Key Left

This is a good one. What is the actual 991 turning radius by model type?
I have an early factory C2 and C2S Technical Info Bulletin which states it's 33.39 feet. Later texts after the launch of the C4 and C4S state 36 feet for all types ( although CV joints must add something). Now the with launch of the C Turbo and Turbo S Porsche states in Christophorus that due to four wheel steering it's back down to 35 feet. What gives, and what does front drive really add to the 991 turning radius?

StudGarden

When its cold outside I get 0.79 football fields.


Yeah I know, its harmless "acorn" noises. Still can't bring myself to stop cringing though.

Key Left

I get those noises, too. But really, I think Porsche is maybe trying to hide something, here. Two wheel drive and four wheel drive cannot have the same turning circle? And four wheel steering seems to net somewhere in between. I think Porsche should be a little more forthcoming and clear.

Suzy991

Just looked at the German technical specs in their brochure.

C2(S): 11.1 m (36.4 ft)
C4(S): 11.1 m (36.4 ft)
TT(S): 10.6 m (34.8 ft)

Not sure if this is measured between walls or at the wheels though...

I was wondering why the AWD model should have a bigger turning radius than the RWD car? Isn't it the maximum turning angle of the wheels (and width of the front tyres) that limit it? Or is that different on an AWD car? I'm not that technical, so I'm trying to learn something here

Suzy (via iOS app)

kosmo

what? its the same accordingly to your post.
Obv the TT has RWS.

Richard Williams

Hi everyone,

Yes... the 991 Turbo S does the same turning very closely... the sound is like something to get used to... hey, they're like HUGE wheels so what do you really expect? We have to learn to love em.. eh?

Now the 991 turns as well as my 996 Turbo but it's a lot longer, actually 3.5 inches I think... but, the turning radius is like a little car too... it's great... BUT... when you want to drive around with the window down on the drivers side it aint going to happen no more either... the echo baffles of air inside the cockpit with the window down just does not work over like 35 mph. Probably since it's not really just a turbo anymore.. the new one is really a racer.. There's no doubt about it either.. she's going 93 when you would usually be going 78 in the 997 turbo when you're in 3rd gear before the change or not... ususally that's where we let up on the gas and slow down fast in the 3rd gear to be not so obvious for a ticket, ha ha... Deseree, my new 991 Turbo S is whole new ball of wax.... with the paddle shifting etc. she's definitely a different car since she's what Porsche gave us as a real racing car all bells and whistles too.... there will be plenty of unplanned tickets and I recommend a good radar detector for yours too, ha ha.....

So what do y'all think about them? I'd love to hear some matching comments too.....

Thanks,
Richard

chuck911

Turning radius is a function of steering angle and wheelbase. Tires, awd, etc, have nothing to do with it. With rear steering Porsche is able to emulate both a short wheelbase at low speed and a long wheelbase at high speed, so with those cars its complicated. But unless steering angle is restricted, what is the reason to think there should be any difference between 2 and 4wd 991's? Why would cv joints "add something"? Read through the comments above. Porsche increased the wheelbase of the 991 and the turning radius increased. Car geometry 101.

Key Left

The c2 cars are 33.39 feet, 10.4 meters, per the Porsche manual I have. The AWD's are 36.4 feet. This makes sense since AWD upfront requires some sort of CV joint which is not as nimble as a ball joint. The TT falls in between due to RWS. Please correct me if I am wrong here.

chuck911

Both rear and fwd cars use ball joints for steering. CV joints transmit power. Two completely different things. Turning radius is determined by wheelbase and how sharply the steering wheels are able to turn. That's it. The only way a CV joint could increase turning radius is if it physically limits how sharply the steering wheels are able to turn. It has nothing to do with being "nimble". The same ball joints are used on both 2 and 4wd cars.

The cars with rear wheel steering do not fall in between. Rather, they exhibit- get this!- BOTH a shorter AND a longer turning radius! A long wheelbase enhances the stability of very fast cars. (One reason it was inevitable that the 911 got bigger as it got faster.) Rear wheel steering allows Porsche to emulate this high speed stability without the sacrifices of a long wheelbase. It can also emulate a shorter wheelbase yielding a tighter turning radius at slow speeds. There's a video out there where Preuninger talks about this "virtual" wheelbase at the same time it shows the rears steering, but I'm not finding it now.

Taking it all together it all makes sense now, doesn't it?

Hammer911

not the video Chuck referred to, but here's some text...


Then there’s also the matter of the electric steering system (replacing the more communicative hydraulic steering) which has been controversial since its debut in the 991 Carrera. According to Andreas, the steering software has been heavily revised for the GT3 and after a lot of testing it gives as a much feel as the old car and is in a “different world” as far as electric steering systems go. However, the front wheels aren’t the only ones doing all the pointing. The GT3 will also be equipped with rear wheel steering. Essentially, the rear wheels will move opposite to the direction of the front wheels making the car more agile while cornering. As Andreas puts it, “It creates a virtual reduction of the wheelbase by about 200 mm.” I thought this type of thing was reserved for vehicles with much, much longer wheelbases like the GMC Silverado 1500/Sierra 1500 and Suburban/Yukon. Then I found this list on wikipedia and read that its been used on Honda Accords, Preludes, Nissan’s 240SX and 300ZX and even Mazda’s MX-6. So for an extra 15 kilograms of weight, the rear wheel steering helps increase stability at high speeds while reduce turning radius at low speeds.

chuck911

Its not crystal clear from those quotes, but when he's talking about increasing agility by a "virtual reduction" of about 200mm he's talking about what happens at lower speeds. At higher speeds its the opposite, increasing the "virtual wheelbase" in order to improve stability. The reason I wasn't able to find the video is I kept thinking of Preuninger when in fact it was Achleitner.

chuckbdc

So Porsche gets you used to a a specific turning radius at low speeds, and then you can't trust it making tight circles at high speeds? They are out to sell replacement fenders. Add this to the conspiracy theory thread.

Key Left

[QUOTE=chuck911;11093775]Both rear and fwd cars use ball joints for steering. CV joints transmit power. Two completely different things. Turning radius is determined by wheelbase and how sharply the steering wheels are able to turn. That's it. The only way a CV joint could increase turning radius is if it physically limits how sharply the steering wheels are able to turn. It has nothing to do with being "nimble". The same ball joints are used on both 2 and 4wd cars.

CV joints due tend to limit steering angle versus just pure ball joint set ups, in the front. They are simply not able to articulate as much. C4's have a Porsche reported turning radius three feet greater than C2's, although it's not made clear by Porsche. That is why I think the TT partially needed RWS to be more nimble than the C4's. The GT3 is only rear drive, but still gets the same RWS as the TT, but then the TT is billed as the "benchmark" so it has to have every bell and whistle.

Hammer911

"So Porsche gets you used to a a specific turning radius at low speeds, and then you can't trust it making tight circles at high speeds? They are out to sell replacement fenders. Add this to the conspiracy theory thread"

Either your humor has zero moisture content, or you are stretching on this one. Could one really hope to make the same radius turn at, say 80mph as you are at 10mph? The G-force meter display would have to look like this:

chuck911

Yeah chuck you lost me there too. Watch (and listen!) closely to the video. Especially the bit where the turbo leaves the driveway. Watch closely how the rear steers. Then later on the road. Together with Achleitners (and journalists) comments its clear the steering is engineered to seamlessly transition from turning opposite the fronts at very low speeds to turning with the fronts at very high speeds. Seamlessly being the key word. They do not get you used to anything. And really, in a sense its not even anything new. They already have engineered steering to be progressive. The initial few degrees of steering wheel input deliver less steering result right off center than what you get as you keep turning. Its been that way a very long time now. You probably never noticed. Which, if you listen to Achleitner, is just the way he wants it.