Ballast Any idea what this tire filling is?

[fried1765]

Well like my Boeing Tech Lead told me years and years ago: One test is worth a thousand theories.

In this case, it works. A couple years ago it got down to the 10-20s during the day for almost a full week. Both temps and the length of time are unusual for this area (SC TN); hence it could be considered worst case for my location and situation. The rear (nor the front) tires never froze, they were totally drive able. There's a thread on it around here somewhere.

So I'm pretty happy with it, especially given that the chances of me actually being outside and working in 10-20 degree weather is somewhere between slim and none, your snotty reply notwithstanding.

Yup!
Your Boeing Tech Lead was quite correct.
"One test is worth a thousand theories"
The real story for you though would seem to be that you do not any freeze protection at all, with "chances between slim and none" of your tractor being outside in 10-20 degree weather.
For information purposes, you could try a simple test, with varying concentrations, using your home freezer.
I did that!