| Parameter | Value |
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This tire calculator provides a quick, accurate estimate of axle load distribution, tire contact patch, ground pressure and likely sinkage for tractors, combines, haulers and loaders, helping operators pick safe inflation, ballast and tires. Use the phrase tire calculator once in this paragraph to locate the tool in search and reporting.
Table of Contents
Input parameters and what they mean
- Machine type, choose tractor, combine, hauler or loader.
- Total weight, pounds, the vehicle loaded for work.
- Front axle share, percent of total weight carried by front axle. Use 40 if unknown.
- Total axles or wheels, used to compute load per wheel.
- Tread width, inches, nominal working width of the tire.
- Nominal tire load, pounds, optional rating from tire placard for overload checks.
- Recommended pressure, psi, optional, if empty the calculator uses a surface based default.
- Surface type, select asphalt, gravel, firm soil, soft soil or peat.
- Ballast, pounds, any extra weight fitted to the machine.
- Safety margin, percent, extra margin used when giving guidance.
What the calculator derives
- Axle loads and per wheel loads in pounds.
- Contact patch area for front and rear tires in square inches.
- Contact patch length in inches, computed as area divided by tread width.
- Ground pressure under each tire shown in psi.
- Estimated sinkage in inches based on surface bearing capacity.
- Rolling resistance force and available traction in pounds force.
- A simple slip risk rating – low, medium or high.
- A guideline safe speed in miles per hour, for operational planning.
- Rough tire life expectation in hours for planning maintenance.
- Pressure versus contact patch table for several sample pressures in psi.
Key formulas and calculation steps
Below are the core relations shown in compact form.
Load on front axle, lb = total_weight_lb × front_share_percent ÷ 100 + ballast_lb × front_share_percent ÷ 100
Load per wheel, lb = axle_load_lb ÷ wheels_on_that_axleConvert load to force, N = load_lb × 0.45359237 × 9.80665
Contact area, m² = normal_force_N ÷ pressure_Pa
Contact area, in² = contact_area_m² × 1550.0031Patch length, in = contact_area_m² ÷ tread_width_m × 39.3701
Ground pressure, psi = normal_force_N ÷ contact_area_m² ÷ 6894.757
Rolling resistance force, lbf = Crr × normal_force_N × 0.22480894
Available traction, lbf = mu × normal_force_N × 0.22480894Sinkage estimate, in = factor × (ground_pressure_kPa ÷ bearing_kPa) × 0.0393701 × 100
Practical example
- Total weight 13,200 pounds
- Front axle share 40 percent
- Total wheels 4
- Tread width 19 inches
- Inflation pressure 10 psi
- Surface type peat
- Ballast 220 pounds
- Front axle load equals 13,200 × 0.4 plus 220 × 0.4 equals 5,288 lb on the front axle.
- Two front wheels: 5,288 ÷ 2 = 2,644 lb per tire (≈ 11,768 N).
- At 10 psi the contact area per tire is normal_force_N ÷ 68,947 Pa ≈ 0.171 m², about 2,650 in².
- Patch length = area ÷ tread width = 2,650 ÷ 19 ≈ 140 in (use for relative comparison).
- Ground pressure computed from the patch returns near the target psi, confirming consistency.
- Estimated sinkage on peat with a conservative bearing gives a few inches of sinkage, indicating soft ground for this setup.
Interpretation and field guidance
- Use these results to compare scenarios, not as certified numbers. Verify critical values on scales and with pressure gauges.
- If per tire load exceeds the tire placard rating, reduce load, raise pressure or use higher rating tires.
- On soft ground reduce pressure to enlarge contact patch, monitor rim and sidewall protection.
- For road moves increase pressure to reduce rolling resistance and heat.
- Use ballast only when traction benefits exceed compaction costs.
- Check weather and soil moisture before heavy moves; moisture significantly reduces bearing capacity.
Common pitfalls and tips
- Sidewall markings are maximum ratings not ideal working pressures.
- Keep units consistent during field checks: pounds, inches and psi.
- Compare contact patch and rolling resistance estimates to forecast fuel use and rutting.
- Perform simple field tests where possible: set candidate pressure, drive a distance and inspect rutting and handling.
Pressure versus contact patch reference
| Pressure, psi | Front patch, in² | Rear patch, in² |
|---|---|---|
| 6 | 4400 | 3200 |
| 8 | 3300 | 2400 |
| 10 | 2640 | 1920 |
| 12 | 2200 | 1600 |
| 15 | 1760 | 1280 |
Conclusion and next steps
Use this tire calculator for fast decisions about inflation, ballast and tire selection before field operations. Confirm critical values on scales and consult tire manufacturer data for load ratings and inflation schedules. The tool helps planning, reduces risk and improves efficiency in the field.
Further reading
- Tire and Vehicle Engineering for Off Road Operations — John R. Black
- Soil Mechanics for Engineers — Mark H. Ellis
- Off-Road Vehicle Dynamics and Stability — Peter S. Rogers
- Agricultural Tires: Selection and Care — Michael L. Turner
- Heavy Equipment Tire Technology — Laura J. Haines
David Parry — Senior Engineering Analyst
Specializing in electronics and physics-based simulations with 20+ years of engineering experience. David ensures the mathematical and physical accuracy of the tools at ProCalcLab.
