Optimal tire pressure

I was wondering whether different types of driving require different tire pressure ie. highway vs. city vs. track? How about in snowy conditions? What is the recommended pressure for front & back tires? Thanks

It the optimal pressures are stated in the manual depending on your car and tire size. The only place to deviate is at the track. At the track if left at the recommended pressures the tires go way beyond the highest pressure they would even see on the road, sometimes even higher then the max rating of the tire. I think most people run around 38 hot or there about at the track.

If you do a search you will see this has been asked 100's of times... Here we go again. 36F 40R cold

I run 36 / 44 psi.

I prefer 35F 38R (cold) for street. Track pressure depends on the particular track, ambient temperature and how hard I'm driving, but in general is much lower than street. Out of necessity, track pressures are usually measured hot, so direct comparison to street (cold) pressures is not possible.

For a 4S the manual recommends 36/44, but I usually overfill by a pound or 2. ps...where are the pics!!

Running N1 Michelin Pilot Sport Rib's on a 996 Turbo X50 and I have a Longacre Pyrometer that I use religously. I too thought people were crazy when I read how low they were running their tire pressures. But after doing my own testing, they are right. I'm still trying to find the correct pressures; I'm close and getting closer but for even spirited driving the recommended pressures are too high. It's been around 91 deg. here lately and I've gone as low as 31psi in the front and 39psi in the back and my center tire temps are still higher than the avg. of the outside and inside temps...meaning? Pressure still too high. I'm getting closer... real close at the rear. Next I'm dropping down to 30F and 37R and I think the rear will be correct but the front will probably have to come down even lower... I've even gone so far as to e-mail Porsche (I used to work for Porsche Cars North America) and ask why they recommend such high pressures; hopefully I'll get a response.

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You overfill?! Wow, the recommended pressures ALWAYS feel overfilled to me as is.

Dustinr provides a lot of detail that might not make a lot of sense... Rather than fill tires to a specific pressure, temperature measurements can be made to determine if a tire is overfilled or underfilled for a specific time of day under a specific driving load. This (infra-red) temperature guage costs about $50 and can be used at any time. Just point and click to get the tire temperatures at the inside edge, the center, and the outside edge. If the center of the tire is colder than the edges, you need more pressure. If the center of the tire is hotter than the edges, you need less pressure. If one edge is hotter than the other, you either need an alignment or you've purposely adjusted your alignment for a specific response (racing). Also: Before you try this at home, get some chalk, draw lines across your path and run over the chalk lines. Then check your tires to make sure you're getting full contact across all four tires.

just follow the manual for regular driving... 36F 44R if you track or do AutoX things will change a little bit...

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That's what the owners manuel states for 18" wheels....

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The answer is yes. Optimal pressure varies greatly depending on what tires you have and what you are optimizing for. Gas milage? Tire wear? Performance? Ride? Rim damage? Etc. There is no simple "right" answer. And, the cold pressure is of little value. What you are really concerned about is operating pressure. Obviously operating pressure varies greatly depending on how you are driving, where you are driving, temp, etc.

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+1. It's all relative.

Here's Porsche's lame response to my question as to why they reccomend such high pressures: Hello Mr. Reed, It's important to remember that your vehicle's recommended tire pressure is its cold tire inflation pressure. It should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it. The performance that tire manufacturers build in, low tire pressures can take away. Adjust your tire pressures as indicated on the vehicle tire placard or in the owner's manual. Check your inflation pressures at least once a month and before highway trips. Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling. Kind regards, The Porsche Contact Center 1-800-PORSCHE ([phone removed]) To paraphrase... "We have no clue, we only know what the book says"

Translation #2: "We want no law suits of any tire pressure kind"

I e-mailed them back and asked if they could forward my question to the engineering dept. or their racing development dept. because I wanted a technical explanation and this is what they sent back... Hello Mr. Reed, As our technicians are out in the field at the dealerships, the best person to speak with in regards to this inquiry would be the Service Department at your local Porsche dealer. You can locate your dealer at www.porschedealer.com . Should you need further assistance, please don't hesitate to contact us at 1-800 Porsche, Option 5. Warm regards, The Porsche Contact Center 1-800-PORSCHE ([phone removed]) So they send all of their engineers to the dealerships to just hang out? Wow...that's cool. Haha...

So... how low is too low? I'm at 28F 36R right now. These are the N1 Michelin Pilot Sport Rib tires. I keep lowering the pressures and the centers are still higher than the avg of the outside and inside; although the insides are starting to get hotter (barely) than the centers on the rear. The fronts are 10-15 degrees hotter at the center than the inside & outside. Is this maybe why Porsche went to 19" wheels? In order to get the sidewall stiffness and correct tire contact patch they went to a bigger wheel with a lower profile tire?

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What exactly do you expect Porsche to say? They have no idea how you drive, how closely you watch your pressures, what the condition of the roads you drive are, etc, etc. There is no way they can give you any advice other than to follow the manual or talk to the local techs. The better source would be the tire engineers but I don't think they will discuss it too much either. Way too much liability.

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First, 10-15 degrees is very little variation. Second, in general you drive straight on the centers (depending on camber) and corner on the sides so what you are doing right before you take temps makes a huge difference. In general I would expect the centers to be warmer than the sides on a street car. Porsche went to 19" wheels because they look cool. The cup cars still use 18 inch. FWIW, I keep my tires at 34 front and 36 back cold.

Ok... since we are talking tire pressures. My local PCA (zone 1, NNJR) suggest 2-3lbs on top of factory recommendations on the track. WTF? After my adjustments, I was getting as high as 52psi at the end of the session... After much discussion with other people, there is a wide variations of what people use (on the same model cars)... the range is as low as -10psi and +3psi for the front and -6psi and +3 psi on the rear. With this much variations... Id say tire technology has come along way.

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What tires? That makes no sense to me. It actually sounds dangerous but they must have has a reason for those pressures. Street tires are obviously different than race tires but for comparision, Hoosier engineers suggest somewhere around 36 to 38 hot. That means you have to start at around 28. For our Michelin slicks we start under 20 lbs cold and stay under 30 hot. 52 seems insane to me. Do you know the logic behind the recommendation? Is it specifically for 996s or just DE cars in general?

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These are recommended for just street tires and just DE cars in general.... no I dont understand their logic.... and dont like it. 52 psi does sound high. I will try to dig up why they recommend this... I talked to one instructor and said that for street tires the temp on street tires rises slower. one reason is that the flex on the tires is less on higher pressure. If you lower your pressure the flex (eg: cornering) is greater and is a bigger concern (tire fatigue). To him +7 psi of recommended 36/44 wasnt a big deal, because they are cold pressure from the start... BTW our sessions are 20-25min, 2 in the morning and 2 in the afternoon.

Several years ago I did an Audi DE at Louden in NH and they mandated 5lbs. over(cold) recommended tire pressure. They also checked your cold pressure during tech. inspection before you went on the track.I don't have an explanation as to why though.

I've instructed with Audi Club and they do tend to recommend a bit of overfill, but that's primarily because most of the drivers run 32psi all around. However, I don't think the same should be applied to a P-car; different tires, different weight distribution etc. For new drivers in P-cars at DE days I recommend the factory settings until the driver starts getting fast, expecially in the turns. Then check hot pressures, equalize them side to side and keep them under 40psi.

Using Michelin PS2 an an example in AX/DEs. Has anyone tried driving AX or DE at high (>40#) and lower (34-38#) tire pressure. The higher tire pressure (>40#), from my experience, has a lower grip level leading to slower times. Of course there are other variables not factored in, but in general I do not let my tires get above 38#.

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I have the same tires. I was keeping them at no more than 40 hot. Last de i kept them at about 35-36. They felt much better.

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ok... but Porsche recommend 36/44 cold. Running them at under 40 hot has more tire flex no? isnt this bad? I ran them under 40psi during DE and I agree they do feel better.... but either way, running them hi above cold temp or low hot temp doesnt make sense to me... It almost seems like tire pressures are just one of those trial and error thing till you find something that your comfortable with, a very personal choice.

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No question adjusting tire pressures is totally a black art. Ask 10 people, get 10 different answers. Anyway, a couple of things to keep in mind about adjusting tire pressure on the track As you get faster your hot pressures increase, primarily because you generate larger slip angles in the turns, creating more friction = more heat = more pressure. As a general rule I like to keep hot pressure under the max tire pressure shown on the sidewall. On a hot day at the track if I'm driving hard, I can see an increase of 15 psi or more over cold pressure. Second, tire pressure can be used to tune the handling. Lower pressure gives you more grip by increasing the size of the contact patch, so I run lower pressure up front to help reduce understeer. Just my $0.02.

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I just ran my PS2's at my last autocross 3 weeks ago at 36lbs all around and found them to be much grippier than factory rear pressure recommendations. I also found that the rear would follow the front end much better than at over 40lbs. Granted this is on stock suspension, with 35,000 miles but I actually got TTOS on a faster left hand sweeper. It was great fun as when I got the car the tires where grossly over inflated and at 44lbs all around. The car understeered horribly and wasn't much fun in tighter corners.

I agree with JimB on the pressures. 34 / 36 cold for a track day with PS2 (or lower) . After a couple of laps they can easily come up 5 - 10psi depending on the track. Once they get over 40psi hot it is like driving on ice they really lose grip ... I can't imagine overfilling, sounds dangerous to me .. lower psi is better i have a stock 996, stock alignment, next track day I'm going put as much negative camber in as I can and see if that increases the grip level ..