Interesting findings on tire pressure

I was washing my father's new '02 Passat 1.8T wagon this morning. When I was drying off the gas door, I found the following info regarding the tire pressures. I think it is useful to everyone here. I also check the tire pressures on the Passat to compare it with the factory recommended numbers. I bought the Passat about 2 weeks ago as the father's day gift and it was built in APR/02. Then, I also look into the factory tire pressure decals on my 996, my brother's 986 S, & my wife's '00 X5 4.4 sport pkg. Here's the info: BMW X5 (255/285-F/R) F R 19" tires full load 36 39 Passat (195/65R15 tires) full load 1050lbs &lt;100 miles & half load 28 28 &lt;100 miles & full load 30 39 100+ miles & half load 30 28 100+ miles & full load 33 42 ACTUAL TIRE PRESSURES 32.5 32.5 996 750lbs load (4 persons) 36 44 TIRE PRESSURE 32 32 WHEN DELIVER 986S 529lbs load (2 persons) 29 36 So, I guessed the tire pressures are related to the vehicle weight and speed of course. But from what I have seen on the 986, the car should not need anything more than 36 at 2 persons of load. I am driving my 996 with ONLY myself in most of the time, so, that's why I found 32/34 on my car is the best setup. I think the only reason why PORSCHE recommends such a high tire pressure is because of the vehicle load assumption. Hope these can help you guys to figure out your optimal tire pressures, Cheers! <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Lawrence, what is actually in the car means nothing, zilch. Just because the dealer didn't prep the car correctly doesn't mean that pressure is what the car should have. Greg

Actually, this is even more interesting. The Ferrari 360 Modena is outfitted at the factory with four different tires. The company provides a dedicated door plaque for each with a different set of pressures for each. - Goodyear Eagle F1 Fiorano: 32F / 32R - Pirelli P-Zero System: 32F / 29R - Bridgestone Potenza S02A: 32F / 32R - Michelin Pilot Sport: 26F / 28R Gee, I wonder why a car manufacturer would go through the trouble of recommending such ridiculously low pressures let alone different ones for different tires.

[quote]Originally posted by 02_996_C2: <strong> 996 750lbs load (4 persons) 36 44 TIRE PRESSURE 32 32 WHEN DELIVER </strong><hr></blockquote> Hmmmmm? 4 people in a 996, total weight 750 lbs. That's 187 lbs each. Two 187 pounders in the back seat. Hmmmmmmm. Pretty dense people. Either that or two 375 pounders in the front seat. Hmmmmmmm. German test subjects must be as big as summo wrestlers.

Greg, I don't agree with you! I strongly believed the germans prep their cars as close to spec as possible when they roll out of the assembly line. Especially you are talking about a Porsche, BMW & VW, these are the best quality vehicles in the world. Have you ever come to a VW ad that shows you how VW engineerers managed to get the doors on all VW cars as close to each other as possible? I strongly think the tire pressures on all Porsches are pumped in certain specs according to the factory. This is shown in my '02 996 C2 & my bro's '01 986S! Even Ferrari recommends some realistic numbers on their tire pressures according to VIKEN. Well, your assumption may be correct on a FORD! <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

[quote]Originally posted by 02_996_C2: <strong>Greg, I don't agree with you! I strongly believed the germans prep their cars as close to spec as possible when they roll out of the assembly line. Especially you are talking about a Porsche, BMW & VW, these are the best quality vehicles in the world.</strong><hr></blockquote> I have purchased more than a few dozen German cars in my life and have never taken delivery of a car which had cold pressures set at factory specs. Most of them were much lower and none was consistent throughout the same axle. My guess is, even if the factory sets the right pressures, it changes throughout the course of the time it takes for the car to reach PDI and the dealer. Furthermore, neither PDI nor the dealer spends the time to reset the pressures. My overall impression of German cars is that they may be some of the finest driving vehicles but quality ain't there. [quote]<strong>Have you ever come to a VW ad that shows you how VW engineerers managed to get the doors on all VW cars as close to each other as possible?</strong><hr></blockquote> No, but they never are that way on any German car.

VIKEN, every manufacturer has their range of tolerances in production. German cars may not be the most consistence in terms of quality control, however, they are among the best. I have owned so many different brands of cars including LEXUS, TOYOTA, HONDA, NISSAN and all german brands, the most reliable/consistence in quality car I have ever had is not from any of the Japanese manufacturers either. I think this is depend on your luck. But I strongly believes German cars are among the best. Tire pressures may be off when you get your vehicle delivered from the dealer. That's why I look at the production date as a reference too. Our 996 & Passat were delivered to us right after it was built (within 2 months of production date). Look closely to other vehicles on the market and you will see how well the german cars were built! The built quality on the Ferraris & Lambos are even worse...

Here is some interesting stuff I found in the Porsche (Technical Manual) documentation: Recommended tire pressures: Carrera Coupe (18x7.5 and 18x10 wheels) Front: 36 psi (2.5 bar) Rear: 44 psi (3.0 bar) We already knew this but here is the interesting part... GT3 Coupe (18x8 and 18 x 10 wheels) Front: 32 psi (2.2 bar) Rear: 39 psi (2.7 bar) No rear seats just a little heavier than a regular coupe (2977 lbs vs. 2917 average weights). Interesting... that Porsche would recommend lower pressures for a car only available in Europe. Sounds like more of the same old US drivers can't handle ROW M030 or lower tire pressures??? Hmmm...

Palting: Now wait just a minute. I am 6'2" and weight 187 pounds, so I am dense? My current car is about 200 pounds less than a C4S and the recommended cold pressure is 30psi. I will probably go with something like suggested above - 32/34 cold.

[quote]Originally posted by 02_996_C2: <strong>The built quality on the Ferraris & Lambos are even worse...</strong><hr></blockquote> I happen to have one of them in my garage next to two German cars, care to know how it compares? Also, have you seen a Murci�lago up close? Most likely not since you think the build quality doesn't measure-up.

I can assure you that no car comes from the factory with with tire pressure set exactly as it should be, especially cars that have to make the long trip over the Atlantic and then maybe sit on a dealer's lot for a while. Every manufacturer sets their tire pressures very high from the factory to help prevent flat-spotting for the 3+weeks they will be required to sit in the ship or at the port of entry. When the technician at the dealership does the PDI (Pre-Delivery Inspection) on a vehicle he is supposed set the tire pressures according to the manufacturers recommendations. Working with technicians on a daily basis, I can tell you that happens alot less than you would think. Even if they do, their gauges might not have been calibrated in a while and most use the ones like you see at gas stations. Some technicians even think they know better than the factory and set them to what they think is right. Someone said it best on the list previously...the correct tire pressure is going to be the one that is right for that day. One that takes all the variables into account, such as vehicle load, ambient temp, suspension set up, alignment, etc.. If you are tracking the car, then the best way to tell is a pyrometer. This measures the heat build-up in the tire and will be a good indicator if your pressures are set correctly. If you are just street driving, then it becomes a matter of what you prefer (as long as you don't go out of the range of safety). Do you want gas mileage? Ultimate grip? smoother ride? On the street the best indicator is tire wear pattern. In general if they are wearing on the inside and outside edges, they are underinflated. If they are wearing more in the center, they are over-inflated.

Excuse me VIKEN, isn't Murci�lago a German & Italian venture? When I said Lambo means the Diablo & Countach. Eveyone knows the Murci�lago has the AUDI like interior & built quality, but guess what? another german owned car company! I knew you have a 360 in your garage. I have compare a 360 & a leathered 996 interior, 996 is still better in terms of built quality. Don't get me wrong, the design of the 360 looks better than the 996 inside & out. But I am talking about built quality, not design! German built vehicles - may not be the very best, but simply among the best!

[quote]Originally posted by 02_996_C2: <strong>Excuse me VIKEN, isn't Murci�lago a German & Italian venture? When I said Lambo means the Diablo & Countach. Eveyone knows the Murci�lago has the AUDI like interior & built quality, but guess what? another german owned car company!</strong><hr></blockquote> Oh, I didn't realize you were comparing some cars from a past era with the present era German cars. Sorry about that. [quote]<strong>I knew you have a 360 in your garage. I have compare a 360 & a leathered 996 interior, 996 is still better in terms of built quality. Don't get me wrong, the design of the 360 looks better than the 996 inside & out.</strong><hr></blockquote> <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" /> <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" /> <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" /> [quote]<strong>But I am talking about built quality, not design!</strong><hr></blockquote> Me too.

Viken, Wassup! Very unlike yourself. No need for petty arguements. Let them drive at whatever pressure they want. But for me, I do thank you for all the infomation I have gotten on my car. Thanks and keep up the good work.

[quote]Originally posted by bloke: <strong>Wassup! Very unlike yourself. No need for petty arguements. Let them drive at whatever pressure they want.</strong><hr></blockquote> Petty arguments? Where?

Viken, At least you got your sense of humor back today. As for me back to work so I can be more miserable.

[quote]Originally posted by 02_996_C2: <strong>Greg, I don't agree with you! I strongly believed the germans prep their cars as close to spec as possible when they roll out of the assembly line. </strong><hr></blockquote> Strongly believing something doesn't make it true. I haven't done any scientific research but how much pressure is in your tires at delivery is hardly a noteworthy spec. I sure wouldn't put any credence in that. If your car was delivered with a quart of oil low (mine was) does that mean all Porsche should have less than the stated oil level? Absolutely not, the dealer just overlook this and other things as well. Greg

Greg, please read what i said, every manufacturer has their range of tolerances on production. I also mentioned germans prep their cars as close to spec as possible. There is always human errors, overlook of things. I also said, depend on your luck!!! A quart of oil less when you got your car, still within safety margin...not going to hurt your car/engine. Differences in tire pressure in your car is also kind of tolerances in manufacturing standpoint. That's why not all 996 has the engine problem. Some do, some don't. That is tolerances, or your luck! I just want to share my findings with everyone here, just trying to tell everyone 44psi on tire is ridculous! That is! You can run anything you want anyway. Just read that, the PAG recommends number is way off!!!! Nothing offensive, but back to the point, PAG rec. tire pressures are questionable and german cars are prepped among the best is unquestionable. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

With respect to tire pressures what can go wrong with having PAG's recommendations for tire pressures? I imagine if for street it shouldn't be a problem but for track use that's a different story since tires get so hot tire pressures go way up above 44 psi. I set mine at 36 rear/32 front for track but inflate to normal specs for street. Regards. Mike

OK. Let's see if we can confuse the issue some more. Here are pictures of PZero's on a friends '02 996 TT that he runs at the recommended pressures of 36/44 on the street, and slightly HIGHER when he runs on the track. And, boy, does he run on the track. He's been to Dijon, Nurburgring, and Dijon again, all in the last few months. Without further ado, here are the pics: Early on: Much later:

palting how many miles on the tires in the "much later" pictures? they certainly don't appear worn out in the center of the tread alhough the outer edge has lost almost all tread.agreed? what do you think viken? <img src="confused.gif" border="0">

[quote]Originally posted by ignacio: <strong>palting how many miles on the tires in the "much later" pictures? they certainly don't appear worn out in the center of the tread alhough the outer edge has lost almost all tread.agreed? [...] </strong><hr></blockquote> Hi guys, These tires are (were!) mine, so here are the details. (Hey Palting, nice to see you here too!) Pictures 2 (front tire) was taken at the end of a track-day in Dijon. Picture 1 (rear tire) has been taken a few days later, after about 500-600 km driven on the street. I then had to replace the rear ones in prevision of some other track-days and of some longer trips. Picture 3 is from the left rear tire. But this is not the same tire as pic 1 and 2. This tire survived 4 days at the Nuerburgring, 2 days in Dijon, and quite a few 'normal' km. After my last day in Dijon, it was obvious that the left-hand tires were much more worn out than the right-hand ones. Yeah, Dijon and the N'ring both turn clockwise. About the pressure: I've no real clue what pressure to use on the track, that's why I keep the street settings. I've been recommended to set it a little bit higher, but I'm still looking for good advices... BTW, I'll spend next Sunday and Monday in Imola/IT, and will ask the instructors about that. Greetings, --Pierre

I discussed this with a friend of mine who is a Carrera Cup driver. When racing, they use: 20-21 cold which becomes when hot 30-31 on both front and rear.

Hey, Pierre, good to see you here! You'r my kind of guy. The kind that doesn't obsess about his Porsche. Just takes it and drives it! OK, there's the skinny on those tires, guys.

[quote]Originally posted by 993RS: <strong>I discussed this with a friend of mine who is a Carrera Cup driver. When racing, they use: 20-21 cold which becomes when hot 30-31 on both front and rear.</strong><hr></blockquote> I don't think we should confuse the issue by including racing slicks into the picture.

[quote]Originally posted by 993RS: <strong>I discussed this with a friend of mine who is a Carrera Cup driver. When racing, they use: 20-21 cold which becomes when hot 30-31 on both front and rear.</strong><hr></blockquote> RS, You can't equate a race tire's pressure with anything street legal. Interesting data point, but totally irrelevant. As Viken noted earlier, Ferrari even recommends different pressures for different tires.

Why irrelevant? It seems to point out to me that for extreme racing low tire pressure is used. At the other end, Porsche AG recommends high tire pressure to optimize tire safety in street usage (less deformation).

RS, The reason it is irrelevant is because you are trying to make a comparision of racing slicks to street tires. Anyone that has driven on both of them knows that what works for one will mostly likely not work for the other. Kind of an apples to oranges comparision. NO make that watermelon to lemons. And when I race on DOT R compounds I start with 31/33 and end up with close to 40. What does that tell you? Absolutely nothing. Greg

Sorry, I was not clear: he has a Carrera Cup car but is competing in Club Sport which races with Pirelli Pzeros not slicks.

993RS- Does your friend with the cupcar feel that the pressures he's using is optimal setting for his car and has he tried other pressures for a comparison. What was the discernible difference running at those pressures versus running on higher pressures? Last- can I have your car : )? Regards. Mike

[quote]Originally posted by 993RS: <strong>Sorry, I was not clear: he has a Carrera Cup car but is competing in Club Sport which races with Pirelli Pzeros not slicks.</strong><hr></blockquote> Are you sure they are street tires and not R compounds? There is a P-Zero C that is a in between a slick and a street tire. I think its replacement will be called the Corsa.

[quote]Originally posted by 996FLT6: <strong>993RS- Does your friend with the cupcar feel that the pressures he's using is optimal setting for his car and has he tried other pressures for a comparison. What was the discernible difference running at those pressures versus running on higher pressures? Last- can I have your car : )? Regards. Mike</strong><hr></blockquote> Mike, Think about it for a sec. Why would a racer in a well known series run a tire pressure that will give him less than optimal performance? Part of the set up process is to try different pressures and find what works best for the conditions. This type of trial and error process goes on in all forms of racing and even Driver's Ed events. Heck I do the same with my street car. Not trying to be a smart *** your question just struck me odd. Greg

Greg just wanted to know what discernible differences when they did try out the different pressures on a cup car. Do they vary pressures depending on weather/track conditions etc. Mike

Mike, All tires have an optimal pressure where they get the best performance. It will vary from track to track and day to day, much of it depending on the ambient and track temps. Most teams will use nitrogen so the difference between the cold and hot temps is minimized. And in most pro series a tire engineer within the team or from the tire manufacture will be there to give guidance on suspension geometry, temps and pressures. His job is to make sure the car is set up to get the most out of the tires. I think a ten lb gain is high. I don't use nitrogen and I will see a 8lb gain or so depending on the day, but that depends on the conditions. Often I will end up with a different pressure in each tire, the drivers side tire usually takes the lowest pressure since it gets "used" the most. Clear as mud, eh?

Greg-it's all good now : ). Now to make things all bliss can I have both your cars to match with 993RS's : )? Regards. Mike

Greg, Yes, his is running P Zero Corsa tires. Mike, I am kind of far away... Regards, Phil

Mike, Sure you can have them both, just pry them out of my cold dead hands first Phil, You ought to try the Corsa for your street tire. If you are only getting 4-5K miles on regular tires. The performance difference is dramatic. Try a set, heck your buddy could probably get you a set of takeoffs that would work also. Greg