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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHTire pressure
Reported or suspected cause
over inflation
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No successful repair reported for this finding.
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Leading evidence: 'over inflation' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'over inflation' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Recommend 44 psi is too high' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
At autox I run 30/34 and got to that rear number by chalking sidewalls, front landed there because that made the balance seem about right.
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I run a few PSI down from Porsche's 36/44 rec on the street.
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I run with mine maxed out because I want that bite under cornering loads - but I pay the price, especially with directional tires that are front/rear biased.
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Suggestion
Wear patterns on my last three sets of rear tires indicates to me that the Porsche recommended 44 psi is too high.
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I run with mine maxed out because I want that bite under cornering loads - but I pay the price, especially with directional tires that are front/rear biased.
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Suggestion
While I did experience this wear on the last set after lowering, the wear I am referring to is centres worn concave, while shoulders still with significant tread.
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Wear patterns on my last three sets of rear tires indicates to me that the Porsche recommended 44 psi is too high. I'm going below 40 on this next set.
If the "incorrect" wear is the heavy wearing on the inboard shoulders, your negative camber is probably too aggressive. I run with mine maxed out because I want that bite under cornering loads - but I pay the price, especially with directional tires that are front/rear biased.
I run
34/38ish, since it's usually just me in the car.
Porsche specifies different pressures for 18" and 17" tires. Based on your number, I guessing you have 17" tires. I'm on 17" Michelin PS3s (not the plus) and like about 37 psi much better.
While I did experience this wear on the last set after lowering, the wear I am referring to is centres worn concave, while shoulders still with significant tread.
Better question then what others do is "how low can you go for savety of tires.
This" Pigheaded Dutch selfdeclared tirepressure-specialist "can help you with determining this lowest safe pressure at wich even wear, best comfort and gripp.
Pressure advice was in earlyer days to give the tire a deflection for the speed, that wont overheat any part of rubber of tire, when driving that speed constantly.
This rule did not go for higher speeds as used by Porches sometimes , there they assumed this speed not to take that long and not with weights on tires for wich pressure was calculated.
I once got hold of the official formula that ETRTO ( european) uses , and went running with it.
Now use my own formula that is even saver.
Goal is to give the tire a heatproduction so deflection , the same as when maximum load and reference-pressure on and in tire.
So if you are only crusing , maximum speed you use and wont go over for even a minute, is probably below 140kmph/87mph.
If you give tirespecifications and data of car to determine the real weights on tire( the most tricky part in it all) , I can calculate a save lowest pressure with some reserve for unequall loading R/L, pressure loss in time or inacurate reading, etc etc.
Then you have maximum comfort and gripp , and save for the speed you use AND WONT GO OVER FOR EVEN A MINUTE!!!!!!!!!.
So if you are crusing, and you are passed by another Porche with higher speed, then dont go racing with him/her, then your tires will overheat, and beginning permanent damage is done. In time this damage will build up , whatever you do afterwards, and then mayby only after 2 years that much damage that the tire blows or treath seperation, and accident with only damage if you are lucky. Then you already forgotten that time that you raced 2 years ago, and blame the tiremaker or my determined lower pressure .
I run a few PSI down from Porsche's 36/44 rec on the street. I think these are super safe pressures that sacrifice comfort to minimize overheating at prolonged high speeds from sidewall deflection, especially on the rears. At autox I run 30/34 and got to that rear number by chalking sidewalls, front landed there because that made the balance seem about right. If road comfort is a priority, I'd look for shocks that can provide you a better ride (old shocks can give you a sloppy but still harsh feeling ride). Running super low pressures just for comfort seems like a roundabout way of achieving your goal. You might also get an alignment that takes some negative camber out. More negative camber generally hurts ride quality. If you're just cruising, you probably won't miss the camber. Just mind that rear end when you do get after it somewhere twisty. If it's still too stiff riding, maybe a sports car is the wrong tool for your use case
Why is everything with this car so complicated and subjective? I've been using the Porsche-provide numbers all along. With the conditions of the roads in my area, you risk losing fillings whenever you take the car out for a drive. I'll give lower pressures a try.
I'm going to try 34 front..and 38 rear think that the shocks should be OK on my 03 Cab at 38,000 miles, and new Sumitimo 18's ...a garage kept "cruiser"
I bought this car because to takes me back to my first 911, an 80 that I bought around 82.....(long story about how I probably almost became a Ferrari person)
It was a tripe Black Targa, that I kept for about 3 years....now all these years later,
6 911's, 4 Boxsters, 2 356's and a 914 later...
It just caught my attention and I "needed a 911 to justify my PCA membership of 40 years....
So, it's a weekend cruiser...and social PCA event car......
I did some looking into this a while back and after experimentation am now happy with 34/39psi with 19�s and stock widths and sidewall on my C4s. There is no perfect psi, just what works best for you to deliver the best ride/handling while satisfying needs of the tire for even wear. And of course requires proper alignment and camber settings.
