The ITF Court Pace Rating (CPR) measures the effect of ball-surface interaction. This concept includes: friction, which primarily determines the reduction in the horizontal component of post-impact ball velocity, and, vertical restitution, which determines the time between successive bounces.
CPR is derived from a theoretical model of a ball-surface impact that assumes that
the ball and surface are rigid during the impact and that the ball slides throughout
contact with the surface. These assumptions necessitate that the ball impacts the
surface with negligible spin and at a particular speed and angle.
Apparatus
Test apparatus consists of:
- A means of projecting a ball at the specified speed and angle onto the
surface without imparting spin of greater than 3 rev/s, such
as a compressed air-powered ball cannon.
- A means of monitoring the trajectory of the ball before and after impact such
that its horizontal and vertical speeds can be measured with a maximum
uncertainty of ± 0.05 m/s (see figure 2).
- A minimum of three high-specification balls (see table 1).
Note: Angle of travel can be deduced from the vertical and horizontal speeds.
Figure 2. Test apparatus for measuring court pace.
Calibration of apparatus
The reference test devices are those belonging to the ITF, and all other devices are calibrated with respect to them. Calibration of test devices is achieved using standard surfaces every two years.
Note: The spin rate of the ball can be checked using a high-speed video camera or
stroboscope photography.
Test procedure
- Adjust the ball-projecting apparatus to deliver the ball at an incident angle of 16 ± 2° and speed of 30 ± 2 m/s. If possible, avoid using the test locations(s)and balls during this preparation stage.
- Project each of the three test balls onto the test surface three times (nine impacts in total), moving impact location for each shot. If the surface is disturbed or damaged by the test (e.g. movement of clay particles), the impact location should be changed or surface restored before the next shot.
- For any surfaces that have an inherent directional pattern – such as natural or artificial grass – test shots should be fired in the typical directions of play, i.e. parallel to the length of the court.
Calculation of results
Include the following results in the test report for each impact:
vix = horizontal inbound velocity (m/s)
viy = vertical inbound velocity (m/s)
vfx = horizontal outbound velocity (m/s)
vfy = vertical outbound velocity (m/s)
e = coefficient of restitution (COR)
μ = coefficient of friction (COF)
T = mean ball temperature for test location/sample (°C)
c = temperature coefficient (0.003)
eT = adjusted COR for temperature T
a = pace perception constant (150)
b = mean coefficient of restitution for all surface types (0.81)
CPR = court pace rating
where:
The test value is the mean CPR for all impacts, excluding court markings. The variation (measured only in on-site tests) is given by the maximum difference in the mean CPRs for each location, excluding the court markings.
Classification
Surfaces are categorised as follows:
| Category | CPR | | Slow | ≤29 | | Medium-Slow | 30-34 | | Medium | 35-39 | | Medium-Fast | 40-44 | | Fast | ≥45 |
Table 2. Court Pace Rating categories.
Court surface construction is an inexact science. As a guide, the tolerance in the mean CPR value for a court installed by experienced contractors using quality materials and conventional methods at a reasonable cost is ± 5 CPR from the quoted value. This tolerance applies to a new court as/unless specified by the end-user. The maximum variation in CPR between the test location means, excluding the court markings, should be ≤10 CPR.
Note: CPR may vary depending on the nature of the materials that support the uppermost playing surface of a court.
The coefficients of friction and restitution of a surface are categorised as follows:
| Category | COR | COF | | High | ≥0.85 | ≥0.71 | | Medium | 0.79-0.84 | 0.56-0.70 | | Low | ≤0.78 | ≤0.55 |
Table 3. Coefficient of restitution and friction categories
Surfaces with a COR of less than 0.70 are not recommended for use as tennis courts.
The maximum variation in COR between the test location means, excluding the court markings, should be ≤0.05. The maximum variation in COF between the test location means, excluding the court markings, should be ≤0.05.
 | | Calculation of CPR - Click image to see a larger version |
Figure 3. Court Pace Rating conversion chart.
Friction (COF) and vertical restitution (COR) are combined to give CPR, using the equation shown above. Surfaces are typically perceived to play ‘faster’ as CPR increases, which can result from a decrease in friction and/or restitution.
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Last Updated: 15 March 2011
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