@troubledturtle That's the "transmetal" form of rattrap that they introduced in season 2 or 3. I think the writers felt (particularly by that point in the show, with the power inflation that was happening) that this "spy" style character didn't have enough going for it relative to the rest of the cast, and that too many characters lacked mobility.
Like, they had to keep writing stories where rattrap, cheetor, rhinox and dinobot were stuck where they were, or had to hoof it across miles and miles of empty terrain, or else needed Optimus to carry them to the action.
I suspect they had originally given themselves the constraint that "rattrap must be cool for reasons other than pew pew" and needed to design more compelling toys, but didn't want to do so by buffing him along intimidation/firepower lines.
So they gave him wheels, lol.