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Effect of tire size on odometer readings
- The odometer “calculates” the distance based on the number of revolutions for the tire.
- The diameter of a bus tire is 36 Inches.
- Tire treads are worn evenly over the entire surface of the road. Therefore; 1/8” tread wear amounts to 2/8” reduction in diameter.
- The revolution of a tire is equivalent to the circumference of the tire.
- The Circumference of the tire is equal to PI times the diameter.
- 1 Mile = 5280 feet.
- The Circumference of a 36 inch tire is PI * 36 = 113.1 Inches or 9.42 feet
- The Circumference of a 35 6/8” inch tire is PI * 35.75 = 112.3 inches or 9.36 feet
- Calculate the revolutions required to travel 1 mile (5280 feet). 5280 / 9.42 = 560.51 revolutions
- For every 560.51 revolutions of the tire, the odometer will register 1 mile.
- In 560.51 revolutions, a 35 6/8” tire will travel… 560.51 * 9.36 or 5246.37 feet.
- For each 560.51 revolutions, the odometer will increment by 1 mile even though the vehicle has only traveled 5246 feet. Therefore, a vehicle with tread wear will report more miles driven by the odometer.
- The difference in distance is 33.63 feet for each mile driven. Actually traveling 157 miles will cause the odometer to be off by 1 mile.
- The percentage of error is… (1 - 5246.37 / 5280) * 100% = 0.64%
- 1/8” tread wear on a 36-inch tire reduces the circumference by 0.8 inches.
- Over the length of 1 mile, this adds up to 33.6 feet.
- After “actually” traveling 157 miles, the odometer will be “off” by 1 mile. It will read 158 miles.
- Smaller diameter tires will effect odometer reading more than larger tires.
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