Juddering tyres when slow speed turning
- Thread starter Chris89
- Start date
Typical of the car when fitted with summer tyres at temperatures below 15°C. Pirelli P-Zeros are a bit noisier than Michelins, but all summer tyres will do it when cold. Winter tyres don’t do it. The phenomenon (often, but I believe wrongly, called the Ackerman effect) is mentioned in your handbook or Porsche’s Good To Know app. It‘s annoying, but it will go away when the weather is warmer.
Happens on all cars with wide tyres. The Ackermann effect describes where the inner wheel in a turn describes a smaller radius than the outer. If you imagine a tyre on a full lock, and a number of lines on the circumference from inner to outer, the sections of tyre travel a different distance during the turn. Something has to give and the tread blocks slip/judder to compensate which, as mentioned above, is more noticeable when the rubber is cold and less flexible. That's my understanding anyway
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All above correct, and not just Porsches, AUDI TT etc all can show this at low speed, low temp.
Get a bit of surface undulation like reversing out of a driveway and it can be more pronounced.
Enjoy your car!
Get a bit of surface undulation like reversing out of a driveway and it can be more pronounced.
Enjoy your car!
Oddly enough Ackerman was the lawyer who submitted the patent and not the inventor of the principle devised in the early C19th for articulated horse-drawn carriages … when vehicle wheels were somewhat thinner than they are today! It relies upon the instantaneous centre of radius of each front wheel being coincident at a point on the rear axle axis, and therefore preventing wheel slip.
I doubt that you’ll find any modern vehicle which uses pure Ackerman geometry which means that there is a conflict between the geometry of the front wheels - particularly for large steering inputs - which when combined with wide-section tyres and harder summer tyre compounds causes the tyres to skip across the road surface. It’s quite pronounced on my P-Zero shod 987.2CS but I seem to recall reports that the PS4/PS4S is less prone to the phenomenon.
I wish I had £1 for every time this subject has been raised on the forum when temperatures head below zero!
Jeff
I doubt that you’ll find any modern vehicle which uses pure Ackerman geometry which means that there is a conflict between the geometry of the front wheels - particularly for large steering inputs - which when combined with wide-section tyres and harder summer tyre compounds causes the tyres to skip across the road surface. It’s quite pronounced on my P-Zero shod 987.2CS but I seem to recall reports that the PS4/PS4S is less prone to the phenomenon.
I wish I had £1 for every time this subject has been raised on the forum when temperatures head below zero!
Jeff
my understanding is that the problem is not so much due to the outside and inside wheels taking a different path, which is what Ackerman steering geometry seeks to address, but that with a wide tyre turning a tight circle the side of the tyre on the inside of the curve takes a shorter path than the outside of the tyre. This results in the rubber tread blocks having to distort and then slide. When they are nice and warm, they distort more easily and so slide quietly, but when cold and hard they skip and jump noisily. The road surface will make a difference too.
Sadly I can confirm that the PS4S do it as well. It sounds terrible however, the Ackerman effect is horrendous on a Merc GLC. Its well noted in the Merc world (and I have personal experience) with the manufacturer issuing a fix of new steering knuckles. Needless to say this doesn't rectify the clonking. Merc also did a TB on replacing summer tyres for all seasons FOC!
The only inconvenience is you look a bit of a plonker when everyone looks round to see what the horrible noise is
Dan
The only inconvenience is you look a bit of a plonker when everyone looks round to see what the horrible noise is
Dan
Never had it with Cup2 tyres. Tread blocks not so deep and larger/fewer.
tscaptain said:Mmm...perfect for those wet, winter days[ralphmusic said:
They are OK, really..
Tetris Keyring
PCGB Member
I remember the first time i had it. Thought I’d hit something or something had broken. Just accept it as part of the Porsche experience ;-)Chris89 said:
Wollemi said:
Graham,
I‘ve seen this explanation before and whilst I don’t deny in principle that may well be occurring I think the dynamics of the situation are far more complex.
Consider an idealised situation in which each wheel remained vertical, a smooth tyre surface which was absolutely flat and Ackerman geometry being maintained for any lock. If you think of the tyre width as being made up of an infinite number of infinitely thin bands each with the same centre of rotation, there would (I think!) only be tangential motion of each band and no lateral motion.Throw-in the fact that Ackerman geometry isn’t maintained and that wheel camber, toe-in and castor, suspension mount flexibility, tyre profile, asymmetric tread patterns, block shape and flexibility and sometimes different compounds across the tread width also will be at play and it’s easy to see that the dynamics of the steering wheels are highly complex … to say the least! And on top of that there are also outside air temperature effects on the tyre compound to take into account. [
]To me the upshot of all this is that each front wheel is fighting to follow its own path with the inevitable conflicts occurring at the tyre contact patches and - as you say - the tyre blocks flex and each wheel scrabbles for grip.
Just my tuppence-worth of course, and likely to be a load of old codswallop!
Jeff
Jeff,
Your very comprehensive analysis of the many factors contributing to the by now well known Porsche front wheel juddering on tight lock at slow speeds, is in my opinion certainly not codswallop.
All of my 5 Caymans suffered this to a lesser or greater extent dependent upon tyre choice, steering geometry, and ambient temperatures. So far in my experience with my Alpine A110, no such juddering is evident. Whether this is down to the relatively narrow section tyres, or the double wishbone suspension, I am not technically qualified to comment upon. Soon I shall be fitting wider section wheels with Michelin Cup 2 tyres. I shall be interested to see if this changes the current absence of juddering on tight steering locks.
Brian
Your very comprehensive analysis of the many factors contributing to the by now well known Porsche front wheel juddering on tight lock at slow speeds, is in my opinion certainly not codswallop.
All of my 5 Caymans suffered this to a lesser or greater extent dependent upon tyre choice, steering geometry, and ambient temperatures. So far in my experience with my Alpine A110, no such juddering is evident. Whether this is down to the relatively narrow section tyres, or the double wishbone suspension, I am not technically qualified to comment upon. Soon I shall be fitting wider section wheels with Michelin Cup 2 tyres. I shall be interested to see if this changes the current absence of juddering on tight steering locks.
Brian
Your supportive comments are much appreciated Brian. I think that it’s fair to say that the narrower the tyre section and the closer the steering geometry is to Ackerman on tight lock - and therefore avoiding conflicting arcs of movement of the front wheels - the greater the chance of avoiding the phenomenon. I’m sure that these are factors which are contributing to the fact that you’re not experiencing the problem on your Alpine and as you say it will be interesting to see if this is still the case when you fit the wider section wheels, although I suspect that you’ll notice very little or no difference.
Quite clearly the juddering isn’t restricted to Porsches, as Dan has noted, with Mercedes offering customers all season replacements for their summer tyres as a means of overcoming the problem, which implies that there were a significant number of complaints from owners.
Thankfully it’s just a temporary annoyance for us Cayman owners at this time of the year … even if we do like to complain about it annually!
Jeff
Quite clearly the juddering isn’t restricted to Porsches, as Dan has noted, with Mercedes offering customers all season replacements for their summer tyres as a means of overcoming the problem, which implies that there were a significant number of complaints from owners.
Thankfully it’s just a temporary annoyance for us Cayman owners at this time of the year … even if we do like to complain about it annually!
Jeff
Briggy
PCGB Member
New tyres will help, but the cause will still be there. You hear of people changing brands and blaming the original because it's gone away. The treads on new tyres are deeper, so will bend and flex more easily, rather than skip. Think of how very short hair is difficult to flatten when you press it, whereas hair that's an inch long is much easier.
As others have said, it's caused by the inner edge of the tyre following a different turning circle circumference (and hence distance) than the outer edge of the tyre. If you had a solid axle at the rear, the inner wheel would slip as you went round a bend, which is why differentials were invented. It's perfectly normal, especially with wide wheels.
As others have said, it's caused by the inner edge of the tyre following a different turning circle circumference (and hence distance) than the outer edge of the tyre. If you had a solid axle at the rear, the inner wheel would slip as you went round a bend, which is why differentials were invented. It's perfectly normal, especially with wide wheels.
I have it on my 2007 Cayman S and my BMW one series which has quite wide low profile tyres. I notice it only when reversing and turning out of my driveway on full lock.... not any other time. when I changed tyres on the Beemer to another brand it disappeared, maybe due to deeper tread or a change in temperature. I've never thought of it a juddering more ,like suspension wear 'event'
Eddie
2007 987 Cayman S
1987 944 Turbo
Eddie
2007 987 Cayman S
1987 944 Turbo
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