Tyre/Wheel Query

[Guest]

Wasn't sure how to title this one.

I've not had my 981 very long and I've never had a car with such wide low profile tyres. I notice that when using full steering lock at very low manoeuvring speeds, there is some feedback through the steering wheel. There is also a sort of grumbling noise and vibration from the tires. I assumed it was because of the nature of the wide tires, but thought I'd better get advice in case it's a problem.

It is only when travelling at parking type speeds and when using lots of steering lock. The tyres are Pirelli P Zeros 235/40/19 and 265/40/19.

[Highland Fling]

This is quite normal according to a similar enquiry I made to my OPC techie, when I owned my first Porsche Cayman way back in 2008.

 

A combination of castor angles, camber and toe geometry, and also PASM if fitted, all combine to create this low speed parking grumbling and slight steering wheel juddering.

 

Brian    

[Trickle]

Perfectly normal! Very common gripe. 

[DJMC]

Yes, I had this too on 981 with 20" and PZeros. Switching to Goodyear F1 A2 has improved the situation and I've not noticed it so far. But it may be more prevalent in winter, so we'll see...

[Guest]

Thanks guys. Doesn't bother me, just checking if I have a problem. This place is a great resource for such things.

[John Whalley]

Sorry to come rather late to this topic.  Recent 981 owner and even more recent to this Forum.  I think the full lock manoeuvring tyre jumping is most likely due to a lack of normal Ackermann steering geometry on Caymans, Boxters and 911 variants.  Others may know whether these cars are actually fitted with reverse Ackermann steering, parallel steering, or a limited Ackermann system.  The reason Porsche opt for their geometry must be to increase cornering speeds, a layout that is inevitably something of a compromise in parking manoeuvres.  All a matter of tyre loads and slip angles.  I suspect these cars need to be tracked to properly demonstrate the benefits.  

http://www.me.ua.edu/me364/PDF/Steering_Ackerman.pdf

[SpannerMan]

Always found this in my 986/996s, but not with my CR...oddly enough

 

[Windymiller]

Phew - I‘ve noticed that with my 987 too since ‘swapping places’ with wifey on the driveway, and now having to use full lock as soon as I’m off the drive to turn into the road. 

 

Had worried it was a steering rack issue, it was replaced by the previous owner, but no signs of leaks so just ignored it. Now I know not to worry at all, if it’s just another ‘quirk’ of Porsche’s. 

[Bushman]

mine does it too, scared the crap outa me the first time and spend many moments praying to the rubber gods under the wheelarches seeking answers. it got worse when i had wear and play in the track rod ends and outer coffin arm ball-joints. I'm told a lot of it is due to tyre tread block movement and creep, they grip the ground, distort, stretch and ping back, bouncing the carcass and causing tyre shudder.