The company-made cart under my Raffin 31er puts the crank at 43 inches
from the ground, 9 inch radius.  The Raffin Company has very nice
wheels available in three sizes, and last time I checked would sel
them separately.  Examples can be seen at http://www.raffinorgans.com/

I don't recall the price, but I do recall that they are not
inexpensive.  Then there's overseas shipping to consider.  For more
details please contact me privately.

Hal O'Rourke