Minus-Sizing Calculator
Go down a wheel size, often for winter tires. Use the calculator below. Results update as you type.
How the Minus-Sizing Calculator Works
The Minus Sizing Calculator works by taking 1 in or more off the rim and finding the size that holds the original overall diameter with a taller sidewall. It allows narrower widths for winter and off-road use.
- Enter the original size, for example 225/45R17.
- Enter the rim decrease, for example −1 in (16 in wheel).
- Read the match: 205/55R16 at −0.38%.
- Read the sidewall gain: 3.99 in to 4.44 in.
The Formula
The Minus Sizing Calculator formula is Sidewall_new = Sidewall_old + (Rim Decrease × 12.7 mm).
Rim_new = Rim_old − N in Sidewall_new (mm) = Sidewall_old + N × 12.7 Aspect_new = Sidewall_new ÷ Width_new × 100Worked example for 245/40R19: sidewall rises from 98 mm to 110.7 mm. On a 245 mm width that is 45.2%, so 245/45R18 is the match at −0.13%.
Conversion Table
The Minus Sizing Calculator conversion table gives the Minus-1 size for 10 original fitments. Every match is within ±0.38%, and every match adds 0.45–0.55 in (11–14 mm) of sidewall.
Several matches drop 20–30 mm in width. The 215/50R17 to 185/65R16 swap trades 30 mm of width for 0.50 in more sidewall.
| Original | Minus-1 Size | Old Sidewall (in) | New Sidewall (in) | Diameter Change |
|---|---|---|---|---|
| 225/45R17 | 205/55R16 | 3.99 | 4.44 | -0.38% |
| 225/40R18 | 205/50R17 | 3.54 | 4.04 | -0.06% |
| 235/45R18 | 215/55R17 | 4.16 | 4.66 | -0.06% |
| 245/40R19 | 245/45R18 | 3.86 | 4.34 | -0.13% |
| 255/45R20 | 255/50R19 | 4.52 | 5.02 | +0.01% |
| 245/35R20 | 245/40R19 | 3.38 | 3.86 | -0.13% |
| 275/55R20 | 275/60R19 | 5.95 | 6.50 | +0.26% |
| 235/55R19 | 235/60R18 | 5.09 | 5.55 | -0.26% |
| 215/50R17 | 185/65R16 | 4.23 | 4.73 | +0.02% |
| 255/40R19 | 255/45R18 | 4.02 | 4.52 | +0.01% |
What Is the Minus-Sizing Calculator?
The Minus Sizing Calculator is a tool that finds tire sizes for a smaller wheel at the same overall diameter. Minus sizing is the standard method for winter tire packages.
A smaller wheel means a taller sidewall, a softer ride, more pothole protection and often a cheaper tire. The check that matters most is brake caliper clearance: a smaller wheel must still clear the brakes.
Common Uses
The Minus Sizing Calculator has 4 uses: winter packages, ride comfort, cost savings and off-road setups.
- Build winter packages: Fit narrower, taller winter tires.
- Improve comfort: Add sidewall for rough roads.
- Save money: Buy smaller, cheaper wheels and tires.
- Set up off-road: Add sidewall for airing down.