At what speed may the tires entirely rest on the top layer of water with no contact with the pavement?

When considering the question of at what speed tires might entirely rest on the top layer of water, it's important to recognize the phenomenon of hydroplaning. Hydroplaning occurs when a vehicle's tires lose contact with the road surface due to a film of water, leading to a loss of traction.

At higher speeds, especially as vehicles approach 55 mph, the chances of hydroplaning significantly increase because the vehicle's speed can outpace the tire's ability to displace the water on the roadway. This means that the tires can become buoyed by the water layer, resulting in the tires effectively riding on the surface rather than maintaining contact with the pavement.

While lower speeds reduce the risk of hydroplaning, the threshold for this dangerous situation tends to hover around the 55 mph mark, making it a critical speed for drivers to be aware of when driving in wet conditions. Therefore, recognizing that hydroplaning is most likely to occur at speeds around this value supports why this choice is considered the correct answer.