Tire Pressure

[DamageINC123]

Any suggestiuons on tire pressure? I have a set Michelin Pilot Sport. 225/45/17 front and 265/40/17 rear. I am currently running 30psi in front and 36psi rear.

[goldenwarrior1]

Any suggestiuons on tire pressure? I have a set Michelin Pilot Sport. 225/45/17 front and 265/40/17 rear. I am currently running 30psi in front and 36psi rear.

Quote from your owners manual; :huh:

Tire Pressures for Cold Tires

Summer tires and snow tires

Front 17 inch wheels:

36 psi (2.5 bar) overpressure

Rear 17 inch wheels:

36 psi (2.5 bar) overpressure

Spare wheel

911 Carrera, Targa

Front and rear 60 psi (4.2 bar) overpressure

Collapsible spare wheel

911 Carrera 4, Carrera 4S

Front and rear 36 psi (2.5 bar) overpressure

These tire pressures are valid only for Porsche approved tires.

For replacement tires it is imperative that you consult the Technical Data and Tires, Wheels

sections of this manual and follow the recommendations contained therein.

[DamageINC123]

My owners manual says 29psi front and 36psi but my tires are not factory Porsche. Just looking for suggestions. I guessI will stick with the manual.

[goldenwarrior1]

My owners manual says 29psi front and 36psi but my tires are not factory Porsche. Just looking for suggestions. I guessI will stick with the manual.

Never hurts to ask a question! Correctly inflated tires receive appropriate support from the contained air pressure to provide an even distribution of load across the footprint and help stabilize the tire's structure. And while most drivers recognize that this has a significant impact on tire wear, rolling resistance and durability, only a few realize underinflation also has a noticeable influence on how quickly and precisely the tires respond to the driver's input.

Disadvantages of Underinflation

An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle's tires are underinflated by only 6 psi it could weaken the tire's internal structure and eventually lead to tire failure. Lower inflation pressures will allow more deflection as the tire rolls. This will build up more internal heat, increase rolling resistance (causing a reduction in fuel economy of up to 5%) and reduce the tire's tread life by as much as 25% while increasing the probability of irregular treadwear. Drivers would also find a noteworthy loss of steering precision and cornering stability. While 6 psi doesn't seem excessively low, it typically represents about 20% of a passenger car tire's recommended pressure.

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when encountering potholes or debris in the road, as well as experience irregular tread wear. Higher inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and transmit more noise into its interior. However, higher inflation pressures reduce rolling resistance slightly and typically provide a slight improvement in steering response and cornering stability. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures.

[N41EF]

Somewhere I have a link from a study I read for grad school. It related to how a tire with too high of pressure will hydroplane at a lower speed because the contact area is smaller, less give to the tire, and less control. I think of stuff like that and chuckle when I read about people inflating tires to the max-safe pressure trying to get better milage. All the mialge won't matter when you get blown off the highway in a rainstorm.

IIRC, the speed at which a tire will hydroplane is indirectly proportional to some factor (dealing with the "roughness" of the surface) divided by the square of the pressure in the tire.. IE pressure goes up, hydroplane speed goes down.

I tend to follow the manual on pressure, and adjust it slightly, if any based on tire wear. I have a neighbor who is pretty technical, he checks tire temp in several places across the tread and adjusts pressure to get even temps

[mikefocke]

My owner's manual for a 986 Model Year 01 page 241 says 29PSI (2 bar) for the front tires.

The 05 987 manual says 29 for the 17 and 18 inch front tires on a 987. 32 for the 19" fronts.

I run 30/36 on my 986 and get 18k on my rear tires..

[DamageINC123]

Thanks Mike. I appreciate your input and have enjoyed reading your articles you have posted on the net. Thanks for all the help and research!!

Edited December 8, 2009 by DamageINC123