Driving to altitude - temperature impact

[Hops]

Took a drive up in the mountains today, and it turned out to be an interesting test of temperature on tire performance. I have a 987S with 18" PS2, about 1/3 from new to done.

I left home, which is about 1200 ft, and within an hour was at 7000 feet, then within another hour back to under 1000 ft. The temperature swing during this drive was 49 to 32 to 53, and it revealed how tires perform across this range of temperatures. We all know that summer tires are not designed to run at cold temperatures, but what happens, and how does it feel? How unsafe is it to push the limits at low temperatures?

I found that the sticky feeling of the tires started to go away significantly in the upper 30s. Certainly in the 40s it was not the same as running on a nice 80 degree afternoon, but the car started pushing more prominently from 40 to freezing. The good news is that nothing surprising happened with the lessening grip. The balance of the car translated into good control even in these conditions, but there was much more understeer and it was harder to hold the same lines as normal. The tires were struggling to maintain solid contact, which left the car feeling somewhat unsettled. At the end of the day, shaving about 10-15% off of "warm speed" kept things well under control, but you still lose some ability to save yourself using extreme braking or turning. Simply less headroom.

As I returned to warmer conditions, I could feel the traction coming back, and the driving became much smoother in and out of the corners, with the tires growing more stable and predictable. I could literally feel my level of confidence change lower and higher moving into the cold and then back out.

Hopefully this info is useful to someone... yes, you can drive summer tires at freezing, on dry roads. And yes, you do need to drive a bit more conservatively to account for the difference in traction.

If anyone else has tried this experiment, I am curious to hear if you found identical results or if you would describe anything differently. Also, what happens well below freezing?