The term 'Tireless Racer' can be summed up by the crossword solution of 'SLED'. A SLED is a vehicle that is used for transportation over snow and ice, and is typically pulled by horses or dogs. It is also used in recreational activities such as sledding and racing. Tireless Racers are those who use sleds to race against each other, often in grueling conditions. They must have great endurance and strength to complete the race, and are admired for their determination and skill.