Rear Wheel Steering
 

For some reason, the other day a thought popped into my head about an old commercial for the Yukon Denali. The big selling point was that the rear wheels could turn, making it easier to turn the truck. I was just wondering why, other than a select few, more cars don't have this option, especially larger vehicles. Would this not save from having to need such a large PS pump?

I remember that system, the QuadraSteer. It's still often used in 3-axle trucks and buses back here, but it's not reported to decrease fuel economy so considerably. Might be more due to the extra weight, which is not so much considering the whole vehicle weight. But what made it not so popular was the price tag, as it was an optional feature.

In the late 80's there was a Honda Prelude with 4WS, and I believe Honda is bringing it back in one of the 2014 Acura models (saw a commercial for it a few days ago). I imagine complexity and therefore cost are the reasons we don't see it more.

I remeber the Honda Prelude with 4ws. That system was passive and used the lean of the body to turn the rear wheels. The handling was worse and the system was often defeated by owners seeking good performance.

I'd bet active systems need a *bigger* powersteering pump too as the rear would be all hydraulic unless it is done electric instead. Still higher loads.

This feature is only useful if a tighter turning radius is needed.

The VR-4 version of the Mitsubishi 3000GT had 4-wheel steering, and active aero, back in what, like 1993? It was way ahead of its time.

From Wikipedia

"The first generation model incorporated many of Mitsubishi's contemporary performance-enhancing technologies, such as full time four-wheel drive, four-wheel steering, active aerodynamics featuring automatically adjusting front and rear spoilers, sport/tour exhaust modes and electronically controlled suspension (ECS)."

My mother's kept eating ECU's though. :p

They are fairly common in japan. Since all most all of their cities over there have areas that are more tightly packed than NYC and LA.
In the US there isn't really a need for a turning ability that is that tight or the added complexity of a system that will most likely break down.
We keep our cars a lot longer than they do.

the C3 and sierra denali rear steer systems are/were virtually bullet proof. the real problem was it was a $2000 option and noone wanted to pay

Few people wanted to pay extra money for something that inreased weight and complexity while offering few real-world benefits. I don't see how turning two more wheels would reduce load on the PS pump, either.

On 4 axle trucks and busses (2 front, 2 rear), they seem to have resorted to two steering axles up front in Europe.

A local outfit sells cross-steering trailers for semi's.
Renders, X-Steering

Dunno how bad it is in the US, but here in Europe things can get so tight that when these big guys turn, a triple-axle trailer may actually see one or two of them reverse, and they scrub heavily in the process.

Not good for the tyres, and it certainly takes more fuel - but wether that's visible in the overall FC is doubtful, as they spend most of their time going more or less straight.

AWS is only seen on mobile cranes these days.
Some cars have rear axles that have a bit of flex in them, and they steer along passively.