Define tractor. There are some earth movers that stand close to a hundred feet tall, and since they are movable, they would have to be concidered tractors.
I think Harv got it./w3tcompact/icons/wink.gif Like the other guys asked, what kind of tractor. If you're talking about a farm tractor, the Big Bud might qualify.
The Marion 6360 stripping shovel is biggest of the lot. A single link from one of its eight crawler tracks weighs three and a half tons. It stands 21 stories high and its bucket can lift 270 tons of dirt -- twice the weight of a blue whale. Four of these rigs would outweigh the Titanic
The same Marion Company that built the largest earth mover also built the two NASA Crawler Transporters -- the tractors that carry Space Shuttles to the launch site. They weigh 20,000 tons loaded. No other land transportation system comes close.