Bicycle Rim Width Compatibility Tool
Check that the tire fits your rim width. Use the calculator below. Results update as you type.
How the Bicycle Rim Width Compatibility Tool Works
This tool works by dividing tire width by internal rim width and comparing the ratio with tire and rim makers' compatibility tables. It flags very narrow and very wide pairings.
- Enter the internal rim width, for example 21 mm.
- Enter the tire width, for example 32 mm.
- Read the ratio: 1.52.
- Confirm the pairing in the tire maker's ETRTO-based chart.
The Formula
The formula is Ratio = Tire Width ÷ Internal Rim Width.
Ratio = W_tire ÷ W_rim_internal Width Change ≈ grows on wider rims, shrinks on narrower rimsWorked example: a 28 mm tire on a 25 mm internal rim gives a ratio of 1.12. On a hookless rim that pairing is below the 29 mm minimum in the 2023 ETRTO guidance for a 25 mm rim.
Conversion Table
The conversion table shows the tire-to-rim ratio for 9 internal rim widths and 6 tire widths. Ratios run from 0.71 (25 mm tire on a 35 mm rim) to 4.62 (60 mm tire on a 13 mm rim).
Ratios near 1.0 mean the tire is barely wider than the rim. Ratios above 3.5 mean a large tire on a narrow rim.
| Internal Rim | 25 mm Tire | 28 mm Tire | 32 mm Tire | 40 mm Tire | 50 mm Tire | 60 mm Tire |
|---|---|---|---|---|---|---|
| 13 mm | 1.92 | 2.15 | 2.46 | 3.08 | 3.85 | 4.62 |
| 15 mm | 1.67 | 1.87 | 2.13 | 2.67 | 3.33 | 4.00 |
| 17 mm | 1.47 | 1.65 | 1.88 | 2.35 | 2.94 | 3.53 |
| 19 mm | 1.32 | 1.47 | 1.68 | 2.11 | 2.63 | 3.16 |
| 21 mm | 1.19 | 1.33 | 1.52 | 1.90 | 2.38 | 2.86 |
| 23 mm | 1.09 | 1.22 | 1.39 | 1.74 | 2.17 | 2.61 |
| 25 mm | 1.00 | 1.12 | 1.28 | 1.60 | 2.00 | 2.40 |
| 30 mm | 0.83 | 0.93 | 1.07 | 1.33 | 1.67 | 2.00 |
| 35 mm | 0.71 | 0.80 | 0.91 | 1.14 | 1.43 | 1.71 |
Use the ratio to spot extreme pairings, then confirm with the tire and rim makers' ETRTO-based charts.
What Is the Bicycle Rim Width Compatibility Tool?
The Bicycle Rim Width Compatibility Tool is a tool that checks whether a tire width suits a rim's internal width. Rim makers and tire makers publish approved width ranges based on ETRTO tables.
Internal rim widths grew from 13–15 mm on older road rims to 21–25 mm on modern road and gravel rims. That shift changes which tires are approved.
Common Uses
This tool has 4 uses: wider-tire upgrades, wheel upgrades, hookless checks and gravel builds.
- Upgrade to wider tires: Check the ratio on current rims.
- Upgrade wheels: See how wider rims change tire fit.
- Check hookless rims: Spot pairings below the minimum.
- Build gravel bikes: Match 40–50 mm tires to rims.