Apex Lowering Springs 35mm for Volvo C30 1.6D 2.0D 2.4 T5 D5 S40 2.0TD 2.4i T5 M

Model: C30 1.6D 2.0D 2.4 T5 D5 S40 2.0TD 2.4i T5. My car has a sports suspension, and has already been lowered from the factory, how should I estimate the lowering specified by Apex® ?. 
 The lowering of the sports suspension specified by the factory must be deducted from the lowering specified by Apex®.

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