Tire Size Comparison
Compare two tire sizes side-by-side for overall diameter, sidewall height, contact patch width, and speedometer error percentage. Essential when upgrading wheels, plus-sizing, or fitting larger off-road tires.
Tire Size Calculator
Compare two tire sizes and see speedometer error, rev/mile and clearance impact.
How It Works
Tire diameter = (Section width × Aspect ratio × 2 ÷ 25.4) + Rim diameter. The calculator computes both diameters, the percentage difference, and the resulting speedometer error — your speedometer reads the same RPM but the tire travels a different distance per revolution.
How to Use This Calculator
- Read your current tire size from the sidewall — e.g., 225/55R17.
- Enter the size in the “current” field.
- Enter the proposed replacement size in the “new” field.
- Compare overall diameter difference — anything over 3% will trigger your TPMS or ABS.
- Adjust the proposed size or check legal limits for your region (most states cap at 3% deviation).
Worked Example
Reference Table
Common plus-sizing patterns. The goal is to keep overall diameter within ±3% so the speedometer, ABS, and traction control remain accurate.
| Plus-size pattern | Original | Upgrade | Diameter change |
|---|---|---|---|
| Plus 1 | 215/65R16 | 225/60R17 | +0.3% |
| Plus 2 | 215/65R16 | 235/55R18 | +0.6% |
| Plus 3 | 215/65R16 | 245/45R19 | +0.4% |
| Wider same diameter | 225/55R17 | 245/50R17 | +0.3% |
| Off-road / lifted | 265/70R17 | 285/70R17 | +2.7% |
| Stretched look | 225/45R17 | 215/45R17 | −0.4% |
Frequently Asked Questions
What does 225/55R17 mean?
225 = tread width in millimeters. 55 = sidewall height as a percent of width (55% of 225 = 124 mm). R = radial construction. 17 = wheel diameter in inches.
Will bigger tires affect my speedometer?
Yes. A larger overall diameter makes the speedometer under-read your actual speed. A 3% larger tire on a car indicating 60 mph means you are actually going 61.8 mph. Many states require speedometer accuracy within 5%.
Can I put a different size on the front vs rear?
Staggered fitments (smaller front, wider rear) are factory on many sports cars (BMW M, Porsche, Corvette). For non-staggered cars, mixing sizes can trigger AWD damage and ABS faults — stick to the OE size on all four corners.
Will wider tires improve fuel economy?
The opposite — wider tires increase rolling resistance and aerodynamic drag, typically reducing fuel economy 1–3%.
Do I need to recalibrate my speedometer after changing tire size?
For changes under 3%, recalibration is optional. For larger changes (off-road builds, 5%+), most cars need a calibration tool — Hypertech, Superchips, or a dealer-level OBD tool can adjust speedometer ratios.
