TECHNICAL ADVICES

Mechanical lead

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Mechanical lead

In order to fully exploit the advantages of 4 wheel drive and to avoid premature wear of transmission and tyres, the peripheral speed of the front axle must be higher than the rear.

The "MECHANICAL LEAD" (L) is the percentage relative ratio between the peripheral speeds of the front and rear tyres.

Commonly, the correct advancement of the tractor with double traction foresees a value of L included between +1 and + 5% (peripheral speed of front tyres > peripheral speed rear tyres).

Values of L out of this range could cause problems of handling instability (L < 1, the rear axle "pushes" the tractor in excessive way respect to the frontal axle) or cause excessive creeping between the front and rear tyres (L > 5, excessive mechanic effort of all the transmission chain ).
In both the cases, rises difficulty in the management / insertion of the "gears" and the tyres are subjects to rapid and uneven wears.

 

Calculation of the front lead

The measure must be implemented with the following conditions:
- Tractor equipped with standard front ballast
- Nominal tyres pressure
- Tract of smooth and level surface at least 50 m.

          Rc (front) * RM - Rc (rear)
A = ------------------------------------ * 100 = (+1 +5 )
                   Rc (rear)

where: Rc (front) = rolling circumference of front axis tyres.
  Rc (rear) = rolling circumference of rear axis tyres
  RM = mechanical ratio between front and rear axle.

 

Measure of the rolling circumference on the field

The measure must be calculated in the following way:
- remove the double traction (the rolling of the front and rear wheels have to be independent)
- mark the front and rear tyres sidewall, on the middle of the tyre-foot print area
- mark the rolling surface in correspondence of the middle of the tyre-foot print area
- move the tractor forward so that the front and rear tyre complete exactly 5 revolutions
- mark on the rolling surface the point at the end of the 5th revolution, respectively for the front and rear tyres
- measure the distance crossed respectively to the front (f) and rear (r) tyres

 

- CALCULATION OF Cr (front) = F[m] / N° of revolutions = a / 5

- CALCULATION OF Cr (rear ) = R[m] / N° of revolutions = p / 5

 

Measure of the mechanical ratio on the field

The measure must be implemented in the following way:

- insert the double traction
- mark the front and rear tyres sidewall, on the middle of the tyre footprint area
- move the tractor forward so that the rear tyre complete exactly 5 revolutions
- count the complete number of revolutions of the front tyre
- calculate the fraction of revolution of the front tyre in this way: count the number of lugs included between the one in the middle of the foot print area and the previously taken as reference point. Divide this counted number by the total lugs number


CALCULATION OF RM = (FRONT TYRE revolutions. + rev. fraction) / COMPLETE REAR TYRE revolutions

 

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