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Tractor Wheel Slip

Also known as wheel slip · tyre slip · ballasting check · traction slip

s=d0−dLd0s = \frac{d_0 - d_L}{d_0}

Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!

See also
Drawbar Power — Slip is the difference between the power the engine makes and the power the drawbar delivers.Fuel Use per Unit Area — Both too much slip and too much ballast show up as fuel per hectare.

Learning zone

Slip is how a pneumatic tyre transmits torque to soil. A driving wheel always travels a little less distance per revolution than its free rolling circumference, and that deficit is not a fault — it is the mechanism. The soil is being sheared, and shear requires displacement. A tyre with zero slip is transmitting no useful pull at all.

The field measurement needs no instruments. Mark a rear tyre and a starting point, drive ten revolutions under working load, and mark where you stop. Repeat over the same ground with the implement raised or unhitched. The loaded run is shorter, and the shortfall as a fraction of the unloaded distance is the slip. Ten revolutions is the convention because it averages out the marking error; using the same ground for both runs matters more than most people expect, because the surface changes the unloaded distance too.

The target bands are narrow and they differ by drive configuration: 10–15% for two-wheel drive, 8–12% for mechanical front-wheel drive, and 8–10% for four-wheel drive or tracks. Both directions of error cost money, which is the part that surprises people. Too much slip is the obvious failure — fuel burned turning tyres, and topsoil smeared and compacted where the lugs shear it. Too LITTLE slip is the expensive one nobody diagnoses, because it feels like a well-set-up tractor: it means the machine is over-ballasted, carrying weight it does not need, and paying rolling resistance on that weight through every pass of the season.

So the correct response to excessive slip is ballast or lower tyre inflation pressure, never more throttle. Reducing inflation pressure enlarges the contact patch and is usually the cheaper of the two, though it must stay within the tyre's load-and-speed table. And the correct response to a slip reading of 3% is to take ballast OFF. The reason the measurement is worth doing at all is that neither condition is detectable from the seat — a tractor that is 20% over-ballasted feels exactly like a tractor that is right, and quietly burns fuel for the whole season.

Tractor Wheel Slip
s=d0−dLd0s = \frac{d_0 - d_L}{d_0}
d0dLs
Where
  • ss= Wheel slip (%)
  • d0d_0= Unloaded distance (m)
  • dLd_L= Loaded distance (m)
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