I was a very, very bad boy. I drove on the current set at 25F. I did a 220-mile road trip to Source 1 Automotive, near Cincinnati, three weeks ago. (Turbos! Squeee!
But different thread.) My garage is warm, and I made sure the tires were properly inflated for the temp. I live next to the freeway and so was able to keep tire temps up the entire way. Outside temp warmed into the upper 30’s by the end of the trip. I inspected the tires upon arrival at Source 1, and no cracking that I could see.
I did this on my previous set of Zero Neros, only once, same trip to Source 1, two Novembers ago, also with 20’s at the start of the trip. The tires survived long enough to do the cross country trip to San Francisco last year for NSXPO, AND two track days there.
Pirelli has clearly built in some margin for these tires, but I don’t advise doing driving in severe cold regularly.