Sistema di misurazione trattore

Mechanical Lead of a tractor: how important is it?

The Rolling Circumference and the Mechanical Lead of a tractor which follows represent two fundamental factors when choosing the right tyre. These parameters allow us to obtain a correct Running Cost of the tractor.

Definition of Rolling Circumference

The Rolling Circumference of a tyre represents the distance covered in one complete revolution of the tyre with a defined set of load, pressure and speed conditions. Every agricultural vehicle is compatible with tyres which have specific dimensions and rolling circumferences. Tyres of the same size which belong to different competitors can show remarkable differences in terms of Rolling Circumferences. For instance:

BrandTyre treadSizeRolling Circumference
TrelleborgTM1000IF650/60R344955
MichelinAXIOBIBIF650/60R344933
TrelleborgTM1000IF710/70R426190
MichelinAXIOBIBIF710/70R426115

In this case asking a consultant for advice is a good decision.

Definition of the Mechanical Lead of a tractor

The Mechanical Lead is strictly related to the definition of Rolling Circumference of tyres. Its definition comprises the concepts of Mechanical gear and Rolling Circumference of the tyres. Having previously explained the Rolling Circumference of the tyres we define the Mechanical gear as the transmission’s mechanical gear between the front and the rear axle. This parameter changes depending on the tractor manufacturer, for instance a tractor which belongs to a certain brand has a different mechanical gear if confronted with a tractor of another brand within the same segment. Even tractors of the same brand present a different mechanical gear.

Mechanical Lead measurement test
A picture of a Mechanical Lead measurement test

The mechanical gear-rolling circumferences (front and rear) pairing defines the Mechanical Lead: the peripheral speed of the front tyres must be superior to the one of the rear tyres. The optimal value of the Mechanical Lead is comprised between +1% and +5% but it can also be comprised between 0% and 5,5% depending on the tractor. A Mechanical Lead which is optimal allows to make the most of a 4RM vehicle, consequently avoiding both the premature wear of the tyres (premature and uneven wear) and the wear of mechanical parts. In addition, when the Mechanical Lead is not correct there can be problems such as an excessive fuel consumption and difficulties during the engagement of the gear.

We can therefore say that the Rolling Circumferences and the Mechanical Lead represent one the parameters which determines the Running Cost of a tractor. In fact, the correct choice of the front and rear tyre pairings to guarantee the efficient functioning of the tractor and a correct cost management of the agricultural business is fundamental.

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