Just read a good part of this thread and just wanted to say Thanks for all the great info--it's a very impressive collection of cool info.

I have wondered about RAS on a GTS and all of the thread's collective comments are very helpful. Thanks all

 

 

Exactly. And I'm not sure what you're envisioning. That's why I asked if you had any insight into RAS's functional requirements.

I'm envisioning one set of requirements and I think you envision/speculate-on/have knowledge of a more complex set of requirements. I'm trying to figure out more-precisely what you are writing about and the provenance of what you write. If the provenance of what I write isn't clear then let me know. You will note that I write things like 'suspect', 'I think', etc.

Based upon what I've read about RAS, I thought I understood what it does and when it does it. Your posts cast doubt on my understanding.

Bottom line: I'm trying to get you to tell me why I'm wrong.

Great! So, you are closer to the 'inside'.

Lot's of folks post information. Sometimes it's right. Sometimes its wrong. Sometimes its hard to understand.

I'm not trying to argue. I'm trying to get a better understanding of what RAS really does and perhaps some insight into 'the guts' of the system.

Of course they are.

I went back and re-read all of our posts. I agree completely with the majority of what you wrote. There were two sentences you wrote that piqued my curiosity. These are the (minority) sentences about which I'm not sure. As I wrote previously: what I think you are writing about is absolutely possible. I'm trying to figure out if what I think you are writing about is the same thing you think you're writing about and if it has actually been implemented or is notional.

I re-post these two sentences below and highlight some specific portions:

The above two bold italic phrases are what interested me. They imply a much-more sophisticated control system than I expected given how Porsche markets RAS. (On the other hand, I can also conjecture reasons why Porsche Marketing might not be allowed to market the more sophisticated RAS operating modes.)

Do you mean to imply that RAS will adjust toe for a small fraction of a second when one tire hits a bump and the corning forces on the other three wheels change? And/or, that RAS will adjust toe one way on braking and corner entry, adjust it again at mid-corner and again at exit under acceleration (by incorporating inputs in addition to speed and steering rate?) This is what I mean when I use the terms 'dynamic' and 'high-speed' as applied to RAS' toe changes.

It would be really cool if RAS did all that. More rear toe-in (up to a point) during heavy braking from high-speed would improve stability. I haven't even thought about how or why specific dynamic toe changes through the rest of the corner would be beneficial. Do you know?

It would be much simpler and safer (due to various failure modes) to simply let RAS command a toe change for a given speed and steering wheel rate and then let the 'passive toe control system' (e.g. bushings, control arms, etc.) deal with all the 'other stuff' (e.g. bumps, friction changes, etc.) This is also 'dynamic' but much-less so that what I think you propose and doesn't require RAS to be a 'fast' control system.

I think that all the benefits you describe would derive from the latter. The former, while possible, seems unnecessarily complex.

Humans are quite slow as far as inputs are concerned in Control System Land. First derivatives of human input are easily calculated by 'slow' control systems that sample and respond to human input at low double-digit cycle rates (e.g. 25-ish hz.) It's the 'rest of the world' that requires higher sample and control rates (i.e. a 'fast' control system that must run at hundreds or thousands of cycles per second.)

I believe that the literature says this. But, that phrase is devoid of information. A passive toe control system (i.e. a well-designed rear suspension without active, commanded, actuators) can be said to 'adapt to driving situations' (by the writers of Marketing Materials.)
Perhaps there's more detailed information if the body of ZF's literature? Is it findable through the posted link?

Of course. This brings of the concept of 'fail-safe'. (As an aside, the "Daytona" link I posted is a case where circumstances led to the control system(s) improperly entering a 'fail-safe' mode.)

Here's what I think:

The toe-out RAS produces at low speed is - I think - unlikely to lead to situations that complicate vehicle stability control (because it's low speed.) Furthermore, attempting dynamic toe changes in mid-emergency (as opposed to simply commanding RAS to a 'fail-safe' static toe) could lead to hard-to-discover failure modes that might compromise stability (heard of Phugoid oscillation?) (If not see this: )

The toe-in change commanded by RAS at high-speed increases stability. At high-speed it is even-more necessary to be vary careful about what the system as a whole does and minimize control complications in exceptional circumstances. The more 'things' you have trying to affect the system's response the higher the likelihood that you will have detrimental coupling effects. And, it's the corner cases (i.e. 'emergency') that have the most 'bugs' that are excruciatingly difficult to find because testing the exceptional conditions is often very difficult, very expensive, or more-or-less impossible. So, designing the simplest control system with minimum necessary inputs and outputs to meet requirements is what you do.

I'm not saying that it isn't possible to field a system that commands dynamic toe changes under non-nominal (exceptional) conditions. It's just a lot harder to get it right. So, again, while possible, I question if VSC does - when stability control 'goes active' - anything other than tell RAS to 'go to neutral' and 'turn off.'

 

duh, I posted in old thread instead of an active one on this topic, my bad

 

I agree. I grew up paralel parking "1960s & 70s "boats!" And to me, there's too much train car feel. I first noticed it in the Panamera 4 gts, so perhaps I was looking for it.

The rear steer saves from 11.1M to 10.6M turning radius per Porsche site, so there you go.

Nice perhaps, definitely not necessary unless you want every possible track advantage imho, and I don't track my 2019 991.2 4 gts.

 

I track, and I deliberately did not get RAS.
I don’t like it. It messes with the feel and feedback of the car when you are on the edge. I don’t want my toe changing mid corner. If I have a tyre loaded up, I don’t want a computer unloading it without my input.

How pure is RAS? Well Porsche deleted it from the S/T!

Not because some B.S. journo said it was for weight saving.

They deleted it because they wanted a pure driving experience. I don’t need help parking or getting around a corner. I’ll bet my car is considerably more stanle than anything that has RAS.

I have driven a GT2-RS on the track many times, and If I buy one, the first mod will be to delete RAS


I understand I am a track rat, and I am old school.

For the younger guys, I’m sure its something you would and could get used to. So each to their own.

But certainly don’t think your car is superior with it, its not.

I’ve pulled out, disconnected and switched off every nanny possible and my car is pure and a dream to drive.
it is not nervous and skittish, it is not constantly making unnecessary corrections. It is calm and pure.

Street commuters, have at it. It’s not for me.

Again, its not in the purest Porsche of all, the 911 S/T.

(I bring that up because every RAS owner argument as always that Porsche engineers know best. Well, they kept it out of the drivers car! )

 

💯 Just curious, do you prefer ceramic brake option? I do for many reasons, including ability to brake later, no fade, no brake dust, etc.

 

For street, the no dust is of benefit.

They certainly work. I’m not a fan of the hard pedal. You have to push harder to get them to work. I find steel more progressive. Whilst PCCB last forever on the street, once they go beyond their heat range on the track, wear rates are ridiculous. Making them far too expensive to track.

Also the fear of chipping one if you went in the gravel.

Granted pedal feel is a personal thing, and they do pull the car up. So they are fine.

 

Porsche engineers may not know best, but they think RAS is faster/more stable on the track. That's the only reason it's on the 992 GT3RS.

 

Well the reason its not on the S/T is the driving experience is better without it.

All of these things are to help the driver. But everyone of them make you adjust your driving style.

Strip them all off, and no adjustments needed, its pure feedback. It’s raw and nice.

It’s not for everyone. Many people like the car to do everything for them. My preference is not. Its just a personal preference. I learn’t to drive in cars that had no nannies at all. As cars starting getting them, they were awful. Constantly interfering. Today they are much better, but I can still feel them. I drive on the street full traction control off. Its not reckless or dangerous, its normal.
The car is composed and gives earlier and purer feedback.

But I drive my car. I’m not on my iphone and commuting. I’m concentrating on whats going on. So I don’t need the car to compensate for my lack of attention. YMMV

 

My 991.2 (2017) GTS purchased didn't come with RWS but has 10mm lowering. According to SearchLabs A.I., "Yes, the 2017 Porsche 911 Carrera GTS has a lower suspension than the Carrera S, but only for the coupé model. The GTS coupé has a 0.78-inch lower suspension thanks to the PASM sports chassis, compared to the Carrera S's 0.39-inch lower PASM adaptable sport setup. The GTS also has a lower front spoiler and a higher rear spoiler extension to reduce lift forces compared to the Carrera S. However, the Cabriolet and Targa GTS models don't have the lower suspension and instead have the same setup as the Carrera S."

I have had my car to 3 tracks, and got along just fine without RWS. However, if you are buying the car as an "investment" and plan to "flip it" in the near future are, the car will command more interest and $$$ with RWS and Front Axle Lift (FLS). I don't have FAL either.

The pic below is my car attached the dealer prior to my purchasing it. I have had it almost 3 years, trouble free except for replacing the water pump (Under warranty). Send me a PM with an email address and I'll send you a 32 page article I just finished....with lots of 991.2 GTS info.