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OptimumG Magic Number Analysis

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Tim, I am sure you are familiar with OptimumG's Magic Number Analysis method. I don't see it mentioned much these days, presumably because it is far overshadowed by more exotic methods. That said, I have found it usefull in revealing the effect of the various suspension parameters on steady state handling balance. In particular, revealing how sensitive the balance is to changes in a given parameter (i.e. spring rate, bar rate or roll centre height).

While the method is "simple" in that the inputs can fit on a single spreadsheet page, getting valid input values is often quite a challenge. In my earlier post on creating a kinematic model in SusProg3D, all that effort was essentially to fill two cells in the magic number spreadsheet with roll centre height values that were not merely a guess. Another input value that presents some challenge is the cg height.

This thread documents some of my experimentation with the Magic Number method:


Hi James, I am familiar with the OptimumG Magic Number, I used to work there after all 😉 I would also say that the concept of a magic number, or more formally LLTD (Lateral Load Transfer Distribution) isn't invented by that company. I'm sure you understand that, I'm more saying that for the benefit of others reading this.

It's true that this method is simple, but I would also agree it's very useful. Certainly from the perspective of understanding concepts like elastic vs geometric weight transfer. As you say, there can be quite a lot of upfront work getting to the point of being able to calculate it properly as well.

LLTD for entry, mid and exit as well as the elastic and geometric contributions to it is something I'm usually keeping track of in the setup sheet of cars I'm running as well. In my opinion, even though simple, it's very worthwhile keeping an eye on and tracking.

Thank you for sharing this! :D

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