Book excerpt: Did you know . . . That the first tractors had metal wheels with no tyres? That a tractor can weigh as much as five elephants? That a tractor can pull as much as 500 horses can? Tractors are big and powerful! They can plough, lift, dig, mow and power through the biggest farms, the longest roads and your very own backyard. Find out everything you want to know about these amazing machines in theBig Book of Tractors.