Possible Ackermann Effect

All Porsche Macan Related Discussion
User avatar
Neil1911
Posts: 3157
Joined: Sun Apr 14, 2019 12:00 pm
Location: Sheffield, England

Post by Neil1911 »

Harder compound either due to weather or chemistry presumably emphasises it, you can be sure though it'll be accelerating the tyre wear alarmingly.
http://www.porsche-code.com/PP37WLA6, a Dolomite Silver S, collected from Stockport OPC on Valentine's Day 2023, after a 399 day wait.
Ex.: Gen2 S, Volcano grey 1/9/19 - 3/2/23 & 39,235 Smiles, RIP

TheTraveller
Posts: 621
Joined: Fri Nov 02, 2018 9:30 pm
Location: South Yorkshire

Post by TheTraveller »

The Ackerman causes the front wheels to turn through different angles whenever the steering wheel is turned from the straight ahead position.
But added to that fact, the tyres are so wide, the inside and outside edge of the tyre on each wheel would also like to turn through a different angle, but that’s impossible. So they tend to scrub, instead of a true turning motion.
User avatar
pmg
Posts: 2985
Joined: Wed Jun 20, 2018 7:31 pm

Post by pmg »

TheTraveller wrote: Mon Jan 24, 2022 10:15 pm The Ackerman causes the front wheels to turn through different angles whenever the steering wheel is turned from the straight ahead position.
But added to that fact, the tyres are so wide, the inside and outside edge of the tyre on each wheel would also like to turn through a different angle, but that’s impossible. So they tend to scrub, instead of a true turning motion.
It remains possible to run most Macans on the narrower 19 inch wheelsets if not 18's. However "fashion" has pushed most new supplied vehicles to be supplied on the wider 20's or 21's.

This Sunday's Harry's Garage video on 50 years of the Lotus Elan stressed how Chapman had gone for a narrow 155 tyre to improve feel. years ago SAAB used to fit very narrow tyres to improve their cars winter grip performance. ;) ;) ;)
2019 Macan S Porsche code PKW8WKI8
TheTraveller
Posts: 621
Joined: Fri Nov 02, 2018 9:30 pm
Location: South Yorkshire

Post by TheTraveller »

Years ago, some will remember that most cars had cross ply tyres. Which were much thinner than radials, and were an all round tyre, OK for general driving, when vehicles had no where near the speed and performance they have now. And they were better in winter to cope with snow we used to have, in the UK.
User avatar
SAC1
Posts: 3784
Joined: Wed May 24, 2017 8:24 pm
Location: near BATH

Post by SAC1 »

TheTraveller wrote: Tue Jan 25, 2022 7:46 am Years ago, some will remember that most cars had cross ply tyres. Which were much thinner than radials, and were an all round tyre, OK for general driving, when vehicles had no where near the speed and performance they have now. And they were better in winter to cope with snow we used to have, in the UK.
In those days those crossply tyres generally had a narower tread width dimension to the height of the sidewall - most were 80 series. The weight of the car pressing down on the stiffer sidewalls helped "cut" through the snow and good steering precision. Wheelspin was less because of the [generally] lower power and torque of the engine in comparison to todays cars. Even so, the essential users still relied on crossply "Town & Country" or "Mud & Snow" tyres for mobility in harsh winter conditions. Separate sets of winter wheels were unheard of though! with the O.E. steel "summer" wheels still used.

As an example a SWB 90 Land Rover had 6.00 x16 crossply tyres, or 152 mm wide, compared to a 20" shod Macan with 295 section rear tyres - nearly twice as wide

The Ackermann Effect is more pronounced with the ultra-wide, ultra-low profile modern summer tyres as they generally have continuous tread ribs with little lateral give on low speed full lock turning. All Season and Winter tyres have broken tread ribs with individual tread blocks. This enables the tyre to shuffle / squirm more on low speed turns and reduces the drag / pull effect. So have a less pronounced feel and noise at the steering wheel compared to summer pattern tyres.
Steve

2020 GTS in Sapphire Blue
(sold) 2017 SD in Rhodium Silver
PorscheMack
Posts: 1701
Joined: Mon Jul 12, 2021 3:46 pm

Post by PorscheMack »

I'm surprised how owners experiencing this are so relaxed 🤔 Owners on the GLC forum were spitting features which went someway towards MB taking the condition seriously and applying appropriate action.
Macan GTS (Gen 3) (Mar 24-???)
http://www.porsche-code.com/PRKIVM50
Macan GTS (Gen 3) (Mar 22-Nov 23)
http://www.porsche-code.com/PNIECDM4
davlewis
Posts: 93
Joined: Wed Oct 13, 2021 8:08 am

Post by davlewis »

Wow thanks for all the responses! Great info! I think I made its worse, as I may have accidentally gone in on the turn a little hot and had to put the breaks on harder than I normally would. This probably exacerbated the effect somewhat. Doing the same maneuver today at a more sedate speed resulted in me hardly noticing it. I will however keep an eye on things and probably raise it with my local OPC.

It's odd how I never experienced this on my X3 with 21" wheels in more or less the same profile. I am probably misunderstanding something key with regards to the Ackermann Effect.
- Macan Volcano Grey / Bordeaux Red Interior
- First time Porsche Owner
User avatar
Nuclear Nick
Posts: 3814
Joined: Wed Feb 17, 2016 3:42 pm
Location: Bristol

Post by Nuclear Nick »

PorscheMack wrote: Tue Jan 25, 2022 10:37 am I'm surprised how owners experiencing this are so relaxed 🤔 Owners on the GLC forum were spitting features which went someway towards MB taking the condition seriously and applying appropriate action.
By all accounts the MB issue was very much worse and justifiably owners demanded a fix as it was clearly a design flaw. The Macan doesn’t suffer the effect anything like as bad and many owners don’t ever experience it. It’s worse on my 911 especially as I don’t use winter tyres on it as I did on the Macan. But designing out the effect would deaden the steering and spoil the ability to precisely point the car and get the desired feedback in the bends.
Nick

Defender 90 V8

991.2 C2 GTS

Macan Turbo - sold

BMW K1300S, BMW R1250 GSA
PorscheMack
Posts: 1701
Joined: Mon Jul 12, 2021 3:46 pm

Post by PorscheMack »

Nuclear Nick wrote: Tue Jan 25, 2022 5:08 pm
PorscheMack wrote: Tue Jan 25, 2022 10:37 am I'm surprised how owners experiencing this are so relaxed 🤔 Owners on the GLC forum were spitting features which went someway towards MB taking the condition seriously and applying appropriate action.
By all accounts the MB issue was very much worse and justifiably owners demanded a fix as it was clearly a design flaw. The Macan doesn’t suffer the effect anything like as bad and many owners don’t ever experience it. It’s worse on my 911 especially as I don’t use winter tyres on it as I did on the Macan. But designing out the effect would deaden the steering and spoil the ability to precisely point the car and get the desired feedback in the bends.
Let's hope so :D
Macan GTS (Gen 3) (Mar 24-???)
http://www.porsche-code.com/PRKIVM50
Macan GTS (Gen 3) (Mar 22-Nov 23)
http://www.porsche-code.com/PNIECDM4
TheTraveller
Posts: 621
Joined: Fri Nov 02, 2018 9:30 pm
Location: South Yorkshire

Post by TheTraveller »

SAC1 wrote: Tue Jan 25, 2022 10:05 am
TheTraveller wrote: Tue Jan 25, 2022 7:46 am Years ago, some will remember that most cars had cross ply tyres. Which were much thinner than radials, and were an all round tyre, OK for general driving, when vehicles had no where near the speed and performance they have now. And they were better in winter to cope with snow we used to have, in the UK.
In those days those crossply tyres generally had a narower tread width dimension to the height of the sidewall - most were 80 series. The weight of the car pressing down on the stiffer sidewalls helped "cut" through the snow and good steering precision. Wheelspin was less because of the [generally] lower power and torque of the engine in comparison to todays cars. Even so, the essential users still relied on crossply "Town & Country" or "Mud & Snow" tyres for mobility in harsh winter conditions. Separate sets of winter wheels were unheard of though! with the O.E. steel "summer" wheels still used.

As an example a SWB 90 Land Rover had 6.00 x16 crossply tyres, or 152 mm wide, compared to a 20" shod Macan with 295 section rear tyres - nearly twice as wide

The Ackermann Effect is more pronounced with the ultra-wide, ultra-low profile modern summer tyres as they generally have continuous tread ribs with little lateral give on low speed full lock turning. All Season and Winter tyres have broken tread ribs with individual tread blocks. This enables the tyre to shuffle / squirm more on low speed turns and reduces the drag / pull effect. So have a less pronounced feel and noise at the steering wheel compared to summer pattern tyres.
You mention the early Land Rover. They had their own anomaly to deal with. The 4wd diff lock should not be engaged, in roads that didn’t have a slippyness too them, eg, rain, snow or muddy fields. Because there was no give in the tyres, they could suffer transmission wind up. Where much tension is created throughout the system, and could in extreme cases damage it or snap a drive shaft. This effect could be noticed, by jacking the vehicle up on one corner, and as soon as the wheel left the ground it would spin, thereby releasing the wind up from the system.
But all the electronic systems built into the complex transmission nowadays, eleviates this phenomenon.
Post Reply

  • Similar Topics
    Replies
    Views
    Last post