Mid-engine cars
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By fpena944
#197226
My 2014 Cayman is the first car I've had with electric steering. I would like to ask all of you how your 981 behaves when turning the steering wheel all the way to one side.

The problem I'm running into is that when I do turn it the whole way and begin moving I get a feeling the front tires are "skipping" across the pavement. It happens more in the wet than dry but still it's quite noticeable where even a passenger would ask if that is normal. Once I then straighten the wheel a bit it goes away.

I have no other symptoms of issues with my steering - it feels perfect except in this case.

On my other cars with hydraulic steering I don't get any of this happening so not sure if this is product of this type of steering or if there is something wrong with the car.

I've done diagnostics on my Durametric and nothing is showing up.
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By N_Jay
#197228
fpena944 wrote: Thu Jan 26, 2023 9:18 pm My 2014 Cayman is the first car I've had with electric steering. I would like to ask all of you how your 981 behaves when turning the steering wheel all the way to one side.

The problem I'm running into is that when I do turn it the whole way and begin moving I get a feeling the front tires are "skipping" across the pavement. It happens more in the wet than dry but still it's quite noticeable where even a passenger would ask if that is normal. Once I then straighten the wheel a bit it goes away.

I have no other symptoms of issues with my steering - it feels perfect except in this case.

On my other cars with hydraulic steering I don't get any of this happening so not sure if this is product of this type of steering or if there is something wrong with the car.

I've done diagnostics on my Durametric and nothing is showing up.
I notice my 987 near steering lock starts pulling the wheel in.\, and you can feel as lot of scrub.
I seem to remember my 914 being similar, and figured it was to give you all the steering angle available and let the driver decide instead of having some mechanical lock before the wheels turned further than aligned to turn.

OR I am rationalizing/////
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By worf
#197273
This ‘skipping’ also known as “Acorn Effect” of the front tires at full or near-full lock is a perfectly normal consequence of the Ackerman Geometry of the front end. It is more pronounced on cars with big front tires … sports cars.

Nothing to see here…
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By fpena944
#197307
worf wrote: Fri Jan 27, 2023 2:32 am This ‘skipping’ also known as “Acorn Effect” of the front tires at full or near-full lock is a perfectly normal consequence of the Ackerman Geometry of the front end. It is more pronounced on cars with big front tires … sports cars.

Nothing to see here…
So my 996 doesn't have this same type of geometry? I mean I feel a little something on turns but not as pronounced as it is on the 981.
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By N_Jay
#197339
I wonder if it has anything to do with wheelbase vs. tire patch? 914 and Cayman are fairly short and wide.

Lots of discussion on the web, but many links come back to a "Porsche" question, so also wonder if it has much to do with some types or suspension geometry?
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By Cuda911
#197352
Worf is correct. My '14 Cayman does the same. Scared the crap out of me a few times at first. However, 100% normal.

Interestingly, though, never had it happen in my '07 or '10 Cayman.
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By worf
#197359
fpena944 wrote: Fri Jan 27, 2023 10:09 am So my 996 doesn't have this same type of geometry?
No habla 996.

But… I’ll bet it had 225 front tires? And your 981 …

fpena944 wrote: Fri Jan 27, 2023 10:09 am I mean I feel a little something on turns but not as pronounced as it is on the 981.
… has 245s? Yes?

N_Jay wrote: Fri Jan 27, 2023 12:54 pm I wonder if it has anything to do with wheelbase vs. tire patch? 914 and Cayman are fairly short and wide.

Lots of discussion on the web, but many links come back to a "Porsche" question, so also wonder if it has much to do with some types or suspension geometry?
There is no reason to wonder about it:

https://en.wikipedia.org/wiki/Ackermann ... g_geometry

Porsche engineers want a negative scrub radius so as to avoid “rut following.” This results in high offset front wheels. Add in Yugo-sized brake calipers, steam roller-capable front wheels(*) and you’re left with not a lot of space for the lever arm on the steering knuckle. There are likely other constraints too that are traded-off for performance.

So, Porsches tend to have less “Ackerman” thus the skipping (like driving over acorns and thus “Acorn Effect”) at near or full-lock.

(*) High contact patch area per ton of weight.

The Acorn Effect is a thing for any car with the above constraints. “Normal” cars have “more Ackerman” because the Soccer-Mom-Mobile engineers are told by the marketing people that no Acorn Effect is more important than not tram-lining, more important than big brakes, and more important than contact patch.

Sidewall stiffness across various tire make/model will causes variations in onset of Acorns. Camber too. And toe. Oh… and caster. Lol. So alignment is important. Caster is I think the biggest alignment variable. But I’d need to ponder that before betting a body part on it.
fpena944, amdavid liked this
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By JRMaroon
#197373
My 2014 Cayman S did the same thing, scrubbing fronts while turning in reverse. Replaced the Pirellis with Michelin Pilot Super Sports (current offering at the time) and no longer scrubbed while backing up. It is normal tendency for the car and better tires eliminated the issue.

Fernando, what tires are on the car? Mine was LOUD in the cabin with Pirelli P ZEROs. Much quieter with the Super Sports.
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By Fox_
#197775
worf wrote: Fri Jan 27, 2023 1:53 pm
fpena944 wrote: Fri Jan 27, 2023 10:09 am So my 996 doesn't have this same type of geometry?
No habla 996.

But… I’ll bet it had 225 front tires? And your 981 …

fpena944 wrote: Fri Jan 27, 2023 10:09 am I mean I feel a little something on turns but not as pronounced as it is on the 981.
… has 245s? Yes?

N_Jay wrote: Fri Jan 27, 2023 12:54 pm I wonder if it has anything to do with wheelbase vs. tire patch? 914 and Cayman are fairly short and wide.

Lots of discussion on the web, but many links come back to a "Porsche" question, so also wonder if it has much to do with some types or suspension geometry?
There is no reason to wonder about it:

https://en.wikipedia.org/wiki/Ackermann ... g_geometry

Porsche engineers want a negative scrub radius so as to avoid “rut following.” This results in high offset front wheels. Add in Yugo-sized brake calipers, steam roller-capable front wheels(*) and you’re left with not a lot of space for the lever arm on the steering knuckle. There are likely other constraints too that are traded-off for performance.

So, Porsches tend to have less “Ackerman” thus the skipping (like driving over acorns and thus “Acorn Effect”) at near or full-lock.

(*) High contact patch area per ton of weight.

The Acorn Effect is a thing for any car with the above constraints. “Normal” cars have “more Ackerman” because the Soccer-Mom-Mobile engineers are told by the marketing people that no Acorn Effect is more important than not tram-lining, more important than big brakes, and more important than contact patch.

Sidewall stiffness across various tire make/model will causes variations in onset of Acorns. Camber too. And toe. Oh… and caster. Lol. So alignment is important. Caster is I think the biggest alignment variable. But I’d need to ponder that before betting a body part on it.
Interesting.

Explains why my audi occasionally tramlines, I'd always blamed the wider tires.
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By fpena944
#197799
@worf - 225s on the 996 with 18" wheels, 235s on 19" wheels on the Cayman
JRMaroon wrote: Fri Jan 27, 2023 2:36 pm My 2014 Cayman S did the same thing, scrubbing fronts while turning in reverse. Replaced the Pirellis with Michelin Pilot Super Sports (current offering at the time) and no longer scrubbed while backing up. It is normal tendency for the car and better tires eliminated the issue.

Fernando, what tires are on the car? Mine was LOUD in the cabin with Pirelli P ZEROs. Much quieter with the Super Sports.
Goodyear Eagles. They were pretty much brand new when I bought the car but I'll go back to Michelins or Bridgestones (what I have on my 996) when they wear out.
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By worf
#197804
fpena944 wrote: Mon Jan 30, 2023 11:09 am - 225s on the 996 with 18" wheels, 235s on 19" wheels on the Cayman
Rolling diameter of ‘modern’ Porsches is about 2 inches more than ‘classic’ Porsches. So, even with same size wheels and same width modern Porsches have more contact patch.

So, 981 has more tire width, more patch than 996 even if ‘twas 225s. It may or may not have more or less sidewall. But, bigger patch is most-likely why you feel this more in the 981.

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