My first instinct would be to just use a stacked bar/column chart, as pie charts aren't very easy to read. Then I had my thoughts confirmed when I looked closer at this chart:
The blue slice is not 25% of the area...it looks to be more like 30%. Not sure how that happened.
I fully second Luke's comments ; even otherwise , I don't see how the image of the gear wheel in any way adds to the visualization ; for a real visualization which adds to the user experience , see the following :