The luggage rack can be made from solid or hollow steel tubing or from solid aluminum tubing. It is asymmetric. The rear 15" of the right side extends to a width of 10" from the left side. The left side of the rack is conventional and could carry a pannier. Use of a pannier on the right side is problematic. The inner right tube on the top surface of the rack is the usual position for a pannier, but most panniers will not attach there because of the outer right tube. A pannier could be hung from the outer right tube, but this will be an unusually wide configuration and the pannier will sway due to the distance from the upright supports on the right side of the rack.
The outer right tube covers only the rear 15" because if it were brought all the way forward, it would interfere with the cyclist's leg. It will be necessary to verify that there is sufficient leg clearance as designed.
The top plane of the luggage rack defines one edge of the suitcase. Thus it is essential that the extension of this plane passes above the top point where the seat stays meet the pivot of the seat tube. The rack must be built in such a way that the rear wheel is in a properly packed position when folded. The luggage rack remains attached to the bike when packed and prevents the bike from moving within the suitcase. It may be tricky to design the rack so that the (packed, deflated) tire to rack dimension is 20" and the rack has sufficient clearance from the tire. Perhaps there should be a snap-in plastic fender that prevents the tire from rubbing against the saddle bag.
It would be possible to permanently braze the rack to the frame. I rather like this option, since heavy duty touring (such as my round-the-world trip) tends to break luggage racks. A friend of mine had a bike built with an integral luggage rack. The main structure for this rack was a tube the same diameter as the seat tube, joined to the seat tube and extending horizontally over the rear tire.
There are three sections forming the frame for the suitcase:
1. The bicycle luggage rack. The rear surface measures 15"x10".
2. A rigid half frame measuring 16"x20"x10". The left and right sides each contain three tubes of lengths 16", 20" and 16"
3. A rigid half frame measuring 15"x20"x10". The left and right sides contain two tubes of length 15" and 20".
When assembled as a suitcase frame, sections 1, 2 and 3 are joined to form a shape 30"x20x10". This shape provides the protective enclosure for the folded bicycle.
When the bicycle is unfolded, one of the 16" tubes of section 2 telescopes inside the 15" tube of section 3, forming a frame of size 16"x20"x10". This is a saddle bag that is carried on top of the luggage rack.
Sections 2 and 3 are made of hollow tubing. The material could be aluminum, plastic or composite.
There are two fabric sections for the suitcase, each with two zippers. When the suitcase contains the folded bicycle, the two sections slip over the suitcase frame and zip together. When the suitcase is collapsed as a saddle bag, one of the fabric sections (bag #1) slips over it and is zipped shut. The other fabric section (bag #2) is rolled up and packed.
Bag #1: Front is 26 x 20". This includes a 10" x 20" flap with a zipper along three edges.
Back is 16" x 20".
Top: 16" x 10"; Right: 20" x 10"; Bottom: 16: x 10".
A zipper runs along the left opening from top to back to bottom. It mates with the flap zipper or with the bag # 2 zipper.
Bag #2: Front is 4" x 20".
Back is 14" x 20".
Top: 14" x 10"; Left: 20" x 10"; Bottom: 14: x 10".
A zipper runs along the front plane to mate with the flap zipper from bag #1.
A zipper runs along the right opening to mate with the left edge zipper from bag #1.
The fabric bags should include handles usable in either configuration. The saddle bag should include straps by which it can be buckled to the luggage rack. The luggage rack extends roughly 3" to the left side of the bike centerline and 7" to the right of center. The saddle bag should be centered on the bike, not on the luggage rack. The saddle bag could be mounted as:
10" wide, 16" high, 20" long (with 5" extending beyond the back of the luggage rack)
10" wide, 20" high, 16" long for tall riders like me. The top front of the bag should attach to the seat or seat post.
16" wide, 10" high, 20" long