Just returned a ‘25 RWD loaner for my ‘23 GTS…some differences

[BjörnfromHamburg]

The explanation exceeds my english-skills.
The dynamics of 4 wheels being powered, emphasizes steering dynamics ("pushes more") so the ackermann effect kicks in earlier.

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[f1eng]

The explanation exceeds my english-skills.
The dynamics of 4 wheels being powered, emphasizes steering dynamics ("pushes more") so the ackermann effect kicks in earlier.

That makes no sense for low speed manoeuvring at near maximum steering angle, which is where the anti-Ackermann geometry has the chattering (stick/slip) effect.

 

[BjörnfromHamburg]

Well, at low speeds is where I clearly experience it and got it explained.
It's a big difference between my 4WD and 2 WD cars, but I gladly withdraw and am ready to receive better explanations for this phenomenon.

 

[f1eng]

Well, at low speeds is where I clearly experience it and got it explained.
It's a big difference between my 4WD and 2 WD cars, but I gladly withdraw and am ready to receive better explanations for this phenomenon.

It is simply that at low speed the inner front tyre is actually rolling on a smaller radius than the outer, ie the Ackermann effect known for over 100 years. But due to the steering being optimised for hard cornering in most sporty cars the steering almost always has anti-Ackemann geometry which means the tyres are generating a side force at low speed as they fight each other since they have different slip angles which are "wrong" for Ackermann even though "right" for high load cornering.

With flexible sidewalls and sticky rubber this force just causes a bit of tyre deflection.
With low grip (summer tyres in winter) and low profile tyres ( laterally inflexible) one or both tyres end up doing slip/stick juddering.

What influences it is the actual steering geometry, actual tyre compound and construction and the temperature because of the temperature/friction coefficient characteristic of the tyre in question. Wear probably has a small effect too.

Front wheel drive, rear wheel drive and all wheel drive don't influence the effect manoeuvring at low speed.

 

[BjörnfromHamburg]

Thanks for clarification!

 

[RoseyPSU]

Did you ask the dealer if there was another button somewhere to set the regen type? I use that a lot and would miss it.

You can set a diamond button, but I believe it is only to off/on. You can also set how you want regen to work with Sport and Sport Plus. It's a button I rarely used (I always keep it on) so it wasn't something I missed going from a '20 to a '25.

 

[snstevens]

You can set a diamond button, but I believe it is only to off/on. You can also set how you want regen to work with Sport and Sport Plus. It's a button I rarely used (I always keep it on) so it wasn't something I missed going from a '20 to a '25.

That is my concern. In the 2021 version you hold the button to get to Automatic Regen. Do they provide the "Automatic" option as one of the commands you can assign to the diamond button?

 

[SergeyIndy]

That is my concern. In the 2021 version you hold the button to get to Automatic Regen. Do they provide the "Automatic" option as one of the commands you can assign to the diamond button?

2025: Diamond can be assigned to Regen Auto/Off or On/Off.

 

[RoseyPSU]

That is my concern. In the 2021 version you hold the button to get to Automatic Regen. Do they provide the "Automatic" option as one of the commands you can assign to the diamond button?

Yes, what @SergeyIndy said. I just went out and checked.

 

[freeforall]

I have 0 Ackermann effect on my MY23 ST (RWD) since I changed the front tires from Pirelli P Zero to Goodyear Eagle F1 Asymmetric 5.
I have 21 wheels and the Ackermann effect was kicking with no exception when going in or out from my parking lot, as it was very low speed and maximum steering angle. It was extremely annoying. This winter was very cold in Paris this year and yet I didn’t experience a single Ackermann effect with the Goodyear.
So the Goodyear seems to better react in cold weather vs the pirelli and if you hate Ackermann effect as I did (especially that it was frequent in my case) you may want to consider different tire models to solve the behavior (not sure what you have on your GTs)

 

[Sly_North]

You write it as definite but I think there is no mechanism by which either 4 wheel drive or rear wheel steering could cause it. So I completely disagree.

It is a straightforward combination of sporty steering geometry, (anti Ackermann) very low profile tyres and summer tyres having low grip on a cold surface and is explained by the data.

+1, I don't see how AWD vs RWD would affect the Ackerman effect.

Just a precision : AFAIK Taycan uses a Ackerman geometry, not a anti Ackerman one
Anti A. geometries are very rarely used, only on racing cars like in F1.

 

[rb33gl]

Def. due to RWD, that the Ackermann effect did not occur.
Typical 4 WD thing.
Especially when tires are very hard/ cold (summer-tires and very cold temperatures make noise, whereas the winter-tires don't)

Mine does the Ackerman effect all the time on full lock at slow speeds. RWD with air suspension & RW steering.

 

[f1eng]

Just a precision : AFAIK Taycan uses a Ackerman geometry, not a anti Ackerman one

If it didn't have anti-Ackermann there would be no chattering since at low speed both tyres would be tracing the ideal unloaded radius.

It is true I mainly designed Formula 1 cars but anybody calculating steering geometry to be ideal for typical sports car weight transfer would find they need anti-Ackermann.

 

[Sly_North]

If it didn't have anti-Ackermann there would be no chattering since at low speed both tyres would be tracing the ideal unloaded radius. [...]

Which is impossible to achieve mechanically for any radius, it would require a computer to get the correct angle of each wheel. Cars actually achieve an approximation of the Ackermann geometry.
Wiki (bold mine):

A simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins, which is the pivot point, and the centre of the rear axle. The steering pivot points[clarification needed] are joined by a rigid bar called the tie rod, which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point.

Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low-speed maneuvers. [...]

So indeed, AFAIK, modern (Porsche) cars use a pseudo-Ackermann approximation, and not an anti-Ackermann.

 

[f1eng]

Which is impossible to achieve mechanically for any radius, it would require a computer to get the correct angle of each wheel. Cars actually achieve an approximation of the Ackermann geometry.
Wiki (bold mine):

So indeed, AFAIK, modern (Porsche) cars use a pseudo-Ackermann approximation, and not an anti-Ackermann.

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