GT4 Spring Rates and Handling

[gtsralph]

There have been numerous discussions on roll bars and camber settings, generally focusing on improving GT4 handling, but nothing so far as I can see on spring rates or dampers.

I have been looking at spring rates on my car (not a GT4) and the GT4 rates front to rear seem to be quite different to other Caymans, whether cooking, Clubsport, or one-off versions.

The GT4 main spring rates are 45 and 80 Nm/mm with a front:rear ratio of 1.00:1.78. The rears are fitted with tender springs (not sure of their rate) but from what I have seen none at the front.

Mathey fit 140 and 140 Nm/mm main springs to their MR Clubsport so a ratio of 1.00:1.00 with front and rear tender springs of 80 and 80 Nm/mm - ratio is typical for Cayman race cars

An example of a sporty cooking model is a 981 X71 manual which has 30 and 47 Nm/mm main springs so ratio of 1.00:1.57

For what it is worth I am running 60 and 80 Nm/mm main so 1.00:1.33 and tenders of 40 and 50

What puzzles me is why the sportiest road Cayman has a front/rear spring rate ratio (1.78) greater than cooking models (typically c1.55), and further away from race cars’ 1:00.

Any thoughts on what characteristic Porsche were trying to overcome/achieve with this part of the GT4 chassis specification?

[gtsralph]

isaldiri said:

Are your tender springs fully blocked under static load btw?

The tender springs are not fully compressed at rest and under load they first compress fully then the load goes to the main spring, if that answers your question.

[gtsralph]

isaldiri said:

It does indeed cheers. Just one final question if I could, is the transition perfectly seamless between the springs and you don't feel a 'step' so to speak under load when the tender gets fully loaded and the main spring takes over? Thanks.

No step

[gtsralph]

Hey guys, I just asked a technical question, not to start a bar brawl.