i’ve been googling for a few minutes and also went to ask.com
cant find anything.
basically, i want to know what the equivalent to 7kg / 5kg spring rates on our coilovers are to springs that are made for domestic applications.
SAE ratings are in lbs and are Rate/IN which i assume to mean rate per inch, where are ours are kg per mm, is that not right?
if i wanted something like a 7/5 or a 8/6 set up what spring rates would i want in rate/in?
1 kg = 2.2 lb
1 inch = 25.4 mm
so then 7kg / mm = 7 x 2.2 = 15.4
= 15.4 lbs / mm
15.4 x 25.4 = 391.16
therefore 391.16 lbs / inch is equivalent to 7kg/mm
is that right?
even if i did someting wrong there it is still wicked to apply school to real life… YAY for $35,000 educations that help solve simple equations like this
alright another question.
lets say that the springs i use are X long, but i cannot get exactly that length.
should one choose a taller or shorter spring?
what are the pros and cons of each?
How much taller and or shorter?
If its a CM either way it wont matter. but if its more it can.
You plan to put these on D2’s?
Good stuff Bing 
You can check your answers really easily when doing stuff like this with dimensional analysis so that you’ll know for sure that you’re right. You just take your units and multiply them by conversion factors, then cross out the ones that appear on top and bottom.
Ex:
kg/mm * lb/kg - the kg at the top and bottom cross out and you get lb/mm, multiply by mm/in and the mm cross out leaving you with lb/in.
You can also use this to create your own conversion factors when you don’t want to ask people or google or something like that.
OR better still…
go to google and type in the following:
10kg/mm = ? lb/in
google will take over the world
Truer words have never been spoken!
yes adam, i do.
when i put new dampers in my coilovers i noticed my springs were quite weak.
rather than buy new springs from D2 i am going to get them elsewhere. i’ve alreayd matched up the height and I.D. so i just needed the spring rate.
^^^ Good Call…
What springs are you going with?
If you paid 35k to figure out that equation you went to the wrong elementry schools 
On top of it all he got it wrong
Google says it is 391.981902 lbs/in not 391.16 lbs/in 
7 (kg / mm) = 391.981902 pound / in
Google knows all!
hehe
gotta keep those digits in there for accuracy bing jesus christ
oh yeah, i wouldnt want to be off by .8 of a lb.
Adam,
depending on price i am going to use QA1, they will be 8/6 approx
i can actually compress the D2 springs by hand now, so the last thing i want to do is keep using them. if any of your guys are noticng your ride to be a bit too bouncy with the D2’s then perhaps you should check yours.
keep in mind i have well over 50,000km’s on mine including a winter and 4 months on blown dampers.
Careful! Heavier springs should only make the bouncing worse:
A car is a weight resting on top of 4 springs which will bounce like any other weight on springs unless there is something to stop it. In cars this is the job of the damper/strut that acts like an arm pulling down on the spring, slowing its rebound speed. Ideally, the damper is just strong enough to allow the spring to rebound back to its rest height as fast as possible (damped condition).
If the damper is too weak the spring wins the tug of war and the car is actually pushed up past its ride height until gravity takes over and pulls the car back down again, pushing on the spring. This happens over and over until the weak damper finally saps enough energy and stops the car (and your ass), from bouncing (under-damped condition).
If the damper is too strong, the spring looses and the car takes too long to return to its proper height - leading to a harsh ride and less stability (over-damped condition).
You can verify this by pushing down on a corner of your car (you pushing down with 100lbs is the same as hump in the road pushing up).
Its very likely that either your new dampers are shot (i.e. leaking?) or are simply too weak for your springs. It’s very unlikely that your spring rate has decreased - not that it matters because this alone would not lead to more bouncing. As far as you being able to compress the springs by hand is concerned I would suggest measuring this. If your springs are 3.5kg/mm (196lb/in - DC sells these) you can probably compress them about 0.5in(~100lb) by hand. If you are getting more than this something is wrong.
There’s a nice handling guide at: http://www.wtrscca.org/tech.htm
i just rebuilt my coilovers with brand new dampers.
the springs are rusted and i can compress them by hand.
i’d say i’ve got it right.
whats more is that people run more aggressive spring rate on these very dampers with no problems.