RE: Prior Convictions: Back seat steering

RE: Prior Convictions: Back seat steering

Friday 26th January

Prior Convictions: Back seat steering

Four-wheel steer seems like a win-win on paper, so why isn't it ubiquitous yet?



Four-wheel steering is back. Not that it ever, entirely, went away, but its history isn't unlike that of 3D movies: it has been dabbled with, trialled, sometimes even heralded, but never really accepted into the mainstream showbiz of new cars.

The theory behind active rear steering is straightforward enough. (M'colleague Lewis Kingston will, perhaps, be along at some point to outline it in one of his excellent 'PH Origins' columns.) When you're at low speeds, it makes the rear wheels turn against the fronts, to improve the turning circle and agility. At higher speeds (from 40mph and above, typically) it turns the rear wheels in the same direction as the fronts, to improve stability. A win-win, right?

Well, not always. Early systems were sometimes too sluggardly to turn, or made cornering too unpredictable, like a 3D movie shoving a freaking shark in your face one minute but being visually entirely bland the next. That was until five years ago, when ZF launched its AKC (Advanced Kinematics Control) system - the acronym for which kind of makes me think of fried chicken every time I read it. Mmmm...


There are two types of AKC system, one with actuators at each rear wheel (Porsche uses this on its 911s); one with a larger, central actuator (as Porsche uses on the Panamera), though with the same basic premise: they extend or shorten suspension arms to increase or decrease the rear wheels' toe angle.

Typically the range of adjustment can be up to five degrees or thereabouts, though most dynamics engineers will tell you that the vast majority of their work is done at considerably less than that. On full 'oppo', AKC keeps the new Rolls-Royce Phantom 8's turning circle down to just over 13m; but it's the little movements, on the way into a corner, of around one degree, possibly even less, where manufacturers seem to like the extra agility AKC can bring, or that they can fit a more direct steering rack and yet retain better higher speed stability.

But while AKC has been picked up and used by manufacturers including Audi, BMW, Porsche and Ferrari, to much greater success than any previous systems, it is still on the fringes. Since AKC's introduction, about 300 million cars have been produced worldwide, yet AKC (three piece meal with an extra piece, please) has only found its way onto around 125,000 of them.


Still, they are high profile cars: GT 911s, the (frankly quite terrifying) Ferrari F12 Tdf, and the 812 Superfast, for example.

With what success? A fair amount, mostly, although not entirely. There's that F12 Tdf, for example, where, branded as Virtual Short Wheelbase, it wanted to oversteer a lot, but seldom with any particular indication about how much it was going to. The Rolls Phantom has few dynamic vices for a car of its kind, but I wonder if some mid-corner, mid-speed steering stiction is down to its rear-steer's hesitance. And while the Porsche 911 GT3 is one of the most magnificent driver's cars on sale, and while AKC tends to be advised to just stay out of it if you're sliding, I do wonder if, in those transient cornering moments, it's making life slightly harder than no-rear-steer.

The advantages are there, then, but at the end of the day it's a by-wire system that will decide how much steering to apply how it wants, and when it wants, based on how it has been tuned during development. Perhaps little surprise, then, that Porsche does it best so far. And it'll also be interesting to see how Renaultsport - whose latest Megane gets active rear steering - will do when we say what it's like next week. If things keep progressing, perhaps active rear steer will start to become widespread on premium and sports cars, rather than a set of automotive red and blue lenses which we'll drop into the bin on our way out of the door.

Author
Discussion

Icehanger

Original Poster:

256 posts

157 months

Friday 26th January
quotequote all
Having worked/working on AKC programs, the next few years you will see most manufactures releasing some form of rear steer.
Its a fascinating product (Well to me anyway haha), and watching some very large vehicles doing high speed lane changes with it with very little body roll is mind blowing.

stolenink

25 posts

110 months

Friday 26th January
quotequote all
Seeing as 99.9% of driving does not involve hanging the rear-end out (unless a Mustang is involved of course...), 4WS popularity in small and medium options, the Sain-esco-idl-sons car parks will be the focus point, surely. We can't all drive Unobtainium-mobiles, so FWD+4WS applications should be much simpler to implement...?

Am I over-simplifying?

havoc

24,137 posts

170 months

Friday 26th January
quotequote all
Article said:
A win-win, right?

Well, not always. Early systems were sometimes too sluggardly to turn, or made cornering too unpredictable, like a 3D movie shoving a freaking shark in your face one minute but being visually entirely bland the next. That was until five years ago, when ZF launched...
rolleyes

Yet another copy-and-paste press release from PH. Well done guys - great checking of facts there!

I don't recall ANYONE moaning about delayed responses when the Honda Prelude was launched with 4ws in 1987. In fact, i seem to recall none other than LJK Setright praising it to the heavens and owning a Prelude pretty much from that point on.

Please see here (for a generally better article on the subject altogether, actually...not often you can say that of Autocar):-
https://www.autocar.co.uk/opinion/new-cars/why-ret...

Fetchez la vache

5,089 posts

149 months

Friday 26th January
quotequote all
Do you still need to be careful you don't park too close to a wall?

Black S2K

784 posts

184 months

Friday 26th January
quotequote all
havoc said:
Article said:
A win-win, right?

Well, not always. Early systems were sometimes too sluggardly to turn, or made cornering too unpredictable, like a 3D movie shoving a freaking shark in your face one minute but being visually entirely bland the next. That was until five years ago, when ZF launched...
rolleyes

Yet another copy-and-paste press release from PH. Well done guys - great checking of facts there!

I don't recall ANYONE moaning about delayed responses when the Honda Prelude was launched with 4ws in 1987. In fact, i seem to recall none other than LJK Setright praising it to the heavens and owning a Prelude pretty much from that point on.

Please see here (for a generally better article on the subject altogether, actually...not often you can say that of Autocar):-
https://www.autocar.co.uk/opinion/new-cars/why-ret...
Indeed - the 4WS Prelude is probably the best-handling car I've ever driven, whatever the weather. I still miss it.

Long John Kick Start did a far more erudite job of explaining why it is so very good.



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Max_Torque

12,836 posts

152 months

Friday 26th January
quotequote all
Like anything, it needs to be 'tuned' to suit. RWS has become financially viable (currently only on expensive car) because the technology basically leverages all the development work done on front wheel steering systems (electric PAS). In the old days,engineers tuned the rear suspension kinematics via some basic modelling, and then a lot of seat of the pants fiddling. Today, increasingly, it's the software that sets how a car handles, meaning the hardware stays the same (high volume = cheaper) and cars can change how they feel in different 'modes' (the current buzzword in automotive circles). Of course, the other advantage is that a simple dealer software update can "fix" problems that crop up after SOP, whereas, previously, that would have been an expensive recall......

fblm

15,265 posts

198 months

Friday 26th January
quotequote all
Most manufacturers CBA adding the weight, complexity and development time of RWS to eek out the last 5% on their utterly bland range of tedious euro boxes... shocker!

lee_erm

705 posts

128 months

Friday 26th January
quotequote all
Passive rear wheel steer is common. That's in the deliberate sense of passive.

Control blade rear suspension is one example with passive rear wheel steer.

romac

56 posts

81 months

Saturday 27th January
quotequote all
Black S2K said:
havoc said:
Article said:
A win-win, right?

Well, not always. Early systems were sometimes too sluggardly to turn, or made cornering too unpredictable, like a 3D movie shoving a freaking shark in your face one minute but being visually entirely bland the next. That was until five years ago, when ZF launched...
rolleyes

Yet another copy-and-paste press release from PH. Well done guys - great checking of facts there!

I don't recall ANYONE moaning about delayed responses when the Honda Prelude was launched with 4ws in 1987. In fact, i seem to recall none other than LJK Setright praising it to the heavens and owning a Prelude pretty much from that point on.

Please see here (for a generally better article on the subject altogether, actually...not often you can say that of Autocar):-
https://www.autocar.co.uk/opinion/new-cars/why-ret...
Indeed - the 4WS Prelude is probably the best-handling car I've ever driven, whatever the weather. I still miss it.

Long John Kick Start did a far more erudite job of explaining why it is so very good.
Ah yes! the late great LJKS and his Preludes (and Bristols)!

The Honda Prelude was different in that it was a purely mechanical system. It used (IIRC) a planetary gear system to vary the amount and direction of turn based on the steering lock applied. Little lock = same direction (you could crab the car out of a tight parallel park spot); Medium lock = nothing, Large lock = opposite. From the back seat on a roundabout, it sometimes felt like oversteer (which it was, but controlled!). Because it is mechanical, it is predictable, and hence exploitable.

rudecherub

1,996 posts

101 months

Saturday 27th January
quotequote all
Another thing Harry Ferguson was working on when he died, was four wheel steering, which would have gone along with his four wheel drive, and ABS system.

CoolHands

8,787 posts

130 months

Saturday 27th January
quotequote all
I don’t understand the “Back Seat Steering” quote. Why / what is it there for?

Nanook

33,166 posts

122 months

Saturday 27th January
quotequote all
romac said:
Black S2K said:
havoc said:
Article said:
A win-win, right?

Well, not always. Early systems were sometimes too sluggardly to turn, or made cornering too unpredictable, like a 3D movie shoving a freaking shark in your face one minute but being visually entirely bland the next. That was until five years ago, when ZF launched...
rolleyes

Yet another copy-and-paste press release from PH. Well done guys - great checking of facts there!

I don't recall ANYONE moaning about delayed responses when the Honda Prelude was launched with 4ws in 1987. In fact, i seem to recall none other than LJK Setright praising it to the heavens and owning a Prelude pretty much from that point on.

Please see here (for a generally better article on the subject altogether, actually...not often you can say that of Autocar):-
https://www.autocar.co.uk/opinion/new-cars/why-ret...
Indeed - the 4WS Prelude is probably the best-handling car I've ever driven, whatever the weather. I still miss it.

Long John Kick Start did a far more erudite job of explaining why it is so very good.
Ah yes! the late great LJKS and his Preludes (and Bristols)!

The Honda Prelude was different in that it was a purely mechanical system. It used (IIRC) a planetary gear system to vary the amount and direction of turn based on the steering lock applied. Little lock = same direction (you could crab the car out of a tight parallel park spot); Medium lock = nothing, Large lock = opposite. From the back seat on a roundabout, it sometimes felt like oversteer (which it was, but controlled!). Because it is mechanical, it is predictable, and hence exploitable.








Should never have sold mine. Well, not for the £650 I let it go for.

LowiePete

283 posts

73 months

Saturday 27th January
quotequote all
I have 4-wheel steering on my Laguna Coupe and I don't regret paying
out the extra for that option for a second! While the tighter turning circle
than a Clio is useful, that occupies so little of my driving time it barely
counts.

At 4am I can set the cruise control to 62mph and just steer until I reach
the lower speed limits - we don't have motorways in East Anglia - but
other than on roads with tight 90 degree bends the car just goes where
I point it with me rarely touching the brake pedal. On more "spirited"
runs I can steer with a confidence not found in other cars I've owned.

I'm disappointed that the new Alpine A110 doesn't have 4Control, but I
don't think it'll be long for it to appear as an option on future models.

Regards,
Steve

PepeelgordoTheFirst

1 posts

10 months

Sunday 28th January
quotequote all
Seconded. My 1997 Prelude has no weird steering characteristics, bar the almost uncanny pivot feeling when making a low speed tight turn. It's agile and grippy, though my wife is still better at reversing into a bay than me, I never quite compensate enough for the tiny turning circle. Asking with its soaring naturally aspirated engine and pleasingly simple cabin it's a keeper.

rockin

5,856 posts

180 months

Sunday 28th January
quotequote all
I had a surprise seeing one of these Mercedes taxis do a U-turn week - major rear wheel steering!

Check out this link - the rear steering is shown at 2 minutes....
https://www.youtube.com/watch?v=QNhQzeIGZ_8

Jazzy Jag

1,358 posts

26 months

Sunday 28th January
quotequote all
I had a succession of 4ws Preludes and a 2.2 Accord.

I believe that LJKS said it was more relevant to everyday driving that 4 wheel drive.

I actually preferred the older mechanical 4ws to the later electronic system.

The first time I brought a 4ws car home, I got to my usual turn in point, chucked it on full right lock and nearly parked on my neighbour's drive

hehe

Loved it!!



Oldwolf

398 posts

128 months

Sunday 28th January
quotequote all
I too had a 4ws Prelude in the late 80's, but only for 24 hours. Nearly drove into a lamppost on the way out of the forecourt as it turned so neatly but had an incredible trip across the Cumbrian moores in the rain, awesome car.

Also had a Volvo 850GLT with passive rear wheel steer for a few months and it's a toss up with that and R19 16v phase 2 for best front wheel drive car I've driven. That includes 205GTI, Golf GTi mk1 and 2 and Mi16 405.
Actually I've drive some fun cars, maybe there's a t-shirt there...
I might be old but I got to drive all the great cars.!

LordGrover

29,908 posts

147 months

Monday 29th January
quotequote all
I was a serial Prelude owner in the 90s, loved them. Had three in a row.
Ruined reversing for me though. Ever since I've struggled with 'ordinary' steering, especially reversing into tight spaces - the ludes were so much better. boxedin

Black S2K

784 posts

184 months

Monday 29th January
quotequote all
LordGrover said:
I was a serial Prelude owner in the 90s, loved them. Had three in a row.
Ruined reversing for me though. Ever since I've struggled with 'ordinary' steering, especially reversing into tight spaces - the ludes were so much better. boxedin
Ha! I used to keep kerbing the rear rims, as they were invariably parallel to the kerb when one reversed in.

And I completely lost the ability to reverse-park a 2WS for a while.

Much as my wife loves driving the 86, she still reckons the 'Lude was the better-handler. I maintain they're just completely different.