ypshan

I just finished a DE at the Pocono. My stock P-Zero tires were set to 2 psi above factor cold (i.e. 38 front 46 rear) as suggested by the club website. After a few hot laps, I measured the rear tires and found that they are at 57 psi. I got worried since the tire sidewall says max psi is 51.

I am wondering what should I do in the future. What's your setup? Is there any 'official' information from Porsche or Pirelli?

Thanks.

docjackson1

that's a good question. i don't have the answer, but logically, it seems that the pressures in the books and on the tires are cold pressures. i would think that the hot pressures(pressure after driving) are considerably higher, and that the tires are engineered to be able to take the increase, as long as you start with the cold pressure. that is just my guess.

Patrick

My guess is that the cold book pressure is based on somewhat less of an increase cold to hot than what you'll have at the track. With my street tires, I start about ten pounds low, and hot I end up near the book pressure. With the track tires, I go much lower. I start at 20 front and 24 rear, to end up about 30/34.

Play around with it and good luck!

Viken

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by ypshan:
<strong>I just finished a DE at the Pocono. My stock P-Zero tires were set to 2 psi above factor cold (i.e. 38 front 46 rear) as suggested by the club website. After a few hot laps, I measured the rear tires and found that they are at 57 psi. I got worried since the tire sidewall says max psi is 51.

I am wondering what should I do in the future. What's your setup? Is there any 'official' information from Porsche or Pirelli?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">You should not run such high pressures no matter what and especially on the track. The factory recommended pressures are ridiculous and dangerous if you push your car on the track. You should try to run *cold* pressures in the lower to mid 30's and reach hot pressures of around 40 psi.

Ruf-Racer

Viken is right on as always! FYI, I too start with low 30's and work from that point.I monitor via Smartire system as a trend indicator,and measure pressure and temperature between runs as the day progresses. I have to say again that dry nitrogen really works for me! Fifty seven pounds is a scary number. I run P Zero on the street,on the track and in my open road race hobby!

Bentley

P Zero's typically run 50 to 51 P.S.I. [COLD TEMPERATURE RATING ALWAYS] and a increase of 6 P.S.I. is to be expected through prolonged driving. Just test your pressure in the morning before driving and adjust your tire pressure downward for the anticipated pressure increase from the transient heat. Since the tires are well designed for these thermal increases this is nothing to be alarmed over. They will cool down with a resultant reduction in pressure.
When a tire is being engineered, most good tire fabricators design in a 20% overpressure margin for sidewall and bead safety. Pirelli does do this. A common problem when overpressure occurs while driving fast is blowing out of the valve stem, not rupturing the bead or cleaving the sidewall.

Viken

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Bentley:
<strong>P Zero's typically run 50 to 51 P.S.I. [COLD TEMPERATURE RATING ALWAYS] and a increase of 6 P.S.I. is to be expected through prolonged driving. Just test your pressure in the morning before driving and adjust your tire pressure downward for the anticipated pressure increase from the transient heat. Since the tires are well designed for these thermal increases this is nothing to be alarmed over. They will cool down with a resultant reduction in pressure.
When a tire is being engineered, most good tire fabricators design in a 20% overpressure margin for sidewall and bead safety. Pirelli does do this. A common problem when overpressure occurs while driving fast is blowing out of the valve stem, not rupturing the bead or cleaving the sidewall.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">This is absolutely the worst advice I have ever seen on tire pressures. I suggest that you disregard the above at all counts unless you want to kill yourselves.

1AS

My experience with PZero's on a hot day confirms what Viken predicts. I ran the recommended pressures on my ttX50 on a warm summer day. The pressures went sky-high when I rechecked them after 5 laps (including 2 initial slow "warm-ups"). Even though I lowered the pressures to achieve the factory numbers hot, the tires were ruined.The car developed a terrific vibration that ultimately was attributed to belt damage and shift. Porsche replaced all four with Contis. I wound up bleeding over 10psi from each tire, suggesting proper staring cold pressures in the 30 range. AS

JimBob Jumpback

Now dont yall be lisnen to dat bubba viking. yall shoold be a lisnen to bubba bendedlee. 51 psis is jist about rite fer a porch kar. affer yall be gittin it hot, den yall havin sum good tired pressoor at pet neer 70 psis an dat be perfekt. lissen da bendedlee, cuz he be wun pert smart bubba.

ol JimBob gonna bee dere ta watch an I be sellin da moonshine fer yall ta watch cuz it be more betta entertanenment dan WWF.

thankey yall bended-lee. yall gots anee udder gooder advise?

ypshan

One thing I don't get is why would Porsche recommend a 44 psi rear?

I believe I can easily push over 55 psi even if the cold pressure in the rear is 44 psi as by the manual. If it's unsafe to do so, why would Porsche USA set itself up for such a huge liability trap?

Bentley

It is interesting that the disparager of my advice on tires for the street offers no technical support for his erroneous conclusions.
A reader should read the Pirelli Factory Data on P Zeros or check the Continental Factory Data for its tires and decide who is correct. If that is too difficult, check 'The Tire Rack' and see whose advice is correct. Remember: trust but verify.

JimBob Jumpback

yall tell em bendedlee. ol JimBob thinkz yall is smarteder dan viking. yall iz my heeero along with gorgedvee8 and mr carlos woof-woof. now yall in rell gooder kumpanee cuz JimBob likeys yall. i agree yall is smarteder dan all dem bubbas what run dem tireds an evn da porch inginears wat says lower pressoors dan yall sayz. it be taykiin lotsa freejoles ta say dat porch is wrong anna viking is wrong anna everwun escepted bended lee is wroung.

docjackson1

viken, are you saying that porsche's tire pressure recomendations are incorrect for all conditions, or just for racing? why do you feel that they would give incorrect recommendations? and with all due respect, what expertise do you base your recommendations on. i am not trying to challenge you, as i am not sure of the correct answer-i am just trying to understand why and how you draw these conclusions.

docjackson1

patrick-you are assuming that everyone has your level of understanding regarding tire pressures and porsches. i disagree with your statement that viken does not have to offer technical support for what he says. i am not saying that viken is incorrect. i am just saying that documentation would help people like myself, who are inexperienced, understand the scientific basis for his statements. the same applies to the gentleman who states that 57 lbs. is okay. scientifically backed or sourced statements is the basis for a fact.

Patrick

Doc,
No, I'm not assuming that at all. And I'm sorry if it came off that way. I reread my earliest post and realized it could be taken that way, so please rest assured that was not my intent. And my post just above is narrowly aimed!

Porsche's recommendations are based on a lot more than driveability. They have to consider tire wear, fuel economy, etc. I've read (and this is just hearsay) that the euro specs for the same wheel/tire combo's are lower. (Anyone?)

If you search these forums (not just 996 turbo) for discussions on tire pressure and you will see that there as many opinions on tire pressure as there are which Porsche is best. And you will find some good advice.

There is supposedly factual information available that would suggest that running a higher pressure increases the tires "bite". I have found be experimenting that this is not true with my car and tires. As I said in my post, I used to drop my street tire pressures by just about the amount that they increased from heat, and that provided very good results with the P-zero assyms. I started at the same point with my Kumho ecsta V700's, and found that at pressures in the low to mid 40's, the rear of the car was very loose. (scary at 47psi.) I lowered the pressure until I found the handling was acceptable and the sidewalls were rolling about as much as I wanted. (That's subjective, too.)

And that is the way it works. You get advice from someone at the track with a lot of experience, (someone who is doing well), and you find out it really doesn't apply because you drive a 996 and he drives a 993. Then you adjust and figure out what works best for you. Then you try a different brand of tire, and you start all over. I'm just starting out at this myself, but I'm learning.

However, it doesn't take much time to figure out that running over 50psi, especially at the track, is at best a handfull. (And I agree with Viken, downright dangerous).

Pat