If you increase the diameter of the tires on a dirt bike, the speedometer will typically show a lower speed than the actual speed. The extent of this difference can be estimated by considering the change in tire circumference.
When you increase the tire diameter by an inch, the circumference of the tire increases by approximately the difference in diameter multiplied by π (pi). Since the circumference of a circle is calculated as 2πr (where r is the radius), a one-inch increase in diameter results in an approximately π-inch increase in circumference.
To estimate the difference in speed shown on the speedometer, you can use the formula:
Speedometer Difference = (Increase in Circumference / Original Circumference) * 100
For example, if the original tire circumference is 70 inches and you increase it by one inch, the increase in circumference would be π inches. Plugging these values into the formula:
Speedometer Difference = (π / 70) * 100 ≈ 4.5%
Therefore, in this example, you could expect the speedometer to show a speed that is approximately 4.5% lower than the actual speed. Keep in mind that this is a rough estimate, and the actual difference may vary depending on factors such as tire pressure, tire profile, and speedometer calibration.