Regrooving a tire by hand - GIF

[Frank S]

Is it still a speed rated tire?

Probably not. In general tires that state reproveable on the sidewall are regrooved long before they are completely bald. Semi-truck tires the new grooves are cut about 1/4" possibly a little more. car tires don't have a very think tread belt on them so maybe 1/8"

The guy did a masterful job of creating an even tread pattern, but I have to wonder if the reason for the liquid he dabbed on it was to cover where he went too deep and exposed the cord or steel belt.