Plus-One Tire Size Calculator

This calculator works by adding 1 in to the rim diameter and finding the width and aspect ratio that keep the overall diameter closest to the original. It tests widths from the original up to 30 mm wider.

1. Enter the original size, for example 205/55R16 (24.88 in).
2. Let the tool test 17 in sizes.
3. Read the best Plus-1 match: 225/45R17 at 24.97 in.
4. Check the change: +0.38%, well inside ±3%.

The formula keeps D_new ≈ D_old with Rim_new = Rim_old + 1.

Each extra inch of rim needs 12.7 mm (0.5 in) less sidewall. Worked example for 235/65R17: sidewall falls from 152.75 mm to 140.05 mm. On a 255 mm width, the aspect ratio is 54.9%, so 255/55R18 (29.04 in) is the match.

The conversion table gives the closest Plus-1 size for 10 original sizes. Every match sits within ±0.41% of the original diameter.

Most matches go up 10–30 mm in width and down 5–15 points in aspect ratio. The 245/45R18 keeps its width and goes to 245/40R19.

The Plus-One Tire Size Calculator is a tool that finds tire sizes for a wheel 1 in larger than stock while keeping the overall diameter. Plus-1 is the most common wheel upgrade.

A Plus-1 swap gives a shorter sidewall, sharper steering and a wider tread option without changing speedometer readings. The trade-off is a firmer ride and more exposure to pothole damage.

This calculator has 4 uses: wheel upgrades, trim swaps, brake clearance and handling upgrades.

• Upgrade wheels: Find tires for 1 in larger aftermarket wheels.
• Swap trims: Fit wheels from a higher trim level.
• Clear bigger brakes: Use a larger wheel to clear upgraded calipers.
• Sharpen handling: Reduce sidewall flex for quicker steering.