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-   -   Wholly acorns and front end shutter! (https://rennlist.com/forums/991/1123493-wholly-acorns-and-front-end-shutter.html)

LexVan 01-11-2019 02:20 PM


Originally Posted by adcampo
In follow up to LexVan. I'm at 32F/39R cold temp in the TPMS gauge.

If you must drive a little, I'd go 36/40. The acorn effect will be less noticeable, but it won't go away completely. Overall traction will still be greatly reduced below 40 degrees. And stay out of Sport and Sport Plus so you get more and faster PSM engagement. It's a little safer.

adcampo 01-11-2019 02:49 PM

Thanks all. I'm going to be tucking her away for winter soon enough. Got some plans to polish the paint, ceramic coat the wheels and some other little projects to keep me entertained until spring.

K9PJ/4 01-11-2019 03:34 PM


Originally Posted by AlBinVA (Post 15558592)
Timely thread.

I too was out at 8:00 this AM in RVA. Ambient temp at 28. No way around it, had doctor appt I had to go to. Driving on P0's with 14k miles so tread is not fresh on rears. I was very apprehensive but put myself in a position where I did not make sharp turns, heavy acceleration or quick braking. I have experienced cold weather issues before, but today was just fine. It's not something I do as common practice but beats having to keep another set of rubber on hand for the few times I encounter these temps. It is my DD but being retired means I can pick and choose my outings for the most part.

Thanks AIBinVA. Friends and the mountain roads are calling, we will be moving
back to your area soon. I would send a PM, but haven't figured out how to do that.

vitman 01-11-2019 04:14 PM

No Acorn effect here in Fort Lauderdale despite very cold temps even dipping into the 60s. Brrrrr!
Thank goodness for the seat heaters and heated steering wheel.

K9PJ/4 01-11-2019 04:34 PM


Originally Posted by vitman (Post 15558927)
No Acorn effect here in Fort Lauderdale despite very cold temps even dipping into the 60s. Brrrrr!
Thank goodness for the seat heaters and heated steering wheel.

47 degrees in WCF. That is enough to leave our 911S RAS in the barn!

AlBinVA 01-11-2019 08:23 PM


Originally Posted by K9PJ/4 (Post 15558825)
Thanks AIBinVA. Friends and the mountain roads are calling, we will be moving
back to your area soon. I would send a PM, but haven't figured out how to do that.

Click on my user name for drop down menu

Cuda911 01-12-2019 03:49 AM


Originally Posted by K9PJ/4 (Post 15558582)
Is this thread directly related to the shudder I experience? My experience is when backing it sounds/feels like I am driving over a series of 4" diameter logs.
The first time it occurred I stopped, and examined the street for debris and the suspension for damage. Driving forward and avoiding sharp turns it would go
away, time depending on temperature.

The first occurrence was with a 2014 Boxster (Virginia)
The next car a 2016 base 911 was a little worse (Virginia)
Now we have a 2017 911S with RAS is the worst (even here in Florida on 50 degree days)

All with Pirelli rubber.

Our '14 Cayman does that. Still freaks me out when I back up. It'a CPO, so I took it in quite a few times to have the dealer check. Normal. It' the LSD. And yes, tires can make a difference. Same tires are on my 991, but none of that clunking.

evilfij 01-12-2019 04:29 AM

Was 23 degrees this am. No issues.

jnolan 01-12-2019 01:38 PM


Originally Posted by adcampo (Post 15558038)
Finally, the P Zero's are worth absolutely ZERO in freezing temperatures. Even after the doing some driving. My aggressive driving confidence on a cold day is pretty pretty low. I can imagine that thing calling some unexpected hot shoe out.

I would fault Pirelli (and all the other mfgers) were it not for the fact that they actually tell you not to drive these tires in cold weather. They also warn that at low temperatures the rubber compound can become so hard that it is brittle and will crack.


digits 01-12-2019 01:53 PM

Please, please, don't drive on your summer rubber when it's below freezing. Summer tires don't like the cold. Driving on them, or even flexing them, after they've been at cold temperatures 1) isn't safe 2) can damage the tires.

Tire rack says avoid letting them get below 20F even when stored and if you do then definitely don't drive on them until they've been warmed.

https://www.tirerack.com/tires/tiret...jsp?techid=220
https://www.tirerack.com/tires/tiret...jsp?techid=273

An NHTSA bulletin tells the same story; although it looks like GM took the bulk of the heat, it's all the same rubber:

"Advise customers of these vehicles that they are equipped with a high performance summer-only tire that will have reduced traction performance at temperatures below approximately 40F (5C). GM recommends installing winter tires if driving below these temperatures. Avoid driving, moving, or test-driving vehicles equipped with high performance summer-only tires below 20F (−7C), as operating at these temperatures can cause damage to the tires."

Source: https://static.nhtsa.gov/odi/tsbs/20...82862-5448.pdf

What does Pirelli say? Well - I had a hard time finding any clear statements from from Pirelli for a particular tire or compound - no surprise there given that I assume they employ lawyers. Maybe someone else found some obvious statement that I missed.

But, if you look at the language in their warranty they slipped up (leave it to the lawyers from one part of the company to look out for themselves) because Pirelli put this language in there:

3. UHP Summer Tires
"Rubber compounds formulated for ultra-high performance summer tires can lose flexibility and may develop random surface cracks at temperatures below 45F. Therefore, extra care should be used in handling tires below this temperature. These compounds are optimized for maximum dry and wet performance in warm conditions. Special tread compounds in these tires will have decreased performance, such as lateral and braking traction, at temperatures below 45F or when driving on snow or ice. Therefore, it is recommended to install winter tires in these conditions."

Source: https://www.pirelli.com/mediaObject/...y_Brochure.pdf

Be safe everyone.

K9PJ/4 01-12-2019 02:26 PM

There was something published by PCA, PCNA or another semi-reliable source a couple years ago indicating that the caster settings
are responsible, and that Pirelli exacerbates the condition. Have not seen anything more recent to validate this info.
I should print more and rely less on on cloud sources.

LuftKopf 01-12-2019 02:47 PM


Originally Posted by adcampo (Post 15558038)
I know the acorn effect is a well documented issue. And extremely alarming if you don't know about it.

It's a really cold ( 20's) and sunny day in the DC area today, but I decided to take my 991. in for a hand wash at my local place. I pulled out of the garage and that front end shuttered and crunched like nobody's business. I can't imagine what it looks and sounds like from the outside.

And I realized it takes a good 15-20 minutes of light/moderate driving before the oil/water temps come up. On the other hand, the heated seats take only 2-3 which is nice. I also noticed that the shifting is much slower in all modes when the car is cold. I'm sure that's some cleaver German engineering.

Finally, the P Zero's are worth absolutely ZERO in freezing temperatures. Even after the doing some driving. My aggressive driving confidence on a cold day is pretty pretty low. I can imagine that thing calling some unexpected hot shoe out.

I have Michelin A/S3+s on two street cars. Excellent grip year round (never drive on snow & ice). Huge fan. (Track car has RE-71rs).

Wujohn 01-12-2019 04:51 PM

When I turn my wheels all the way (u turn or parking situation - low speed) I get what sounds like the acorn effect. It feels as if my car is hopping; very disturbing feedback on the steering wheel. Is that normal? Not weather related as I am in SoCal.

Bob Z. 01-12-2019 05:24 PM


Originally Posted by Wujohn (Post 15561152)
When I turn my wheels all the way (u turn or parking situation - low speed) I get what sounds like the acorn effect. It feels as if my car is hopping; very disturbing feedback on the steering wheel. Is that normal? Not weather related as I am in SoCal.

Normal, happens to me as well.

Wujohn 01-12-2019 05:36 PM


Originally Posted by Bob Z. (Post 15561210)
Normal, happens to me as well.

Thanks Bob.


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