Sharp objects, strong impacts or other mistreatment can cause visible and invisible structural defects
Also tyre pressure that is too low causes structural defects
High temperatures and sunlight can destroy the rubber
Hydroplaning depends on water depth, tread depth and driving speed.
In order to measure hydroplaning, a car is driven into a basin with 8 mm water and speeds up. As soon as the motor works harder without speeding up, hydroplaning starts.