[chadr03]

If weight is your only concern larger gears can be machined thinner below the teeth and spoked to be much lighter. A gear rim will typically have significant stiffness and rating if there is at least two tooth depths of solid material below the root but beyond that most of the material is not very highly stressed. So you can get quite high ratios without significant addition of weight when compared to a solid gear.

That being said a limitation in large reduction gearing is deflection across the pinion under load. The larger the ratio the the pinon selected will be as small as possible causing it to be relatively flexible. When the pinion deflects all of the loading will move toward one end of the tooth effectively reducing the face width.