Thank you stiletto and thanks for clearing it up ! now it make sense as i saw there are some high gear ratio kit for gy6.
after asking around with some friends, the wheels might be from a bike with a single swing arm, ill try to googling it around.
ive found out how to some sort of method to measure rolling resistance from this pics. hopefully we can start some sort of database of rr for bikes as there are none outhere?
