Rennteam 2.0 - EN - Forum - Re: Suspension problem? - Page1

Nov 21, 2013 11:59:45 AM

993Targa: Rennteam Pro; Loc: ZH , Switzerland; Posts: 2522, Gallery; Registered on: Sep 16, 2004

Suspension problem?

I noticed something recently, that wasn't there before. When I make a very sharp turn at low speeds, for example backing out of a garage, I feel some light shocks. Similar like a flat tire on the right front side. Obviously checked tire pressure, but that is fine.

Also driving up a steep hill (normal road), I feel some light shocks, like the tires are slipping. Had it with the wide (295) summer wheels, but also, after changing yesterday, with the 275 winter wheels. At higher speeds I don't feel anything strange. Any idea what it can be?

I will make an appointment with the dealer in any case, just want to see if you guys have an idea?

--

2012 Cayenne S White/Espresso

Ex: 993 Targa, 986S, 986 and 964 C2

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Nov 21, 2013 1:13:58 PM

GR: Senior; Loc: S Bucks, England , United Kingdom; Posts: 779, Gallery; Registered on: May 17, 2005; Reply to: 993Targa

Re: Suspension problem?

I would suggest that its the tread blocks on summer tyres in cold conditions. They go very stiff and behave like this when put under high load at slow speed. Winter rubber being softer just flexes (like the summer tyre in warm conditions).

--

Gen II Cayman S

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Nov 21, 2013 1:21:24 PM

993Targa: Rennteam Pro; Loc: ZH , Switzerland; Posts: 2522, Gallery; Registered on: Sep 16, 2004; Reply to: GR

Re: Suspension problem?

Could be it. I will try it and make the same manoeuver with warm(er) tires. kiss

--

2012 Cayenne S White/Espresso

Ex: 993 Targa, 986S, 986 and 964 C2

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Nov 21, 2013 1:33:54 PM

RC: Rennteam Administrator; Loc: Rennteam HQ , Germany; Posts: 59579, Gallery; Registered on: Mar 26, 2002; Reply to: 993Targa

Re: Suspension problem?

Does your Cayenne have air suspension? Dealer should check on it.

--

RC (Germany) - Rennteam Editor Porsche 991 Turbo S, Cayenne GTS (958), BMW X3 35d (2013)

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Nov 21, 2013 1:38:17 PM

993Targa: Rennteam Pro; Loc: ZH , Switzerland; Posts: 2522, Gallery; Registered on: Sep 16, 2004; Reply to: RC

Re: Suspension problem?

No it doesn't. The tires kind of make sense because it started when it got colder. The front tires are very wide, so turning very sharp it explains it. I only switched to my winter wheels yesterday..

--

2012 Cayenne S White/Espresso

Ex: 993 Targa, 986S, 986 and 964 C2

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Nov 21, 2013 1:58:00 PM

RC: Rennteam Administrator; Loc: Rennteam HQ , Germany; Posts: 59579, Gallery; Registered on: Mar 26, 2002; Reply to: 993Targa

Re: Suspension problem?

993Targa:

No it doesn't. The tires kind of make sense because it started when it got colder. The front tires are very wide, so turning very sharp it explains it. I only switched to my winter wheels yesterday..

I didn't feel any difference (I have 21'' summer wheels and 19'' winter wheels) but I exchanged my wheels a couple of weeks ago when it was warmer, so maybe I didn't notice.

--

RC (Germany) - Rennteam Editor Porsche 991 Turbo S, Cayenne GTS (958), BMW X3 35d (2013)

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Nov 21, 2013 3:14:54 PM

GR: Senior; Loc: S Bucks, England , United Kingdom; Posts: 779, Gallery; Registered on: May 17, 2005; Reply to: RC

Re: Suspension problem?

All my Porsches have done this from the 986 on. It feels like the outer tread block is too stiff to flex so its suddenly slips to keep alignment with the wheel. Then the next tread block repeats it so it feels like a juddering in the steering. Like 993Targa, I have only really noticed it when manoeuvring on large lock and the car is very cold.

Its nothing to worry about and it goes away if the tyres warm up.

--

Gen II Cayman S

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Nov 21, 2013 3:34:23 PM

sfo: Rennteam Pro; Loc: London , United Kingdom; Posts: 2093, Gallery; Registered on: Aug 17, 2011; Reply to: GR

Re: Suspension problem?

isn't this the ackerman effect or some such?

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Nov 21, 2013 4:33:23 PM

bridggar: Veteran; Loc: UK , United Kingdom; Posts: 1223, Gallery; Registered on: May 25, 2007; Reply to: sfo

Re: Suspension problem?

Agree with GR on this - my 991 skips when cold! (my Volvo did it with Pirelli tyres also)

--

991 (what a car!) XC90 - Black/Black 2 kids, 1 dog

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Nov 21, 2013 5:11:54 PM

GR: Senior; Loc: S Bucks, England , United Kingdom; Posts: 779, Gallery; Registered on: May 17, 2005; Reply to: bridggar

Re: Suspension problem?

Ackerman is a simple geometric solution to having a fixed rear axle and maintaining the front wheels on their respective radii. I wasn't aware of any affect yes

--

Gen II Cayman S

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Nov 21, 2013 6:52:29 PM

fritz: Rennteam VIP; Loc: BaWü , Germany; Posts: 10248, Gallery; Registered on: Jul 23, 2003; Reply to: GR

Re: Suspension problem?

GR:
Ackerman is a simple geometric solution to having a fixed rear axle and maintaining the front wheels on their respective radii. I wasn't aware of any affect

That's right. The Ackermann geometry was originally intended to counter a tendency in early 4-wheel horse-drawn carriages to force the steering wheels to scrub over the road surface when taking a corner by allowing the outer front wheel to describe a larger radius than the inner one. This geometry would have reduced the resistance that the horse(s) had to overcome, and the system was carried over into motor vehicles when they were introduced almost a century later.
The increased tendency to this scrubbing noise in modern cars will be due neither to the Ackermann geometry nor a lack of it, but to there being no way of allowing the outer parts of current very wide tyre contact patches from describing a larger turning radius than the inner part of the same patch without slippage between the tyre and road surfaces. This slippage between sticky tyres and high-friction road surfaces (particularly in parking garages) generates the noise you hear.

--

fritz

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Nov 22, 2013 4:43:47 PM

John H: Rennteam VIP; Loc: Cheshire, UK , United Kingdom; Posts: 7682, Gallery; Registered on: Oct 20, 2005; Reply to: fritz

Re: Suspension problem?

+1

Sometimes called "scrabbling"...

Normal on full lock due to the greatest difference in turning radii between inner and outer wheels and the camber induced.

Exacerbated in cold weather due to harder rubber...

--

"Things turn out best for people who make the best of the way things turn out."

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Nov 22, 2013 8:26:15 PM

KMM: Expert; Loc: Boston, MA , United States; Posts: 1745, Gallery; Registered on: Feb 5, 2004; Reply to: sfo

Re: Suspension problem?

sfo:

isn't this the ackerman effect or some such?

I think this is the result of not enough Ackerman correction at full lock.

The question is, why does it do it when in reverse, and not going forward (in my experience).

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Nov 22, 2013 9:18:46 PM

GR: Senior; Loc: S Bucks, England , United Kingdom; Posts: 779, Gallery; Registered on: May 17, 2005; Reply to: KMM

Re: Suspension problem?

Don't know about you but I reverse out of my drive slowly on full lock but then take lock off quite quickly when accelerating away. With castor/camber angles, this will take much load off the outside edge off the inner wheel and therefore the scrabbling won't be noticeable. I was taught that Ackerman doesn't take into account camber or castor as its just a geometric solution in plan view

--

Gen II Cayman S

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Nov 22, 2013 10:40:02 PM

fritz: Rennteam VIP; Loc: BaWü , Germany; Posts: 10248, Gallery; Registered on: Jul 23, 2003; Reply to: GR

Re: Suspension problem?

GR:

Don't know about you but I reverse out of my drive slowly on full lock but then take lock off quite quickly when accelerating away. With castor/camber angles, this will take much load off the outside edge off the inner wheel and therefore the scrabbling won't be noticeable. I was taught that Ackerman doesn't take into account camber or castor as its just a geometric solution in plan view

That's right. When the so-called Ackermann system was patented, no-one had yet come up with the concepts of camber angles or castor angles. Smiley

I say "so-called Ackermann system" because that was not in fact the name of the inventor. Ackermann was a German merchant living in Britain in the early 19th century who patented the invention there on behalf of a friend, a coach builder (in the original sense of the name) who ran a business in what is now southern Germany.

--

fritz

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Nov 27, 2013 7:58:12 AM

993Targa: Rennteam Pro; Loc: ZH , Switzerland; Posts: 2522, Gallery; Registered on: Sep 16, 2004; Reply to: fritz

Re: Suspension problem?

So the "problem" disapeared when I changed to the wintertires and the smaller (20") wheels. I think it was a combination of the colder temperature, the end of the lifecycle of my wide (295) summer tires (4mm) and the rough surface. Thanks for your input! kiss

--

2012 Cayenne S White/Espresso

Ex: 993 Targa, 986S, 986 and 964 C2

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Feb 4, 2014 2:17:40 PM

993Targa: Rennteam Pro; Loc: ZH , Switzerland; Posts: 2522, Gallery; Registered on: Sep 16, 2004; Reply to: 993Targa

Re: Suspension problem?

Unfortunately the problem surfaced again. Brought the car to my dealer and they kept it for two days but weren't able to fix/locate the problem. They are now in contact with Porsche directly.

Luckily I have the extended 2 years warranty. For me it's not too much hasle, I drop the car off at my commute and get a loaner (981 or 991). But I'm curios what exactly the issue is...

--

2012 Cayenne S White/Espresso

Ex: 993 Targa, 986S, 986 and 964 C2

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