Four-wheel steering demystified

1988 Honda Prelude

A flashback to 4WS systems

For a brief period in the late ’80s, four-wheel steering seemed like the next big thing. It had almost faded away by the late ’90s, but over the past decade, 4WS has reappeared on models from Nissan, Renault, BMW, Acura, even Porsche.

With 4WS apparently making a comeback, let’s clear up some misconceptions about its early days.

4WS was just so ’80s

Although the first production automotive systems for it didn’t appear until the ’80s, steering a vehicle at both ends for greater maneuverability is old. Tiller trucks with rear-steering controls actually predate the automobile itself, and engineers toyed with four-wheel steering for passenger cars as early as the 1930s.

The Porsche 928’s Weissach axle was an important precursor to 4WS. Most production cars experience some rear toe changes during cornering due to rubber suspension bushings compressing or deflecting; this is called compliance steer and can cause oversteer with abrupt changes in throttle position.

To combat this tendency, Porsche arranged the 928’s rear suspension bushings so the rear wheels toed in (rather than out) if the throttle was closed. This passive rear steering later became common—Citroën, Isuzu, Mazda and others employed it.

Photo: 4WS in the 1988 Honda Prelude

The First 4WS Cars

The Prelude was the first active 4WS car sold in the U.S., but Nissan’s Japanese-market R31 Skyline came earlier, launched in late 1985.

The rear-wheel-drive Skyline offered Nissan’s first-generation High Capacity Actively Controlled Suspension system. Like Porsche’s Weissach axle, HICAS’ original intent was mitigating compliance steer on powerful RWD cars.

Nissan recognized passive rear steering’s limitation—its dependency on cornering loads. They don’t necessarily build quickly enough to provide useful toe adjustment. Nissan’s solution was to use computer-controlled hydraulic pistons to selectively compress the Skyline’s rear subframe bushings, effectively steering the rear semi-trailing arms plus/minus 0.5 degree to improve stability in high-speed maneuvers.

Photo: 1989 Nissan Skyline GTR

Early Systems Worked The Same

Throughout the ’80s, Japanese automakers raced to blanket the 4WS field with patents, resulting in several different production systems:

Honda’s first 4WS system, launched in April 1987 on the Prelude, was all mechanical, using a shaft to connect the front-steering rack to a slider operating the rear tie rods. A planetary gearbox determined rear-steering degree based on steering-wheel angle. At small angles, the rear wheels would steer up to 1.5 degrees in phase with the fronts, but at larger angles (more than 246 degrees of steering rotation), the rear wheels would steer up to 5.3 degrees opposite the fronts, trimming the turning radius about 10 percent.

Mazda’s 4WS, introduced on the Capella/626/MX-6 (see page 15), only weeks after the Prelude, was more complex and heavier, using a rear-steering shaft to transmit steering angle to a hydraulic actuator and calculating rear toe angles electronically based on steering angle and road speed. Below 22 mph, the rear wheels steered out of phase for a smaller turning radius, switching (via an electric motor) to in-phase steering at higher speeds.

Mitsubishi’s system debuted on the Galant VR-4 in late 1987. It worked electro-hydraulically on the rear suspension links, with no mechanical connection between the front and rear wheels. The rear wheels steered up to 1.5 degrees in phase with the fronts at speeds over 31 mph.

Nissan’s HICAS-II and Super HICAS replaced HICAS in 1988–89 and also used a computer-controlled hydraulic actuator to move the rear lower lateral links. This allowed toe changes plus/minus 1 degree depending on speed and steering angle. At higher speeds, the rear wheels would initially steer out of phase with the fronts to improve turn-in response and then switch to in-phase steering for greater stability. There was no rear steering at low speeds. Nissan converted Super HICAS from hydraulic to electric actuation in mid-1993.

Toyota’s Dual-Mode 4WS, first introduced on the Japanese-market Celica in late 1989, was conceptually similar to Mazda’s, combining a steering shaft, rear hydraulics and computer controls, and providing either in-phase or out-of-phase rear steering depending on speed, steering-wheel angle and rate of steering-wheel movement. The Toyota system could be locked in 2WS and offered normal and sport 4WS modes with different rear-steering rates.

Honda’s second-generation 4WS, launched on the next-gen Prelude in September 1991, was new, using computer controls and an electric motor rather than a steering shaft and planetary gearbox. This system, intended to address the mechanical layout’s limitation, was similar to more recent 4WS systems, although newer systems have greater integration with other chassis electronics.

Photo: Madza’s 4WS system

4WS wasn’t popular

It’s true 4WS got a lukewarm reception in the U.S. and Europe. The handling effects were subtle, and some reviewers couldn’t tell the difference even in back-to-back tests. The systems were usually expensive, turning off buyers.

In Japan, however, four-wheel steering remained popular throughout the ’90s, even appearing on family cars like the Japanese-market Accord and Camry. 4WS was flashy and high-tech, appealing to some buyers, and the shorter turning radius the Honda, Mazda and Toyota systems provided helped in narrow Japanese streets (although parallel parking required some acclimatization).

The option eventually succumbed to the Japanese recession, but 4WS remained available through 2001 on the Japanese-market Prelude and the 2002 Skyline. 

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