wet Jennite, we again found no advantage for 4ws. The two Hondas felt pretty much alike through the course and turned in exactly the same speed, 24.0 mph. The 2ws Mazda was actually quicker than the 4ws model, 24.5 to 23.0 mph. And although both Mazdas understeered, the 4ws 626 understeered more. We also felt its tail wiggling a bit through the course, though without any discernible effect on its handling.
Increasing the cone spacing to 100 feet brought out greater differences between the cars. The 4ws Honda felt more secure than its sibling, keeping its tail well in line without displaying excessive understeer. The 2ws car was also admirably stable, but its tail was more likely to step out as the car's traction limit was reached. Despite its advantages, however, the 4ws Prelude could not improve on the 2ws car's 44.5-mph speed.
In contrast, the 2ws Mazda was again dearly superior to the 4ws version, by 42.5 to 40.5 mph. It also felt much better. The tail of the 4ws car was very loose and threatening, and we found it difficult to scrub off excess speed without getting sideways. The 2ws 626 didn't feel comfortable with its tail out, either, but it was much less likely to adopt that attitude.
Mazda 626, 2WS/4WS
Roadholding, 300-ft-dia skidpad: 0.77/0.77 g
50-ft cone spacing: 24.5/23.0 mph
100-ft cone spacing: 42.5/40.5 mph
Lane change, low speed: 27.0/25.5 mph
Lane change, high speed: 46.0/46.0 mph
The 4ws cars didn't improve their standing on the wet lane-change courses. The two Hondas felt very much alike on the low-speed course, exhibiting steady understeer. But the 2ws model ran 28.0 mph, 1.0 mph faster than its 4ws sibling.
Similarly, the 2ws Mazda beat the 4ws car, 27.0 to 25.5 mph. The 2ws car negotiated the course with slightly less understeer, though the 4ws 626 felt equally stable in other respects.
In the high-speed wet lane change, the two Hondas felt roughly equal, though the 2ws car was a little more prone to swinging its tail out. Again, however, it was also faster than the 4ws Prelude, running the course at 49.5 mph, versus 47.5.
The 4ws Mazda improved its position in this test, but only enough to tie its 2ws sibling, at 46.0 mph. And the 2ws 626 felt much better, exhibiting only moderate tail-happiness. The 4ws car wagged its tail constantly, no matter how carefully it was driven.
Despite the theoretical advantages of 4ws on slippery pavement, both 4ws cars in this test were slower than their 2ws counterparts in three of the five wet trials and no faster in the others. And although the two Hondas were about equal in controllability, the 4ws Mazda was clearly less stable than its sibling in most of the tests.
Conclusion
When we conceived this test, we expected that any handling benefits of 4ws would be most apparent in the wet. Instead, we found just the opposite. The 4ws Prelude performed better in the dry and worse in the wet than the 2ws Prelude—not a worthwhile trade-off. And although our comparison of the two Mazdas is somewhat tainted by their different suspension calibrations, the 4ws 626 was no better at all than the 2ws car in the dry and was decidedly inferior in the wet. We can only conclude that, as currently developed, neither Honda's nor Mazda's system represents much of an advance in steering technology.
These new steering systems don't come free, either. Honda's 4ws package adds 28 pounds to the Prelude's curb weight and $1300 to its price. Mazda's 4ws system adds almost 100 pounds to the 626 and, adjusting for the suspension differences of the two cars tested, costs about $1385. Both systems do improve low-speed maneuverability, which is valuable, but we doubt that many buyers would spend so much money just to make parking easier.
Does this mean that 4ws is not, after all, a significant advance in automotive engineering? The only reasonable answer is that it's too early to say. Remember that the Honda and Mazda systems are the first production applications of what is, in effect, a brand-new technology. And just as Honda's and Mazda's approaches are vastly different, other manufacturers are certain to develop their own unique approaches. Of the two systems introduced thus far, the Honda design is the more successful. It costs and weighs less, is much less complex, and does deliver a few clear benefits. But both it and the Mazda system require further refinement if they are to realize their potential. We remain hopeful that, sooner or later, 4ws will live up to its promise. Honda and Mazda deserve credit as pioneers, but, for now at least, 4ws is no great leap forward.
4ws on the Road
Driving cars on a test track is the best way to define their absolute performance, but driving them in the real world is no less important to a thorough evaluation. When one is struggling to avoid crunching pylons flashing backward along both flanks, it's easy to overlook subtleties that can be critical in everyday driving. To make sure we overlooked nothing in our examination of four-wheel steering, most of our staff drove all four cars in this test on public roads near our Ann Arbor offices. Each staffer drove the cars back to back, both normal driving and hard flogging were encouraged, and some staffers drove in both rain and shine. Our purpose, as in our track testing, was to see what differences we could detect between the 4ws and 2ws cars.
We went to unusual lengths to ensure that each test driver could evaluate the handling of the cars objectively. First, we taped over the identifying labels on the 4ws cars and the corresponding locations on the other two. Second, because Honda's 4ws package includes distinctive alloy wheels, we exchanged two wheels and tires from the 4ws Prelude with a set from the 2ws car. Finally, we asked our test drivers to avoid tight maneuvers at low speeds, because the 4ws cars' tighter turning abilities would quickly identify them. Not until the drivers had finished their four-car stints and reported their findings were they permitted to play carhop in our parking lot.
Most of the testers had to concentrate hard to detect any difference at all between the two Hondas. In fact, one staffer, who mistakenly thought he knew which Prelude had 4ws (the cars were painted different colors), completed his drives of both Hondas without realizing his error.
Although some drivers observed that the 2ws Prelude displayed more lift-throttle oversteer than the 4ws car, most of us found steering effort to be the most apparent difference between the two. The 2ws Prelude has a delightfully fluid steering feel, with a very linear buildup of force as the wheel is rotated from center. The 4ws car steers almost as nicely but requires a bit more effort. It feels stickier, as if it has more mechanism to move—which, of course, it does. Given the lack of other differences between the two cars, our drivers unanimously preferred the 2ws Prelude.
Telling the Mazdas apart was much easier. Every staffer observed that the steering of the 4ws car was much lighter than the 2ws car's. In the 4ws 626, the steering wheel moves off center with almost no resistance, and the effort barely increases as the wheel is turned further. In contrast, the 2ws car has a positive on-center notch, and its steering effort builds strongly as it's turned into a corner. The difference in steering effort between the two Mazdas is five or ten times as great as that of the two Hondas.
The two Mazdas also felt very different to our testers through the seats of their pants. The 4ws car changes direction with a willingness that makes the 2ws car seem almost sluggish; one definitely feels something special in the way it turns into a corner, all four tires at once. Nonetheless, most of the staffers regarded this behavior as twitchiness. Coupled with its light steering effort, the 4ws Mazda's eagerness to turn made it seem a little too nervous in a straight line, especially at high speeds. No one found the 4ws car unstable, but it didn't track with the sureness of its 2ws stablemate. Even in corners, the combination of light steering and sudden turning provided too little road feel for most of our testers. Admittedly, that impression would probably fade with time.
In our parking lot, our testers had nothing but praise for the tighter turning circles of both of the 4ws cars. Although the improvements over the 2ws versions look modest on paper, they contribute to markedly better maneuverability. In a 4ws car, one can whip into parking spaces and around tight comers with remarkable ease.
But is that enough? Improved low-speed maneuverability may be valuable on the tightly packed roads of Japan, but it's hardly essential in America. In the absence of other significant handling improvements, all the test drivers felt let down by both Honda's and Mazda's 4ws systems.
As one tester put it, "Four-wheel steering turns that extra pair of wheels a lot more than it turns my head." —Csaba Csere
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The Link LonkJanuary 26, 2021 at 04:15AM
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Tested: How Beneficial Is Four-Wheel-Steering in 1988? - Car and Driver
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