A car can hydroplane in as little as...

• A. 1 inch of water
• B. 1/4 inch of water
• C. 1/10 of an inch of water
• D. 1/100 of an inch of water

Answer: (C)

Hydroplaning happens when a layer of water builds between the tire and the road, causing the tire to lose contact and traction. The depth of water that can trigger this depends on speed and tire condition, but in many real driving situations, about one-tenth of an inch of water is enough to start hydroplaning. When that amount of water sits in the tire’s path, the tread has to evacuate it quickly; if the wheel is moving fast enough or the tread is worn, a water wedge forms under the tire and grip is lost. Among the given options, that smallest depth is the one most likely to cause a loss of traction at typical highway speeds, which is why it’s the best choice. The deeper options would also cause hydroplaning, but they aren’t the minimum depth needed to start the phenomenon.