Mike in CA

It is. The mechanical link isn't a backup, it's the actual steering as before, except that now the assist is provided by an electric motor instead of hydraulics.

ADias

USMC_DS1 is correct, as the 991 e-steering is a sophisticated (read prone to fail) software driven closed loop system. That system can, and actually does, steer the car. Its software logic aims at filtering feedback and correct L/R imbalances. When all is fine, the ride down the boulevard is just fine.

Mike in CA

One point that he was making was how the e-steering was similar to aircraft systems that were fly by wire with no mechanical connection and hence no backup in the event of failure. I simply stated that's not the case with the Porsche 991 steering, nothing more. As an aside, PDK is also a very sophisticated piece of technology, but I wouldn't say it's necessarily "prone to fail", would you? I don't think either of us have had any problems with it.

ADias

No question that the 991 has a direct/mechanical rack & pinion steering mechanism. Up to the 997.2 the assist was hydraulic and it just meant a reduction of force required by the driver to turn the wheels. Fast forward to the 991 and the steering assist is far more than a force assist. It is a complex (as in many lines of software code, electric sensors and electric actuators) making up a 'closed loop' (closed loops have meaning to systems engineers) which reads the road and actively steers the car. The 991 always has 2 drivers - the nut behind the wheel and a computer in the e-steering closed loop system. These are facts.

The PDK is more complex than a simple manual transmission, no 2 ways about that, and certainly will have failure points, but it is a tradeoff that some of us accept. There is no need to accept a trade-off in steering a car though. If you want a more 'controlled' less-sensitive steering at high speed for a German autobahn, perhaps PAG could have fitted its e-steering as an option for that application. In the US, where I do not know any public road or road track (not ovals) where 140MPH is attainable (at least on a sustained mode), I see no need to dumb down a perfectly good steering. Incidentally, the 997 already has a less sensitive steering (mechanical non-linear rack) compared to the 996 and previous generations. It comes a point when further dumbing something down exceeds reason.

zanwar

Based on your logic, the 997 also has two drivers - the human behind the wheel, and the hydraulic fluid in the power steering system.

Mike in CA

Tony, the two points I made above were clean and simple; the 991 steering is not fly by wire, and something is not necessarily prone to failure by definition just because it's sophisticated (see PDK). Beyond that, everything else you point out is very interesting, but I have no further issue with it one way or the other, and given everything else in this thread, I certainly don't care to argue more about it.

ADias

There's logic and there's logic. Hydraulic steering assist is strictly a force leverage. The 991's 'closed loop' control is an active steering brain capable of making steering decisions independent of driver input. I know few understand the all-important technical nuances.

zanwar

So you've cracked and decompiled the steering code in the 991 and figured out through reverse engineering that it helps to steer the car under normal situations? Or in fact the very presence of this code must indicate that something nefarious is taking place inside that power steering system? The published documents allude to corrective signals being sent to the steering as warnings to the driver in situations of critical slip angle. This is just a logical extension of PSM, not much different to firing a brake pulse to the outside rear in an oversteer situation. I think it also happens to be quite smart. That's the only reason I've continued to participate in this conversation. I have a great deal of admiration for the development engineers at Porsche and I dislike reading commentary trashing their work.

ADias

Let's not be silly. PAG's documentation clearly describes the 'closed loop'control and what it does. PAG's e-steering is not a threshold warning at all.

It is a great piece of Weissach engineering no doubt, but it is what it is. And BTW... in engineering... simplicity is better.

I have no dog on that race. It happens I know a bit more than the average Porsche owner about that issue. I offered it here and some prefer to live in denial. Their choice.

zanwar

You've read way more into the phrase 'closed loop control' than the published facts. You've speculated in order to support an argument. If simplicity in engineering was always superior, they would have put electric power steering on the car a long time ago. It's a far more simple solution that a complex physical device involving pumps and fluid under pressure. Anyone familiar with engineering would understand that.

ADias

OK, there are still a few forum readers who know the difference and know who's correct. Fine with me.

I am curious - if you do not mind my asking. Are you an engineer?

TrackDays247.com

Hydraulic vs. electric has a different feel for some reason.

Para82

I prefer the look of the 997, it looks more Porsche to me. For that kind of money I would rather own the 2013 Viper GTS.

I never pay more than 55k for a car though whether it's used or brand new, I just think it's too much money for wheels.

Right now what has my eye is the 2013 Shelby GT500 priced at 55k - 200mph and 650hp with adjustible Bilstein suspension sounds like a lot of bang for buck.

alexb76

Totally agree with you!

Without getting into too much details, it is basically an electronics layer that is NOT necessary and will FOR SURE (and confimed after test drive) impacts the feel and feedback! Hydrolic is Power Assist, so basically like a lever, your input is amplified and transfered into the wheels and that's it, and Porsche had it perfected to provide enough assist vs. feedback hence the famous 911 steering feel.

You both are technical (engineer vs. software), so let's end this silly debate, there's NO way you can say the e-steering feel and feedback is the same as hydrolic and that's the end of it!

mattyf

Neutral observer:

If you put a motor parallel to your steering mechanism, it had better be closed loop. I can't even imagine how you try to control the motor otherwise. With a pot on the steering wheel? I don't think so.

...But using a motor vs hydraulics, this is not necessarily more prone to fail. DC brushless motors and their control electronics are incredibly reliable. If sized properly it's the bearing in the electric motor that will fail before anything else and that will be after millions and millions of revs. I'd venture to trust it more than hydraulic lines. But as to the feel, that will be up to the controls engineers and the transfer functions they write.