Time dilation, a concept from Einstein's theory of relativity, becomes significant at very high speeds, especially as an object's speed nears the speed of light. For high-speed wheels, such as those on race cars and spacecraft, time is experienced differently than for a stationary observer. As the wheels turn rapidly, they undergo slight time dilation, which means their internal functions, like wear and heat generation, proceed slightly more slowly than those of the vehicle or an outside observer.