Compare Tire Sizes
Current tire size
205/55R16 Width (mm)
Aspect ratio
Rim (in)
Speedometer Difference Tool
Tire Size Speed Calculator
Calculate speedometer difference after changing tire size. Enter the original tire size and new tire size to compare indicated speed, actual vehicle speed, diameter change, and tire size speed error.
New tire size
205/60R16 Width (mm)
Aspect ratio
Rim (in)
Good match
The overall diameter is within 3%.
Speedometer Calibration
Speedometer Reads
Actual Vehicle Speed
| Measurement | Current | New | Difference | Percent |
|---|---|---|---|---|
| Overall diameter | ||||
| Section width | ||||
| Sidewall height | ||||
| Circumference | ||||
| Revolutions per mile | ||||
| Revolutions per kilometer | ||||
| Ground clearance change | ||||
| Speedometer at 30 mph | ||||
| Speedometer at 60 mph | ||||
| Speedometer at 70 mph |
Calculate speed difference after changing tire size
This tire size speed calculator compares your original tire diameter with the new tire diameter, then shows how that change affects the speedometer. If the new tire is taller, the vehicle moves faster than the speedometer reading. If the new tire is shorter, the vehicle moves slower than the speedometer reading.
Use the speedometer comparison above to test common driving speeds, then review the live table for speedometer error at 30, 60, and 70 mph. The same calculation also helps estimate odometer change because both speed and distance are based on tire revolutions.
Tire size speedometer error chart
Example: changing from 205/55R16 to 205/60R16 increases tire diameter by +3.2%. That makes actual speed higher than the speedometer reading.
| Speedometer reads | Actual speed | Speed difference |
|---|---|---|
| 30.0 mph | 31.0 mph | 1.0 mph |
| 60.0 mph | 61.9 mph | 1.9 mph |
| 70.0 mph | 72.3 mph | 2.3 mph |
How tire size affects speedometer reading
A vehicle estimates speed from wheel rotation. Tire diameter controls how far the vehicle travels with each rotation, so even a small tire size change can move the real speed away from the dashboard reading. This is why speedometer error usually tracks the tire diameter percentage difference.
Tire size speed difference formula
Actual speed equals indicated speed multiplied by new tire diameter divided by original tire diameter. For example, if the new tire is 3% taller, the actual speed is about 3% higher than the speedometer shows.
Tire size speed calculator FAQ
What is a tire size speed calculator?
A tire size speed calculator estimates actual vehicle speed after changing tire diameter. Enter the original tire size and new tire size to compare speedometer reading, actual speed, and speed error.
How do I calculate speed difference from tire size?
Divide the new tire diameter by the original tire diameter, then multiply the speedometer reading by that ratio. A larger diameter makes actual speed higher than indicated speed, while a smaller diameter makes actual speed lower.
Will bigger tires make my speedometer read slow?
Yes. Bigger tires travel farther with each rotation, so the vehicle usually moves faster than the speedometer shows unless the speedometer is recalibrated.
Do smaller tires make the speedometer read fast?
Yes. Smaller tires travel less distance per rotation, so the speedometer usually shows a higher speed than the vehicle is actually traveling.
How much does tire size affect speed at 60 mph?
The speed change follows the tire diameter percentage change. A 3% taller tire makes actual speed about 61.8 mph when the speedometer reads 60 mph.