I remember studded snow tires and they certainly do work on icy roads , don't remember the crushed walnut but that would make sense .
Don't know if the DOT allows them anymore , or if they even make them anymore
Studded one pair my my old boots just for icy conditions and believe me they work
Who paid for the test?
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I've driven lots of studded, lots of excellent snow tires, lots of bald tires (even in the snow). Studs work better in the snow.
Consider the very best snow tire made. It works fine, right? Does adding studs to that excellent snow tire make it perform worse in the snow?
Just be aware that there is a powerful legislative movement to resist allowing studded snow tires on public roads. Your government does not care if you slide off the road as much as they would rather not wear out the pavement.
Once upon a time, all the tire stores provided studded snow tires. In this newer age of mass merchant distribution of tires, they don't have time for good service or specialty tires. Furthermore, the wider range of tire sizes cuts down on the potential for customers obtaining stud-able tires. I would be genuinely surprised if the average person could even find a tire dealer to install studs in their tires. That seems to be a disappearing art.
Of course, I stud my own tires.
Don't see how studded snow tires can improve traction on wet roads. Snow? Yeah, a bit, but not so much that you'd notice.
I was born & raised in the PNW. In the winter, we had real snow tires, none of that "All Season" crap like today. And, they had walnut shells crushed and embedded right into the rubber itself. If you were real serious about your snow tires, you had them studded as well.