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Tire Size Correction Formula:
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The tire size correction factor is a dimensionless number that represents the ratio between new tire diameter and old tire diameter. This factor is used to adjust your speedometer reading when changing tire sizes to maintain accurate speed and distance measurements.
The calculator uses the simple formula:
Where:
Explanation: When you install larger tires, your speedometer will read slower than your actual speed. Smaller tires will make it read faster. The correction factor helps adjust for this change.
Details: Accurate speedometer readings are crucial for maintaining proper speed limits, calculating fuel economy, and ensuring odometer accuracy. Incorrect tire sizes can affect these measurements by up to 10% or more.
Tips: Measure your tire diameters accurately in inches. Typical passenger car tires range from 24-28 inches in diameter. The calculator requires both new and old tire diameters to be greater than zero.
Q1: How do I measure tire diameter?
A: You can calculate diameter from tire size markings (e.g., P215/65R15) or measure it directly by marking the ground, rolling the tire one full revolution, and measuring the distance traveled.
Q2: What if my correction factor is 1.05?
A: This means your speedometer reads 5% slower than actual speed. At 60 mph indicated, you're actually going 63 mph (60 × 1.05).
Q3: Does this affect my odometer?
A: Yes, the same correction applies to odometer readings. Larger tires will cause your odometer to record fewer miles than actually traveled.
Q4: Can I use this for any vehicle?
A: Yes, the calculation works for cars, trucks, motorcycles - any wheeled vehicle where tire size affects speedometer accuracy.
Q5: How do I adjust my speedometer?
A: Many modern vehicles can be reprogrammed. Some may require a speedometer gear change or aftermarket correction device.