hondas did not come with dual disc brakes until they went with the comstar rims in 1977. No cb550s ever came with dual disc although there are provisions on the fork legs. cb650s came with dual disc but it is a comstar mag rim. cb550s are pretty easy to convert, just get longer bolts and bolt on a second disc, oh and throw out your speedo and pseedo drive as it probably won't work with the second disc. go search www.sohc4.us for posts on cb550 dual disc.