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on my truck i had tire size 235-75-r-15. i am going to a 16'' rim 7"" wide. what tire size should i use to maintain the same distance travled per one wheel turn to keep the same tac. rpm or lower rpm to get the same gas mileage or better. thankyou i will await your answer.jim
 

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Your 235-75-r-15 tire is 28.9 inches in diameter. The section width is 9.3 inches and the section height is 7 inches. If you go to a 235-70-r-16 tire your new diameter will be 29 inches with a section width of 9.3 inches and the section height 0f 6.5 inches. Slightly larger circumference and a bit better mileage maybe.

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Go to www.4lo.com and use the tire size calcualtor to find the approximate diameter of a tire (forget about the "LT" in front, works with standard car sizes) and the gear calculator to determine the rpm/speed of the tire you have, then enter the new diameter to figure out what size gets you closest to those figures. Use "1" for transfer case ratio (1:1). There are other sites with similar calculators, that's just the one that's easiest for me to remember. The gear calculator will calculate whichever piece of data you leave out -- just remember to leave one out.
 
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