Malcolm Smith is a Cambridge don who came to McLaren with an idea in 2003. He was fascinated with parallels between electric circuitry and suspension systems, reasoned that a suspension system was just a big circuit. With an electrical circuit you have a resistor, inductor and capacitor.
With a suspension, the equivalent of the resistor is the damper, the inductor is the spring. But there was no suspension equivalent of a capacitor - and Smith was bugged by this. It was from here that he came up with the idea of the inerter, aka the j-damper in F1 parlance.
In fact it's not a damper, it's a device within the suspension that, like a mass damper, evens out load distribution on the tyres and increases grip but which, unlike a mass damper, is part of the conventional suspension. It is this distinction that's led to its acceptance, whereas the mass damper has been banned since mid-'06. A mass damper, as pioneered by Renault, was outside the suspension.
By contrast the inerter is part of the suspension and moves within it. As well as evening out load variations it's also useful in managing the attitude and giving a better compromise of suspension movement (for low-speed grip) and a stable aero platform (for high-speed grip). A car with a stiff suspension - to get good aero performance at high speed - will suffer greater load variation on the tyres at slow speeds than a softly suspended car. The inerter allows the stiff suspension without quite as much penalty in the slow corners.
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