Funny you mention this, just put the 8kg's in a couple of days ago and was meaning to post.
Much better, really good now. Just playing with the damping to get it to my taste. Rear is much more compliant and less harsh, funny how a heavier spring makes for a better ride. Got me thinking if I should have gone for 8kg for the the fronts too...with the FK silver line was harsh but it did not have adjustable damping which has made the difference here I think.
The 8kg does add some height and that I need to address is the car is too high now.
Will get the springs off again soon and measure them. It's something BC should show in their literature but sadly don't, more on that later on.
On the 6kg I had the adjusting collars both in plus some height dialled in (but without the OEM top spring pads). The car was corner weighted with that set up as I was happy with the ride height.
Since then I added the OEM top spring pads to the 6kg which increased height marginally.
Now it's even higher with the the 8kg minus 1 adjusting collar. My theory was to match the height of the 6kg spring and adjuster collars to go back to my original height. What I did not take into account the fact that the 8kg compresses less at rest than the 6kg. So when off the car the 8kg plus adjuster/pads needs to be shorter than the 6kg set up if I want to get the same ride height.
So I think when looking at the height of the spring we need to take into account the weight that will be on it at rest to determine how much it will settle to be able to compare how much higher or lower one spring will be compared to another.
I don't want very low for a few reasons - too much rear camber is costly on tyres and handling (road), too lowmakes grounding and issue around here. So I am aiming to get back done to the height I it was when corner weighted. On the other it feels a bit too high at the rear now and certainly looks it.
Here is pic of the springs to show what I mean:
View attachment 19130
On the RIGHT is the 6kg spring with the adjuster collars set to give the height I want (minus top spring pad).
On the LEFT is the 8kg with one collar wound right to the top and the OEM top spring pad. When unloaded it matches the height of the 6kg but when on the car it's made it noticeably higher.
So I'm going to try removing the remaining collar and the top sorting pad and see from there.
Not sure I can actually make it lower than that.
Here is a straight comparison of the springs LEFT 6kg and right 8kg.
View attachment 19131
At this point should comment on my experience and thoughts of BC as a company and the products for the benefit of others thinking of them as there aren't many Z's in UK with them on.
The product is really good, cannot complain at this price point. However the research for our cars is lacking and it grates me that their reply to the bottoming out was 'we've never heard of an issue with the 6kg springs'. It's just not good enough to trot out that excuse especially when an actual customer has just told you of the issue...in my experience the 6kg kit should be offered with a warning of bottoming out (or not at all in UK) and they should make mention that the drop in height will be less with the 8kg springs compared with the 6kg.
For other cars I believe they have done development in the UK with customer cars but so far nothing on ours. If they did they would know the 6kg spring is too soft for the rear. I was hoping for more of a helpful reply from them but their attitude to service in this case grates and If I could I would not have spent another penny with them. However on the other hand with this forum and the great people on it we are doing our own R+D and at the end of the day I have a suspension set up that gives the adjustability I want and works well at a price unmatched by any other brand so far (I do not want non-adjustable springs or dampers on the car again).
Hope this helps other out there.
