Minus-Sizing Calculator
Find minus-size tire options for a smaller wheel. Keep the original diameter, gain sidewall height, and check the gap from stock.
Compare sizes using smaller wheels.
Minus-Sizing Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Minus-Sizing Calculator Works?
The Minus-Sizing Calculator works by subtracting 1 inch from the rim diameter and finding the taller-sidewall size that keeps the overall diameter closest to stock. The tool uses 4 steps.
Enter the stock size
Type the factory size, for example 245/40 R18.
Drop one inch
The calculator sets the rim to 17 in, removing 25.4 mm from the bead seat diameter.
Search narrower widths
The calculator tests the stock width and widths 10 mm and 20 mm narrower.
Check brakes
The calculator reminds the user to confirm caliper clearance on the smaller wheel.
Minus-Sizing Calculator Formula
The Minus-Sizing Calculator formula is SH₋₁ = SH₀ + 12.7 mm, and AR₋₁ = SH₋₁ ÷ W × 100.
Rim₋₁ = Rim₀ − 1SH₋₁ = SH₀ + 12.7AR₋₁ = SH₋₁ ÷ W × 100- SH₀
- Stock sidewall (mm)
- SH₋₁
- Minus-One sidewall (mm)
- W
- Minus-One width (mm)
Worked example
A 245/40 R18 tire has a 98 mm sidewall. A Minus-One size needs about 110.7 mm on a 17-inch wheel. On the same 245 mm width, the aspect ratio is 45.2%, so the match is 245/45 R17 at 652.3 mm (-0.14%).
Minus-Sizing Calculator Conversion Table
The Minus-Sizing Calculator conversion table lists the closest Minus-One size for 7 stock sizes and the sidewall height gained.
| Stock size | Minus-One size | Diameter change | Gap | Sidewall gain |
|---|---|---|---|---|
| 225/40 R18 | 205/50 R17 | 637.2 → 636.8 mm | -0.06% | +12.5 mm |
| 245/40 R18 | 245/45 R17 | 653.2 → 652.3 mm | -0.14% | +12.2 mm |
| 235/45 R18 | 215/55 R17 | 668.7 → 668.3 mm | -0.06% | +12.5 mm |
| 225/45 R17 | 205/55 R16 | 634.3 → 631.9 mm | -0.38% | +11.5 mm |
| 255/35 R19 | 255/40 R18 | 661.1 → 661.2 mm | +0.02% | +12.8 mm |
| 275/55 R20 | 275/60 R19 | 810.5 → 812.6 mm | +0.26% | +13.8 mm |
| 245/45 R19 | 245/50 R18 | 703.1 → 702.2 mm | -0.13% | +12.2 mm |
What is Minus-Sizing Calculator?
A Minus-Sizing Calculator is a tool that finds a tire for a wheel smaller than stock while keeping the overall diameter close to the original. Minus sizing is the standard method for building winter and off-road wheel sets.
A smaller wheel adds sidewall height, which improves pothole protection and ride comfort. A narrower minus-size tire cuts through snow and slush with more pressure per square inch.
Brake caliper size limits minus sizing. Many vehicles list a minimum wheel diameter in the owner's manual.
What are the uses of Minus-Sizing Calculator?
There are 4 main uses of the Minus-Sizing Calculator, including winter wheel sets and comfort conversions.
Winter wheel sets
Size a narrower, taller winter tire on a smaller wheel.
Comfort conversions
Add sidewall for rough roads without changing height.
Off-road builds
Gain sidewall flex and rim protection for trails.
Lower cost
Use smaller tires, which often cost less per tire.
Related Wheel Sizing & Conversion Tools
View All 134 Subtools →Find sizes near a target diameter.
Solve for nominal aspect ratio.
Filter candidates using specified limits.
Compare alternatives on one rim diameter.
Compare sizes using larger wheels.
Compare sizes using two-inch wheel increases.