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California98Civic · 03-24-2019, 11:34 AM

This site offers the formula for how to use tire size to calculate tire diameter:
https://auto.howstuffworks.com/auto-...size-chart.htm

tire diameter:

(CROSS SECTION WIDTH x 0.ASPECT RATIO x 2 ÷ 25.4) + WHEEL DIAMETER = OVERALL TIRE DIAMETER

For Example:

235/45ZR-17

(235 x 0.45 x 2 ÷ 25.4) + 17 = 25.327"

And here's a calculator for the rest of your query:
https://tiresize.com/gear-ratio-calculator/

03-24-2019, 11:34 AM	#2 (permalink)
California98Civic Cyborg ECU Join Date: Mar 2011 Location: Coastal Southern California Posts: 6,299 Black and Green - '98 Honda Civic DX Coupe Team Honda 90 day: 66.42 mpg (US) Black and Red - '00 Nashbar Custom built eBike 90 day: 3671.43 mpg (US) Thanks: 2,373 Thanked 2,174 Times in 1,470 Posts	This site offers the formula for how to use tire size to calculate tire diameter: https://auto.howstuffworks.com/auto-...size-chart.htm tire diameter: (CROSS SECTION WIDTH x 0.ASPECT RATIO x 2 ÷ 25.4) + WHEEL DIAMETER = OVERALL TIRE DIAMETER For Example: 235/45ZR-17 (235 x 0.45 x 2 ÷ 25.4) + 17 = 25.327" And here's a calculator for the rest of your query: https://tiresize.com/gear-ratio-calculator/ __________________ See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.