A pretty simple way to do this is to place the segments as straight bars then create an Art Brush from that:
The ratios will remain the same. So, to create a 25px stroke for our circle with a 25% / 75% split, I used a 25px x 25px and 25px x 75px rectangles for the art brush.
Here's how to create an Art Brush, borrowed from Adobe's website:
Create a brush
- For scatter and art brushes, select the artwork you want to use. For pattern brushes, you can select the artwork for the side tile, but
it isn’t necessary. For detailed guidelines to create pattern brushes,
see Guidelines for constructing pattern tiles. To know more about
pattern brush options, see Pattern brush options.
- Click the New Brush button in the Brushes panel. Alternatively, drag the selected artwork to the Brushes
- Select the type of brush you want to create, and click OK.
- In the Brush Options dialog box, enter a name for the brush, set brush options, and click OK.