passive four wheel steering?????

[itsa93sl1]

i just got a 93 impreza ls ,folded up in the owners manual was the window
sticker,one of the standard features are "four wheel fully independent
suspension with passive four wheel steering" can anybody tell me what
passive four wheel steering is? thanks for the help corey

 

[bgd]

That is interesting.
I can't even comprehend any movement in rear wheels being beneficial. Is
there a sideways crab movement or a circle type movement?
How does it handle on slanted roads in the snow?
I spotted this for a 2000 rs 2.5- no other details. The review claims the
car handles like its on rails in wet weather.
New subarus have scared me into looking at a 500 dollar dodge ramcharger 8
feet off the gound with a 318 sipping it down similar mileage to a new
soob.where will that precious impreza be 25 years from now... I can imagine
crank shutters, broken rods, gaskets and then junked in a decade.
*Yawn*

87 GL anybody? Being strangely chauvinistic I called my car a heterosexuals
subaru...

 

[strchild]

Putting the term into Google gleaned the following Wikipedia article:

http://en.wikipedia.org/wiki/Steering

About halfway down the page you will find a tiny paragraph stating:

"Some vehicles now offer a form of "passive" four-wheel steering, where the
bushings by which the rear suspension attaches to the automobile are
designed to compress in a precise direction under the forces of steering,
thus slightly altering the rear suspension geometry in such a manner as to
enhance stability."

Another article, seemingly more in-depth:

http://www.ozebiz.com.au/racetech/theory/align.html

And again, about halfway through:

"It should be noted that in recent years, designers have been using bushing
compliance in street cars to their advantage. To maximize transient
response, it is desirable to use a little toe-in at the rear to hasten the
generation of slip angles and thus cornering forces in the rear tires. By
allowing a bit of compliance in the front lateral links of an A-arm type
suspension, the rear axle will toe-in when the car enters a hard corner; on
a straightaway where no cornering loads are present, the bushings remain
undistorted and allow the toe to be set to an angle that enhances tire wear
and stability characteristics. Such a design is a type of passive four-wheel
steering system."

The two articles correlate well enough for me. (-;

~Brian

 

[Clifford Heath]

I can't even comprehend any movement in rear wheels being beneficial

Alfa Romeos have used rear-axle steering for many decades.
My 1969 GTV has a live axle, located fore-aft by trailing arms
and laterally by a trunnion arm having a compliant bushing
directly above the diff, is such a case. As the car rolls past
about 6 degrees, the inner end of the axle is drawn forwards
by the trailing arm, inducing rear steering which tends to
prevent early loss of grip.

The action of the legendary Alfetta (115 series) De-Dion rear
end is even better, because the lateral location is done by a
Watts linkage, carefully calculated to keep the axle almost
dead straight until you reach about 8 degrees of roll, then to
progressively (by more rapidly than in my GTV) to bring in the
same kind of rear steering. As far as I know, this general
form of rear end had been around for decades even then.

Both cars are amazingly forgiving yet generated unequalled levels
of grip for their times - just a joy to drive. (Neither has the
rear toe-in mentioned by Brian though.)