Machinery

Subscribe and save

Farmers Weekly from £127
Saving £36
In print AND tablet

SUBSCRIBE NOW

sub_ad_img


Tyres 3: Correct tyre pressure

Course: Tyre management | Last Updates: 9th October 2015

 
Neil Sharman
Technical and field engineering manager UK and Ireland
Trelleborg
Biography >>
FADS2BASIS2

High pressure

It’s not uncommon for operators to run tyres at too high a pressure and this can cause a number of problems.

Tyres become hard and ridged when they are pumped up to a higher pressure than recommend and this makes for a pretty uncomfortable ride.

Grip is also reduced, mainly because there is a smaller surface area in contact with the ground and fewer lugs, thus giving less traction. Spinning wheels damage soil structure and increase fuel consumption, too.

Tyre wear can increase giving a shorter life to the tyre.

Tyres also become more sensitive to impact when they have a high inflation pressure.

Low pressure

Running at very low pressures also has its problems. Increase in fuel consumption, as power is lost through flexing and having too much of the tyre in contact with the ground.

This flexing and bouncing has the added problem of stressing the sidewalls and causing serious damage to the casing. It also causes heat to build up in the rubber, which makes the tyre wear quicker when doing road work.

Stability is reduced too, particularly at higher speeds on the roads.

There’s a higher risk of the tyre turning on the rim during heavy draft work.

Weights and loads

When any equipment is mounted on the rear of the tractor it increases the weight on the rear axle and removes weight from the front axle.

The balance of this weight between the two axles is known as the load distribution.

And it’s important that tyre pressures are adjusted to take this load distribution into consideration. Incorrect loading and tyre pressures can result in too much stress in the tyres, causing them to wear faster, get damaged or cause injury from tyre failure.

Most tyre manufacturers publish tables to help you do this. Many have more sophisticated tools where you can look up the correct inflation pressure and some have digital and app-based tools, too.

If you want to manually work out the extra load an implement puts on an axle you can use the following calculation:

Additional weight = implement weight × distance ÷ wheelbase (see diagram below)
Tyrediagram.jpg

This is a basic calculation, but can also be used for harvesters and trailers. You’ll still need to look up the recommended pressure from manufacturer’s figures though.

The best load calculators in the market are designed to calculate load per axle according to a tractor’s configuration. Some can also recommend the optimum pressure for the selected application or ground conditions.

It’s worth taking a bit of time to have a play with these tools as they’ll save you money in the long run and help you do a better job.

Soil compaction

The biggest preventable cause of soil compaction is incorrect tyre pressure. The tyre pressure in your tyre is approximately the same as the pressure you exert on the soil.

You want to aim for as low a pressure as possible in the field. This must not be achieved at the expense of the tyre turning on the rim though.

With the pressure on the soil’s surface the same as the tyre inflation pressure, using a wider tyre at a lower pressure will help reduce the compaction, increase traction and save fuel.

Road transport

It is very important to have the correct tyre pressure when travelling on the road.

Under inflation can be very dangerous causing the tractor to be unstable when cornering. The increase in heat build up also leads to rapid wear.

Equally, over inflation can cause the tractor to be unstable due to the lack of tread area in contact with the road. It also leads to irregular tread wear.

In an ideal world, tyres pressures would be adjusted to suit the job in hand, but realistically this isn’t going to happen. A good compromise is to adjust the pressure to suit the job the tractor will be doing most. But if you are switching form heavy draft work to a large amount of road haulage, it is wise to add some more air.

Central tyre inflation systems are expensive, but they do allow you to run tractors with the optimum tyre pressure at all times.

Tyre technology

Tyre technology is also helping to get round some of these problems. Increased Flexibility (IF) tyres so that the load you can carry at speed at a low pressure is dramatically increased.

This is down to a new sidewall design that means you can set your tyre pressures low for fieldwork safe in the knowledge that they will still perform at high speeds.

Summary

Tyres are the only contact between your machine and the ground.

It is important that tyres be maintained in a good condition at all times and when the time comes to change them, the correct replacements are fitted.

The tyres fitted to your vehicle when new were selected by both the vehicle and tyre manufacturer taking in to account all aspects of work, the size and the horsepower of the vehicle is likely to undertake.

Changes to the tyre size, structure, load and speed ratings should not be made without first seeking advice from the vehicle or tyre manufacturer.

If in doubt about the correct tyre pressure for the type of work being carried out, contact the manufacturer or your tyre dealer.

Please login or register to take this test.