Well there's not much to it. There are 5 settings and the softest one that works best for you is the best.
So the best way to set it is to start at the lowest setting and ride it to get a feel for how it reacts. Then
try each of the others and choose the one you like best! You'll probably find one setting (like 1 - 2) for
one up and a different one (like 3 - 4) for two up.
The proper way to setup suspension is to change the spring to suit the (usual) load. The preload adjustment
only changes the force needed before it starts to work. This scooter probably wants a 200 lb spring. I posted
about some $99 shocks, they say their shocks adjust from 160 lbs to 190 lbs. I'm not sure exactly what that
means, there are 2 shocks so 320 to 380 lbs? So if you and the wife weigh 300 together set it to full soft, if
you weight 400 set it to full hard?
Riding 1 up I noticed the scooter bouncing a lot like lots of tiny bumps in the road (even though you couldn't
see any) then I remembered I set it full hard so I changed it to soft or one click firmer and it feels OK now.
I'm still not impressed with the suspension (but I compare it to my Ducati with the Ohlins stuff), it feels kind
of firm but there's not much travel so it might be difficult to make it much better...
