Definition of "treadless"

But no sooner had I got the hang of it than those treadless vanity boots shot out from under me. That was the last thing I remembered.

1999, Lisa Michaels, Split: A Counterculture Childhood, page 73

Because his tires were small and almost treadless, he could not maintain the speed of a Volga, which passed him, its fat tires lifting packed snow onto his windshield.

2008, Michael Beres, Chernobyl Murders, page 60