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#### Sierra SnowTurtle

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My 2004 Rav4 4x4 tire size: Factory 235/65/16

235mm x .65 ratio =152.75mm ~ 6.01in (sidewall height)

6.01in X 2 + 16in = 28.02in (tire height)

Circumference = 28.02in*Pi = 88.02in. (distance per rotation)

Larger tire: BFG A/T 235/70/16

235mm x .70 = 164.5mm~6.47in (sidewall height)

6.47in X 2 + 16in = 28.95in (tire height)

Circumference = 28.95in*Pi = 90.95in. (distance per rotation)

For the sake of this theory Iâ€™m assuming 21 Miles per gallon.

21 miles ~ 1330560 in

To cover 21 miles:

1330560in/88.02inches per rotation =

15116.5644 rotations of my 235/65/16 factory tire

Or

1330560in/90.95in per rotation =

14629.5766 rotations of a Larger 235/70/16 BFG tire.

The odometer is calibrated to factory size tire so regardless of the tire size, the computer recognizes one rotation of the wheel as 88.02 inches traveled.

14629.5766 rotations of larger tire * 88.02in = 1287695.3403in ~ 20.323 mile

So the 21 miles traveled on the larger diameter tire will only show up as 20.323 miles on the odometer, a difference of .677 miles per gallon or 8.124 miles over 12 gallons (roughly the size of the tank). Therefore unless the odometer is recalibrated after switching to larger sized tires the distance traveled will appear less than it really is.

Again, just a theory.