When I went to the Alberta oil sands for Business Insider last month it was hard to miss the biggest dump truck in the world: the Caterpillar 797B.

One of the many unique aspects of the Cat 797 are its tires: More than 13-feet-tall, weighing 11,860 pounds, each Michelin or Bridgestone 59/80R63 XDR tire costs $42,500 and that's when you buy the full set of six required by each $5.5 million truck.

They're one of the largest tires in the world and were made for the original Caterpillar 797.

The 59/80R63 XDR: