SFT equipment is almost useless, except for a general idea of how a 4WD vehicle would handle on a test track. The best assessment of Braking Action I ever had was from RTM ATC one icy morning in the ‘80’s. I ‘phoned in advance to ask about the 24 runway state before departure in my BAe146 from NWI, the answer was “Don’t even try it, Sir. We can’t even skate on it, without falling over”.