I have to preface this article with the fact that I have never worked as a suspension technician. However, I do have a masters in engineering, but my time working as a car mechanic with my older brother taught me that the piece of paper they give you at the end of college isn't much use when you're wrestling a diesel four wheel drive gearbox onto a spigot shaft.
What I will try to do here then is marry together the literary research I have carried out over the years, with the practical knowledge I have garnered from hanging around suspension technicians.
The question we will try to answer today is, which part of the shim stack should I target to make a rider feel more comfortable?
There are probably technicians who could answer this question just from raw experience, and trial and error. By using an analytical approach though, we can reduce testing time, and document a lot of that information gathered through experience. Every technician has to retire some time, and it's an awful pity to lose all that knowledge.
Let's start with what we know already.
From our previous articles, we know the average speed of the suspension movement on different sections of the track, and that we can use dyno's to measure the suspension damping force effectively for the speed's we see on the circuit.
What we don't know, is which part of the shim stack is affected by how much force. If we know the answer here, it becomes straightforward to know which part of the stack to adjust. So how can we calculate the stiffness of each part of a shim stack?
Fortunately, there are lots of very clever people in the world, and one website I came across www.shimrestackor.com, has developed a piece of software that you can input all the shim dimensions from your stack, and it will print out a stiffness graph. You do have to pay a license fee for the software, and for the purpose of this article, I cam across a formula on the site that I could use as a rough substitute to demonstrate my point. The following formula basically calculates the stiffness of each shim, and by adding all the stiffnesses together, you can see how stiff the stack is at each point.
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