The "use digital pin with jitter suppression" of infrared speed sensor did remove the "0" delta entries in previous charts.
My previous comment suspect that 0.83msec of brassed piece might be too short time for triggering infrared speed sensor interrupt was correct ! I did increase the time by a factor of 2.5 in attaching a 2.5cm brassed piece tangential on to of the existing piece (again with superglue):
Here you can see that chart curve looks good now, no spikes anymore!
And this is first time measured new speed record of 13.6m/s or 48.9km/h:
(with axis labels as requested by Tom)
The last open question is why high speed only happens from 69th til 76th interrupt (less than a second in total), then goes up to 116 (117th interrupt) and then down to 108 again -- maybe that is a sign that wheel cannot keep road contact the whole time?
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Hermann.