trip/odomteter affected by bigger tires? -
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Unread 06-15-2008, 11:29 PM   #1
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2007 MK Compass 
Join Date: Jun 2008
Location: Charlotte, NC
Posts: 10
trip/odomteter affected by bigger tires?

Hey, I'm not sure exactly how the mechanics of the trip or odometer (or the gas mileage calculator on the computer) works exactly, but i was wondering if it is linked at all to the speedometer, or would be affected by bigger diameter tires before anything is reprogrammed or recalibrated... anyone know the answer?

in other words if i am really going 9% faster then the speedometer is saying bc of my tires, would that mean i have gone 9% more miles than my trip has shown me as well?


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Unread 06-16-2008, 04:31 AM   #2
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2001 TJ Wrangler 
Join Date: Nov 2007
Location: CT
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I've read in other posts (on the topic) that if you put larger tires on your vehicle, you do have to take it in to have the speedometer recalibrated. I think larger tires make your speedometer have a lower reading then you're actually travelling (depending on how big of a tire you put on-the larger the tire, the greater the discrepancy).

I'm sure Gramps can break it down numbers wise.
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Unread 06-16-2008, 05:30 AM   #3
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2007 MK Compass 
Join Date: Aug 2006
Location: Madison/Janesville, Wisconsin
Posts: 5,624
Actual miles travelled and MPG:
New tire diameter divided by old tire diameter = multiplier

Miles shown on odometer times multiplier = total miles

Total miles devided by gallons used.

Mine as an example:

I had my speedo recaled to 28", that's the most that they can go. You can use 27.3 if you had the standard tires and didn't recal the speedo.

29.1 / 28 = 1.039 (round to 1.04)
262.7 x 1.04 = 273.208
273.208 / 11.464 gal = 23.83 mpg

Actual speed is just the opposite.
Old size devided by new size X Speedo reading.

28 / 29.1 = .96
@ 60 mph = 60 x .96 = your speedo reads 57.6

Artificial intelligence is no substitute for natural stupidity

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