I know I’ve read about this before, but I couldn’t find it using the search feature.

I’ve had 8 water cooled 911’s and most of them have done it, but now I’d like to know what actually causes it because my new to me 991.2 does it worse than any of the other Porsches I’ve owned.

It’s worst when the car is cold. An example is where the car has been in the garage overnight and when I pull out and make the sharp left turn (right is the same), it feels like I’m driving over some fairly large rocks. There is also a crunching sound audible inside and outside the car.

I don’t think it’s hurting anything, but it’s bad enough that I know I’ll have to explain what’s going on frequently, so can you guys help me feel smart when I’m asked?

 

Search "Ackerman" effect

 

^what he said. Skinnier and less grippy front tires exacerbates the effect. Cold weather exacerbates the effect. Wider stickier tires mitigate or eliminate the effect (not my goal in putting on sticky tires, but it's true).

 

I had a 991.1 S, and definitely notice the unpleasant Ackerman induced grinding noise on the hard turn coming up my driveway. Sold that 2 years ago and now have a 991.2 Carrera GTS. With this car I have not heard the noise. Fine with me: I hated that noise.

"The Ackerman causes the front wheels to turn through different angles whenever the steering wheel is turned from the straight ahead position."

 

Thanks for posting this, my 991s does that too...

 

Well then… tires it is!

Thank you for the responses peeps.

 

Pirellis?

 

The sound is most common when running summer performance tires in cold temps. Summer rubber compounds that are sticky when warm are like bricks when cold. The noise is a symptom of how little grip you have running summer tires on cold pavement. Change to UHP all seasons or winter tires in temps below 50ºF, and your noise will go away.

 

this is one of three reasons why I store my car in the winter: road salt is everywhere, other idiot drivers who can't drive in the snow/ice and rock hard tires with no grip.

 

It's why I put proper tires mine so I can enjoy it year-round. Winter garage queens are a waste.

I do avoid snow and ice, but the number of days that's a factor in my climate in the average year is less than 10 or so. Moreover, if I get caught out in an unexpected dump, I can get home in confidence.