holminator

Compelling argument; 31/34 it is. Thanks again. Still there is just something about the term "comfort pressure" that makes my anus switch in a bad way. :0) With regard to the speeds I actually drive at, where, and how I'm not in jail for it, well, I'm just not "smart" enough to say much, but I certainly do miss living in Stuttgart-Botnang. :0)

simsgw

Yes, the term is something of a backhanded slap at American speeds, isn't it? You see, a lot of us complained privately and publicly about the original specification for 997 pressures. That's one reason I spent a track day formally evaluating the right pressure under those extreme conditions. And we were not dawdling. Christian, who worked with me, campaigns his European GT3 in the Nurburgring series, and I ran Formula Ford until the other drivers got too young... uh, until I got too old. We drove true track speeds and used the procedures recommended by the tire manufacturer to arrive at the pressures the current manual recommends. Lots of us around the country were getting the same answers.

So far as I know, they've said nothing publicly, but obviously Stuttgart finally agreed that the only people who need those high pressures with big differentials front to rear are the ones who live with an unlimited Autobahn nearby and they use it at times when traffic is light enough to permit sustained high speeds.

I lived in Europe in the sixties and let's face it: 165 mph is damned fast anywhere. But "comfort pressure" sounds like the guys at Stuttgart were miffed at Porsche Cars North America for insisting we wanted a pressure spec that didn't make the handling iffy at trivial speeds like a hundred mph, and we might even appreciate the extra tire life that correct pressures provide. "Oh, alright. If Americans are such vimpy fellows, ve will provide a spec for your little tushies."

Gary

Nicoli35

After changing wheels to the winter set, the dash display asked "Did you change wheels? please reset TPM". hehe. I went and set TPM to 20" winter tires and it auto-calibrated everything. Awesome!!

simsgw

I will watch the pressures this Sunday, Chuck. I won't be going full track speeds because the car is still in break-in, but it will be interesting anyway. We'll see what temps the Pirellis reach under those conditions, which will be about like fast driving on public roads. Well... let's say 120% of public road driving. I'll be cornering a lot harder than I am willing to do with novices coming the other way in motorhomes and Buicks. But the straights, and thus the braking, will be a lot milder with power limited to 4000 rpm.

Gary

simsgw

It's nice they are getting the TPM design settled down. I never owned one, but I've read the complaints of people who owned the initial types of TPM on ... on the 996 I think it was. The new one seems quite intuitive to me. (Aside from saying "plus three" in the adjust-pressures window when it means you already are three pounds high. Must be a German thing. I read that backwards the first time, just like holminator did. I thought it meant "go add three pounds.")

You do know you will need a decent pressure gauge eventually don't you, Nico? Swapping wheels every time the pressures get off isn't cost effective in the long run...

Gary

Nicoli35

hehe..undoubtedly. Thanks Gary

Enjoy your track time coming up! Love reading about that. I haven't tracked a car before but am a member of the PCA and hoping to attend some events as the weather clears up next year. I could use some driver's training at least.

ADias

Where have you read anywhere in Porsche documentation a reference to 'comfort pressure' ?

Look at the label I posted on post #8 - no reference to comfort or performance. Just a 4 cell table relating to weight and speed. Pick the cell where you fall. Simple!

simsgw

Yes. That is the term used in 991 documents, Tony. For example, page 265 of my owners manual is headed:

Comfort tire pressure for summer tires up to 165 mph (270 kph)

and the following text reads: Instructions about setting the load condition precede a matrix of values for 19" vs. 20" wheels and part vs. full load and Carrera vs. Carrera S. And of course each entry in the matrix is provided in psi, bar, and kPa. Sigh.

See what I mean about consulting engineers having more work in the future?

Gary

simsgw

DE time is an excellent idea for any Porsche owner. Not only is it entertaining, but over the years, it can save your car or even your life. Cindy always insisted we had been saved half a dozen times by my track training back in the sixties. I always said it was only five times, because the convertible we didn't run over in our motorhome would barely have slowed the Bounder. Track training only saved their lives, not ours.

Anyone nearby should come out to the Fairplex (in Pomona Ca) this Sunday (Nov 18). We have waived late registration fees for this last event of the season. Novice ground school is 5-7:00 Saturday afternoon at the Jockey Club inside Fairplex. (Use Gate 1.)

I just copied your quote and my note to a new thread, Nico. Just realized this is the last chance this season for L.A. drivers.

Gary

ADias

Thanks Gary! It definitely looks that PAG is pandering to the soft boulevard crowd.

It may be then that 31/34 is a softer limo setting. Then I would say 32/36 (or 33/37) should work fine for sport driving. After all the 991 and the 997 weigh about the same and patch sizes are similar. I use those pressures on my 997.2 S and in my driving style they quickly rise to 37/42 with solid grip on M-PSS.

Re. PSI, bar, kPA conversions, some of us do the conversion in our heads.

Is there a PDF version of the 991 Owners Manual available? PAG has an online doc site but that does not replace a comprehensive self-standing documents.

simsgw

Christian and I found that 32/34 was a little too high when we ran those tests. In fact, the heat distribution across the tread was not correct in front until we lowered the Michelin PSS tires to 30 psi. And the front/rear differential needed to be only two pounds with the driving style of racers. (Most of us prefer the rear end to be a little 'loose'.) We factored in street conditions and less experienced drivers to arrive at 32/35 for the best tire performance.

Then we suggested 997 drivers would find that irritating as hell because the TPMS would be in a constant alarm state. As you know, it was designed to look for 34/40, the light-load Autobahn pressure. Christian muttered something about disconnecting the TPMS; I settled for running my tires at 34/37 except on track days. So that was the final number I suggested to 997 drivers who asked, and it's what I say when students with a 997 ask my advice on pressures. Novices don't need the distraction of big red exclamation marks flashing while they're on track. But the real conclusion for 'sport' driving was 30/32. It's just that a 997 thinks the tires are going flat when you run them at those pressures.

I expect to be very happy with 31/34 at the track Sunday, but you know I'll provide an objective report when I'm done. For my style of driving, it might work better with only a two psi differential, but a DE day is not a race. Three psi apart will be fine.

Probably, but I haven't searched for it yet.

Gary

ADias

I was referring to 32/36 (or 33/37) for the road, not track. For track given typical temp changes, I imagine 31/34 is probably the sweet spot, as it will yield 37/41 hot.

cole328

Hi Gary - I have always enjoyed reading your posts given your knowledge. Had a quick question re; adjusting for tire pressure using the TPM, as the manual is confusing on the issue. I have a Panamera GTS, but the basic system is the same as the 991, so I happened across this thread.

Anyway, prior to getting this car, I was always under the impression that tire pressure should be checked in the morning, when tires are cold, and I used a very good gauge. Anyway, if now relying on TPM given the indicated setting (standard, partial load), should I assume that the TPM should be looked at in the morning as well, and the "fill" function used when the tires are cold? Obviously, as one begins to drive, the TPM is going to indicate (+2 or so), as the tires heat up, which was kind of a neat ongoing monitoring.

So, I was somewhat confused if the general goal was to have "0's" all around when the tires are at a normal operating temperature (which would take into account ones driving style), or "O's" all around in the morning>?
I assume the latter, but thought I would check in and get some clarity.

Much thanks

ny991

Cole, I sincerely hate to tell you this, but Gary passed away last February or March. We all miss him and his legendary informational posts. He is a legend here, and always will be!

cole328

wow.....had no idea....my condolences to his family and friends....he was a great guy...