print this out at 100% and it should be in scale.. (brake-profile2i)
cut out the profile and then place against the rim to see if the lump of a caliper will clear the spokes....

i used plastic from the side of a square ice cream container, but anything half solid will do.

yes i know it's neesan crap, but... meh

the concept can be used for any brake setup.

brake-profile1i shows the cardboard template used to work out the clearance to the calipers. it is important to have a tight fit at the edge of the hub/disc to make sure you get the same position every time.