EcoModder Forum Adjusting for larger tire size

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 02-13-2018, 04:10 PM #1 (permalink) EcoModding Apprentice     Join Date: Jan 2018 Location: Lawrence, Kansas Posts: 100 Aerokee - '97 Jeep Cherokee XJ sport 90 day: 18.22 mpg (US) Scrambler - '74 Honda CL200 Motorcycle 90 day: 55 mpg (US) Thanks: 70 Thanked 38 Times in 24 Posts Adjusting for larger tire size Hi folks I have 31" tires while the stock tires are 28" diameter. 28" tires revolutions per mile: 742 31" tires revolutions per mile: 670 742:670 = 1.1074:1 So I multiply the odometer readings by 1.107 when I calculate my MPG. This works perfectly as I have observed, via a gps-powered iOS app "Speed Box speedometer", that when I'm traveling 70 mph I'm actually going 77 mph. And at 65 mph it's actually over 70 mph. That adds up because 70 * 1.1 = 77 and 65 * 1.1 = 71.5 However! At lower speeds, like 55 mph and below, the car speedo and the speedo app read dead on. They're the same. So should I still be multiplying the mileage by 1.107 if I never drive faster then 40 mph??
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 02-13-2018, 05:21 PM #2 (permalink) Not Doug     Join Date: Jun 2012 Location: Show Low, AZ Posts: 10,855 Chorizo - '00 Honda Civic HX, baby! :D 90 day: 35.35 mpg (US) Mid-Life Crisis Fighter - '99 Honda Accord LX 90 day: 30.79 mpg (US) Gramps - '04 Toyota Camry LE 90 day: 25.88 mpg (US) Thanks: 7,048 Thanked 2,024 Times in 1,545 Posts I do not understand why the speedometer and the app read the same 1 - 55 MPH, but not 56+.
 02-13-2018, 06:19 PM #3 (permalink) EcoModding Apprentice     Join Date: Jan 2018 Location: Lawrence, Kansas Posts: 100 Aerokee - '97 Jeep Cherokee XJ sport 90 day: 18.22 mpg (US) Scrambler - '74 Honda CL200 Motorcycle 90 day: 55 mpg (US) Thanks: 70 Thanked 38 Times in 24 Posts It's not like the app and speedo both read 54 mph, yet the speedo reads 55 and the app reads 60. It's more gradual
 02-13-2018, 07:40 PM #4 (permalink) Master EcoModder   Join Date: May 2012 Location: Tampa, FL Posts: 1,682 Volt, gas only - '12 Chevrolet Volt Premium 90 day: 38.02 mpg (US) Volt, electric only - '12 Chevrolet Volt Premium 90 day: 132.26 mpg (US) Yukon Denali Hybrid - '12 GMC Yukon Denali Hybrid 90 day: 21.48 mpg (US) Thanks: 196 Thanked 403 Times in 289 Posts ... it's a multiplier. __________________
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Yes, multiply the odometer reading by however many percent larger the new tires are, even if you don't drive fast.

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 The Following User Says Thank You to Daschicken For This Useful Post: mannydantyla (02-14-2018)