Nugget

Yes, I am sure you are wrong.

Nugget

This is inaccurate. The ride height does not change at all when you adjust the PASM suspension settings or the Sport Chrono settings.

alexb76

Maybe he means that shock travel is less due to stiffer shocks?! Just saying...

No HTwo O

IIRC, a PASM car is 10mm lower than a non-PASM car. Maybe this is what he meant.

cyberay

FWIW I have found with different cars, Porsche included, that overinflation will result in wandering and increased sensitivity to cross winds due to reduced tire contact area. The area is reduced because the increased pressure pushes the center of the tire out. I've also found that the amount of overinflation needed to cause this wandering effect is not consistent across all cars. Just for the heck of it, try reducing the pressure somewhat and see whether there is a difference.

Tim_Allison

I installed Hankook Evos all the way around on my car this spring and had the car aligned at the local dealer. There's some good info about these tires on 911's on the Tire Rack site. Here's what I've experienced. The break-in is at least 500 miles; the tires are very sensitive to pressure - amen to the post above - adhere to Porsche's recommended pressures; and they do not inspire confidence at speed. The best thing I can say about them is that they are quiet. When the backs wear out, I'll replace all 4 with the Pilot Sports. I also learned a long time ago not to mix the N ratings on 911's.

bhvrdr

I wanted to tag onto this thread because I just had an interesting experience that relates.

The Background:
I bought my car with brand new v12 evo2 tires on it. I went into the deal thinking these tires would be junk and the first thing id replace but after driving the car for a few months I was shocked that it was hard to find anything not to like about them.

Fast forward 8k miles and the rear tires needed replacing. I also decided to have the alignment checked at Porsche in Palm Beach.

Its worth noting that prior to the alignment and new tires I set cold pressures to 39F/40R. The car had good handling and stability at high speed.

When I received the car back from Porsche and with the new rear tires on the tire pressures were set to 35F/43R. This is not surprising as it is technically in line with Porsche recommendations.

The Problem:
That said when I got the car back I have noticed it was somewhat scary to drive at speeds above 70mph and unsafe at speeds above 90mph. I encounter what almost feels like rear end tramlining or like the rear sidewalls are flexing after inputs. Switch a lane and the rear end oscillates one or two times before settling when it follows the front end over a lane. Try and drive straight and the rear end seems to move around a bit requiring steering corrections. I could envision if I didnt make a change right away and tried to take this car to a lap day it could easily turn into a tank slapping type situation.

The Troubleshooting:
FIrst I figured the brand new rear tires certainly needed a 100 miles or more of wear-in to get rid of the slipperiness from the production process. Tires are going to be a bit squirmy when new anyways. I put in 500 miles and performance did not improve appreciably.

So next I inspected the rear suspension and no signs of leaky shocks or bad bushings. I wasnt going to rule this out but I like to make sure I rule everything else out before I just start replacing a ton of expensive parts on a car that may or may not fix the issue.

So I decided to just go out in the garage and lay down behind the car and look at it for a minute or so. Start the thinking process. What I noticed is that the rear tires are getting more center tire use and the fronts of course with lower pressures where getting full use of the tread.

The Solution:

I set both F and R tire pressures to 39psi and problem solved! Im astonished at how much of a difference it made. Night and day. The car went from truly dangerous at high speeds to feeling very comfortable and confidence inspiring.

The Analysis:
This got me thinking about N-spec tires for Porsche cars versus non N-spec tires. There is no question this is not just marketing or "paying for approvals" like some oil specs can be. The N-spec Porsche tires are clearly a different construction as the exact same model and size tire from the same manufacturer that is non N-spec. The tires weigh significantly differently and even the tread widths are often different by almost a full inch in some cases.

So why would deviating from Porsche recommended tire pressures on non N-spec tires make such a huge difference in solving a handling issue?

My theory is that we know Porsche has gone to significant lengths over the years to make a car that has an inherently flawed handling and stability design with the rear engine hanging of behind the rear axle be able to be one of the great handling sports cars of its times. I think its clear that particularly the rear tire construction has had a lot to do with this. In order to run very high tire pressures in the rear (which porsche needs for load in the rear) you need a tire that is designed for it and the N-spec tires clearly are. Its my theory when you try and run these high pressures in some non N-spec tires they simply are not designed for these pressures. It may not be the case for all non N-spec tires but the v12 evo2 clearly has somewhat soft sidewalls and construction and I dont believe they are designed for such high pressures.

Thats my .02.

Mike

Nugget

Care to cite some specifics? I've seen zero evidence to support this conclusion and I've driven pretty much every available tire for our cars, both on and off track.

bhvrdr

Sure its not hard to look up. Simply look up any Nspec tire and its non Nspec counterpart.

Example
Pirelli P-zero 295/30/19 100Y XL - N2 Spec -
Weight: 31lbs
Tread Width: 11.7"
Overall Diameter: 26"

Pirelli P-zero 295/30/19 100Y XL - Non N spec, non other manufacturer Spec
Weight: 28bs
Tread Width: 11.5"
Overall Diameter: 26.1"

Not only is the tire a slightly different size but the Nspec tire weighs 3 more lbs. Imagine the difference in construction there and that doesnt even speak to possible differences in compound yet.


The same was so for the PS2 but you cant find the old non Nspec PS2 tires anymore to compare. The Porsche spec PS2 tires though have been through 3 revisions so they are not the same as the old PS2 that general consumers would purchase. The Porsche Spec PS2 tires have been though N0, N1, and now N2. They were always significantly different than the non Nspec PS2 though. Almost an inche wider than the non Nspec PS2.


Lets look at another one where both Nspec and non Nspec are still available:

Pilot Sport Cup 2 305/30/19 - Non Nspec
Weight: 26lbs
Tread Width: 11"
Overall Diameter: 26.3"

Pilot Sport Cup 2 305/30/19 - N0-spec
Weight: 28lbs
Tread Width: 11"
Overall Diameter: 26.3"

Same exact size but 2 lbs difference pointing to a significant construction difference.

There's alot more easy comparisons to be made for 991 fitments though since they are still making a lot of both Nspec and non Nspec variants in the 20" sizes.

Examples:
Michelin PS4S 305/30/20 - non Nspec
Weight: 30lbs
Tread Width: 11.2"
Overall Diameter: 27.2"

Michelin PS4S 305/30/20 - N0 - spec
Weight: 31lbs
Tread Width: 11.6"
Overall Diameter: 27.2"

TIrerack explanation regarding N-spec

https://www.tirerack.com/tires/tiret....jsp?techid=26

mike

Nugget

Thanks. I'm still not sure how that leads to any conclusions about non N-rated tires like the Hankooks or R888s or even Hoosier R7s where the manufacturer has chosen not to pay Porsche for the rating.

bhvrdr

The only conclusion it leads you to is that you know they were not specifically designed or tested by Porsche for your application so you need to go by reviews from others who have used them or from testing yourself to see what are the right pressures for them and what characteristics they are going to give you.

Again though, this is not an issue of not paying. It is an issue of not being tested and constructed to Porsche specifications. That doesnt mean a non Nspec tire wont perform great. Porsche has VERY unique tire requirements as they are the only manufacturer I can think of that hangs an engine off the rear end. The load on the rear tires on a RWD car that is also rear engine is like no other car. Similarly the cold full load tire pressures of up to 46psi are not going to sit well with every tire you put on the car. They will on a tire specifically designed and tested for that pressure but in the case of the v12 evo2 they dont like that pressure at all.

I can tell you 100% that the v12 evo2 does not like the high pressures in the rear that porsche recommends. It leads to them ballooning a bit on the bottom and only driving on the center of the treads which gives scary high speed handling.

Mike

aaks38

So my two cents, every time I have installed new tires, regardless of the manufacturer, I have had this unstable feel. What I came to realize is that new tires have a tread height around 10/32 which causes tread squirm on the 911 as these cars are hard on tires especially the rear. Once the tire gets down to around 7-8/32, the deflection and squirm are reduced and obviously go away with lower tread height. Ironically I noticed the N rated tires are 8-9/32 height on the rear tires.

bhvrdr

i think that may partly explain a bit more squirm but of corse not all of it. All the n-spec tires i looked up also start at 10/32 as far as the summer tires. This pressure change made all the difference in the world on brand new tires.

jchapura

Hey Mike, would you be willing to experiment a couple more times to determine whether it's the front or rear pressure adjustment that's contributing most to the better feeling?

Maybe try F/R 35/39 and then 39/43?

I ask because I've had the same feeling on "old" tires and am about to go to coilovers and replace the rear wishbones in the search of that "confident" feeling. I've played with tires pressures to no avail.

bhvrdr

ok i can absolutely confirm its the rear pressures making the largest difference.

34/39 was ok just a tiny bit more slop in the front but otherwise it felt safe and stable

35/43 the rear end oscillates with lane change behavior or back and forth motions on the strering wheel. One move of the steering wheel gives a back and forth unsteady move of the rear end.

39/39 was rock stable with alot of tightness

39/46 again introduced rear end instability. It feels downright dangerous above 80mph