XIV. Examples of actual course certifications
1. Simple loop
(i) Course identification
Tiger Trot 5K, Fuquay-Varina, NC (NC04034PH) (map in PDF)
(ii) Calibration
Tire: 700 x 20C at 105 psi
Length: 400 meters
Pre-measurement rides (69.7 degrees): 192.312, .31, .29, .29; ave, 192.30 rev .
Post-measurement rides (89 degrees): 192.09, .07, .05, .065; ave, 192.069 rev .
Constant for the day: 192.30 x 1.001 x 1000/400 = 481.23 rev/km = 774.466 rev/ml = 2406.15 rev/5km
(iii) Course measurement
Ride 1 (73-74 degrees): From the chosen start to a reading of 2406.15 rev, where a temporary finish was marked.
Ride 2 (76 degrees): Permanent marks were made at mile intervals of 774.47 rev. The distance from the 3-mile mark to the temporary finish was measured as 82.875 rev.
Total rev = 3 x 774.47 + 82.875 = 2406.285
The second ride gave 0.135 rev more than the first, so the temporary finish was made the permanent one.
Difference between measurements: 0.135 x 100 / 2406.15 = 0.0056 % (0.28 m)
2. Out and back with the start the same as the finish
(i) Course identification
Race of Grace 5K, Raleigh, NC (NC04027) (map in PDF)
(ii) Calibration
Tire: 700 x 25C at 105 psi
Length: 400 meters
Pre-measurement rides (66 degrees): 190.26, .30, .26, .27; ave, 190.27 rev .
Post-measurement rides (67 degrees): 190.24, .23, .23, .25; ave, 190.24 rev .
Constant for the day: 190.27 x 1.001 x 1000/400 = 476.15 rev/km = 766.29 rev/ml = 1190.375 rev/2.5 km = 2380.75 rev/5km
(iii) Course measurement
Ride 1 (68 degrees): A temporary mark was placed at a reading of 1190.375 rev, that calculated for a U-turn at 2.5 km. A reading of 2383.615 rev was obtained on return to the start. (The return path was not exactly the same as the outward path.)
Ride 2 (68-67 degrees): From start around the temporary mark back to the start for a reading of 2383.76 rev. The first ride gave a smaller reading so it was chosen to fix the course.
Calculated adjustment of the U-turn: The following calculation showed how much nearer the U-turn had to be made so that start and finish were coincident.
(2383.615 - 2380.75)/2 = 1.4325 rev
Difference between measurements: 0.135 x 100 / 2406.15 = 0.0056 % (0.28 m)
Ride 3 ( 67 degrees ): Permanent marks were made for the mile splits at intervals of 766.29 rev. A stop was made a few feet before the the temporary U-turn, the reading from the wheel rim at a mark on the ground was noted, and the computer reading frozen by moving it slightly on its mount so that electrical contact was broken. The wheel was then rolled 1.43 turns back from the temporary turn and a permanent U-turn marked. After again establishing the position where electrical contact was broken, the computer was activated and marking of the splits resumed by passing around the new U-turn.
Alternative procedure: The second ride could have been dispensed with if the last ride had continued on from the 3-mile split. However, if the last ride had indicated that the course be lengthen more, the U-turn would have had to be adjusted again.
3. Complex courses with many certified and non-certified points determined without rezeroing at each point
(i) Description of courses (map in PDF)
In this group of measurements a 10K and a half-marathon were certified at the same time. Both had the same start and finish. The 10K was 1.25 loops followed by a U- turn to the finish. The half-marathon was 2.5 loops followed by a U-turn to the finish.
(ii) Course identification
Inside-Out Sports Classic 10K, Cary, NC (NC03042PH)
Inside-Out Sports Classic Half-Marathon, Cary, NC (NC03043PH)
(iii) Calibration
Tire: 700 x 23C at 105 psi
Length: 400 meters
Pre-measurement rides (66 degrees): 190.26, .30, .26, .27; ave, 190.27 rev .
Post-measurement rides (67 degrees): 190.24, .23, .23, .25; ave, 190.24 rev .
Constant for the day: 190.27 x 1.001 x 1000/400 = 476.15 rev/km = 766.29 rev/ml = 1190.375 rev/2.5 km = 2380.75 rev/5km
(iv) Course measurement
Start: 12:35 am (78 deg) Finish: 6:30 pm (70 deg)
All measurements were done from or to a point A on the eastern junction of Grisdale with Jackson.
Two rides were made from the start, S, to A ; two from A to the finish, F; and two of the complete loop to get the distances s, f, and l, respectively. Finally, two rides were made to locate the U-turns and splits.
In the case of the U-turns and splits run in a clockwise direction, if the calculated distance had been reached on the second ride before reaching the mark set in the first ride, that mark was taken as the final mark for the split. If not, then the final mark was set according to the second run.
In the case of splits run in an anticlockwise direction, the opposite was true.
In both of the above cases the distance to be run was maximized.
(v) Calculations
U-turn for 10K, t = 0.5 (a – s -- l – f )
U-turn for half-mar, u = 0.5 (b – s – 2l – f )
Where: a = 10 km expressed as wheel revolutions
b = half-mar expressed as wheel revolutions
For splits, measurement distance, x, was calculated from the split distance in revolutions, d, according to the appropriate formula in the following:
x = d – s
x = d – s – l
x = d – s – 2l
x = a – d – f
x = b – d – f
(vi) Results
Distance
Ride 1
Ride 2
Smallest revs
% difference
s
257.70
257.86
257.70
0.062
f
15.57
15.575
15.57
0.032
l
3441.66
3441.46
3441.46
(0.006)
Location of Splits and U-Turns by Measuring Distance from A (x)
s
f
l
day constant
257.700
15.570
3441.460
477.33
Miles
Km
Rev
x, calculated and marked
Mark remeasured
% diff
1
1.60934
768.19
510.49
2
3.21869
1536.38
1278.68
3
4.82803
2304.56
2046.86
5.00000
2386.65
2128.95
2129.30
0.0164
4
6.43738
3072.75
2815.05
8.00000
3818.64
119.48
119.52
0.0335
5
8.04672
3840.94
141.78
6
9.65606
4609.13
909.97
6
9.65606
4609.13
148.60
10.00000
4773.30
1074.14
1074.20
0.0056
7
11.26541
5377.32
1678.16
12.00000
5727.96
2028.80
2029.20
0.0197
8
12.87475
6145.51
2446.35
9
14.48410
6913.69
3214.53
15.00000
7159.95
19.33
19.34
0.0517
10
16.09344
7681.88
541.26
541.29
0.0052
11
17.70278
8450.07
1309.45
12
19.31213
9218.26
836.64
20.00000
9546.60
508.29
508.33
0.0069
13
20.92147
9986.45
68.45
HM
21.09749
10070.46
T
529.29
529.39
0.0198
U
1457.14
1457.54
0.0276
(vii) Conclusion
In the first two examples of course certification measurements the computer was rezeroed after each stop so that there was no chance of spurious impulses affecting results. However, in this third example, 22 stops were made on one ride to establish certified and non-certified points without rezeroing, so that spurious impulses were a possibility if the wheel rolled back at a stop. However, checks throughout the ride showed that the synchronization between the zero spoke and the zero point of the computer was not destroyed, and therefore no spurious impulses had been generated. Moreover a final ride to remeasure the certified points gave excellent agreement.
I would recommend that rezeroing after each stop to make measurements, but this is not absolutely necessary. Any spurious impulses will not go undetected if checks on synchronization are made.
