Plus-One Tire Calculator
Find Plus-One sizes for a wheel one inch larger with the same overall tire diameter. Compare diameter differences and sidewall height loss.
Compare sizes using larger wheels.
Plus-One Tire Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Plus-One Tire Calculator Works?
The Plus-One Tire Calculator works by adding 1 inch (25.4 mm) to the rim diameter and finding the width and aspect ratio that keep the overall diameter closest to stock. The calculation has 4 steps.
Enter the stock size
Type the factory size, for example 205/55 R16.
Add one inch
The calculator sets the new rim to 17 in, adding 25.4 mm to the bead seat diameter.
Search widths
The calculator tests the stock width and widths 10 mm and 20 mm wider.
Show the best match
The calculator returns 225/45 R17 at +0.38%, with the diameter gap and sidewall loss.
Plus-One Tire Calculator Formula
The Plus-One Tire Calculator formula is AR₁ = (OD_stock − (Rim + 1) × 25.4) ÷ (2 × W₁) × 100.
Rim₁ = Rim₀ + 1SH₁ = SH₀ − 12.7 mmAR₁ = SH₁ ÷ W₁ × 100- Rim₀, Rim₁
- Stock and Plus-One rim diameters (in)
- SH₀, SH₁
- Stock and Plus-One sidewall heights (mm)
- W₁
- Plus-One width (mm)
Worked example
A 225/45 R17 tire has a 101.25 mm sidewall. A Plus-One size needs about 88.5 mm of sidewall on an 18-inch wheel. On a 225 mm width, 88.5 ÷ 225 = 39.3%, so the Plus-One size is 225/40 R18 at 637.2 mm (+0.46%).
Plus-One Tire Calculator Conversion Table
The Plus-One Tire Calculator conversion table lists the closest Plus-One size for 7 common stock sizes with the diameter gap and sidewall change.
| Stock size | Plus-One size | Diameter change | Gap | Sidewall change |
|---|---|---|---|---|
| 195/65 R15 | 205/55 R16 | 634.5 → 631.9 mm | -0.41% | 126.8 → 112.8 mm |
| 205/55 R16 | 225/45 R17 | 631.9 → 634.3 mm | +0.38% | 112.8 → 101.2 mm |
| 215/60 R16 | 235/50 R17 | 664.4 → 666.8 mm | +0.36% | 129.0 → 117.5 mm |
| 225/45 R17 | 225/40 R18 | 634.3 → 637.2 mm | +0.46% | 101.2 → 90.0 mm |
| 235/45 R18 | 235/40 R19 | 668.7 → 670.6 mm | +0.28% | 105.8 → 94.0 mm |
| 245/40 R18 | 245/35 R19 | 653.2 → 654.1 mm | +0.14% | 98.0 → 85.8 mm |
| 225/65 R17 | 245/55 R18 | 724.3 → 726.7 mm | +0.33% | 146.2 → 134.8 mm |
What is Plus-One Tire Calculator?
A Plus-One Tire Calculator is a tool that finds a tire size for a wheel 1 inch larger than stock while keeping the overall diameter nearly unchanged. Plus-One is the most common wheel upgrade on passenger cars.
A Plus-One change removes about 12.7 mm (0.5 in) of sidewall. Steering response sharpens, and ride comfort drops by a small amount.
Plus-One sizes often add 10 mm of width, so the tire maker's rim width range and the vehicle's inner clearance need a check.
What are the uses of Plus-One Tire Calculator?
There are 4 main uses of the Plus-One Tire Calculator, including wheel upgrades and trim-level swaps.
Wheel upgrades
Pick the right tire for an aftermarket wheel 1 inch larger than stock.
Trim-level swaps
Fit the larger wheel package from a higher trim of the same model.
Brake upgrades
Fit a 1-inch larger wheel to clear a big brake kit.
Handling tuning
Shorten the sidewall for sharper steering with stock height.
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