Clearance is actually not a big problem on this bike. Maybe I will build a pair of 451mm wheels, in order to have one at hand for other projects.
The bigest problem on this bike is: the chain comes off when switching on the higher gears. The reason for that is the huge chainwheel. I fitted an old front derailer to keep the chain in place, but this makes the chain scratch the derailer in some gears. Everything runns smooth with my favourite ratio: 16/72, and I am used to ride my fixed-gear swift folder, so I do not switch much anyway. (The swift folder is ment to ride fixed gear, otherwise it would have been called SWITCH FOLDER... but this belongs to a different topic)