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

[JohnPM]

AFAIK, modern (Porsche) cars use a pseudo-Ackermann approximation

Why would you say that when the passage you highlighted says the opposite? On a related note, is reading Wikipedia a substitute for actual knowledge and professional training and experience? All those years we have wasted in universities and doing our jobs when all we needed was a browser

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[MichaelPNW]

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)

Appreciate this information. I will likely wait out this winter as I’ll be ready to replace my tires later this year anyway. I had been considering going to a 20”, but perhaps will consider a tire better suited for cold weather at 21” and cross my fingers for next winter.

It is my drive in and out of my garage that is the most irritating along these lines.

@freeforall did you notice a reduction in road noise between the tires?

 

[Sly_North]

Why would you say that when the passage you highlighted says the opposite? On a related note, is reading Wikipedia a substitute for actual knowledge and professional training and experience? All those years we have wasted in universities and doing our jobs when all we needed was a browser

Went to my car, turned the wheel full lock, and... the inner wheel turns more than the outer wheel:
It's indeed a pseudo-Ackermann geometry, not an anti-Ackermann one. I was correct, my Unversity knowledgfe is correct, and Wiki is correct, and the passage I quoted agreed with what I said.

 

[f1eng]

Went to my car, turned the wheel full lock, and... the inner wheel turns more than the outer wheel:
It's indeed a pseudo-Ackermann geometry, not an anti-Ackermann one. I was correct, my Unversity knowledgfe is correct, and Wiki is correct, and the passage I quoted agreed with what I said.

Why do the tyres stick/slip at low speed in low grip conditions then?

 

[Sly_North]

Why do the tyres stick/slip at low speed in low grip conditions then?

That's the definition of the Ackermann effect, caused by an Ackermann geometry, not an anti-Ackermann geometry (thhough, it would be much worse with an anti-Ackermann one). It's due to 1) no car has a perfect Ackermann geo; 2) we have a pseudo-Ackermann set for high speed, which does NOT match low speed turning.
Why it doesn't happen on other "normal car" ? Smaller tires with much less friction. Here, the friction pulls the tire away off the rim, and something has to give up -> the tire bumps back in place, giving this noise.

 

[f1eng]

That's the definition of the Ackermann effect, caused by an Ackermann geometry, not an anti-Ackermann geometry (thhough, it would be much worse with an anti-Ackermann one). It's due to 1) no car has a perfect Ackermann geo; 2) we have a pseudo-Ackermann set for high speed, which does NOT match low speed turning.
Why it doesn't happen on other "normal car" ? Smaller tires with much less friction. Here, the friction pulls the tire away off the rim, and something has to give up -> the tire bumps back in place, giving this noise.

What a complete load of old balderdash.

You qualify for the ignore list. Goodbye.

 

[JohnPM]

Went to my car, turned the wheel full lock, and... the inner wheel turns more than the outer wheel:
It's indeed a pseudo-Ackermann geometry, not an anti-Ackermann one. I was correct, my Unversity knowledgfe is correct, and Wiki is correct, and the passage I quoted agreed with what I said.

A statement about what "modern cars do not use" is not a logical basis to make a statement about what they do use. Without tracking the turning centres each wheel (which are different for cars with RWS, of course) it isn't possible to say whether the steering geometry achieves angles that are higher or lower than the Ackermann geometry. Practical experience makes clear that they do not match Ackermann geometry, however.

 

[freeforall]

Appreciate this information. I will likely wait out this winter as I’ll be ready to replace my tires later this year anyway. I had been considering going to a 20”, but perhaps will consider a tire better suited for cold weather at 21” and cross my fingers for next winter.

It is my drive in and out of my garage that is the most irritating along these lines.

@freeforall did you notice a reduction in road noise between the tires?

The car is so beautiful with 21, you will regret going to 20 if you got used seeing it with 21. It is a very personal opinion though ?

Noise wise I did not notice anything different. However I only changed the front tires because the Pirelli were dead very quickly (18k km). I am now at 26k km with Pirelli in the rear and Goodyear in the front.
However one thing I am sure about is that the Goodyear seems to wear way less than the Pirelli (I keep measuring). Another thing I noticed but I can’t be sure about because there are a lot of parameters that influence that: my consumption clearly went down in summer on the highway with the Goodyear. I can’t be sure though, it is either the tires or I am getting old ?

I will be changing my rear tires to Goodyear as well. I suspect that the Pirelli are very performant in hot weather but I think that they have very bad grip when temperatures go down in comparaison to the Goodyear. I did not find a single test for summer tires at 10 degrees Celsius for example. So they are just optimizing their tires for performance at an ideal temperature so it is useless for a daily car in a city like Paris where temperatures can go low (I don’t want to buy winter tires either because it is not justified for my use)

I hope this helps for your future choice of tires.

 

[MichaelPNW]

The car is so beautiful with 21, you will regret going to 20 if you got used seeing it with 21. It is a very personal opinion though ?

Noise wise I did not notice anything different. However I only changed the front tires because the Pirelli were dead very quickly (18k km). I am now at 26k km with Pirelli in the rear and Goodyear in the front.
However one thing I am sure about is that the Goodyear seems to wear way less than the Pirelli (I keep measuring). Another thing I noticed but I can’t be sure about because there are a lot of parameters that influence that: my consumption clearly went down in summer on the highway with the Goodyear. I can’t be sure though, it is either the tires or I am getting old ?

I will be changing my rear tires to Goodyear as well. I suspect that the Pirelli are very performant in hot weather but I think that they have very bad grip when temperatures go down in comparaison to the Goodyear. I did not find a single test for summer tires at 10 degrees Celsius for example. So they are just optimizing their tires for performance at an ideal temperature so it is useless for a daily car in a city like Paris where temperatures can go low (I don’t want to buy winter tires either because it is not justified for my use)

I hope this helps for your future choice of tires.

Very helpful, thank you. In the Seattle area, we don’t get cold enough, long enough for the asphalt and concrete to freeze. And we don’t get ice and snow either at all or for very long as a result. We also don’t get terribly hot in the summers. 25C are rare days. I will do some research into the Goodyears.

 

[Chas1]

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)

Just a btw. I have a ST RWD with Rear axle steer and Ackerman effect in evidence in 21” wheels and virtually zero on 19” standard Porsche wheels fitted for winter and super luxury ride ?.

 

[BjörnfromHamburg]

Also: with 21", fast-cornering is significantly more stable.
Big difference between Winter 20 " and Summer 21" (Ok Winter-tires are softer also)

 

[B61]

The car is so beautiful with 21, you will regret going to 20 if you got used seeing it with 21. It is a very personal opinion though ?

Noise wise I did not notice anything different. However I only changed the front tires because the Pirelli were dead very quickly (18k km). I am now at 26k km with Pirelli in the rear and Goodyear in the front.
However one thing I am sure about is that the Goodyear seems to wear way less than the Pirelli (I keep measuring). Another thing I noticed but I can’t be sure about because there are a lot of parameters that influence that: my consumption clearly went down in summer on the highway with the Goodyear. I can’t be sure though, it is either the tires or I am getting old ?

I will be changing my rear tires to Goodyear as well. I suspect that the Pirelli are very performant in hot weather but I think that they have very bad grip when temperatures go down in comparaison to the Goodyear. I did not find a single test for summer tires at 10 degrees Celsius for example. So they are just optimizing their tires for performance at an ideal temperature so it is useless for a daily car in a city like Paris where temperatures can go low (I don’t want to buy winter tires either because it is not justified for my use)

I hope this helps for your future choice of tires.

Very useful comment, thank you.
I need to replace my summer tires (comes with 21” pirelli) and it looks that i’ll have to take goodyear eagle too.

 

[SergeyIndy]

Very useful comment, thank you.
I need to replace my summer tires (comes with 21” pirelli) and it looks that i’ll have to take goodyear eagle too.

Goodyears if All Season are poorly rated at least here in the US.
Continentals are the only other All Season choice remaining and are better rated.

 

[B61]

I’m getting summer tires ( 305/30 rear, 265/35 front, eagle 1,asymetric 3)… should i ask for asymetric 5?
@f1eng , any comments?

 

[freeforall]

Goodyears if All Season are poorly rated at least here in the US.
Continentals are the only other All Season choice remaining and are better rated.

Poorly rated on what aspect? Are you also referring to Asymmetric 5 as well? Can you share the US rating?

In EU, they are better rated than Pirelli

Also I reviewed multiple tests that suggest the same.

Pirelli

Goodyear

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