How plus sizes are found
For each wheel diameter, every standard width (10 mm steps) and aspect ratio (5 % steps) is checked. A size is kept when its overall diameter is within ±3 % of the original and it is a size actually in use. Results are sorted by how close the diameter is, then by width.
Worked example: 205/55R16
205/55R16 is 631.9 mm (24.9 in) tall. Going plus 1 to a 17-inch wheel, 225/45R17 is 634.3 mm (+0.4 %); plus 2, 225/40R18 is 637.2 mm (+0.8 %). Both stay well inside 3 %. Each step up typically needs a wheel about half an inch wider.
Checklist before buying
- Wheel bolt pattern, centre bore, offset and load rating must match the car — see the wheel offset calculator.
- Larger wheels must clear the brake calipers.
- Load index and speed rating must meet the placard (XL tires are often needed).
- Compare the final choice with the tire size comparison to see the speedometer effect.
Frequently asked questions
What does plus sizing mean?
Fitting a wheel one or more inches larger in diameter (plus 1, plus 2…) with a lower-profile tire, so the overall diameter of the wheel and tire stays about the same. Minus sizing is the opposite and is common for winter wheels.
Why keep the overall diameter within 3 %?
Staying close to the original diameter keeps the speedometer, odometer, gearing, ride height and the calibration of ABS and stability control close to how the car was designed.
Will lower-profile tires ride harder?
Usually yes. A shorter sidewall flexes less, so steering feels sharper but bumps are felt more and the wheels are easier to damage on potholes.
Which sizes does this calculator suggest?
Only sizes that are actually used: sizes that appear in official Swiss type-approval records or on a list of common US sizes. Mathematically possible but unmanufactured combinations are left out.
Do I need a different load index with a plus size?
The new tire must carry at least the load your vehicle needs. Lower-profile tires often need an XL (reinforced) version to reach the same load index — check the placard.