I am a new cyclist and have a few sets of slick tires that I have picked up however I am wondering if they are safe for wet weather. I know many people will say that grip has nothing todo with tread on a road even when wet but what about road grime and other junk on the street. i.e. is it silly to put slick tires on a winter commuter (I don't mind spray from the tire, also there is usually no ice or snow where I am from - Portland) .

A tire compound will always grab better on the road if it is slick, no tread. A tire with awful non-grippy rubber will still be better in the rain than a knobby version of the same awful rubber, because more of it will be in contact with the ground (vs knobs lifting parts of the tire off the road).

What you would really want to be safe in the rain (and on things that get wet in the rain like manhole covers, traintracks, thermoplastic street markings), is good tire compound. And then yeah tires that put as much of that good compound in contact with the road as feasible.

I have ridden slick tires with awful compound that I would trust less in the rain than treaded tires with better compound. There's usually a price difference there.

I have schwabe marathons on at present. The slickish tires are schwabe spicers, Michelin Protek Urban, Vittoria Randonneur.

Thanks for confirming, I will put a couple of those on the winter bike.

Nope - slick tires will be fine - or even better. A little tread won't help at all (though it does help indicate when the tire's worn out). Knobs would have some advantage in snow or mud.

Bike tires can't hydroplane like car tires, so you also don't need to worry about tread that channels water.

Good tires for wet roads are slick, wide, and low pressure.

Tom Brady's trick: reduce your air pressure by 10% to improve grip in cold wet conditions.

If a tyre leaves track in the surface (usually mud, sand, snow etc), then tread does make sense - tyres can dig into it.

If a tyre doesn't leave track (paved roads, concrete, wooden floors etc) - tread have no use, just worsen the grip. Even in the wet!

Years ago (mid 1980a) I had 19mm slick Michelins (pPro iirc) and I couldn't believe the grip they had even on hardpack snow on the side streets. I deliberately tried to break the tire loose from a standing start and couldn't. braking was excellent too. I guess the grip will depend on the tire compound.

Cheers