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Tires/Tire size and replacement


Can tire size P235/50R18 work to replace tire size P 245/45 R18?  I have a brand new full size spare and will be trading the car in as it needs a lot replaced.



First, if the P245/45R18 is an XL (Extra Load), then the P235/50R18 also needs to be an XL (Extra Load).  The diameter of the P235/50R18 is 0.6" larger in diameter, so if this is going on an AWD (All Wheel Drive), that would not function as a single spare because AWD vehicles need to have identical tires all around (with some exceptions!)  If you don't keep the same diameter, then the AWD unit could fail and that would be very expensive to fix.

And lastly, the wheel width requirements have a lot of overlap, but if the wheel is 9" wide (probably not!), then the P235/50R18 will not fit.


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Barry Smith


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.


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.

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

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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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