Plus sizing wheels: bigger rims, same overall height

How plus sizing works

Overall diameter is the rim plus two sidewalls. Add an inch of rim (25.4 mm) and each sidewall has to lose about 12.7 mm. A common rule of thumb for each step up is rim +1 in, width +10 to 20 mm and aspect ratio −5 to −10. Rules of thumb are rough, so check the result with the calculator.

Plus zero keeps the rim and trades height for width: 185/65R15 to 195/60R15 is 1.05% shorter and 10 mm wider.

What changes when you plus size

• Steering feels sharper and the car leans less, because a shorter sidewall flexes less.
• The ride gets firmer and often noisier, and potholes are more likely to bend a rim or cut a tire.
• Bigger wheels are usually heavier, which can cost a little acceleration and fuel economy.
• Low-profile tires often need the XL version to match the original load index.
• The wider tire needs a wheel of suitable width and offset, and room at the fender and suspension.

Before you buy

1. Compare the original and new sizes and keep the diameter within about 3%.
2. Check the wheel: bolt pattern, center bore, width, offset and clearance over the brake calipers.
3. Match or beat the original load index and speed rating.
4. Confirm with the owner's manual and a tire professional. If your model was sold with larger optional wheels, copying that size is the easiest route.

In the US, the 3% window is industry practice rather than federal law. Wheel and tire shops use it because it keeps the speedometer, ABS and stability control close to the factory calibration.