Damn slippy wet london!

If the road is slippy because of rain on ultra smooth surface or road markings, tread does make a difference after you have slipped off the smooth bit. It is more likely to regain grip if you've got tread.

I think that the issue is the coefficient of friction, not the tread per se. Tread on a tyre seems to serve two purposes - dispersing water and increasing friction. The hydroplaning arguments show that the water dispersal is bunkum.Friction can come from tread, but also from material, contact area and mass.

A treadless soft compound, running at a lower pressure (more contact area) will be grippier than a hard compound at higher pressure. All things being equal then, a file tread might be an advantage, but other factors are also, probably more-so, important. Also, this only holds true for a smooth road surface, because tarmac has more 'tread' than any tire I'd want to ride.

/jobst-brandt-mode