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944 S2
 
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S2 tire pressures (18”)

Stock is 36 front and rear. I’m running 18’s now (225/40 and 265/35). I purchased the tires from Discount tire and they gave me 39 FR and 36 RR. Tire rack guide I have suggests 31 on the front and 26 on the back. Does that sound right? Why so different? The guide uses the load rating on the specific tires.

What are you guys running with 18” wheels?
Old 09-09-2018, 12:52 PM
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Stock is 36 front and rear. I’m running 18’s now (225/40 and 265/35). I purchased the tires from Discount tire and they gave me 39 FR and 36 RR. Tire rack guide I have suggests 31 on the front and 26 on the back. Does that sound right? Why so different? The guide uses the load rating on the specific tires.

What are you guys running with 18” wheels?
My '86 Na,the tire pressures are listed on the inside of the gas filler door.
Old 09-09-2018, 04:14 PM
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Only way to be certain you are running the correct pressures is to measure tire temperatures. Buy yourself a Infrared thermometer/pyrometer, they are not expensive and are useful for a bunch of other stuff.
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Old 09-09-2018, 04:49 PM
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Realistically, you will have to experiment a little to find the right tire pressure.
All pressures should be measured cold, or less than one mile of normal driving.

Start out with what the owner's manual, or the tire pressures on the gas door.
Increasing tire pressure will make the ride harsher, but handling may improve.
Lower tire pressure will soften the ride, but handling will decline.

Unfortunately, you didn't provide the tire Load Rating, so the table doesn't really help.

39PSI seems high for the front. 36/36 is what I use and it seems right. I have found that Porsche numbers seem to be the best compromise between handling and ride comfort, with a bias towards handling.
Old 09-09-2018, 08:09 PM
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My Mercedes C350 Sport Sedan has a recommended pressure of 33F/38R. I run Continental Extreme Sport DW tires ( 225/40 and 255/35) on 18" AMG wheels. I get excellent handling and even tire wear with those pressures.

Last edited by Spring44; 09-09-2018 at 10:18 PM..
Old 09-09-2018, 10:09 PM
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Certainly don't take the setting from a tire shop as any type of recommendation on proper pressure. Last time I had tires mounted, I requested 35 psi all around. I left and couldn't believe how bumpy the ride was so I checked them a couple miles down the road. Either he had it out for me or he was watching the gauge reading as he filled the tire and left me with some tires at 41 psi and one at 47. Also, don't take charts and guides as an informed basis to make a decision, these are more of a sanity check meant to encompass as many different applications as possible.

Proper tire pressure is best measured with a pyrometer for high-performance driving. To maximize cornering grip, you need to find the optimum slip angle of the tire which is affected by tire pressure among many other variables. It is not easy to determine (and overkill for normal street driving) so it is best to start with the manufacturer's recommendation and adjust to suit your driving style and desired balance between performance and comfort.
Old 09-10-2018, 05:47 AM
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Quote:
Originally Posted by RedCarGuy View Post
...
Proper tire pressure is best measured with a pyrometer for high-performance driving...
+1, fwiw this is a method that was told to me which determines the optimal tire pressure. Take your car for a drive then measure inner and outer and center thread temperatures on all four tires. Hotter centers mean you let out air, hotter edges mean you put air in. Once temps are even across the tire thread, let the tires cool overnight then measure pressure and you have found the correct cold pressures for your car/tires.
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Old 09-10-2018, 09:12 AM
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944 S2
 
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Quote:
Originally Posted by Pauld_94S2 View Post
Realistically, you will have to experiment a little to find the right tire pressure.
All pressures should be measured cold, or less than one mile of normal driving.

Start out with what the owner's manual, or the tire pressures on the gas door.
Increasing tire pressure will make the ride harsher, but handling may improve.
Lower tire pressure will soften the ride, but handling will decline.

Unfortunately, you didn't provide the tire Load Rating, so the table doesn't really help.

39PSI seems high for the front. 36/36 is what I use and it seems right. I have found that Porsche numbers seem to be the best compromise between handling and ride comfort, with a bias towards handling.
Just to clarify discount tire told me 39lbs on the front with a load rating of 92 and 36lbs on the rear load rating 97 when I purchased my Michelin super sport in 18”.

According to the sheet I got from tire rack that translates to about 31lbs on the front and 26lbs on the rear. Question is why so different?

According to the Porsche owners manual stock is 36lbs with a load rating at 88 on stock 16” wheels.
Old 09-10-2018, 06:40 PM
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Why does it matter if they're different? Load rating of the tire does not take any account of the actual weight of the vehicle. The numbers you're debating over are extremely non-specific to a 944.

You should be placing much more weight on what the engineers at Porsche recommend vs. god knows who made up these "suggested" charts based on tire rating and nothing vehicle specific.
Old 09-11-2018, 08:06 AM
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