Zippy

Here's in interesting on tire pressure. See the following link for entire article:
<a href="http://www.rennsport.ca/articles/technical/Rsr%20pyro.htm" target="_blank">Pyrometer for Determining Proper Pressure</a>
"Each car has its own "normal" tire temperatures. After taking measurements at the track or autocross a few times you will discover what are "normal" temps for your car's tires with the set up you have. The key element is not the actual tire temperature (although that can have a bearing on some issues) but rather the temperature differential (as opposed to the differential temperature). What you want to know is 1) is my tire evenly warm across its surface? and 2) are my tires predictably warm in relation to each other? If you measure your tire temperatures regularly and under many conditions you will begin to know how hot they should be and what things you can change to make the situation better. If you discover that, say, the centre of your right front tire is noticeably warmer than the outer area, you may want to decrease your tire pressure. If you discover that the inner area of the tire is warmer than both the centre and the outside edge, you may wish to decrease your negative camber and so on. Race cars are carefully weighed at each corner to ensure the car is balanced (diagonally proportional) so that when the crew uses a pyrometer they know that the needed adjustments are suspension or tire pressure only. Most of us don't have that luxury, so you will have to learn to take some things into consideration such as weight ratios (front to back, side to side), tire sizes and power. Generally speaking, designers and engineers will give a high powered car wider rear tires to compensate, just as they will give a heavier car larger tires.

Tire pressure is the first thing to adjust, because it is the easiest. The general rule is: keep increasing your tire pressure until the centre of your tire becomes hotter than either side. Then decrease pressure to eliminate the difference. If at that point your tire is noticeably warmer or colder on the inner or outer, and that can't be attributed to something such as more left turns or a weight differential, you then have an alignment situation, which is beyond most of us at home so see your mechanic. What the pyrometer does is provide a tool that you can use to quantify what is going on at that critical contact patch between the road and your tire, and with practice it can give you invalubale knowledge. Good luck."

docjackson1

patrick-are you saying that porsche's recommendation on the street are incorrect, as i am sure that on a hot day, the normally inflated to 44 lbs. rear tires go a lot higher?

Patrick

It's not my opinion that Porsche's recommendation is incorrect for normal street driving, even on a hot day. I do believe that Porsche's recommendation is not based on the best driveability. However, my pressures go up 10 to 12 psi at the track, under pretty heavy use. Under normal driving, even on a hot day, I wouldn't expect to see more than a few psi increase. (My own experience is 2-3 psi.) For spirited driving where you might see larger increases, I would start at a lower pressure.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by docjackson1:
<strong>patrick-are you saying that porsche's recommendation on the street are incorrect, as i am sure that on a hot day, the normally inflated to 44 lbs. rear tires go a lot higher?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">

docjackson1

thanx, patrick

Bentley

No one on this forum is omniscient. And followers of someone acting omniscient without verification is pure folly.
If one READS the second sentence of my posting regarding adjusting the air pressure DOWNWARD BEFORE RACING when the tires are cool to the amount necessary for the thermal increase anticipated commences; the tires will be well within the capabilities set by Pirelli or others.
Those of you who jumped on the 'racing gentleman's' bandwagon without reading and THINKING about the veracity of my second sentence do a disservice to all Porsche owners who are trying to learn the technical truth.
Many owners come to this prestigious forum because it has many capable readers who are interested in contributing years of technical education and experience to others.
Remember: Trust bur verify.

Christer

Hey Bentley

I don't think anyone would dispute that your second sentence suggests downward adjustment of pressure. In fact, taken completely out of context it seems to mirror the opinions of other posters here. However, looking at your complete post it must be taken as a whole and for what it is. Rubbish.

The only thing you have got right so far is that no one is 'omniscient' here. But look at it from our point of view, you have 20 something posts on here with no ID on your profile. We don't know who you are or what your background is. And you are telling us it is OK to drive on the track with 57PSI in the tyres (hot or cold).

You tell us, what do you expect? How about you identify yourself and tell us a little more about what you know (or don't)? Personally I like to see healthy discussion between us all from many different angles. This one I don't like.

Remember: Flame, but pacify.

ypshan

My instructor just told me that the max 51 psi is for COLD tires. He's been in several 996 TT driven very hard with stock tires just like mine. The factory pressure (i.e. 36/44) seemed to provide very good balance and traction.

I may mark the tires with chalk next time and see how much of the edge of the tires are touching the ground when cornering hard. That may provide another indicator of how much pressure is appropriate.

For those who use lower than factory pressure on stock P-Zero tires, do your tires wear out faster on the edges instead of the middle?

Thanks.

Patrick

Marking the tires to see where they roll is a good idea. My last set of Pzero's were worn evenly, but I only drive at reduced pressure on the track. (which was likely the greater part of the wear).

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by ypshan:
<strong>My instructor just told me that the max 51 psi is for COLD tires. He's been in several 996 TT driven very hard with stock tires just like mine. The factory pressure (i.e. 36/44) seemed to provide very good balance and traction.

I may mark the tires with chalk next time and see how much of the edge of the tires are touching the ground when cornering hard. That may provide another indicator of how much pressure is appropriate.

For those who use lower than factory pressure on stock P-Zero tires, do your tires wear out faster on the edges instead of the middle?

Thanks.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">

Ruf-Racer

The originator of this thread referred to his DE experience and I believe there are many highly experienced board members that have been there and done that as the subject relates to DE or similiar events. Perhaps I was too vague in my original reply. My point was simple. I use instrumentation as an [bold]indicator[/bold] of pressure and temperature changes while running. I measure between runs as others have posted. I also attempt to minimize variables. Nitrogen is something I firmly believe in to help minimize a specific and important variable. Dry nitrogen is way better than an uncontrolled ordinary air source in terms of water content!
My experience, my logs and careful preparation with frequent alignment checks certainly don't hurt. All of what I write here is anecdotal but it works for me. With many,many runs (150?) beyond 205 mph for extended periods I put my *** on the line many times and so far so good. I sure as hell know I don't want tire pressures in the high forties when I run like that! Jimbob you be a good bubba and jump in here!

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

R

Bentley

I have NEVER stated that a Pirelli tire is to run at '57 P.S.I.';to say that I have is absolutely incorrect. If you are to quote me, please do so correctly.

Christer

Well if you are going to split hairs then we can sit here all day and argue about something else.

In a thread where a poster reports that after using Porsche specs for his tyre pressures has found that one of them is at 57PSI, you have stated that the tyre can take it. OK, physically take it but in the C O N T E X T your post is not without ambiguity, and that is why several people have reacted to it. Not because we are omniscient, but because we felt that this was a dangerous C O N T E X T in which to post what you did.

Remember: Don't split hairs.

Bentley

There are no hairs being split. If one would have read my SECOND sentence, he or she would see that I provided the methodology to acheive both parameters of the tire i.e., maximum tire pressure AND thermal increase in tire pressure. Perhaps in using the 'King's Language' I should have used a semi-colon rather than a period between the first and second sentences!

SundayDriver

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Bentley:
<strong>There are no hairs being split. If one would have read my SECOND sentence, he or she would see that I provided the methodology to acheive both parameters of the tire i.e., maximum tire pressure AND thermal increase in tire pressure. Perhaps in using the 'King's Language' I should have used a semi-colon rather than a period between the first and second sentences!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I would be happy to debate tire pressure/preformance with you if you will let us know what qualifies you to educate all of us.

As I read it, you advicate a cold pressure of 50-51 psi for Pirelli's which will result in a hot pressure of 56-57 psi - all normal in your opinion. Is that, in fact, what you are saying?

If you want to get into this debate, then let's have an educated debate. Show us that you can do that, share your background and I will do the same.

Bentley

You are a little late in wanting to commence a debate since we have already been having one.
I stated that one would reduce the air pressure of one's tires, in the cold state, the amount he anticipated the tire pressure would increase due to road friction from driving. That way he would be in compliance with Pirelli's recommendations
Unfortunately, I do not know how to make this very simple procedure easier to understand.

SundayDriver

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Bentley:
<strong>You are a little late in wanting to commence a debate since we have already been having one.
I stated that one would reduce the air pressure of one's tires, in the cold state, the amount he anticipated the tire pressure would increase due to road friction from driving. That way he would be in compliance with Pirelli's recommendations
Unfortunately, I do not know how to make this very simple procedure easier to understand.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Fair enough since you are the center of this thread.

I thought I might be able to help clarify some of what is being asked and said. FYI - I am a Mechanical Engineer and worked for a few years as a tire test engineer. That entailed both lab work and road testing, so I understand a thing or two about tires.

I don't often frequent this board but was drawn in by this topic. For those who are interested, listen to Viken - he is steering you correctly in this matter. Or listen to Bentley and provide the entertainment that Jim Bob wants to see.

I'll leave you to your ongoing debate.