The changes to a tractor when a loader lifts a bale of silage

This winter, tractors will be handling all sorts of feed stuffs, straw and cleaning out sheds. Some of this work is heavy for the humble tractor.

Ideally, this tractor will have a large weight hanging out of the rear lift arms to make it more stable and safer with a load on-board. Many loader tractors are four-wheel drive, which makes them, or rather their front axles, more suited to loader work.

A downside of using a four-wheel drive tractor for loader work is that they are often perceived as being more capable than they actually are. More often than not, you will not see any real ballast weight.

While you may get away without a rear weight most of the time, it is inevitable that something will go wrong sooner or later. That may be an overturned tractor or a tractor that has run away because there is no weight on the rear wheels to give bite for braking.

There is not just the safety aspect to consider. There is also the front axle of the tractor to consider, and a damaged four-wheel drive axle is not cheap to repair or replace.

A little earlier this year, we did some investigating into the actual weights a tractor’s front axle is subjected to when fitted with a front loader. The results demonstrated what a powerful tool a modern tractor and tractor mounted front loader is. And what the combination is capable of as a farm handler.

The exercise also demonstrated the incredible pressures that a tractor’s front axle and tyres may be subjected to. Pressures that the combination is not necessarily equipped to handle safely without real ballasting.

Our test tractor was a 2010 Case IH Maxxum 100 equipped with a Case IH LRZ100 loader with fork. This is a Case IH-branded Stoll loader with parallel linkage. At 100hp, the tractor is typical of many loader tractors around the country. With a four-cylinder engine, its wheelbase would also be typical for that size and horsepower.

Our load was a 4x4 wrapped silage bale made by a Lely Welger Tornado baler last year. Ideal for our test, these bales were made in wet conditions and were very heavy.

For the rear of the tractor, we borrowed an 850kg three-point linkage weight.

The testing was done at the Teagasc centre in Oak Park, Carlow. With kind permission from the staff at the Teagasc facility in Oak Park, we used the recently calibrated weighbridge on-site for all our weighing.

We looked at many different scenarios examining the effect carrying a load on the front loader has on both the front and rear axles of the tractor. We did this with and without ballast and at different loader heights.

Weigh-in

Table 1 shows some weights and measurements that we recorded at Oak Park. We measured axle-loading at three benchmark loader heights of 300mm, 1,500mm and 3,050mm. These represented travelling with the bale, unloading the bale off a trailer and loading a bale into a diet feeder. Due to the heavy weight of the silage bale, we expected the results to be significant, but we were still surprised. Note the front-axle load with bale and no ballast!

In this, the most extreme scenario, the front-axle loading was just 240kg less than the entire weight of the tractor (less loader). That is a whopping 5,240kg, or 5.24t, on the front axle.

This scenario could be mirrored elsewhere if silage-baling conditions were similar. The addition of a rear weight on the tractor linkage offset the front axle loading, but not by an lot.

Adding the three-point linkage, a rear weight of 940kg reduced the front-axle loading to 4,680kg. That is a reduction of 560kg on the front axle – not as much as expected. It highlighted the importance of adding a substantial rear weight to the tractor for loader operations.

Adding ballast in the form of rear-wheel weights or filling the wheels with water just adds to the overall weight of the tractor. Yes, ballasting may improve stability but because the weight is not mounted behind the rear axles, ballasting the rear wheels provides no lift off the front axle.

In our exercise, we also found that the loader position has a much larger weight-bearing effect on the front axle than we considered. As the loader is raised, it creates an arc or part of a circle.

Measuring from the centre of the front axle to the centre of the silage bale, we recorded weights at each of our three working heights.

At our first measurement height of 300mm, the distance from the centre of the front axle to the centre of the bale was 2,800mm. At a loading height of 1,500mm, this increased to 3,300mm. This reduced considerably to 2,250mm when the loader was at its maximum loading height.

Front-axle weight measurements for each of these heights with the rear three-point linkage weight attached were 4,620kg, 4,680kg and 4,240kg, respectively. So, with the loader in its most unstable position at maximum height, there is a little bit of comfort in the fact that front-axle weight is reduced to a minimum.

The capabilities of the front tyres and front axles also need serious consideration when working with heavy loads. According to the Case IH Maxxum 100’s operator’s manual, its maximum front axle loading is just 3,600kg. This is considerably lower than the 5,240kg we recorded on test.

The manufacturer makes an allowance for what it describes as restricted operation. From the manual, ‘‘For intermittent operation, the front-axle loading may be increased provided that the ground speed does not exceed 8km/h (5mph)’’.

The maximum axle-loading under restricted operation jumps substantially upwards from 3,600kg to 6,200kg. Key requirements to remember for this level of axle-loading are that it is only done intermittently and the tractor is operated below 8km/h.

The maximum axle-loading figure is considerable. The capabilities of the tractor’s front tyres also need to be considered, especially when purchasing new tyres.

Considerations

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Focus: Winter feeding equipment