BMW C 650 GT Rider's Manual page 74

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72
To increase spring preload:
Use the tool from the on-board
toolkit to turn adjusting ring 1
z in direction A as indicated by
the arrow.
To reduce spring preload: Use
the tool from the on-board
toolkit to turn adjusting ring 1
in direction B as indicated by
the arrow.
Basic setting of spring
preload, rear
Increase 3 notches from the
lowest preload setting. (One-
up without luggage)
Increase 4 notches from the
lowest preload setting. (One-
up with luggage)
Increase 6 notches from the
lowest preload setting. (Two-
up with luggage)
https://www.motorcycle-manual.com/
Basic setting of spring
preload, rear