Newbie question re squirming under acceleration
12-28-2014 | 11:54 PM
#31
Rennlist Member
Joined: May 2014
Posts: 376
Likes: 48
From: Foothill Ranch
Let me send a note to Tirerack and ask them. Years ago I was in the tire biz so my knowledge comes from more than just reading up. Professional experience and then personal experience from my wifes car.
Without getting too technical, I used to think the same thing, that XL rated tires are typically for heavier loads, passengers, luggage, etc as you describe but think about it, our size tires are unusual except for typically Sports Cars, Performance cars so what loads would our cars be carrying. The only load would be performance oriented. Taking corners at high speeds, putting the sidewalls at significant stress. XL provides more stability. I read your link about mixing fronts/rears but that makes no sense to me. Stay tuned.
Without getting too technical, I used to think the same thing, that XL rated tires are typically for heavier loads, passengers, luggage, etc as you describe but think about it, our size tires are unusual except for typically Sports Cars, Performance cars so what loads would our cars be carrying. The only load would be performance oriented. Taking corners at high speeds, putting the sidewalls at significant stress. XL provides more stability. I read your link about mixing fronts/rears but that makes no sense to me. Stay tuned.
Thanks for the comments. However, I don't fully follow the logic for requiring XL both front and back on a 911 - as I see it XL is typically prescribed for heavy axle loads such as a full complement of people and luggage in a station wagon / engine slung out the back in a 911. However a 911 front is lightly loaded - the only issue is the high speed. However I am very happy to be corrected by any tire experts out there 
)
The tyre manufacturers' websites seem ambiguous too:
The Michelin UK website recommends Pilot Sports with normal rating at the front and XL rating at the rear:
http://m.michelin.co.uk/tyres/michel...1-531615-49604
The Michelin Canada site recommends Pilot Super Sport with XL for both front and rear.
http://www.michelin.ca/tire-selector...t/tire-details
But the same site recommends standard load front, XL rear for the Pilot Sport PS2
Either the different models of tires have different characteristics and hence different load requirements for the front tires, OR the guys who set up the websites aren't too precise with the details........
And the Pirelli website doesn't mention XL for either front or rear, so I guess that useful detail didn't make it into their website configurator matrix....
)The tyre manufacturers' websites seem ambiguous too:
The Michelin UK website recommends Pilot Sports with normal rating at the front and XL rating at the rear:
http://m.michelin.co.uk/tyres/michel...1-531615-49604
The Michelin Canada site recommends Pilot Super Sport with XL for both front and rear.
http://www.michelin.ca/tire-selector...t/tire-details
But the same site recommends standard load front, XL rear for the Pilot Sport PS2
Either the different models of tires have different characteristics and hence different load requirements for the front tires, OR the guys who set up the websites aren't too precise with the details........
And the Pirelli website doesn't mention XL for either front or rear, so I guess that useful detail didn't make it into their website configurator matrix....
12-29-2014 | 11:38 AM
#33
Race Director
Joined: Sep 2006
Posts: 19,034
Likes: 255
From: Centerton, AR
Refinishing is different from repair. AFAIK Porsche has no issues with refinishing wheels. In fact, I had one of my Turbo wheels sent out for refinishing after it got scuffed up from an encounter with a mule deer. I do not know how this came out as the wheel refinishing shop ruined the wheel and had to buy me a new one. Turbo hollow spoke wheels are not cheap so that was an expensive mistake.
12-29-2014 | 11:48 AM
#34
Race Director
Joined: Sep 2006
Posts: 19,034
Likes: 255
From: Centerton, AR
Well, at the risk of creating a tire flame war the only authority on tires for these cars is Porsche.
While some owners stray off the tire reservation and fit non N-rated tires or mix and match tires based on some imagined expertise in this field or just simply to save money, there have been enough reports by owners who have strayed off the tire reservation of car road feel/handling issues to reinforce my belief that staying with sanctioned tires is the only way to go.
Sure, you might stumble on a tire combo at your first attempt that delivers acceptable road feel/handling but you might end up going through a number of tires before you are successful.
Not to pick on you but you were remiss in when you were looking at the car to fail to insist upon having a proper set of matched N-rated tires fitted as part of the car purchase.
While some owners stray off the tire reservation and fit non N-rated tires or mix and match tires based on some imagined expertise in this field or just simply to save money, there have been enough reports by owners who have strayed off the tire reservation of car road feel/handling issues to reinforce my belief that staying with sanctioned tires is the only way to go.
Sure, you might stumble on a tire combo at your first attempt that delivers acceptable road feel/handling but you might end up going through a number of tires before you are successful.
Not to pick on you but you were remiss in when you were looking at the car to fail to insist upon having a proper set of matched N-rated tires fitted as part of the car purchase.
12-29-2014 | 01:56 PM
#35
Thread Starter
Track Day
Joined: Dec 2014
Posts: 16
Likes: 0
From: Dubai, UAE
Having now checked the handbook (along the lines of "if all else fails, read the instructions..."), Porsche only recommend XL for the rear tires, not for the front.
The tires currently fitted are exactly in line with the recommendations for a C2S, so I hesitate to conclude that the tire specs are the reason for the swaying. Dealer trip for a checkup being lined up for this week....
The tires currently fitted are exactly in line with the recommendations for a C2S, so I hesitate to conclude that the tire specs are the reason for the swaying. Dealer trip for a checkup being lined up for this week....
12-31-2014 | 07:07 PM
#38
Former Vendor
Joined: Mar 2006
Posts: 2,787
Likes: 12
From: South Bend, IN
If your car is swaying so bad it's hard to control, I would have it checked out right away. Minor swaying from mismatched or worn tires is possible, but usually minor. Bad swaying may be mechanical and needs to be checked out ASAP.
Check your air pressure also. It should be at 36 front and 44 rear.
Your present load ratings are OK. OEM N2 P -Zeros have a service description of 87Y front and 100Y rear. Load ratings can (and usually do) vary if the two tires are a different size. As a measure of reference, so are the OEM Michelin PS2's. There are several versions of the P-Zero in each size. Are yours both N rated? I'm curious what kind of tread depth measurement difference there is between the front and rear tires. Worn tires on one axle and new tires on the other have sometimes presented handling issues because of the tread squirm differences between the two.
Check your air pressure also. It should be at 36 front and 44 rear.
Your present load ratings are OK. OEM N2 P -Zeros have a service description of 87Y front and 100Y rear. Load ratings can (and usually do) vary if the two tires are a different size. As a measure of reference, so are the OEM Michelin PS2's. There are several versions of the P-Zero in each size. Are yours both N rated? I'm curious what kind of tread depth measurement difference there is between the front and rear tires. Worn tires on one axle and new tires on the other have sometimes presented handling issues because of the tread squirm differences between the two.
12-31-2014 | 08:54 PM
#39
Race Director
Joined: Mar 2006
Posts: 15,358
Likes: 183
From: Tampa
I and most track there cares with NON "N Spec" tires. My street tires are Yokohama Advan AD08R which I got from Damon at Tire Rack and I've won Autocross' with them and they also are NON "N Spec" tires.
Totally safe!
The Yokohama AD08R are awesome tires for a sports car. Yokohama just didn't pay the high money fee and submit tires to Porsche for testing is all. The Yoko's specs are right in line with N Spec tires.
This is true with a hand full of non n spec tires like Bridgestone RE-11, Michelin Super Sports...so forth
Totally safe!
The Yokohama AD08R are awesome tires for a sports car. Yokohama just didn't pay the high money fee and submit tires to Porsche for testing is all. The Yoko's specs are right in line with N Spec tires.
This is true with a hand full of non n spec tires like Bridgestone RE-11, Michelin Super Sports...so forth
01-01-2015 | 10:30 AM
#40
Rennlist Member
Joined: Feb 2003
Posts: 1,455
Likes: 7
From: Wichita, KS
Well, at the risk of creating a tire flame war the only authority on tires for these cars is Porsche.
While some owners stray off the tire reservation and fit non N-rated tires or mix and match tires based on some imagined expertise in this field or just simply to save money, there have been enough reports by owners who have strayed off the tire reservation of car road feel/handling issues to reinforce my belief that staying with sanctioned tires is the only way to go.
Sure, you might stumble on a tire combo at your first attempt that delivers acceptable road feel/handling but you might end up going through a number of tires before you are successful.
Not to pick on you but you were remiss in when you were looking at the car to fail to insist upon having a proper set of matched N-rated tires fitted as part of the car purchase.
While some owners stray off the tire reservation and fit non N-rated tires or mix and match tires based on some imagined expertise in this field or just simply to save money, there have been enough reports by owners who have strayed off the tire reservation of car road feel/handling issues to reinforce my belief that staying with sanctioned tires is the only way to go.
Sure, you might stumble on a tire combo at your first attempt that delivers acceptable road feel/handling but you might end up going through a number of tires before you are successful.
Not to pick on you but you were remiss in when you were looking at the car to fail to insist upon having a proper set of matched N-rated tires fitted as part of the car purchase.
01-12-2015 | 03:11 PM
#41
Thread Starter
Track Day
Joined: Dec 2014
Posts: 16
Likes: 0
From: Dubai, UAE
Thanks to all who replied for your sage advice - much appreciated.
Took the car into the Porsche dealership who checked the car over - all is fine with suspension etc except for a screw in each rear tyre causing slow punctures and hence major swaying under acceleration.
Punctures repaired and had a great fast drive with friends on some awesome deserted desert mountain roads at the weekend - car behaved faultlessly even under full acceleration, and now time to swap the Pirelli P-Zeros for some Michelin PS2s (shame the SSs would invalidate the P warranty)
Took the car into the Porsche dealership who checked the car over - all is fine with suspension etc except for a screw in each rear tyre causing slow punctures and hence major swaying under acceleration.
Punctures repaired and had a great fast drive with friends on some awesome deserted desert mountain roads at the weekend - car behaved faultlessly even under full acceleration, and now time to swap the Pirelli P-Zeros for some Michelin PS2s (shame the SSs would invalidate the P warranty)
01-14-2015 | 04:09 PM
#43
Drifting
Joined: Sep 2001
Posts: 2,467
Likes: 14
From: redmond wa
Hello all, as a new Rennlist member I've really appreciated the comments on various issues while I was doing research, and am the new owner of a lovely 2009 997.2 C2S with loads of toys.
Asking for help please with suggestions as to why the car is squirming/swaying from side to side a lot under moderate to firm acceleration. This is happening even on straight pretty even roads. I had thought it may be down to tire pressure or road camber, but even after checking pressures and running on flat 6 lane roads it is still happening. However at constant high-ish speeds there is no swaying at all.
Any suggestions gratefully received. Many thanks
Asking for help please with suggestions as to why the car is squirming/swaying from side to side a lot under moderate to firm acceleration. This is happening even on straight pretty even roads. I had thought it may be down to tire pressure or road camber, but even after checking pressures and running on flat 6 lane roads it is still happening. However at constant high-ish speeds there is no swaying at all.
Any suggestions gratefully received. Many thanks
Brakes !!!Your car, undoubtedly, is equipped with a "virtual" LSD system that uses differential braking to abate left or right only wheelspin. Time constant of PSM/ECU brake application/release is critical. Sticking brake caliper(s), wrong brake pads, brake fluid?
01-14-2015 | 05:36 PM
#44
Pro
Joined: Oct 2014
Posts: 589
Likes: 68
"Torque Steer" is for FWD cars...