Changing coilover spring rate
 

I was curious if I was using the right calculations to determine preload and spring length calculations for using different spring rates. This particular example is using the front Flex Z and maintaining the same drop (1.2"), bump and rebound dimensions. The "B" dimension is off of the instruction manual. Preload on the 6k is set to 0 in this example just to make the math easier, in reality it is about 3/16". The stroke length shown is for the springs only from Tein website, I do not have figures for damper stroke. I would love to hear from the suspension experts out there like CSGMike, Racecomp Engineering, anybody that knows how this works. Thanks.

Load was calculated as 53% of 2800lb divided by two to get single front wheel static load.

It seems like you're on the right track.

You're swapping from a 150 mm, 6 kg/mm spring to a 175 mm 5 kg/mm spring.

Static ride height matches, which should mean that the damper will operate happily. I'd do a quick sanity check when everything is apart, by measuring the free and fully-compressed length of the shock... just to be sure the piston is near the middle of it's stroke at static ride height.

As a side note, it looks like your setup will bottom out slightly less often (and otherwise be more comfortable).

Thanks, good info in your suspension link, I was needing that, should I revise the weight to reflect unstrung weight? I noticed that my actual stroke dimension measured less than calculated.

Only problem is, the spring will fully compress too early. There are more coils in the longer spring.

Mass per length?
Is this a linear density problem?

Mike's got a good point. Depending on the spring's design, it may fully compress or bind near the bottom.

Here's a pic of a 7" 275 lb spring from Hyperco:
https://www.portcityracecars.com/images/P/E24.jpg

If you're compressing it by ~65%, there is potential for full compression or binding.

Take look at the spring travel numbers at the bottom of the page, those are straight off of the mfg website, the 6k will actually bind before the longer 5k. Mfg OK'd this setup for the front, just did not give preload and "B" dimension.