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Old 03-25-2015, 07:15 AM   #1
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Air pressure

I have an 01 S model with the 18" staggered wheel option. My question is what do you guys do for air pressure? I know the plaque says 29 front and 36 rear but with the extra load tires that are so common in these sizes that still feels like a lot. There is ZERO sidewall bulge at that pressure and the front end feels nervous. Has anybody experimented with lower pressures? Thanks

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Old 03-25-2015, 08:34 AM   #2
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Originally Posted by bwillia080261 View Post
I have an 01 S model with the 18" staggered wheel option. My question is what do you guys do for air pressure? I know the plaque says 29 front and 36 rear but with the extra load tires that are so common in these sizes that still feels like a lot. There is ZERO sidewall bulge at that pressure and the front end feels nervous. Has anybody experimented with lower pressures? Thanks
If anything, I put in a couple pounds more. I think with less you are going to see uneven wear from the sides and middle. My wheel man says a little extra helps keep from bending a rim on the many potholes we seem to have also. Not much rubber there for cushion.
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Old 03-25-2015, 08:41 AM   #3
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I run about 30/31 in the front and 38/39 in the rears
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Old 03-25-2015, 09:03 AM   #4
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I have the same size rims. I like 30 F/34 R.
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Old 03-25-2015, 09:06 AM   #5
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Originally Posted by bwillia080261 View Post
I have an 01 S model with the 18" staggered wheel option. My question is what do you guys do for air pressure? I know the plaque says 29 front and 36 rear but with the extra load tires that are so common in these sizes that still feels like a lot. There is ZERO sidewall bulge at that pressure and the front end feels nervous. Has anybody experimented with lower pressures? Thanks
I like the numbers posted here. I go a little higher for daily driving as well. AX and Track days, whole different story!! I assume you ARE talking street driving, not racing pressures...
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Old 03-25-2015, 09:07 AM   #6
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I have the same size rims. I like 30 F/34 R.
Joe - not to get off topic, but what are the rim sizes on your 18's?

thanks!
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Old 03-25-2015, 09:26 AM   #7
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I have tried up and down, winter time summer time
I have settled on the recommend 29/36 on my 18" staggered.
Tires wearing evenly
+ psi harsher ride
- psi a bit squirmy
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Old 03-25-2015, 09:53 AM   #8
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It's my personal policy to never have less than 30 psi in any tire on any vehicle.

Therefore I do 30 and 36.

This said, there really is little reason to doubt the Porsche recommendation.
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Old 03-25-2015, 11:42 AM   #9
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It's my personal policy to never have less than 30 psi in any tire on any vehicle.

Therefore I do 30 and 36.

This said, there really is little reason to doubt the Porsche recommendation.
yup, 30/36 here.
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Old 03-25-2015, 12:06 PM   #10
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Joe - not to get off topic, but what are the rim sizes on your 18's?

thanks!
Well, I know the rears are 18x10, and although I'm pretty sure the fronts are 18x8, I'm not near the car to check, and I'm not positive. 225/18 F and 265/18 R tires (I remember that much). They're the 996 Carrera 5-spokes, optional on the 2003 Boxster S.

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Old 03-25-2015, 12:25 PM   #11
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Well, I know the rears are 18x10, and although I'm pretty sure the fronts are 18x8, I'm not near the car to check, and I'm not positive. 225/18 F and 265/18 R tires (I remember that much). They're the 996 Carrera 5-spokes, optional on the 2003 Boxster S.
Did your car come with those wheels or did you buy them and install them? For the Boxster the Carerra Light wheels are Fronts 18 x 7.5 Rears are 18 x 9. The size you posted are from the wheels used on the Carerra.
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Old 03-25-2015, 03:21 PM   #12
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Previous owner installed them.
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Old 03-25-2015, 03:38 PM   #13
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Originally Posted by KRAM36 View Post
Did your car come with those wheels or did you buy them and install them? For the Boxster the Carerra Light wheels are Fronts 18 x 7.5 Rears are 18 x 9. The size you posted are from the wheels used on the Carerra.
ah - that is what I was looking for. So 18" wheels on a Boxster as a factory option was 7.5" wide in front and 9" wide in back...great!

I'm trying to figure out if my wheels on my 2000 S are stock or not!!
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Old 03-25-2015, 09:04 PM   #14
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The stock tire pressures were defined to ensure that the car has understeer and not oversteer. This is also the reason for the staggered tire widths (narrow in front, wider in rear).

Thus, generally the goal of tire pressure changes to a stock Boxster is to decrease the amount of understeer inherent in the design. To achieve this, slightly increase the front pressure and decrease the rear pressure. 31 front and 33 rear is a good starting point.
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Last edited by thstone; 03-25-2015 at 09:08 PM.
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Old 03-25-2015, 09:17 PM   #15
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the vehicle's manufacturer's recommended inflation is to provide you with the optimal straight line braking for the car, lessening the potential for a collision. of course when you are looking for other optimal characteristics the pressures will vary, but the short line braking is the factor which incurs the highest amount of liability to the manufacturer.
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Old 03-26-2015, 11:48 AM   #16
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Originally Posted by Dlirium View Post
I like the numbers posted here. I go a little higher for daily driving as well. AX and Track days, whole different story!! I assume you ARE talking street driving, not racing pressures...
Yes, absolutely, just street driving.

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