Originally Posted by
cyccommute
Mavic sells the Open Pro in both disc and rim versions. The weights are the same as are the profiles.
The reason why both rim brake and disc brake version of a rim model may have the same extrusion profile is for economics. Why spend several thousands of dollars for a second set of extrusion dies when you can use a single set of extrusion dies for both rim and disc? The point is that disc brakes will apply greater forces to the spoke holes (including an additional torque load, which rim brakes do not have, which makes radial lacing no good for disc brakes). By how much extra force? You figure it out, or ask the manufacturer who has to have calculated this.
And actually, for rim models that have the same extrusion profile for both rim brake and disc brake versions, the disc brake version will actually be a little more heavier than the rim brake version, because the rim brake version would have some of the sidewall material milled away. If you assume 640mm diameter with a 16mm sidewall, with 0.2mm material removed on each side, that's [(320mm^2 x π) - (312mm^2 x π)] x 0.2mm x (0.0027g/mm3 density of aluminum) x (2 sides) = 17 grams.
1mm extra spoke bed thickness on the rim is probably around 30g to 35g extra mass for the above example.