981 tyres scrubbing when turning
Discussion
Its a combination of the ackerman principle which puts the wheels at significantly different angles,
Plus the current huge tyre widths ie there is more tyre surface to drag and skip,
Plus the ultra low profile which all but removes any flex in the tyre wall to compensate.
The only fix I can see is some sort of steering rack that adjusts toe dependant on vehicle speed.
Plus the current huge tyre widths ie there is more tyre surface to drag and skip,
Plus the ultra low profile which all but removes any flex in the tyre wall to compensate.
The only fix I can see is some sort of steering rack that adjusts toe dependant on vehicle speed.
As above but also it's rear wheel drive, the front wheels turn/change direction and they simple hop as they are dragged. Always noticeable when it's cold. I bought my wife a Z3, then an mx5, SLK and they all did it. Nothing to worry about its all physics and a rear wheel drive thing.
ro55a said:
As above but also it's rear wheel drive, the front wheels turn/change direction and they simple hop as they are dragged. Always noticeable when it's cold. I bought my wife a Z3, then an mx5, SLK and they all did it. Nothing to worry about its all physics and a rear wheel drive thing.
I cant really see how rear wheel drive makes any difference? This happens at very low speed and has nothing to do with torque.Please explain.
Yes, I always experience this problem when reversing, as the front wheels change direction and the rears maintain reverse drive they simply drag the fronts when on full or partial lock. When cold, the tyres then tend to hop, hence the noise/vibration. I get this most mornings when reversing off of the drive way.
Ozzie Osmond said:
Mid-engined car, wide track, fat tyres. Yes, my car does it but I really don't see anything to make a fuss about. It's a sports car not a Lexus hybrid waft-o-matic.
The rubbish electric parking brake is IMO a much bigger problem because it interferes with driving the car.
Ozzie, agreed, the tyre problem is annoying but not totally inadmissible on a mid engined sports car. However, the SOLE PURPOSE of ANY parking brake is to interfere with the driving of the car????? Personally I find the electronic brake not much of a problem. Granted the on/off direction is probably not intuitive and the reverse of what it should be but it works well enough when you get used to it. The hill hold is just perfect, I cannot see what the problem is. Apart from a reluctance to move forward that is.... The rubbish electric parking brake is IMO a much bigger problem because it interferes with driving the car.
Edited by jredram on Monday 23 December 01:48
griffter said:
Isn't this down to the LSD (where fitted)?
You are right to suggest that an LSD tends to keep pushing a car in a straight line. However, it's not that which causes this particular effect. Just steering geometry, wide tyres and mid-engine layout.http://en.wikipedia.org/wiki/Ackermann_steering_ge...
In a nutshell, the car is set up for good turn-in and grip with modest steering inputs and at high speeds. The trade-off is a bit of scrabbling in the car park!
mollytherocker said:
I cant really see how rear wheel drive makes any difference? This happens at very low speed and has nothing to do with torque.
Please explain.
Rear wheel drive related I think in the sense the rear wheels of these cars are more heavily loaded with the front wheels less heavily loaded. Thus the front tires being less loaded allows the inside tire in a sharp slow speed turn to skip/scrub some.Please explain.
My front wheel drive VW Golf never did this but of course it had nearly 60% of its weight on the front tires and the steering geometry was guite different with not nearly as much caster. Also, the amount of turn in was limited compared to the Boxster. This is a "weakness" of front wheel drive cars that generally they cannot turn as sharp as cars with no front drive feature.
Other rear wheel drive cars didn't do this either though, but they all had the engine at the front and the most balanced of the cars still had 50% of its weight over the front wheels.
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.
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. Seems to be a common problem with 981 cars
My CGTS skips quite badly on full lock when pulling off from a parking slot
It is related to the wheel size - I changed my 20" wheels for a 18" winter set this week. Now the car manoeuvres with no scrubbing or skipping of the tyres at any steering position
My CGTS skips quite badly on full lock when pulling off from a parking slot
It is related to the wheel size - I changed my 20" wheels for a 18" winter set this week. Now the car manoeuvres with no scrubbing or skipping of the tyres at any steering position
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