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Tires/tire pressure

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Question
Hi Barry!
I think you can help me.

My daytime temp is 33F and night time temp is 23F.

The sticker on the driver-side door shows "30 PSI Cold".
I pumped up my tires, on a Mercury Sable, to 35 PSI. Is 35 PSI too high?

I've read about the tire's sidewall showing the maximum pressure recommended for the tires, BUT I CAN'T FIND THE DARN THING!

The words are hard to read. Where is that recommended temperature?

Thanks for your help.

Chris

Answer
Chris,

Some of the lettering on tires is extremely small, but it isn't needed if you are using the vehicle tire placard and the tire size indicated there.  The fact that you can't read it is merely inconvenient.

If you are using 35 psi where the vehicle tire placard calls for 30, you are probably OK.

There is a rule of thumb that for every 10F change in temperature,the tire pressure in passenger car tires changes 1 psi.  So if you inflate your tires to 35 when it is 50F, then they will be 30 psi at Zero degrees F.  What you want to avoid is not having enough.

Plus, the max listed on the sidewall of tires is somewhat misleading.  That's supposed to be the max usage pressure, and it is NOT the pressure where the tire starts to fail.  It's a long complicated story, but you would have to really over-inflate your tires to get into the region where the pressure is a failure issue.

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Barry Smith

Expertise

I have over 30 years experience in the design, manufacturing, and testing of tires. I have served as the technical advisor to the "800" number. I have authored or co-authored many publications - usually without credit. I can answer almost any technical question, but please don`t ask me to compare brands. I probably have prejudices because of my work experience.

Experience

Member SAE (Society of Automotive Engineers) Member Tire Society (Tire Technical Organization) SCCA Regional Competiton License holder Authored many training manuals on tires, their care and use.

Organizations
SAE (Society of Automotive Engineers) SCCA (Sports Car Club of America) Tire Society

Publications
You may want to visit my web site: http://www.barrystiretech.com/index.html

Education/Credentials
I am a graduate of the University of Dayton, Dayton, OH - BME, 1971 I attended graduate school at the University of Akron - but did not complete my PhD - something I regret.

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