Usable either for converting a mountain bike to drop bars, or for converting a road bike to super-low gearing. Chain Fits oversized seat tubes. We've got 'em, but this part of the page isn't ready yet. These also use a special braze on to stabilize the derailer. This design is mainly used on mountain bikes, with the intent of avoiding running the cable under the bottom bracket, where it is exposed to spray kicked up by the front tire.
Some older designs use a loop of cable housing running from a stop near the bottom of the down tube.
This design hasn't been used since the mid 1970s, but we stock a couple of derailer models that are compatible with this cable routing. Large Chain Ring Size Front derailers shift best when they are mounted as low down as is possible without having the cage foul the teeth of the chainrings. In particular, the bottom edge of the outer cage plate should be closely matched to the curvature of the largest chainring. If you use a front derailer with a larger ring than it is meant for, the rear of the cage will get too close to the chainring before the front of the cage is close enough to provide crisp shifting. If you use a front derailer with a smaller ring than it is meant for, the front of the cage will get close to the chainring while the rear of the cage is still far away from it.