981 tyres scrubbing when turning
Discussion
My 981 does it too - but I'm not convinced it's steering geometry related. In my case it's nothing like the tyre scrub you get in a Lotus Esprit, for example. It's much more like the sort of locking you get with an LSD - but since I haven't got PTV it can't be that either. I'm inclined to think it's more likely to be PSM related - getting it's knickers in a twist first thing and applying one or other of the brakes - I haven't tried turning PSM off and seeing if that makes a difference, so I must remember to try that. If it really was Ackerman related I'd expect it occur when the car was warm and it doesn't.
Possibly related is the abysmal traction I get on our (uphill) gravel drive - again when you first switch on. Driving out forwards I wouldn't expect problems but it tries to light up the wheels however gently I try to pull away (PSM on or off). It's been no real problem with any of the other cars we,ve had.
Possibly related is the abysmal traction I get on our (uphill) gravel drive - again when you first switch on. Driving out forwards I wouldn't expect problems but it tries to light up the wheels however gently I try to pull away (PSM on or off). It's been no real problem with any of the other cars we,ve had.
Used to get this on my Tuscan's and the Sagaris but only when it was cold. I was told it was due to the geo on the cars that the tread blocks on the edge of the tyre skip when on full lock. When its warm you dont notice because they deform to suit but when the tyre is cold and the compound is hard you can basically feel it moving from tread block to tread block.
Might have been utter b**locks but as it only ever happened in the cold I didn't worry. Also noticed that the swap to winter tyres with their different/ more malleable compound cured it which I suppose would back up the theory.
Might have been utter b**locks but as it only ever happened in the cold I didn't worry. Also noticed that the swap to winter tyres with their different/ more malleable compound cured it which I suppose would back up the theory.
I really don't think any of the evidence re 981 or 987 points strongly to steering geometry. If it were I would expect it to get worse not better once the tyres were warm and therefore more grippy. And certainly the feel of it on mine (19", but possibly a red herring) is nothing like any geometry induced scrub that I have experienced before - more a like digital on and off accompanied by a series of clonks. Hence my suspicion of PSM which does grab a brake if it "thinks" you are in trouble. In fact, come to think of it, the clonks are very like those I get when the (abortionate) handbrake does an automatic release.
taylor172 said:
Boxsters and Caymans do it mostly, Panameras also.
It is due to the Akermann angle of the wheels turning around a pivot point, The tyres skip along on their outer edge as the geometry is that to ensure sports car handling and turning characteristics.
It becomes particularly apparent in colder weather as the rubber in the tyres is less maluable and therefore has less natural movement in them to compensate for the stresses. If you fitted winter tyres the sensation would lessen.
It can be different from car to car, Wheel size, Tyre make, Size and even N ratings can effect it.
Perfectly normal, not dangerous and its even mentioned in your handbook
hope that helps.
A perfectly articulate answer posted one page back. Just goes to show that no one listens to a fIt is due to the Akermann angle of the wheels turning around a pivot point, The tyres skip along on their outer edge as the geometry is that to ensure sports car handling and turning characteristics.
It becomes particularly apparent in colder weather as the rubber in the tyres is less maluable and therefore has less natural movement in them to compensate for the stresses. If you fitted winter tyres the sensation would lessen.
It can be different from car to car, Wheel size, Tyre make, Size and even N ratings can effect it.
Perfectly normal, not dangerous and its even mentioned in your handbook
hope that helps. 
king thing on forums!!ro55a said:
A perfectly articulate answer posted one page back. Just goes to show that no one listens to a fking thing on forums!!
Carefully read prior to my posts - perfectly articulate - just not convinced it's right - leastways not on my car - for the perfectly articulate reasons I state, which YOU clearly didn't read. (And before you ask, yes I do know what Ackerman is all about, and why car manufacturers don't choose to use strict Ackerman geometry)king thing on forums!!Edited by bcr5784 on Friday 5th December 20:45
Edited by bcr5784 on Friday 5th December 20:48
anonymous said:
[redacted]
What has a 986 Boxer got to do with the price of fish? (or even a 987 for that matter - it's a different car which may, or may not, suffer from the same foibles) It also happens on a Triumph Herald and Lotus Esprit, which is similarly irrelevant. Explain the clonks on MY car instead of (as usual) making simplistic judgements. Do you actually even know the differences and similarities between the geometry of the front suspension of the various Cayman/Boxster models?I've heard poor Ackerman induced tyre scrub on a number of cars - mine simply does not sound like it.
bcr5784 said:
What has a 986 Boxer got to do with the price of fish? (or even a 987 for that matter - it's a different car which may, or may not, suffer from the same foibles) It also happens on a Triumph Herald and Lotus Esprit, which is similarly irrelevant. Explain the clonks on MY car instead of (as usual) making simplistic judgements. Do you actually even know the differences and similarities between the geometry of the front suspension of the various Cayman/Boxster models?
I've heard poor Ackerman induced tyre scrub on a number of cars - mine simply does not sound like it.
I must say, my 981 on 20"'s does scrub....but never clonk.I've heard poor Ackerman induced tyre scrub on a number of cars - mine simply does not sound like it.
My previous two 987's on 19"'s didn't do anything!!
Be interesting to have an explanation from some of those who have a greater knowledge (apparently) why the problem only seems to be mentioned once the weather turns colder and the compound on the tyres gets harder but those same tyres once warmed up from a run do not exhibit the same symptoms.
anonymous said:
[redacted]
That really is rich coming from someone who is profoundly deaf. Tyres do not clunk (they are made of rubber) - things made of metal do. And someone also said it happens in reverse - not impossible, but much less likely to be tyre scrub in reverse. And unless there are major differences in geometry of the various cars, why don't all cars suffer? Don't ignore facts that don't fit the theory.If its in the manual, why is it even being discussed?
This 981 on 20's is the worst for doing it, forwards or backwards, hot or cold, even compared to my GT3 on 19's, a previous C2S on 19's, an M3 on 18's and an Exige on castors - they all exhibited some form of it, although the M3 and GT3 also had an LSD lock up thing going on in reverse as well.
If anyone thinks their car (981) has a problem over and above what has already been mentioned on this thread, they had best make a nuisance (or eejit) of themselves at their dealers?
This 981 on 20's is the worst for doing it, forwards or backwards, hot or cold, even compared to my GT3 on 19's, a previous C2S on 19's, an M3 on 18's and an Exige on castors - they all exhibited some form of it, although the M3 and GT3 also had an LSD lock up thing going on in reverse as well.
If anyone thinks their car (981) has a problem over and above what has already been mentioned on this thread, they had best make a nuisance (or eejit) of themselves at their dealers?
Get someone else to drive the car in a circle while YOU watch; stand inside the circle, then outside: it will be obvious what is causing the effect and where the noise is coming from.
I would say the most important variables are:
Wheel size
Tyre manufacturer
Profile of tyre
Temperature
Surface
Steering angle
Speed
'It' is slow motion understeer.
I would say the most important variables are:
Wheel size
Tyre manufacturer
Profile of tyre
Temperature
Surface
Steering angle
Speed
'It' is slow motion understeer.
My 981 S does this in both directions. Standard wheels and tyres. Easiest way to demonstrate it is in a car park with a few loose chippings on the tarmac surface.
IMO the "noise" is made when the tyres jerk sideways due the substantially different radii which they are trying to steer while shackled together. This might be described as Ackerman effect causing the tyres to scrub sideways.
IMO the "noise" is made when the tyres jerk sideways due the substantially different radii which they are trying to steer while shackled together. This might be described as Ackerman effect causing the tyres to scrub sideways.
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