Rear Axle Steering....not needed, nice to have, or must have?

[tbinmd]

Have it on my 991.2 GT3, so we spec'd it on the wife's CT4.

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[f1eng]

I guess really depending on where you live. If you live in a city where you need to do parallel parking or tight turns, yes you should get it. Otherwise you wont even feel the need.

I don't know about parking but on the other models it gives a big gain in turn-in for slow corners and a marked improvement in stability in fast ones. The latter probably won't be felt by most with the driver aids on, it will just be going quicker in fast corners when the stability control intervenes than the standard configuration.
It was one of the first options I chose on my long awaited CT build.
I realise I am not necessary a typical buyer though - I am an engineer.

 

[B61]

I don't know about parking but on the other models it gives a big gain in turn-in for slow corners and a marked improvement in stability in fast ones. The latter probably won't be felt by most with the driver aids on, it will just be going quicker in fast corners when the stability control intervenes than the standard configuration.
It was one of the first options I chose on my long awaited CT build.
I realise I am not necessary a typical buyer though - I am an engineer.

IMO, It's not for parking, but for driving stability as well.
For me, RAS and PDCC are the most important functionalities (and I'm not an engineer).

 

[feye]

I don't know about parking but on the other models it gives a big gain in turn-in for slow corners and a marked improvement in stability in fast ones. The latter probably won't be felt by most with the driver aids on, it will just be going quicker in fast corners when the stability control intervenes than the standard configuration.
It was one of the first options I chose on my long awaited CT build.
I realise I am not necessary a typical buyer though - I am an engineer.

This is not just tech for engineers. I need RAS every time I drive the car. U-turns on 2 lane roads just work in one go. Also parking is easier. For me this is by far the best and most useful option.

I also felt that the car was so super nimble, when I drove it the first time.

 

[sakkaro]

This is not just tech for engineers. I need RAS every time I drive the car. U-turns on 2 lane roads just work in one go. Also parking is easier. For me this is by far the best and most useful option.

I also felt that the car was so super nimble, when I drove it the first time.

That was beautiful.

 

[f1eng]

This is not just tech for engineers. I need RAS every time I drive the car. U-turns on 2 lane roads just work in one go. Also parking is easier. For me this is by far the best and most useful option.

I also felt that the car was so super nimble, when I drove it the first time.

I was simply replying to the individual who wrote that it was pointless unless you have a tight parking, or like you tight manoeuvres to perform.
I just wanted to point out that from an engineering perspective there are other significant benefits, though I do realise that they will never be approached by 99% of owners, so I was probably just confirming his point.
I chose rear wheel steer for the chassis dynamics improvement. Any ease of manoeuvrability is a bonus.

 

[feye]

I was simply replying to the individual who wrote that it was pointless unless you have a tight parking, or like you tight manoeuvres to perform.
I just wanted to point out that from an engineering perspective there are other significant benefits, though I do realise that they will never be approached by 99% of owners, so I was probably just confirming his point.
I chose rear wheel steer for the chassis dynamics improvement. Any ease of manoeuvrability is a bonus.

I am glad we have somebody on this form who really knows cars. I am eager to know what you think about RAS when you get yours.

How exactly do you think it improves chassis dynamics? How can I experience it?

 

[f1eng]

I am glad we have somebody on this form who really knows cars. I am eager to know what you think about RAS when you get yours.

How exactly do you think it improves chassis dynamics? How can I experience it?

It improves turn in for slow corners by shortening the effective wheelbase and improves stability in fast corners by lengthening the effective wheelbase.

The history is long/old! Early 911s had scary lift off oversteer, which skilled drivers could use to their advantage - see Vic Elford rallying one - but caused a lot of backwards through the hedge type accidents from unskilled owners and gave the car a reputation of being hard to drive on the limit (correctly).

The reason was known to be to the compliance of the rubber bushings on the semi trailing arm rear suspension causing a reduction of toe-in, or even toe-out in the rear suspension when transitioning from power on to power off.

As an aside a lot of non chassis people attributed this to the engine location and the error has stuck (the little rubber molecules don't know where the engine is when gripping the road...).

Porsche developed a multi link rear axle such that when the bushings flexed they got the toe change direction for stability in most load conditions and this was fitted to 911s from around 25 years ago (not sure exactly when maybe 993?).

Later reductions in costs of transducers and controllers allowed development of rear wheel steer at a practical cost and then it was possible to actually control the effect precisly rather than it be dependant of flex of rubber bushings - and that is the rear wheel steer available today.

I believe the standard suspension still has the multi link flexing bushings contolling toe-in which is excellent anyway so a driver of limited talent such as myself is probably making a pedantic choice when specifying something at such a high level - but I know how clever it is so I have specified it. rather than adaptive cruise control.

We tried it in Formula 1 in around 1993 just to see if it gave us another balance adjustment for trimming the car but since it doesn't increase grip and Michael Schumacher's preferred setup was extreme instability by car norms it was no gain.
It was banned in F1 over 25 years ago.

 

[Roppe]

Wait...Frank? Dernie? ?

 

[f1eng]

Wait...Frank? Dernie? ?

Rumbled

 

[Roppe]

The amount of questions one would want to ask you...but I will simply be thankful for you sharing some insights to the group here. Much honored - huge fan sir! ??

 

[f1eng]

The amount of questions one would want to ask you...but I will simply be thankful for you sharing some insights to the group here. Much honored - huge fan sir! ??

Thanks. i was lucky to have my job as my hobby for decades.
One thing which comes back to haunt me in questions about F1 is that the deliberate misinformation I spread to put competitors off back in the day is often taken as historic "fact" but we were just trying to keep our secrets.
For example every time I made an aero gain I told journalists it was rear suspension geometry whereas the fact is the geometry makes very little difference and we didn't touch it for 5 seasons...

 

[Zetta]

It improves turn in for slow corners by shortening the effective wheelbase and improves stability in fast corners by lengthening the effective wheelbase.

The history is long/old! Early 911s had scary lift off oversteer, which skilled drivers could use to their advantage - see Vic Elford rallying one - but caused a lot of backwards through the hedge type accidents from unskilled owners and gave the car a reputation of being hard to drive on the limit (correctly).

The reason was known to be to the compliance of the rubber bushings on the semi trailing arm rear suspension causing a reduction of toe-in, or even toe-out in the rear suspension when transitioning from power on to power off.

As an aside a lot of non chassis people attributed this to the engine location and the error has stuck (the little rubber molecules don't know where the engine is when gripping the road...).

Porsche developed a multi link rear axle such that when the bushings flexed they got the toe change direction for stability in most load conditions and this was fitted to 911s from around 25 years ago (not sure exactly when maybe 993?).

Later reductions in costs of transducers and controllers allowed development of rear wheel steer at a practical cost and then it was possible to actually control the effect precisly rather than it be dependant of flex of rubber bushings - and that is the rear wheel steer available today.

I believe the standard suspension still has the multi link flexing bushings contolling toe-in which is excellent anyway so a driver of limited talent such as myself is probably making a pedantic choice when specifying something at such a high level - but I know how clever it is so I have specified it. rather than adaptive cruise control.

We tried it in Formula 1 in around 1993 just to see if it gave us another balance adjustment for trimming the car but since it doesn't increase grip and Michael Schumacher's preferred setup was extreme instability by car norms it was no gain.
It was banned in F1 over 25 years ago.

Thank you, Frank ???

 

[Fish Fingers]

Rumbled

I do love this forum. Levels above all the other car forums I have been on.

Members generally seem a lot more technically minded......rather than just saying what cars they 'trashed at the lights since I had it remapped and a new air filter fitted'

Now don't go and spoil it all Frank when you get your car.... with a thread 'just smoked a loser in a GTI on the A9. Couldn't keep up over 120 mph'
?

 

[Derip88]

What is everyone’s thoughts? It’s an option I’d like to have but just wondering how needed it really is? I’ve driven a Taycan without it and was still very impressed with the feel and handling. Just thought I’d see what all the owners thought?

I ordered mine without, car hasn’t arrived but after long thought about it i come from a Lexus LX, so I’ll be used to a long car i guess haha

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