Looking for some info on softer coil over spring rates for my Stance's ......

I have also been looking for info on spring rates on coilovers. Stance comes with 9/7 kg/mm front/rear and Powertrix with 9/7 or 8/6. If something softer was wanted how should the rates be chosen? Softer springs should also go with a different valving?

I'm also wondering how the spring rates on coilovers and stock suspension can be compared. How do the different dimensions of springs affect that? Stock springs are around 3-3.5 kg/mm and some models have softer springs in the front, some in the rear.

Then there are also helper springs…

I have the 9k/7k installed now, and I found it too firm as well - I'd be bouncing up and down in my seat every time I went over bumps. I bought a set of 8k/6k springs from Stance but I haven't installed them yet. So, yeah, this was a pointless reply. :P

If anyone has experience with different spring rates and how they feel on a Z31, I'd sure be curious about it since I was thinking of upgrading to a set of Swift springs at some point.

Im Gonna research the Swift rates tomorrow…

Different dimension springs don't affect choosing stiffness. The fronts should compare directly to stock suspension. On the rear, the location of the spring is changed, which will change the rear arm motion ratio slightly. I believe the rear coilover spring will have a larger motion ratio compared to where the OEM spring sits. This means...... if you want the oem stiffness after moving the spring from the oem location to the coilover position, you need a spring of higher stiffness.

Helper springs don't play into choosing spring rates at all. Due to the inverted mono design you don't need helpers on these coilovers. You can get things revalved but you can just try to run the coilovers at their low setting.

Part of the jarring feeling is that these coilover dampers all have relatively large compression valving to give them a "sportier feel". The settings affect mostly the rebound (which is good). But there is no way to set compression and that is generally too high on these units.

Poke around on ebay or CL. Coil springs of various stiffnesses can be had for cheap if you find the deals. I.D. of the spring matters most--I forgot what the stance/ptrix have (I think 2.5in ID). Free length is pretty flexible, just depends on how much room you have in your adjustment (how much or how little threaded collar is available on your current height setup).

Greg, a random guess in rates you might be interested in may be 6-7 kg/mm front and 4.5-5.5 kg/mm rear. A trick if you want to experiment: just grab a pair of softer springs for the rear (can be had for ~$50-80 depending how hard you look). Throw the 7kg/mm springs from the rear to the front. OR put the 7kg/mm from the rear to the front and try it with oem/SS/eibach springs just to see if at least the front feels okay.

^. This fella......pretty clever

Good ideas, I'll get on it when the time presents itself....thanks!

Stance will tell you the valving is only good for a 2k rate change, but worth trying…

Yup, that is what most of these companies will tell you. I believe the dampers are actually designed for 8kg/mm F and 6 kg/mm R and the 9/7 combo uses the same valving but is within their "+/- 2kg/mm rule". Given that, I think going at low as 6F/4R and as high as 10F/8R should be alright.

Here is a link for all the springs and spring rates that were available for our cars:

http://z31.com/wiki/doku.php?id=modi…market_springs

The conversion between kg/mm to lbs/inch is 1 kg/mm = 56 lbs/inch.

The stiffest/highest spring rate on the list is 325 lbs/inch which equates to about 5.8 kg/mm. (1-1.5 inch lowered)
The stiffest/highest stock spring rate from the SS was 224 lbs/inch which equates to about 4 kg/mm.

There are lots of online calculators for figuring out spring rates based on suspension travel etc, but doing frostvectron's idea of placing the 7 kg/mm upfront would definitely be a good start. It would increase travel by 29%.

frostvectron know what he is talking about. The jarring feeling is the compression which is not adjustable. You need to get 3-way dampers to gain better suspension tuning to maximize comfort and grip. Stance makes higher end dampers but I am sure they will come at a price. I dont know if you ever had the experience to drive or ride in a car with KW v3 setup that has been corner balanced - but that would be the ultimate ride quality and grip setup. Having the ability to adjust the compression makes a world of difference in ride quality.

The other thing pointed out - is the difference in mounting location to a 'true' setup. I find the e30 people to have the best information regarding suspension tuning for STA setups. There is a ton of information on true type setups on STA on their various forums. AE86 guys have some good information too, but they need to cut and weld new mounting points for a true setup so the information isnt as prominent.

Another issue is the allowable extension at a lower ride height in the rear. The control arm likes to bind up in extension not allowing the damper to properly work. This is that bottoming out feeling you get going over large bump or uneven concrete going from higher to lower patch at normal driving speeds. This is an inherent flaw in STA design on these cars, which is very noticeable the lower the static height. There is more than enough on various fixes for this issue

Lastly, tires play a big part in suspension tuning. Stiffer suspension riding on 215/55/16 tires - forget about it - it is always going to be bouncy. Most coilover applications work much better with min XXX/40/17 setups.

PS, OEM seats are also sprung. Suspension can rebound fairly quickly but the seat will keep bouncing giving the illusion of bouncy suspension -- not true.

PS, OEM seats are also sprung. Suspension can rebound fairly quickly but the seat will keep bouncing giving the illusion of bouncy suspension -- not true.

Could you elaborate on this more? I can't wrap my head around this.

Your seats are sprung in which the frequency is vastly different than the suspension. So while the car will rebound quickly over a bump the seat will continue oscillate. These cars where meant for touring from the factory --> comfort. When you start going to sport you need to understand how everything works together. I would replace the seats before replacing suspension.

I agree, first major mod I did to my k-car, acura buckets… it was so much more predictable than the bouncy seats

Interesting, makes sense. Thank you.