Optimal tire pressure
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Joined: May 2008
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From: London, UK
Optimal tire pressure
I was wondering whether different types of driving require different tire pressure ie. highway vs. city vs. track? How about in snowy conditions?
What is the recommended pressure for front & back tires?
Thanks
What is the recommended pressure for front & back tires?
Thanks
Nordschleife Master
Joined: Mar 2004
Posts: 8,573
Likes: 97
From: great white north
It the optimal pressures are stated in the manual depending on your car and tire size. The only place to deviate is at the track. At the track if left at the recommended pressures the tires go way beyond the highest pressure they would even see on the road, sometimes even higher then the max rating of the tire. I think most people run around 38 hot or there about at the track.
Burning Brakes
Joined: Nov 2006
Posts: 915
Likes: 18
From: Northern Nevada
I prefer 35F 38R (cold) for street. Track pressure depends on the particular track, ambient temperature and how hard I'm driving, but in general is much lower than street.
Out of necessity, track pressures are usually measured hot, so direct comparison to street (cold) pressures is not possible.
Out of necessity, track pressures are usually measured hot, so direct comparison to street (cold) pressures is not possible.
Instructor
Joined: Jan 2005
Posts: 117
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From: Reno, NV
Running N1 Michelin Pilot Sport Rib's on a 996 Turbo X50 and I have a Longacre Pyrometer that I use religously. I too thought people were crazy when I read how low they were running their tire pressures. But after doing my own testing, they are right.
I'm still trying to find the correct pressures; I'm close and getting closer but for even spirited driving the recommended pressures are too high. It's been around 91 deg. here lately and I've gone as low as 31psi in the front and 39psi in the back and my center tire temps are still higher than the avg. of the outside and inside temps...meaning? Pressure still too high. I'm getting closer... real close at the rear. Next I'm dropping down to 30F and 37R and I think the rear will be correct but the front will probably have to come down even lower... I've even gone so far as to e-mail Porsche (I used to work for Porsche Cars North America) and ask why they recommend such high pressures; hopefully I'll get a response.
I'm still trying to find the correct pressures; I'm close and getting closer but for even spirited driving the recommended pressures are too high. It's been around 91 deg. here lately and I've gone as low as 31psi in the front and 39psi in the back and my center tire temps are still higher than the avg. of the outside and inside temps...meaning? Pressure still too high. I'm getting closer... real close at the rear. Next I'm dropping down to 30F and 37R and I think the rear will be correct but the front will probably have to come down even lower... I've even gone so far as to e-mail Porsche (I used to work for Porsche Cars North America) and ask why they recommend such high pressures; hopefully I'll get a response.
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Registered User
Joined: Jun 2003
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A little more explanation
Dustinr provides a lot of detail that might not make a lot of sense...
Rather than fill tires to a specific pressure, temperature measurements can be made to determine if a tire is overfilled or underfilled for a specific time of day under a specific driving load.
This (infra-red) temperature guage costs about $50 and can be used at any time. Just point and click to get the tire temperatures at the inside edge, the center, and the outside edge.
If the center of the tire is colder than the edges, you need more pressure.
If the center of the tire is hotter than the edges, you need less pressure.
If one edge is hotter than the other, you either need an alignment or you've purposely adjusted your alignment for a specific response (racing).
Also:
Before you try this at home, get some chalk, draw lines across your path and run over the chalk lines. Then check your tires to make sure you're getting full contact across all four tires.
Rather than fill tires to a specific pressure, temperature measurements can be made to determine if a tire is overfilled or underfilled for a specific time of day under a specific driving load.
This (infra-red) temperature guage costs about $50 and can be used at any time. Just point and click to get the tire temperatures at the inside edge, the center, and the outside edge.
If the center of the tire is colder than the edges, you need more pressure.
If the center of the tire is hotter than the edges, you need less pressure.
If one edge is hotter than the other, you either need an alignment or you've purposely adjusted your alignment for a specific response (racing).
Also:
Before you try this at home, get some chalk, draw lines across your path and run over the chalk lines. Then check your tires to make sure you're getting full contact across all four tires.
Addict
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Rennlist Member
Joined: May 2001
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From: MN
And, the cold pressure is of little value. What you are really concerned about is operating pressure. Obviously operating pressure varies greatly depending on how you are driving, where you are driving, temp, etc.
Racer
Joined: Feb 2007
Posts: 462
Likes: 1
The answer is yes. Optimal pressure varies greatly depending on what tires you have and what you are optimizing for. Gas milage? Tire wear? Performance? Ride? Rim damage? Etc. There is no simple "right" answer.
And, the cold pressure is of little value. What you are really concerned about is operating pressure. Obviously operating pressure varies greatly depending on how you are driving, where you are driving, temp, etc.
And, the cold pressure is of little value. What you are really concerned about is operating pressure. Obviously operating pressure varies greatly depending on how you are driving, where you are driving, temp, etc.
Instructor
Joined: Jan 2005
Posts: 117
Likes: 0
From: Reno, NV
Here's Porsche's lame response to my question as to why they reccomend such high pressures:
Hello Mr. Reed,
It's important to remember that your vehicle's recommended tire pressure is its cold tire inflation pressure. It should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it.
The performance that tire manufacturers build in, low tire pressures can take away.
Adjust your tire pressures as indicated on the vehicle tire placard or in the owner's manual. Check your inflation pressures at least once a month and before highway trips.
Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling.
Kind regards,
The Porsche Contact Center
1-800-PORSCHE
(1-800-767-7243)
To paraphrase... "We have no clue, we only know what the book says"
Hello Mr. Reed,
It's important to remember that your vehicle's recommended tire pressure is its cold tire inflation pressure. It should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it.
The performance that tire manufacturers build in, low tire pressures can take away.
Adjust your tire pressures as indicated on the vehicle tire placard or in the owner's manual. Check your inflation pressures at least once a month and before highway trips.
Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling.
Kind regards,
The Porsche Contact Center
1-800-PORSCHE
(1-800-767-7243)
To paraphrase... "We have no clue, we only know what the book says"
