By way of a brief explanation of the meaning of “Dynamic Index”, in a nutshell it’s the relationship between the mass of the vehicle and it’s wheel base. This is the primary influential factor on the vehicle’s dynamic handling performance.
The DI can be calculated and analysed scientifically, and the results will provide an indication of a car’s behavioural tendencies. Typically, a high DI will display slow reactions to command inputs, a low DI will display extremely fast reactions to command inputs, and a neutral DI will be optimum.
Unsurprisingly, cars that are renowned for exceptional dynamic handling capabilities can be demonstrated to have a neutral Dynamic Index.
We measured the XKR as having an overall mass of around 1800kg. This combined with a relatively short wheel base and the position of the centre of percussion, the calculated DI is found to be exceptionally high. This explains a lot about the way the XKR handles by design, and why the designer was forced to use relatively high spring rates in an attempt to overcome an intrinsic design issue. Possibly a classic case of form over function?
We also evaluated the suspension bushes and discovered that the rear subframe void bushes allowed approximately 15mm of compliance which extrapolates to around 4 degrees of unwanted geometry deflection under normal every day driving conditions! This is very apparent when driving, as the car is easily unsettled by uneven road surfaces, hard acceleration and braking.
Other bushes relating to the front suspension were also identified as requiring a compliance reduction to prevent unacceptable geometry deflection during cornering and heavy braking conditions.
