bccars

I'm very close to locking my 991 config. Only doubt is to get the PTV Plus or not as I basically am not sure what it will do (I read the porsche info, read the forums, read the reviews, but still ...).
In case of tight corners (1st or 2nd gear), it is very fun to exit them wit a little bit too much throttle and kick the tail out slightly. This is were I get confused on the function of PTV. Will PTV Plus help me to control the drift angle ? Or conversely will PTV prevent me from sliding in this case ?

Rainier_991

You can quite easily flick out the backend with PTV if you so wish. Switch the PSM off and with a bit of speed on and some space of course, give the wheel a flick to break the back out. Experiment a bit with just how much as you can get the front to break traction first. The trick is to get the back moving and then to get it to move out faster as you tighten the flick (hope that is more or less clear). Also help with a dash of throttle, those rear tires are sticky.

I don't have one without PTV but it would seem that it is easier to get it to break traction at the rear if you don't have it. The reason would be the mass of the engine banging onto the travel limits of the mounts which would impart a sideways force of some significance (you can see the effect on some videos showing 911's going fast through tight corners - a bit of a wiggle).
PTV effectively bolts the engine onto the chassis in a sharp turn so this can't happen.

It's heavy on tires. But great fun.

chuck911

Rainier seems to be thinking of the dynamic motor mounts. PTV helps turn-in by applying a small braking force to the inside rear wheel. Turning right for example it slightly brakes the right rear. In reality the wheel isn't really braking, its just that the brake applies enough force to result in less power going to that wheel- or, if you are in fact braking then more braking. Either way the result is that inside rear wheel now acts to pull the car that direction, greatly increasing ease of turn-in.

The other questions about, basically, controlling slides, really have to do with PSM, the stability management that helps keep the car going where the computer thinks the driver wants it to go, especially when tires start sliding around. So PTV is working all the time, easy or hard driving, while PSM really only becomes noticeable around traction limits. Turn PSM off and the car can oversteer, you can kick the tail out to your hearts content, PTV or no PTV. You'll probably want PTV but the only way to know for sure is to drive and see.

bccars

Indeed Rainier is thinking about the DEM's.

What PTV does on pre apex corner entry is crystal clear. But it is a different story post apex corner exit. This is where the diff locking comes in. And since my car will have PDK, we are talking about PTV Plus, meaning no mechanical diff, but an electronically controlled diff. And it's clear a mechanical diff has everything to do with controlling a slide, and controlling traction. But it's the electronic part of the diff control that has me baffled.

How will that electronic diff locking operate, only with the brakes ? Or is there something else going on ?

Is the PTV Plus merely software code, or is there something physically different in the diff too ?

Cogito_Ergo_Zoom

I've wondered this, too. I have an S with PDK and PTV +.

And yes, you can easily get the rears to break loose with the PSM off and a judicious prod of the throttle, especially on cold tires. I've been having fun playing around at low speed with the PSM off, much to the detriment of my rear tires. Get sloppy though and it will remind you why 911s of yore had a reputation for sending you off *** first. (Don't ask me if I've confirmed that.)

alg1367

This is actually not how torque vectoring works. You are correct in that it is 'activated' by the brakes (more on that below), but the yaw movement it generates is not a result of pulling (i.e. inside wheel acting as an anchor to induce rotation), but rather as a result of overdriving the opposite outside rear wheel. In either instance you are causing the vehicle to rotate about it's axis, the only difference is in the later scenario you aren't causing deceleration, which is why torque vectoring works with driveline torque only and not merely when you are steering through a turn while coasting.

Now, as to why brakes are used with PTV (not PTV+). Porsche is using the brakes to 'trick' the LSD into distributing torque to the other side (into locking), and thus overdriving the outside rear wheel. In the absence of an actual difference in traction, they are fabricating enough torque difference between the rear wheels so that the diff moves the power. This is likely not nearly as precise as the ZF Vector Drive used in the X5M/X6M and the Audi Sport Rear Differential in the new S cars. That doesn't use a mechanical diff, but rather an electronically controlled differential that ITSELF can apportion power to each side in an infinite and precise manner, based on what the computer tells it to do. The effect can be much more pronounced and precisely controlled (of course those cars are pigs, so they need it to get out of their own way).

Note that the main difference between an open and close diff and torque vectoring via braking across both is TRANSFERING power across the axle by way of transmission (diff), as opposed to taking away power from one side while keeping everything the same on the other....

Enter PTV+. This is a mystery. It's definitely not an open diff with "brake based torque vectoring" (useless), since they wouldn't charge MORE (on carrera) for capability that is already built into the stability control (pure brake based with an open diff). It is also a reasonable assumption that it is not ZF Vector Drive, since ZF makes all the other suspension and driveline components in the car (PASM, PDK, PDCC, etc...) - we know this because when the panamera came out ZF had a press release touting all of this, but there was no mention of PTV+...

PTV+ may very well be an electronic diff that can control power split electronically (i.e. vector drive), but porsche is keeping this simple for marketing reasons....