Custom Plus-Sizing Calculator
Go up by any wheel size and see what fits. Use the calculator below. Results update as you type.
How the Custom Plus-Sizing Calculator Works
The Custom Plus Sizing Calculator works by adding any number of inches to the rim (Plus-3, Plus-4 or more) and finding the size that holds the original diameter. It reports the sidewall left after each step.
- Enter the original size, for example 265/70R17.
- Enter the rim increase, for example +3 in (20 in wheel).
- Read the match: 295/50R20 at +0.02%.
- Read the sidewall loss: 7.30 in to 5.81 in.
The Formula
The Custom Plus Sizing Calculator formula is Sidewall_new = Sidewall_old − (Rim Increase × 12.7 mm).
Sidewall_new (mm) = Sidewall_old − N × 12.7 Aspect_new = Sidewall_new ÷ Width_new × 100 D_new ≈ D_oldWorked example for Plus-4 on 225/45R17: sidewall falls from 101.25 mm to 50.45 mm. On a 225 mm width that needs a 22.4% ratio; the closest real size is 225/25R21 at +1.83%.
Conversion Table
The Custom Plus Sizing Calculator conversion table shows Plus-3 and Plus-4 combinations for 10 original sizes, with sidewall before and after. Sidewalls drop 1.45–2.07 in (37–53 mm) across the 10 rows.
Trucks and SUVs handle large plus steps best. A 265/70R17 at +3 still keeps a 5.81 in sidewall; a 225/45R17 at +4 leaves only 2.21 in.
| Original | Step | New Size | Old Sidewall (in) | New Sidewall (in) | Diameter Change |
|---|---|---|---|---|---|
| 205/55R16 | +3 | 215/35R19 | 4.44 | 2.96 | +0.19% |
| 215/60R16 | +3 | 225/40R19 | 5.08 | 3.54 | -0.27% |
| 225/50R17 | +3 | 245/30R20 | 4.43 | 2.89 | -0.27% |
| 235/60R17 | +3 | 255/40R20 | 5.55 | 4.02 | -0.25% |
| 225/45R17 | +4 | 225/25R21 | 3.99 | 2.21 | +1.83% |
| 245/65R17 | +3 | 245/50R20 | 6.27 | 4.82 | +0.36% |
| 265/70R17 | +3 | 295/50R20 | 7.30 | 5.81 | +0.02% |
| 275/60R18 | +4 | 285/40R22 | 6.50 | 4.49 | -0.05% |
| 265/70R16 | +4 | 295/45R20 | 7.30 | 5.23 | -0.50% |
| 275/65R18 | +4 | 285/45R22 | 7.04 | 5.05 | +0.07% |
What Is the Custom Plus-Sizing Calculator?
The Custom Plus Sizing Calculator is a tool that finds tire sizes for any wheel diameter increase beyond Plus-2. Large plus steps are common on trucks, SUVs and show cars moving to 20 in, 22 in and 24 in wheels.
Each extra inch takes 0.5 in (12.7 mm) from each sidewall. The tool shows when the remaining sidewall gets too short for daily use.
Common Uses
The Custom Plus Sizing Calculator has 4 uses: truck wheel upgrades, show builds, sidewall checks and comparing steps.
- Upgrade truck wheels: Plan 20 in and 22 in swaps from 17 in stock.
- Plan show builds: Find tires for 24 in or 26 in wheels.
- Check sidewalls: See when a step leaves under 3 in (76 mm).
- Compare steps: Test +3 against +4 before buying wheels.