[LastFrontierBimmer]

I find this interesting because I routinely see huge fluctuations in outdoor temps, from +45 degrees to -10 degrees Fahrenheit. Yet my TMPS has not gone off once.

I set the pressure on all 4 tires to BMW-recommended levels for their size and re-set the TMPS when I installed the winter wheels & tires. I choose to run 17" wheels during the winter to combat the harsh winter road conditions. I don't however, think that would result in more stable pressures than those in your 18s.

Perhaps you are running pressure on the low end in search of better traction? This may make them more susceptible to dipping under and back over the TMPS threshold during temperature fluctuations.