Tire Size Calculator
Comparing wheel and tire setups? Enter two sizes to see how overall diameter, sidewall, circumference, and your speedometer change — before you spend a cent.
Current tire
225/45R17- Overall diameter
- 24.97"
- Sidewall
- 3.99"
- Circumference
- 78.45"
- Revs / mile
- 808
New tire
245/40R18- Overall diameter
- 25.72"
- Sidewall
- 3.86"
- Circumference
- 80.79"
- Revs / mile
- 784
225/45R17 → 245/40R18
Speedometer effect with the new size
If your speedometer was calibrated for 225/45R17, here's your true speed on 245/40R18:
| Speedometer reads | Actual speed | Difference |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 mph |
| 45 mph | 46.3 mph | +1.3 mph |
| 60 mph | 61.8 mph | +1.8 mph |
| 75 mph | 77.2 mph | +2.2 mph |
How to read a tire size
A size like 225/45R17 breaks down into three numbers. 225 is the tread width in millimeters. 45 is the aspect ratio — the sidewall height as a percentage of the width (so 45% of 225 mm ≈ 101 mm of sidewall). R17 means a radial tire on a 17-inch wheel.
Overall tire diameter is the wheel diameter plus two sidewalls (top and bottom). That's why a “plus-size” setup — bigger wheel, shorter sidewall — can keep the same rolling diameter while changing the look and feel. Keeping the new diameter within about 3% of stock is the usual guideline for staying speedometer-accurate and avoiding rubbing.
Dialing in a fresh wheel and tire package? Log the specs, photos, and the rest of your mod list in your Ryvve garage so your whole build lives in one place.
Frequently Asked Questions
Enter two tire sizes using their width in millimeters, aspect ratio, and wheel diameter in inches (for example 225/45R17). The calculator works out each tire's sidewall height, overall diameter, circumference, and revolutions per mile, then compares the two so you can see exactly how a new size changes your setup.
Track Your Build in Your Garage
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