We were invited by Jaguar World magazine to attend a test day at Mallory park recently.

The weather was attrocious but the XKR performed exceptionally well and was driven by a professional racing driver who was impressed with the Jaguars improved handling dynamics.

Having completed the development of the poly urethane suspension bush upgrade on the XKR, we spent approximately 3 months on performance evaluation and durability testing.

The significant improvement in performance allows the driver to have considerably more confidence in the car now that the input commands and responses are totally predictable and controllable.

We are very pleased with the end results and hope that anyone upgrading their XKR suspension will experience a new level of driving enjoyment.

These suspension components have been released for sale and can be viewed at: http://www.tdi-plc.com/catalog/index.php?cPath=1_788_826_827_832

As identified previously, the rear sub frame bushes are a “void” design which allows for an unusual amount of movement, which in turn causes an unacceptable degree of geometry deflection.

We designed and commissioned some poly urethane replacement bushes to correct this issue.

The images above show the difference between the standard bush and the poly urethane bush. None that these are development bushes and that the production models will not be yellow!

Additionally, we installed poly urethane panhod rod bushes to reduce the amount of slip between the axle and the body. The bushes are shown below:

The next area to be considered are the springs and shock absorbers, and the kinematic geometry.

As mentioned previously, the spring rates are exceptionally high, presumably in an attempt to compensate for the poor Dynamic Index. The damping rates seem adequate and have the CATS system incorporated.

The geometry that is recommended by Jaguar seems to suggest that they are aware of the poor DI and have attempted to improve the turn-in by manipulating the geometry, at the expense of tyre life and straight line stability. The additional kinematic geometry induced by unwanted geometry deflection tends to exacerbate this issue.

To get an understanding of the Jaguar chassis designers thought processes and to formulate a way forward to provide a resolution to the issues, we undertook an evaulation of the suspension bush compliance and Dynamic Index.

The Jaguar XKR is a highly respected sports tourer which has been applauded by the international motoring press and owners alike.

Although the XKR is indeed a highly capable car, we identified significant handling issues such as:

• Poor chassis stability during normal driving and gentle acceleration.
• Inconsistant chassis response and feedback.
• Slow turn-initiation response.
• Poor rear traction under hard acceleration.
• Poor rear traction stability under hard braking
• Excessively harsh ride
• Excessive under steer

The above traits and charteristics lead to an erosion of driver confidence, a reduction in dynamic performance and of course a loss of driving enjoyment.

Our initial conclusions are that the overall ride quality is poor which displays all of the down sides of heavily sports orientated suspension but with none of the expected dynamic performance benefits. The overall chassis performance is so poor that the ability to easily use the engine’s power is severely limited which makes spirited driving challenging and unenjoyable. We found that under extreme circumstances such as confronting a slight road hump on the apex of a corner, or one rear wheel encountering a pot hole or adverse road camber, the suspension becomes uncontrolled to an unacceptable degree.