Confused by metric and imperial tractor tyre sizes? You’re not alone. Tractor tyres are labeled using both systems, and knowing how to convert between them is crucial when buying replacements or comparing models. This tractor tyre conversion table helps you quickly match metric tyre sizes to their imperial (inch-based) equivalents for easy decision-making.
Why Use a Tractor Tyre Conversion Table?
Tyre sizes can be written in either imperial (e.g., 16.9-30) or metric (e.g., 420/85R30) format. But they often represent the same actual tyre, just using different units. If you mismatch tyres or rims, it can affect rolling circumference, traction, and 4WD drivetrain performance.
Use a 4×4 Tire Ratio Calculator or 4WD Wheel Ratio Calculator to check compatibility once you’ve found your converted size.
Tractor Tyre Metric to Imperial Conversion Table
This chart matches common metric tyre sizes with their closest imperial equivalents. Use it when switching between manufacturers or tyre types that label sizes differently.
| Metric Tyre Size | Imperial Equivalent | Rim Diameter (inches) | Application |
|---|---|---|---|
| 240/85R24 | 9.5R24 | 24″ | Front (MFWD/Compact) |
| 280/85R24 | 11.2R24 | 24″ | Rear (Compact) |
| 320/85R28 | 12.4R28 | 28″ | Rear (Utility) |
| 340/85R28 | 13.6R28 | 28″ | Rear (Utility) |
| 380/85R28 | 14.9R28 | 28″ | Rear (Utility/Field) |
| 420/85R30 | 16.9R30 | 30″ | Rear (Field) |
| 460/85R34 | 18.4R34 | 34″ | Rear (Row Crop) |
| 520/85R38 | 20.8R38 | 38″ | Rear (High HP) |
How to Read Tractor Tyre Sizes
Metric Tyre Format: 420/85R30
- 420 = Width in millimeters
- 85 = Aspect ratio (sidewall height as % of width)
- R = Radial construction
- 30 = Rim diameter in inches
Imperial Tyre Format: 16.9-30
- 16.9 = Width in inches
- – = Bias-ply (R would indicate radial)
- 30 = Rim diameter in inches
To compare accurately, always check the rolling circumference—not just the labeled size. You can do this easily using the Tractor Tire Ratio Calculator.
What Happens If Tyre Sizes Don’t Match?
Installing mismatched tyre sizes can cause serious issues:
- Excessive tire wear
- Driveline binding in 4WD tractors
- Reduced traction and fuel efficiency
- Handling problems and steering resistance
Before changing tire sizes, especially if mixing front and rear tyres, confirm ratios using the
4WD Tractor Wheel Ratio Calculator.
Tyre Size Conversion and Ballasting
Converting to wider or taller tyres often means adjusting ballast to maintain stability. Heavier tyres affect weight distribution, traction, and rollover risk.
Use the Ballast Calculator for Tractor Tires to make sure you’re properly balanced for safe operation.
Tyre Size Changes and Transport
Larger or wider tyres can affect loading angles and transport height. Be sure your ramp length is safe for taller setups.
Try the Garden Tractor Ramp Calculator before you load your machine.
Conclusion
Switching between metric and imperial tractor tyre sizes is easy once you understand the conversion. Use this chart to match sizes accurately and avoid mismatches that could lead to costly wear or damage.
For the best results, pair this conversion chart with these essential tools:
- 4×4 Tire Ratio Calculator
- 4WD Wheel Ratio Calculator
- Ballast Calculator
- Ramp Angle Calculator
- Hourly Rate Calculator
Use this conversion table to choose the right tyres for your job—and keep your tractor working its best.