There are indications in Pete's data of a reduction in cal constant by 50% of the SCPF when on concrete. I say indications because the data are not ideal, some being taken at different temperatures so a straight average will not be perfect.
Stu says that is because the concrete/rubber has a higher coefficient of friction so the tyre slips less.
I say it must be that, in common to all pneumatic tyres without very thick chunky treads, Pete's would show a lower constant on a rougher surface, therefore the concrete must be rougher than the asphalt. However, my simple thin elastic membrane model of the tyre has never explained why this should be so.
I think I need to do some more experimental work to measure the forces in my bike tyre casing. Then, calculating the compression and resulting shear forces on the contact patch, I can see whether or not Cf would be exceeded.
Stu: Measurers are indeed advised not to use front wheel braking.