Originally Posted by Dirtdrop
If the road is harder than the tire, treads do nothing to improve traction. Treads can only improve traction on a soft surface where they can dig in. Mountain bikes need tread. Road bikes don't.
That's an unpredictable and variable "if."
Wet or dry aren't the only surface traction variables. Road or commuter bikes may unexpectedly encounter fine crushed gravel, blown sand, snow, slush, dirt, construction areas, etc.
Country roads, bike paths near beaches and riverbanks, converted rails-to-trails, some stretches along Rock Creek Parkway (DC), or even less-traveled roads popular for century or other organized rides, from time to time present traction challenges.
In some areas of the continent one could probably safely assume excellent road surface traction for most days, but many folks reside in areas where it can change daily, or by mile, or even hourly (by weather).