2007 C70 Rear Spring Rate

[Alsfox]

Hi all,

I'm writing in from Singapore. Recently I had just bought a set of KW coils for my C70 but it was supposingly to be fitted on the c30, the problem right now is the rear suspension which is giving me a big headache as it bounces every time I drive over some humps . I was wondering is the spring too soft, I had found out that the rate is 41.2n/mm. Is it because it's too soft that's why is so bouncy .
What is the original spring rate of the C70.
Your advice and help will be very much appreciated .

Rgds,
Alsfox
Singapore