Speedometer Calculator Speed correction table for any tire size change
Your actual speed is faster than what the speedometer shows. At 60 mph, you're actually going 61.2 mph.
| Speedometer Reads | Actual Speed | Difference |
|---|---|---|
| 20 mph | 20.4 mph | +0.4 mph |
| 25 mph | 25.5 mph | +0.5 mph |
| 30 mph | 30.6 mph | +0.6 mph |
| 35 mph | 35.7 mph | +0.7 mph |
| 40 mph | 40.8 mph | +0.8 mph |
| 45 mph | 45.9 mph | +0.9 mph |
| 50 mph | 51 mph | +1 mph |
| 55 mph | 56.1 mph | +1.1 mph |
| 60 mph | 61.2 mph | +1.2 mph |
| 65 mph | 66.3 mph | +1.3 mph |
| 70 mph | 71.4 mph | +1.4 mph |
| 75 mph | 76.5 mph | +1.5 mph |
| 80 mph | 81.6 mph | +1.6 mph |
| 85 mph | 86.7 mph | +1.7 mph |
| 90 mph | 91.9 mph | +1.9 mph |
| 100 mph | 102.1 mph | +2.1 mph |
How to Use This Calculator
Select your original (stock) tire size and the new tire size you are switching to. The calculator instantly shows the speedometer error percentage and a detailed speed correction table showing the difference at every common speed.
The visual gauge illustrates the difference between your speedometer reading (gray needle) and your actual speed (colored needle). Toggle between MPH and KPH for your preferred unit.
Use the Share button to save or send your specific tire size comparison — the URL updates with your selections so you can bookmark or share the exact result.
Speedometer Error Formula
Actual Speed = Indicated Speed × (New Diameter ÷ Old Diameter)
Odometer Error = Same percentage as speedometer error
Example
Sarah's SUV came with 225/65R17 tires (724.3mm diameter). She wants to install 265/70R17 for better off-road capability (803.4mm diameter). The calculator shows a +10.9% speedometer error — at an indicated 60 mph, she is actually traveling at 66.5 mph. This is well above the safe 3% threshold, so Sarah would need to recalibrate her speedometer or choose a closer size like 245/65R17 (which has only +2.1% error).