Hacker News Reader

Comment by dhosek | Hacker News Reader

There was another idea I remember reading about in the 70s or 80s in (I think) Omni Magazine: Four wheel steering: All four wheels can be rotated. with the steering wheel. Turn the wheels to a full 90° and you can then move the car sideways into a parallel space. A lot more practical than this plan which pretty much destroys all the trunk space. Especially, with an EV where you can connect motors directly to each wheel, I can see this working out very nicely.

View on HN

The GM Hummer EV has that.[1] It can crab-walk.

That vehicle is a remarkable technical achievement. It weighs 9,000 pounds, has 1000 horsepower, costs around US$100,000, and goes from 0 to 60 MPH in 3 seconds. It handles well, using an active suspension system to hide some of the problems of moving so much mass around. The stopping distance is rather long, though. CNN calls it "a brilliant execution of a terrible idea."

[1] https://youtu.be/9pwoY26Q1AI

I had hoped an electric vehicle future would have meant a lot less road noise but if everything is clocking in curb weights in excess of 5,000 lbs I guess it won’t be as serene as I dreamed. Sad.

Weight is a problem for EVs, but it's not as bad for car-sized vehicles.

- Chevy Malibu (IC powered): 3,456 pounds.

- Chevy Bolt: 3,589 pounds.

- Tesla Model 3: 3,550 pounds.

But for trucks:

- Ford F-150, IC-powered: 5,684 pounds

- Ford F-150 Lightning: 6,590 pounds

- Hummer H1 (IC, discontinued): 8,114 pounds.

- Hummer EV: 9,000 pounds.

So, for a car, it's maybe 150 pounds extra for an electric, but for a truck, about 900 extra pounds.

Mitsubishi (and others) in the 80s,90s had 4 wheel steering:

  https://en.wikipedia.org/wiki/Steering#Four-wheel_steering

  https://www.autoweek.com/car-life/a1871191/four-wheel-steering-demystified/

I never drove one; I had a friend that said it really didn't do much for him that he noticed.

Doesn't one of the new mercedes have four wheel steering, but it refuses to be active during parking unless you pay a subscription?

I don't know if this is true or not, but I beg you, don't post comments like this. It's a question, and you could've spent the extra minute of research to _actually find out_ and post that.

This way we are left with negative value: We don't know any better, and instead are mentally burdened with speculation, that we have to actively work to not muddle up with what we know later on.

You can do better!

It would be a poor discussion that never had any questions in it.

True, but this was only a question in the grammatical sense. A discussion with only "questions" like these would be very poor indeed.

Not the same as a full 90-degree rotation though.

I have seen large buses with rear-steerable wheels as you describe/link. It makes a little more sense due to the sheer length of the buses.

I think you'll find that powering a wheel through a full 90 degrees about a vertical axis would be extremely challenging before the availability of electric motors.

Hell, just creating a linkage that allows it to turn that much and also maintains any kind of reasonable suspension geometry and the required clearances, etc at non-extreme angles would be tricky.

The advantages of four wheel steering at driving speeds are largely (completely?) negated by active traction control (supplying power and breaking to each wheel independently). You're not going to see a car turn its wheels 90 degrees because of both the large space needed (the cavity for the wheel to turn in) plus the complexity of linkages that can handle that amount of turning.

This idea might make more sense today than it did back in the day because you can put a small electric hub-motor on the fifth wheel. Downside is that cars are far heavier now than in the 30s so you'd need a beefier lift for the fifth wheel.

[edit]

Looks like Porsche and Renault offer 4-wheel steering in their high-end cars today, which suggest I am wrong about active traction control completely negating the advantages at high speeds.

The Japanese cars (Mitsubishi and Acura) that had 4-wheel steering only used a very narrow range of deflection to the wheels. It was intended to adjust cornering but not designed for major off-axis motion.

Toyota Mega Cruiser has 4WS for small turn radius https://global.toyota/en/detail/7882359

The 4-wheel steering on modern cars is typically to help with low speed turning circle size on longer wheelbase cars, not really for high-speed performance although they do put it to use at high speeds for some marginal benefits.

The interesting thing with the 4 wheel steering systems is that the behavior actually changed depending on speed.

At low speeds, the rears steered (a small amount) in the opposite direction, for a tighter turning radius.

At higher speeds the steered (again a small amount) in the SAME direction as the fronts, for more stability.

Toyota also offers four wheel steering on the LC500 and of course GM will/does have it as a standard feature on the electric Hummer ('crab walk').

Allowing wheels to rotate 90 degrees would also destroy trunk space (and space in the engine compartment).

Reply on news.ycombinator.com