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Tire pressure - Z-rated tires

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Old 08-09-14, 05:59 PM   #1
bryan11
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Default Tire pressure - Z-rated tires

My 2008 IS350 RWD with the sport package and 18" wheels came with a set of z-rated summer tires. I'm driving mostly with my family and am looking for comfortable driving with the ability for fast lane changes and such when needed. Max cold pressure on the tire is 51psi, but all tires were at 36psi when I purchased it. The manual says for my tire size, pressures should be 35psi front and 38psi rear.

What tire pressure do you prefer? Should they be different front and back?
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Last edited by bryan11; 08-09-14 at 06:09 PM..
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Old 08-09-14, 06:14 PM   #2
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I use recommended pressure. Car feels like it is floating compared to my S2000.
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Old 08-10-14, 11:22 AM   #3
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36 is right about where I'd run them.
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Old 08-11-14, 03:32 PM   #4
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Definitely go recommended pressure. And make sure you are checking the pressure when the tires are warm, not cold. Drive on them for 20 minutes and check. It likely won't make more than a few pounds of difference, but it can effect tire wear.
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Old 08-11-14, 04:52 PM   #5
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Quote:
Originally Posted by RangerJoe View Post
Definitely go recommended pressure. And make sure you are checking the pressure when the tires are warm, not cold. Drive on them for 20 minutes and check. It likely won't make more than a few pounds of difference, but it can effect tire wear.
That's wrong. For a passenger car, tire pressures should be measured when the tires are cold.

If I underinflate my tires, the excess flexing of the carcass will heat the tire, thereby increasing the pressure, and it will register the recommended pressure if I measure when the tire is warm (after driving on it). But the tire will be underinflated. That's why tire pressures are specified for cold tires.

On a race car you're trying to achieve certain spring rates with tire pressure, so the tire pressure when the tire comes up to temperature matters (though unless you've got tire warmers you're setting the pressure when the tire is cold, and calculating where it will be when warm).
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Old 08-12-14, 06:32 PM   #6
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That's wrong. For a passenger car, tire pressures should be measured when the tires are cold.
I stand corrected. I have apparently been reading too many racing forums. This guy is right for passenger cars.
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