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Tires/Over sized tires on a 1990 Jeep Cherokee.

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Question
I have a 1990 Jeep Cherokee Laredo.  The placard on the jeep says the original tires where 205 75R/15 and a tire pressure of 30 PSI.  The jeep currently has LT235/75R15 on it.  What is the proper tire pressure for these larger tires?

Answer
Dino,

I do not recommend using LT tires in place of P type tires - and the reason will be obvious in a moment.

In order to carry the same load a P205/75R15 does at 30 psi, an LT235/75R15 needs to use .... Ah..... Mmmmmm.... well, it turns out that it is off the lower end of the chart - and I don't like recommending anything off the chart.  The chart ends at 35 psi, and I consider that the lowest usable pressure, because it is possible to unseat a tire off the rim in extreme maneuvers at low pressures.  So I would recommend you use 35 psi even though it is way too high for the load.  I don't want to be the guy who makes a recommendation that could cause you potential danger.

I would further recommend you do something about the tire size.

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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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