Sigma BC 1009 Manual page 20

5.4 Wheel size chart (Wheel size / hjulstørrelsen / Rengaskoko)
A
B
20
mm x 3,14
1x
km/h:
WS = mm x 3,14
mph:
WS = mm x 3,14
km/h:
WS = mm
mph:
WS = mm
= WS (mm)