Rolling Factor

A figure which expresses the relative force or pressure exerted by a roller on a turfgrass surface. The factor is calculated by the overall roller weight being divided by the sum of the width of a roller/s multiplied by the diameter of the roller/s. The rolling factor allows for general comparisons only between different rollers, either as dedicated rollers or rollers on cylinder mowers for example, to provide an indication of relative firmness / compaction effects they exert.

RF (Rolling Factor)=(Weight of roller(s) (kg))/(Roller width (cm) x Roller diameter (cm) )

The scientific basis for the effectiveness of the formula has been questioned because “the physics of the situation is in actuality quite complex …. and the … formula is in fact of rather dubious validity …’. (Evans, R.D.C. (1990) ‘Cricket grounds. The evolution, maintenance and construction of natural turf cricket tables and outfields’, STRI, p.121)

Limited research has been carried out on what might be appropriate for different sports surfaces, although a figure of 0.2-0.3 has previously been indicated for tennis as possibly being appropriate “for the bulk of rolling aimed at producing firm surfaces”. This figure is representative of that expected from a typical ride-on roller, for which an example is given below. (Perris, J. (Ed), (2000) ‘Grass Tennis Courts. How to construct and maintain them’, STRI, p.82)

Lighter rollers will be used for other surface requirements such as surface firming for improving the speed of a golf or bowling green, whilst higher figures might be aimed for cricket surface consolidation in spring, especially for higher quality surfaces.

As a general comparative guide between different rollers the rolling factor might be an aid in managing turfgrass surfaces, albeit with reservations on effectiveness of outcome.

Example calculations:
A single drum hand roller weighing 250kg, with a width of 80cm and a drum diameter of 45cm has a rolling factor of 0.07.
A ride on powered roller with an unballasted roller weight of 1,000kg, with a width of 91cm and a drum diameter of 45cm has a rolling factor of 0.24.
Hand pushed 3-roller firming rollers for bowling greens with a weight of 120kg, with each roller having a width of 91cm, the inner and outer rollers being 10cm diameter, whilst the central roller is 20cm diameter. If the weight is spread evenly (i.e. 40kg) over each roller the rolling factor will be 120 / ((10 x 40) + ((10 x 40) + (20 x 40)) = 0.075.