It is still in the early stages of brewing some ideas and direction.
But I got the starting bike. I bought it in 2007 at Walmart, Aluminum frame, dual disc brake, dual suspension, but pogostick like with no real oil dampning. This was a great starting point. The only disapointing fact is that Walmart in 2008, in order to lower the price, lowered the quality of he package.
Now it has no disc brakes. And the frame now is steel...and that actually could be a plus, because now I could cut it, modify the frame and weld as I wish. Aluminum can't be welded unless you plan to heat treat the whole frame later. I got some used Mountain bike forks and shock.
I believe there is enough space to place an engine with some mods.
It would be a good size bike for a 10-13 year old to ride off-road only. And under an adult supervision. A bmx backyard trac would be an ideal place.
There are two other similar bikes in 16"(6-8 yr old) and 12" tire(monkey size)
Regarding tires, the best rear tire I think is the Trials Creepy Crawler 2.5x19" (yes 19", but it is 20" outside diam. You need to use a unicycle rim or trials rim). For the front the Max Daddy 2.25"x20". Both these tires are from Maxxis and would be an excellent upgrade from the chinese stock tires. To keep it simple and without all the extra expense of a new rim and spokes, both front & rear tires could be Max Daddys 2.25 x20.
For offroad suspension is key. A Fox 6.5" shock would lift the bike a little and gain some suspension travel. Up front the forks I got are for a 26" rim so with the 20" wheels I might need to adjust the height sliding them down in the crowns.
For engines the options are Chinese HappyTimes type or Cag47-49cc pocket bike engine. The Cag is wider, but lower profile, has a pull starter and has more pep. But the HT might be easier to ride(torquier, mellower), but I might need to figure out a jackshaft, etc. for it, so I can bump start the HT engine.
Or I could go to the extreme with some of those PBU engines.
So everything is still not written in stone. And the design is still evolving and optios sorted out.
I originally wanted to build it for my nephew..., but he is growing fast and by the time I finnish, this bike might be too small for him. Anyway I am enjoying the build.
Enclosed are some pics.