Cranfield University

Laboratory Studies Into Undercarriage Systems
sorge (2005, a), Antille (2006), and Stranks (2006). Interesting to note was the fact that
three of the four tested implement tyres achieved similar results although differing in sec-
tion width and inflation pressure. An increased section height was able to account for a
reduced section width.
For whole undercarriage systems the benefit of the tracks shown by Ansorge (2005, a) was
maintained after the additional passage of the rear axle tyre. A typical wheeled combine
increased the soil density by 19 % compared to a tracked machine with an increase of 14
%. Thereby the effect of the rear axle tyre size had a less effect on soil conditions follow-
ing a front axle track unit than a tyre. Soil displacement increased by 6 mm compared to 12
mm for the tyre over the same depth range and extended to a shallower depth (300 mm)
after the track. This was due to the bearing capacity of the stronger layer in the top 150 mm
observed from the penetrometer studies.
A hypothetical three axle tyre configuration with 5 t load per tyre caused similar vertical
soil displacement compared to a track followed by a rear tyre and to a dual configuration
on the front axle. An undercarriage unit with a track unit on the front axle and a gross
weight of 33 t resulted in a similar vertical soil displacement to that of an 11 t combine
harvester on commercially fitted normal front and rear tyre sizes. A hypothetical 3 axle
machine with unequal tyre sizes and load caused intermediate soil compaction compared to
that of a tracked and a wheeled machine. An equal weight distribution on two 680-tyres
caused nearly as much soil compaction as a traditional wheeled combine configuration on
900 – 700. From this the conclusion can be drawn that a maximum wheel load of 5 t on
appropriately inflated tyres has the same impact on soil density changes as the rubber
track. Therefore fitting a track on a combine has a similar impact as reducing axle loads to
10 t while using large section width/height tyres and maintaining whole machine weight.
Important to note is the residual soil displacement between 500 – 600 mm depth for wheel
type undercarriage systems. Soil displacement for track type undercarriage systems has
decreased to zero at about 500 – 600 mm depth, but the 680Alt, 680-680, and all common
combine harvester tyre combinations maintain a residual soil displacement highlightening
their possible impact on the subsoil.
The overall configuration of the undercarriage system of the combine harvester was more
important than individual weight on a single axle.
Ph.D. Thesis Dirk Ansorge (2007)
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