Nominal vs Published Dimension Comparator
Compare the math with what the maker lists. Use the calculator below. Results update as you type.
How the Nominal vs Published Dimension Comparator Works
This comparator works by computing the nominal diameter from the size code and comparing it with the diameter a tire maker publishes. It reports the gap in inches, millimeters and percent.
- Enter the size code, for example 265/70R17 (nominal 31.61 in).
- Enter the published diameter from the maker's spec sheet, for example 31.9 in.
- Read the gap: +0.29 in (+7.4 mm), or +0.92%.
- Repeat for a second tire model to see which runs taller.
The Formula
The formula is Gap (%) = (Published − Nominal) ÷ Nominal × 100.
Nominal Diameter (mm) = (Rim × 25.4) + 2 × (Width × Aspect Ratio ÷ 100) Gap (in) = Published − Nominal Gap (%) = (Published − Nominal) ÷ Nominal × 100Worked example for 235/65R17: nominal is 29.03 in. A published 29.3 in gives a gap of +0.27 in, or +0.93%.
Conversion Table
The conversion table shows which published diameters equal a −2%, −1%, +1% and +2% gap from nominal for 6 sizes. Find the published value in a row and read the column header.
For a 265/70R17, a published 31.92 in sits at +1%, and 32.24 in sits at +2%. Deep-tread all-terrain and mud-terrain tires often publish values above nominal.
| Size | Nominal (in) | −2% (in) | −1% (in) | +1% (in) | +2% (in) |
|---|---|---|---|---|---|
| 205/55R16 | 24.88 | 24.38 | 24.63 | 25.13 | 25.38 |
| 225/45R17 | 24.97 | 24.47 | 24.72 | 25.22 | 25.47 |
| 235/65R17 | 29.03 | 28.45 | 28.74 | 29.32 | 29.61 |
| 265/70R17 | 31.61 | 30.97 | 31.29 | 31.92 | 32.24 |
| 275/60R20 | 32.99 | 32.33 | 32.66 | 33.32 | 33.65 |
| 285/75R16 | 32.83 | 32.17 | 32.50 | 33.16 | 33.49 |
Find the manufacturer value in the row, read the column header, and you have the percentage gap.
What Is the Nominal vs Published Dimension Comparator?
The Nominal vs Published Dimension Comparator is a tool that shows how far a real tire's published size sits from the theoretical size in its code. Nominal dimensions come from math; published dimensions come from measuring a tire on its measuring rim.
Tread depth, casing design and rim width cause the difference. Off-road tires with deep tread often run taller than nominal; touring tires often run close to nominal.
Common Uses
This comparator has 4 uses: brand comparison, clearance checks, speedometer accuracy and AWD matching.
- Compare brands: See which model runs tall or short.
- Check clearance: Use the published value for tight wheel wells.
- Refine speedometer math: Replace nominal values with real ones.
- Match AWD tires: Pair models with close published sizes.