If you use just the pre load adjuster with the intention of making suspension of the bike feel better, unfortunately you will not gain any better suspension feel.
Springs are made to a “Rate”
That is, that the spring has strength in the wire coil that requires a certain weight to compress it a certain length.
The spring fitted to your bike 17 years ago would have been rated at some average ratio to support the bike and a rider. And probably would have been a linear spring rate. The shock and spring may have about 90 mm of stroke before the coils bind.
Let’s say the spring required 9.5 kilograms of load to compress 1mm. a 9.5 spring is for a heavy person (90 to 110) kilograms) on an average weight bike.
For each additional mm of compression travel it would require another 9.5 kilogram of load.
Over time the strength in the wire coil of the spring would diminish slightly and the spring may only require, say, 9 kilograms of load to compress 1mm.
Or over 17 years of time there may even be a small section of the wire coil that is fatigued and would compress and extend with much less force than 9 kilograms.
If the spring has lost all of its strength the suspension should be compressed or sagged would be a better word and the bike would look very low and there will be nothing to adjust.
Apart from the possible situation in the last paragraph, the spring would still work even though it is 17 years old.
When you compress a spring to a certain point the energy required to do that would work in the opposite direction and the spring would start to extend and it would begin a cycle of compression and extension until it slowed down. This pogo motion would make the bike unrideable unless we have the shock section.
The shock absorber piston and cylinder part of the suspension is to dampen out this pogo motion and allow the spring to come to its neutral loaded position from either compression or extension in only one stroke and at a controlled speed. If it takes more than one stroke to stop the pogo affect the shock is bad.
The adjuster you are now trying to use as a way to make your shock work better is only there to pre load your spring. The only thing that adjuster will do is shorten the usable stroke of the spring and shock and change the height geometry of the bike. Nothing more.
It will not change the way the bike will absorb bumps or smooth out the suspension in any way what so ever.
If you removed the spring from the shock the spring would be at rest and have no stored energy. If you installed it on the bike with the adjuster not applying any force and slightly compressing the spring even with the rider on the bike also, the spring would not work smoothly over the initial movement and you would have a very sharp kick from the suspension as the spring takes the initial load.
That adjuster is there to load some tension into the spring so that it is not at its resting position and to set the correct ride height.
If you turn that adjuster in to create some compression to the spring, the spring’s ratio will stay the same (9.5 kilograms required to compress 1mm) but you will lose some of the stroke. You will raise the rear of the bike a little which should not be noticeable in the handling.
So if you have a poor ride now, just using the adjuster will not make the ride better.
The main problem will be in the shock absorber section of your shock. If it has never been rebuilt it will be shot and it needs to be replaced.
There are 4 different types of shock and fork springs. Linear, Progressive, Digressive and dual rate.
Each has their own advantages and disadvantages. To understand those different types of springs would require another long explanation.
I hope this helps Ray, to understand about the suspension a little better.
