Hi, I have Wilbers (front/rear) on my R12GS since more than 30000km. I understand the basics so perhaps I can help out.
The most important part on the number combination on your spring is the '150' indicating the spring rate.
My Wilbers springs carry the same numbers, and I weigh 86kg, and the pillion weighs 70kg, and then there's the luggage. So you're allright as far as springrate goes. Springrate on these bikes is usually 140, 150, 160.
Now some basic info. Imagine a bike hanging in the air. As it comes down and sits on it's springs, it goes down a bit called the 'static' sag. As a rider mounts the bike, it goes down even more : the 'dynamic' sag. The 'dynamic' sag is supposed to remain equal, no matter how much weight is put on the bike; that's why there's a preload knob for adjustment. The trouble is that it's not easy to find out what the basic dynamic sag is, i.e. when riding solo.
That's where Wilbers are clever : in the factory they put the minimum preload according to weight of rider (as specified when ordered). This exact minimum preload means that the rider will have the correct dynamic sag when riding solo. From there on, he can adjust for more weight by increasing the preload.*
What some people don't realise, is that this factory installed minimum preload can be altered on the spring, for more or less solo weight. Otherwise Wilbers would have to produce hundreds of different springs for different riders' weights. And as a nice advantage to us customers Wilbers springs/dampers can be sold on to a rider with a different weight.
To be specific : you have bought a second hand Wilbers and can have the minimum preload changed so that it fits your weight (preferably by someone who knows how). But, since you are heavier than the specified weight you have this option : when riding solo you can simply adjust the preload above the minimum installed by the factory. This means trying out different preload positions and measuring dynamic sag 'till you get it right for riding solo.
(To make it clear : if you were lighter than the specified rider weight, you would imperatively have to get the factory installed minimum preload decreased, or accept to ride solo with slightly wrong dynamic sag).
As far as damping (rebound) goes, this is a Very Personal Matter. Damping influences roadholding AND comfort. The best way to find out what YOU like, is to testride the bike with different damping settings. If the damping is too open, the bike will start wallowing around, perhaps plushy, but not efficient in roadholding. With the rebound damping too closed the spring will not have the time to rebound before the next bump arrives, actually diminishing spring travel, diminishing roadholding... and the ride will get uncomfortably hard. It is false to think that a hard damping setup will result in better roadholding. In any case it's a compromise that you have to find out for yourself.
Here's what I did : I went on a calm stretch of road with different curves and changing 'bumpiness' (that's important), and tried out different settings, always driving the same stretch. I opened the damping completely to understand the consequences, then closed it completely for the same reason, and then worked with small adjustments till I got it right to my taste. It took me a couple of hours. I like technique so I had a blast.
For those who think this is all too complicated : it isn't, it's actually easy and a hoot ! And the reward is : an incredible improvement over the BMW stock solution.
I'm convinced you'll enjoy your Wilbers !
Have fun
!
*
And here's the big difference with preload on a standard BMW spring : since BMW don't know how heavy the rider is, preload is set somewhere in the middle. It's up to the rider to find out the exact amount of preload he has to install for riding solo. This means the rider has to know about dynamic sag, and measure this for himself. I don't know dealers who explain this, I know even less riders who ride with the right basic set up. BTW the same basic error (BMW not knowing how heavy the rider is, and thus possible wrong preload) exists with ESA.
, I know that these are built to suit individual requirements but I don't know what was specified for this particular shock.
