Quick answer
Agricultural tyres run at far lower pressures than road vehicles, and the right figure depends on the tyre size, the load on each tyre and the speed. Find it in the tyre maker's load and inflation table, not on a guess. In general, use the lowest pressure the table allows for field work to improve traction and reduce compaction, add pressure for heavy loads and road transport, check cold with a low-pressure gauge, and set both tyres on an axle the same.
Why tractor tyre pressure matters
A tractor tyre is designed to flex and spread its load. When the pressure is right for the load, the tyre lays a long, wide footprint on the ground. That gives:
- Better traction and less wheel slip, so more of the engine's power pulls the implement.
- Less soil compaction, which protects root growth and yields.
- Lower fuel use, because less energy is lost to slip.
- Longer tyre life and fewer sidewall cracks and failures.
A common mistake is to pump tractor tyres up like truck tyres. Too much pressure shrinks the footprint, which wastes fuel and compacts the soil on every hectare you work.
Where to find the right pressure
Every tyre maker publishes a load and inflation table for each size. It shows the load a tyre can carry at each pressure and speed. To use it:
- Find your tyre size and load index on the sidewall, for example 18.4R38 146A8.
- Estimate the load on each tyre: weigh each axle with the implement fitted, or use the tractor maker's figures plus ballast and implement weight.
- Divide the axle load by the number of tyres on that axle.
- Look up the lowest pressure that carries that load at your working speed.
The tractor's handbook also gives recommended pressures for common set-ups. If you do not have either, ask us and we will help you find the figure for your tyre.
How pressure changes with the job
| Situation | Pressure | Why |
|---|---|---|
| Ploughing, discing, heavy draft work | Lower end of the table for the load | Longer footprint for grip and less slip and compaction |
| Heavy front-mounted implement or loader | Higher on the front tyres | The front axle carries much more weight |
| Road transport and haulage | Higher, as the table shows for higher speed | Reduces heat build-up and sidewall flexing at speed |
| Trailers and implements | As the table shows for the loaded weight | Free-rolling tyres need enough pressure to carry the load |
Radial tractor tyres are made to run at low pressures and look slightly bulged at the sidewall when correctly inflated. Do not pump them up just because they look soft. Bias tyres have stiffer sidewalls and usually run at higher pressures than radials of the same size.
Signs your pressure is wrong
| Too low | Too high |
|---|---|
| Cracks or ripples low on the sidewall | Fast wear in the centre of the lugs |
| Tyre slipping on the rim (valve pulled sideways) | Wheel slip and poor traction in the field |
| Uneven, rapid shoulder wear | Deep ruts and compacted soil |
| Bouncing or "power hop" on the road | Rough ride and more stone cuts |
Ballast and liquid-filled tyres
Many farmers add weight to rear tyres with water or a liquid ballast to improve traction. If your tyres are liquid-filled:
- Check pressure with the valve at the top of the wheel, and use a gauge designed for liquid-filled tyres.
- Remember the liquid adds to the load on the tyre when you read the inflation table.
- Do not fill more than the recommended level, usually about three-quarters with the valve at the top.
Too much ballast is as bad as too little. It increases compaction and loads the drivetrain.
How to check tractor tyre pressure properly
- Check cold, before work, with the tractor parked on level ground.
- Use a low-pressure gauge. Ordinary car or truck gauges are not accurate at the low pressures tractor tyres use.
- Check both tyres on an axle and set them the same, so the tractor pulls straight.
- Fit valve caps to keep out dust and moisture.
- Check weekly in the season, and whenever you change implements or ballast.
4WD tractors and pressure
On a four-wheel-drive tractor, changing pressure changes the rolling size of each tyre slightly. Keep front and rear pressures as the table recommends, so the front axle's lead stays within range. Big differences make the tractor "wind up", wasting fuel and wearing tyres. Read more about matched sizes in tractor tyre sizes explained.
Need new tyres or advice?
Proclassic has supplied tyres to Zimbabwe's farmers since 1996. Send us your tractor, tyre size and the work you do, and we will help you find the right pressure, or quote replacement tyres from our Galaxy agricultural range. See all sizes on our agricultural tyres page.
Get a price on WhatsApp
Send us these four details and we will reply with stock and today’s price:
- Tyre size, from the sidewall
- Quantity
- Vehicle or equipment, make and model
- Delivery location, or collect in Harare or Mutare
Or call +263 716 194 485 · info@proclassicgroup.com