Are slick bicycle tires more slippery in the wet?

Question

I always assumed slick (tread-less) tires were more prone to loss of traction in the wet. That is until I read this answer on the bicycles SE which claims that bicycle tires are too thin, round and firm to experience hydroplaning. Is there any research to back these claims?

Answer 1

Jobst Brandt, author of "The Bicycle Wheel" (which explains how to build strong bike wheels and which includes a finite-element analysis of spoked wheels) lays out the argument at Sheldon Brown's site:

Commercial aircraft, and especially motorcycles, demonstrate that a round cross section tire, like the bicycle tire, has an ideal shape to prevent hydroplaning. The contact patch, a pointed canoe shape, displaces water exceptionally well.

...

A window-cleaning squeegee demonstrates this effect well. Even with a new sharp edge, it glides effortlessly over wet glass leaving a microscopic layer of water behind to evaporate. On a second swipe, the squeegee sticks to the dry glass. This example should make apparent that the lubricating water layer cannot be removed by tire tread, and that only the micro-grit of the road surface can penetrate this layer to give traction. For this reason, metal plates, paint stripes, and railway tracks are incorrigibly slippery.

Besides having better wet and dry traction, smooth tread also has lower rolling resistance, because its rubber does not deform into tread voids. Rubber being essentially incompressible, deforms like a water filled balloon, changing shape, but not volume. For a tire with tread voids, its rubber bulges under load and rebounds with less force than the deforming force. This internal damping causes the energy losses of rolling resistance. In contrast the smooth tread transmits the load to the loss-free pneumatic compliance of the tire.

In curves, tread features squirm to allow walking and ultimately, early breakout. This is best demonstrated on knobby MTB tires, some of which track so poorly that they are difficult to ride no-hands.

I've ridden both but mostly slicks. I haven't had significant trouble with either on wet tarmac, though I really notice a difference between 25mm and 28mm wide tires on wet mountain descents. The wider tire (and hence larger contact patch) gives much more traction on turns and seems to have a much greater effect than the tire surface pattern.

That said, I doubt many cyclists get fast enough to hydroplane on wet roads. I've done above 45 mph (75 kph) downhill on dry tarmac in good visibility which is more than fast enough to hydroplane a rectangular cross-section tire, but I would never do that in the rain because water hides potholes. Even if that weren't a problem and I had visibility around turns, in the rain you have to pump brakes to keep your rims (which the brake pads grip on almost all road bikes) clear of water which has the side effect of limiting speed.