Most bicycle computers or speedometers (often called cyclocomputers)
can be used
with any size wheel because they are programmable for the wheel size by
the user. Bicycle computers often call this the "wheel cycle" or "wheel
size". Most bike computer instruction manuals only list the
circumference or perimeter size of wheels over 16 inches
however bicycle computers can be
programmed for any size wheel.
The wheel size programming code number is the perimeter or circumference of the wheel in millimeters. For example a wheel that stands 10" high off the ground has a perimeter of 798 millimeters so the tire size programming code number for the speedometer would be 0798.
The wheel size input number for any size wheel can be determined by entering the wheel's diameter using this online conversion calculator: http://www.electricscooterparts.com/bicycle-computer-wheel-size-calculator.html