Measured spring data for 355 OE and H&R springs…

I looked up the Ferrari stock springs {unloaded heights,...} and from that data I can confirm that the factory springs should be in the neighborhood of a 31.75 N/mm F and 44.5 N/mm R spring rates; corroborating your measured data.

The stock springs should have 54.5 F and 55.5 R mm of travel at the static loaded position before coil bind and are applying a pressure of 4071N F and 4384N R at static height and 5833N F and 6898N R at coil bind.

So, you car will naturally compress the springs to 4071N F and 4383N R (unless the weight is changed, or the spring/shock angles are changed). 4071N is the weight on the front tire times the geometry of the a-arm and spring (position on the a-arm**2 and angle of the spring with respect to the a-arm.) That is, the weight on the tire is multiplied by a bunch of geometry and ends up the weight on the spring.

{Note the original factory data and this sweedish data are all in metric units, so I though we would just complete this in metric units.}

From you data, the H&R front spring intersects the factory spring right near the 4070N mark. Thus, since the factory spring is 322mm long and the H&R spring is 299mm long, this should have dropped the front end by 23mm.

From your data, the factory rear springs operates at 4383N and 153mm of length. The H&R rear spring gets to 4383N at 128mm of compression from a static height of 262mm giving 134mm of length. Thus, the rear ride height should have dropped by some 19mm.

{A change in the ride height WILL have some effects on the geometry of the suspension and change the geometric multipliers, so the presented data has more than insignificant error but should be close to the right ball park. If the ride height were changed back to factory, the geometric error would vanish.}

Based on the wire diameter of the H&R rear spring, you should have been able to extract at least another 10mm of compression on the mesurement machine before coil bind, and probably 20mm. {2 more data points}. {That is, I would like to see this data.}

Now, given the static operating points, the H&R springs are operating at an effective rate of 44.5N/mm F and 63.5N/mm R; an increase from factory of 43% F and 41% rear, over small movements. Thus, the overall balance should be about the same. But you are operating at 40% more spring rate than before (small excursion).