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Constant low pressure


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With the right tire pressure and the optimum wheel adjustment, it is possible to save a lot of fuel. Svenske Trailer Magazine followed a mini test where the driver, drove 2 rounds, with a 60 ton wood chip trailer. With low tire pressure and an error adjustment on the tires of the truck, the consumption was increased with five percent.

There is a feverish activity in the minutes before Mattias Arnesson ventures out into the first test round, with a conventional wood chip trailer, a Scania R560 6x2 with four axles Eksjövogn with single-mounted 385/55-22, 5 "wheels and ROR axles.

The team includes Nils-Erik Gustafsson and Bruno Hauer from Josam who adjusts the axles, and the test General; Stefan Nilsson, who is the Product Manager at Bevola. The purpose of today's test is to document whether the correct tire pressure and the adjustment of the tow truck axles can affect fuel consumption.

Not optimal

The test drive, on approximately 120 km, is on hilly roads, and medium-large asphalt roads in Småland. A route that is typical for a wood chip trailer. Before the first test round, Stefan colleague Per-Ola Johansson let some air out of the trailers tires. The tire will now have an air pressure of 6.5 to 9.2 bars. Josams men, makes sure that tire setting are not optimal. - We know that some haulers do not care about whether the tire pressure and wheel setting are within the limit values, which ​​are accepted, says Stefan. Mattias fills the tank just before departure. Along the way, we follow the consumption with great excitement. Naturally, the thirstiest one is the V8, in places where there are more curves on the road and where it is hilly.

Not correct indication

In some areas the consumption appears to be about 6.5 liters on the on-board computer, but when arrived at the destination, it turns out, that the computer did not give the correct indication. Mattias filled 62.01 liters of diesel in the tank, and it is 3.78 liters less than the total consumption on the trip, which the computer calculated. Of the 124.1 km that the vehicle has traveled since the last refill, 62.01 liters of fuel, gives a consumption of almost exactly 5.0 liters in average. Now the air pressure is adjusted to 9.2 bars on the trailer's 8 tire and the wheel adjustments are optimized. The refueling before and after the test run shows that Mattias now filled 58.72 liters, this is giving a consumption of just 4.75 liters per mile (10 km). The difference: About 5 percent, or about 0.25 liters of diesel per mile (10 km). - I tried to drive as I normally do, on both rounds, and I am a bit surprised that there was such a big difference. It is very clear how much fuel can be saved, says Mattias.

Expert Help

For a trailer that has driven 12.000 mils, it is about 3,000 liters of fuel, or about 36,000 SEK in reduced diesel costs, but to adjust the wheels correctly, it is about getting the expert help as is it enforced by Josam for instance. Each axle had values ​​that looked OK during the first test run, but because the axles were a tenth of a millimeter adjusted wrongly on the left and on the right side, the parallelism was not optimal. -At those body builders who have services on their vehicles, the axles usually have better adjustments, but it is also seen that it can look even worse, says Nils-Erik Gustafsson, who is area manager for Josam. He also notes, that axles that are wrongly adjusted lead to increased fictions with the surface of the road (this increases the fuel consumption). This can also be heard on the sound, when the trailer with bad adjusted axles runs into the workshop.

A small adjustment

Niels-Erik was not so surprised when it came to the difference: - It is a few percent more, than we had in a similar test in Denmark some years back, he says. Today, many bodybuilders make inspections of the wheel adjustments before a delivery. In order to facilitate the optimal adjustment, Bevola processes the axles before they are sent to the bodybuilders. - We warm up the axle and we make a small adjustment so that it will have a positive camber angle and toe, in un-loaded condition. This means, when the axle is loaded, it becomes neutral. This result in, less friction and lower fuel consumption, says Stefan. Even on the mounted axles, there are adjustments, but this is, as mentioned before, something that requires knowledge and accuracy. On the contrary, a millimeter misalignment in the wrong direction can increase the fuel consumption.

Check the tire pressure

The issue of tire pressure is not so advanced. It is exclusively about ensuring that the tire pressure is at the recommended level. - There are probably some drivers who are very special, but I believe that most of the drivers do not care. I controlled the air pressure when I changed tires, says Mattias, who now drives a tow truck with a device which regulates tire pressure itself.

The mini tests that the Trailer Magazine followed, does not give any accurate measurement of how the fuel consumption is affected by bad wheel adjustments and low air pressure, but it gives a clear indication, that it pays to keep track of these things. And especially to be noted, the difference between the five percent, simply by changing the trailer's wheels. The vehicle had the same wheel adjustments and tire pressures during both test runs.

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