reacher

No RAS would be a deal breaker for me, I think it's that good. I drove one without it before I got mine that has it, and mine feels so much better on twisty roads. I don't care about parking, but handling at speed is dramatically better. It feels much lighter and nimbler, like a go kart.

​​I have a cab so I just have regular PASM, but if I had a coupe where SPASM was an option I'd definitely go for that as well.

AlbertC4S

BlueNorther

OC 991

People whom don't have it... "don't need it, can't tell the difference etc".
Those that do have it... "love it, wouldn't have another without etc".

But if these types of option came at the same price on a lot car (with or without) I'm willing to bet... most would love it

ipse dixit

No.

Neither RAS nor PASM are a "must"

marinb

Only a partial fact. It also effectively lengthens the wheelbase, making the car more stable in high-speed corners, at speeds above 50mph by turning the rear wheels up to 1.5 degrees in the same direction as the fronts.

Do you take turns (or long sweepers) above 50mph? It may be useful to you.

Gus_Smedstad

Must be fun watching you parallel park at 35+ MPH.

BlueNorther

Yes, the increase in turning radius at speeds above 50 mph is something else entirely. Not sure how many would say the current 911 without RAS is less than stable at high speed corners, though. At least outside of a road coarse.

BlueNorther

Yes, the comment was tongue in cheek. But the comments of increased agility refer to spirited driving in the twisties, not a parking garage.

That being said, I can't say I am having difficulty with the 911 Coupe in the parking dept. The car is already agile, visibility is great, and it is not a large car. I don't like it that the park assist yells at me every time I start the car in the garage because I purposely pulled close to a side or front of space to keep further away from other cars. It is part of being a good driver to have a good sense of where the boundaries of your sports car is without being dependent on monitors that are not perfect IMHO

BlueNorther

Yeah, too be honest I might have gone with RAS except that I wanted 19" winter wheels, and I following the KISS principle in my build. But I'm still skeptical about all the wondrous claims of enhanced driving agility based on the actual specs provided by Porsche.

Racer20

RAS does much more than just reduce turning radius. The alignment of your wheels is always changing with the road depending on suspension geometry and how much lateral force is acting on the tire at the contact patch. The steering feel, response, and stability of a car is heavily determined by how the front and rear toe changes as a car rolls and builds up lateral force as it enters a corner, carves through the apex, and exits.

For example, imagine a car that's set up such that the rear wheels toe out more as the car rolls. As you enter the corner, the rear will progressively toe out more and more, which causes the car to yaw quicker as the cornering force builds up and the car rolls more. This results in darty, non-linear steering, and can even induce a spin if it's really bad. If the rear toe's in too much as the car rolls, the rear end will feel sluggish and unresponsive, and the car will understeer more. Without RAS, automakers have to make a lot of compromises to the rear alignment and suspension geometry to balance this behavior with tire wear, ride comfort, and other things (suspension bushings are a major cause of these types of toe changes). The toe angles and behavior can't be set up perfectly for every situation, and sometimes the rear toe will do some undesirable stuff that the engineers just have to tune around with other things like tire characteristics, stability control, and steering calibration.

With RAS, the engineers are able to decouple the rear wheel's toe change behavior from all the other attributes that they have to manage back there, and tune the rear toe to behave exactly how they want for any given situation. This results in a rear end that "follows" the front much more reliably. They can make the car agile during turn-in and stable mid-corner and through the exit, all without the trade-offs normally associated with those things, like darty steering on the highway or instability under braking. They can dial in just the right amount depending on vehicle speed and cornering load, rather than having to choose a single bushing stiffness or static toe setting that's kind of ok for most situations.

If you don't know what you're looking for, or don't drive the car in the right conditions, you may not notice the difference. Normal city driving and US highway driving won't really show much. But for the track, for the autobahn, or for general twisty road enjoyment, I think it's a worthwhile option.

marinb

That's one hell of a first post. Thanks!

While I agree with what you are saying, one thing that bothers me is that it's only as good as the current computers controlling the rear steering. This will get much better over time as the hw, computers, sensors, algorithms, etc get better. Just like each revision of PDK is noticeable better than the last.

And so for a lot of same reasons I didn't get PDK, I didn't get RAS. However, I do believe the 991.2 RAS cars are noticeably better on the track, just like the PDK cars are much better at exploiting all the power the car has to offer.

Racer20

Haha, thanks!

Yeah, this is definitely true. Another big factor is the engineer's experience with tuning the system. No doubt these mechatronic systems will improve quickly over the next generation or two, but I think they are already good enough to be very worthwhile.

digits

Hah! Quit yer lurkin', Racer20! Clearly, you've got contributions to make - the best I can do is mention how much better I navigate the twisty Starbucks drive-thru lane with RAS. Someone's gotta raise the bar.

911-TOUR

Racer20 is spot on. RAS is Porsche's implementation of ZF's AKC (Active Kinematics Control) system. *Much* more than just reduced turning radius at low speed...

https://www.zf.com/corporate/en_de/p..._control.shtml

sean