My Tire Pressure
05-15-2013, 11:37 AM
#1
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My Tire Pressure
It's such a nice day outside - here in Bradenton, FL - that I thought I would come here and stir the pot with some of my tire pressure experiences. I'm sure a lot of you will disagree with me, but here goes.
I have owned at least one 928 since 1984. During that time I have had many different tires on the cars, with varying tire pressures. My current 89 S4 has a sticker inside the fuel door that says recommended tire pressures are 36 front and 44 rear. I'm not sure how they derived those recommended tire pressures, but in the past when I have used them I would get virtually all the wear from the center of the tire. By the time the center of the tire showed it needed to be replaced, the outer edges were almost new.
I would imagine the recommended tire pressures are for racing - although I don't know that to be true. I'm just guessing. But since this car is my daily driver, and I don't race it, I was looking for a tire pressure that would wear the tires evenly. Here are a couple of pics of the front and rear tires that I just took. As you can see, they are wearing evenly and the sidewall is firm.
The tires are Brigestone Potenza RE750's, 225/50/16 in the front and 245/45/16 in the rear, but since I just got this car in Sept. of last year I don't know how many miles are on them. However, since then I have put about 9K miles on them myself, and they still have plenty of thread. I would hope to get anther 10K out of them - but who knows.
The bottom line is I have been using 30 lbs of pressure on all tires with no adverse steering or performance problems. If I were to put the car on the track, I would certainly inflate the tires to the recommended pressures, but I have not found the need to do so as a daily driver.
If you have not tried this tire pressure, you may want to give it a try and see how it works for you and your driving style. However, your subjective judgement can be easily swayed by any preconceived notions on how this is going to work, so try to be fair with any judgements.
I have owned at least one 928 since 1984. During that time I have had many different tires on the cars, with varying tire pressures. My current 89 S4 has a sticker inside the fuel door that says recommended tire pressures are 36 front and 44 rear. I'm not sure how they derived those recommended tire pressures, but in the past when I have used them I would get virtually all the wear from the center of the tire. By the time the center of the tire showed it needed to be replaced, the outer edges were almost new.
I would imagine the recommended tire pressures are for racing - although I don't know that to be true. I'm just guessing. But since this car is my daily driver, and I don't race it, I was looking for a tire pressure that would wear the tires evenly. Here are a couple of pics of the front and rear tires that I just took. As you can see, they are wearing evenly and the sidewall is firm.
The tires are Brigestone Potenza RE750's, 225/50/16 in the front and 245/45/16 in the rear, but since I just got this car in Sept. of last year I don't know how many miles are on them. However, since then I have put about 9K miles on them myself, and they still have plenty of thread. I would hope to get anther 10K out of them - but who knows.
The bottom line is I have been using 30 lbs of pressure on all tires with no adverse steering or performance problems. If I were to put the car on the track, I would certainly inflate the tires to the recommended pressures, but I have not found the need to do so as a daily driver.
If you have not tried this tire pressure, you may want to give it a try and see how it works for you and your driving style. However, your subjective judgement can be easily swayed by any preconceived notions on how this is going to work, so try to be fair with any judgements.
05-15-2013, 12:34 PM
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On Bilsteins I find 32 is about as high as I can stand on our patched-up central-city streets. 30 is about right for me for comfortable everyday driving.
I read somewhere once that Germans have very smooth, well-maintained streets and highways, maybe 36/44 is good for home market conditions in a 928.
I read somewhere once that Germans have very smooth, well-maintained streets and highways, maybe 36/44 is good for home market conditions in a 928.
05-17-2013, 07:50 PM
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I'm glad you both concur with my thoughts. However, I'm actually surprised. I thought I'd get a big response saying to follow the pressures on the placard and live with the tire wear from the middle of the tire.
05-18-2013, 12:37 AM
#6
S4 and GT fitted with RDK pressure sensor alarm system require pressures of 36 front and 43 psi rear.
These are the vehicles fitted with the Digital Cluster alarm system.
Many owners had trouble with the RDK system and disconnected it and some then varied the tyre pressure to suit themselves.
Porsche discontinued the RDK system with the GTS due to the complaints received, I believe, and they lowered the recommended pressure pressure into the 30s as well as installing 17 Cup rims.
Interesting to note that 928 fitted with RDK indicate the low tyre pressure as a critical alarm condition.
I have two set of manhole wheels and all RDK sensors and pickups work correctly when they are set up as designed and I have no problem with the tyre wear with the alignment and ride height set to specifications with the tyre pressure 36 and 43 psi.
These are the vehicles fitted with the Digital Cluster alarm system.
Many owners had trouble with the RDK system and disconnected it and some then varied the tyre pressure to suit themselves.
Porsche discontinued the RDK system with the GTS due to the complaints received, I believe, and they lowered the recommended pressure pressure into the 30s as well as installing 17 Cup rims.
Interesting to note that 928 fitted with RDK indicate the low tyre pressure as a critical alarm condition.
I have two set of manhole wheels and all RDK sensors and pickups work correctly when they are set up as designed and I have no problem with the tyre wear with the alignment and ride height set to specifications with the tyre pressure 36 and 43 psi.
05-18-2013, 01:46 AM
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Had a 2007 BMW X3 with sport package, besides suspension wheels and trim the top speed limiter was raised to 160mph. The recommended tire pressures were 36psi with a special note to bump the pressures up the 44psi if planning to drive at speeds over 100mph. Higher pressures help to keep the tires from overheating and having a blowout. Porsche may have found this true with only the rear tires on the cars with RDK with the tires available at that time.
By the time the GTS came out tire constructions had changed and the recommendation was 36psi all round.
As a note, I monitored tire pressures and temperatures extensively driving my car under all sorts of conditions included autocross, track, highway and city. Different tire brands and models are all different with what cold pressure works best. The Dunlop Direzzas I currently have on the car work best at 28psi cold for the track snd auto crossing, and 32psi for street and highway. It was interesting to me that at higher pressures the tires would feel squirmy and the centers of the tread would overheat and blister.
When I was runing Bridgestone Potenzas they worked best at 33psi cold for everything. When I talked to Bridgestone about the best pressures and the testing I had done he said it would take 4 psi in either directions to make any difference in how the tire heated and/or handled. I found this to be very true.
By the time the GTS came out tire constructions had changed and the recommendation was 36psi all round.
As a note, I monitored tire pressures and temperatures extensively driving my car under all sorts of conditions included autocross, track, highway and city. Different tire brands and models are all different with what cold pressure works best. The Dunlop Direzzas I currently have on the car work best at 28psi cold for the track snd auto crossing, and 32psi for street and highway. It was interesting to me that at higher pressures the tires would feel squirmy and the centers of the tread would overheat and blister.
When I was runing Bridgestone Potenzas they worked best at 33psi cold for everything. When I talked to Bridgestone about the best pressures and the testing I had done he said it would take 4 psi in either directions to make any difference in how the tire heated and/or handled. I found this to be very true.