Hey All .
Looking for advice .
I rebuild bike 2 Years back , but never bother change shocks. So 20K ml later rear sprung a leak
as expected.
By chance came across secondhand Ohlins BM055 for €200 with 10K on it .
Install shock gone for ride , it was Shocking
, like dinghy on surf .
Setting :
Pre-load -9 mm
Rebound -23clicks
I turned rebound to 12 clicks but still feel like spring to soft and to much travel.
Then I change pre-load to 14 mm and seam improvement but it's early days .
I know nothing about setting shocks , I'm I correct to say :
Pre-load control large bumps and
Rebound control smaller ones ?
2 bikes twice is happy
shocks are reasonably simple in theory but a black art to set all the adjustments properly, (if that makes sense)
Spring is the first thing to specify, all depends on your weight, too light and the bike will sag (travel) too much when you sit on the bike, this causes two main issues. Firstly it affects the steering geometry (slow vague steering) and secondly renders a lot of your suspension redundant as its already compressed by just sitting on it.
If the spring is too heavy for your weight the suspension wont compress making the geometry aggressive and twitchy. As its too hard you will only use a small amount of the travel, wasting the suspensions capabilities. In simple terms it would be very harsh on bumps and not very pleasant to ride. The bike would also find it difficult to grip the road as its not following the surface of the road.
If the spring rate is wrong no amount of adjusting the compression, rebound and preload will fix it
Now you have the right spring chosen, it needs help being controlled as its a basic piece of equipment.
Preload: as its name suggests it pre loads (tensions) the spring, this adjusts the ride height and nothing else, it doesnt make the bike harder/softer the spring is linear and has a spring rate only a different spring changes this. Changing the ride height is adjusting the seat height on a rear shock, this has implications to the steering.
Compression: adjusts the rate (speed) at which the spring is allowed to compress. Done by oil and orifices within the shock. No matter what you set this at, if you sit on the bike it will always end up in the same place as its the spring rate that holds you up. Too much compression and the shock will harsh.
Rebound: adjusts the rate the spring is allowed to extend/return after hitting a bump. Done by oil and orifices within the shock. Too little and the bike will be like a pogo stick as it will bounce back up, too much and the shock will uncompress/return slowly and will many times have hit the next bump while still compressed from the first bump, this lets the bike skip over the bumps and loose contact with the road.
In very simple terms the objective is for the bike to stay steady while your wheels fall in and out of the bumps on the road in a controlled manner so that you dont notice them. If you can get it to do that half decently you are doing well.
But as most have said the first thing to get right is the spring rate and then everything after that tailors the spring to work properly for you. Everything on a road bike is generally a compromise, as one some days you add a passenger or luggage or both.
This is a very sketchy synopsis of bike suspension,
suspension is an area that if done right transforms a bike under braking, cornering and accelerating beyond belief and is worth the time and effort.
as expected. 
, like dinghy on surf . 
