12 years later and I'm adding some notes. I took the rather twisted frame (remember it came from a dumpster) to Tom Teesdale (rip) who gave me a killer lesson on straightening frames. it was like watching a god at work. So simple and no noticeable physical effort on his part. So the bike rides better now.
I since built 2 more. The second was on a full suspension bso mtb bike to see what effect the springs would have (it smooths out the ride). I sprayed it with orange marker paint, then clear when I discovered marker paint doesn't stick.
The 3rd was build on a 20" kids bike. I had so many kids wanting to ride the larger bikes but they didn't fit. The 3rd has more offset in the wheels so the ride is pretty wild. It will flip adults off the back end when their center of gravity falls to behind the rear wheel ground contact point.
I've since taken the bikes to some bike festivals, holiday parades, Ragbrai, art shows and had it at the local bike coop for a while.
The only crashes I've seen is when the riders have really big feet that catch on the front tire.
By coincidence someone donated their version our our local coop. The wheel off set is only 1" so it's pretty mild. 26 x 1.25 tires on an old 27 roadie frame. They did use a 1960s era Shimano disc brake and ape hangers. It's fun but not wildly so.
Historically the first was the INGO scooter with just the larger rear wheel with offset. Made in the 1930s and ridden from Chicago to Florida as a publicity stunt. it's as easy to operate as swinging on a swing. Just bend your knees at the right time.
