Originally Posted by
jrickards
For the purpose of commuting, I generally recommend against knobby tires as they slow down the bike, smoother tires are better for commuting (but they don't have to be perfectly slick). Although the OP didn't ask, bike tires are too narrow to worry about hydroplaning on wet/watery surfaces so you don't need to have grooved tires for the purpose of channelling the water out from under the tire. Some tire compounds are better for grip than others and the grippier ones may be better suited for wet conditions.
As @
WestPablo said, leaves are slippery: try to maintain a straight path (ie., no cornering or meandering) over leaves, they're like the autumn version of ice.
Depends on whether you will be dealing with any dirt track or not. Here's a good article on the subject as it applies to mountain bikes:
Dialing Your Mountain Bike in for Fall and Winter Riding.
In cold, wet, slippery conditions, speed should not be the primary concern. If you have the choice of changing your riding style to be safer or changing your tires to be safer, the mountain biker in me says change the tires. When it's dry again, it's just a few minutes to change them back.