In the various Transformers incarnations, we've seen it seems just about every possible Earth vehicle used as an alternate mode for a transformer.
From supercarriers to motorcycles to tape decks.
Why no road graders?
A road grader is a pretty common construction vehicle. Plenty large enough to serve as a transformers alternate mode not to mention pretty high speed in vehicle mode with a large blade the robot mode transformer could use in combat.
It seems a natural to me.