Some complex springs questions
 

I know some of you guys are infinitely more knowledgeable about different springs for these cars. I am looking for a set for my car to pair with my Bilstien B6 shocks. I would like a bit more spring rate in the front and maybe a little less in the rear. I track the car at least once a month during track season but I live in Chicago with horrible roads. Hard to find something to do both jobs.

What I am looking for is a dual spring rate spring set that drops 0.5" or less. Z1 has nearly all of their springs shown as dual spring rate springs yet when I go looking for more picture I find out they are not. It seems every site shows a different picture of them to the point where I do not know which picture is correct. Some show linear, some show progressive, and some show dual rate.

The two I am looking at currently are below:
RS-R Down Sus 345/417 +9%F / -2% R. -0.4"F / -0.4 R These are shown on the Z1 site as dual rate but when I go to the RS-R site they are shown as progressive. This seems ideal unless they are so progressive that I never hit that increased front rate until full suspension travel. This will not help with braking dive if that is the case. Another thing is the picture Z1 shows is of their "Ti2000" springs which I am not sure they make anymore. Unless they are making them special for Z1. If that is the case then I will likely go with these.

Tien H-Spec +4%F / -11%R -0.28" F / -0.16R These are also shown on Z1 as dual spring and these are more likely to be. Odd that they decrease the rear rate so much. I do not know if that spring rate is based off of the initial travel of the spring rate or the final travel of the spring rate. If assume the latter then this is not going to help much with brake dive but may help with rear traction at the track.

I currently have all the adjustable goodies on my car to get to a 0.00 toe -2.2 camber front & 0.06 toe -1.7 camber rear. I run all times on 300 TW Michelin PSS*BMW tires. I have Hotchkis sways which I have been leaning on to reduce body roll (see that pun? see what I did there?)

Please do let me know if there are any other springs I have missed that may also fit my application or if any of you guys have experience with either of these springs. Also, any knowledge concerning which springs are linear, progressive, or dual rate. I could go a bit lower if I could get a dual rate spring since that would work best for this city and track driving in one vehicle.

The reason for the 0.5" is more than just pairing them with the B6. If I go much lower I will be scraping my diffused chassis mounted functional splitter on just about everything in this city. I built the splitter to reduce understeer and it has paid off in spades on high speed corners at various tracks.

Any and all opinions and advice will be read, appreciated, and considered
Thank you for reading and commenting.
https://cimg6.ibsrv.net/gimg/my350z....c540c618ce.png

Don't have an answer for the rates/drop you're looking for, but I do know you cannot rely on the pictures, you'll have to call the company to get details on specific part numbers. I used to manage listings for an aftermarket company with ~1500 SKUs, but for the product photos I only had a couple dozen pictures to choose from, so the majority of the time the pictures were not representative of the actual product.

That is good to know. Looks like I'll be making some phone calls on Monday. Thank you.

I know we didn't really talk about it but doesn't swift make custom springs?

I actually do not know. I cna call them and see

https://my350z.com/forum/brakes-and-...ion-101-a.html

great resource with lots of info.

I didn’t catch what year your car is, different years have different rates. Different brands developed their springs off of different stock rates to work with available shocks.

duel rate vs progressive, progressive is commonly used interchangeable unless we are speaking Motorsports grade equipment and we are not.

figuring it what is best. Well, it’s always a compromise no matter what. It’s been a while since I looked at available springs so I’m not going to suggest anything aftermarket. I will suggest looking into 07 08 , OEM Nismo springs. They may work well for your needs

07 350z so it's the 314/407 I think? Don't quote me on that.
I have notebook with all the different springs rates and calculated percentages of change.

Turns out my OEM springs are shot. My ride height is all over the place. We measured. Sagging nearly 20mm up front. Rear isn't so bad but that just makes the whole car rake to the front. I've been essentially "lowered" this whole time. I was wondering how you guys got away with 30mm MORE of lowering. It's because you're not. You're only 10mm lower than I am.

The only dual rate springs were the ARK and whiteline. I took a shot at the ARK even though it claims to lower it 0.8-1". Maybe I'll scrape all over Chicago. Maybe not. I am hoping the dual rate will help control body roll at the track so I can loosen up the sway bars and let the suspension act more independently of each other.

I was hoping you would comment so I could ask you a question about preload. My bar is preloaded now. It will be even more so when I put on the new springs. Sometimes in high speed wet corners I get a "skating" feeling. Like my front and rear are locked together and the car doesn't lean. Could this be caused by preload on the swya bars? It's $120 for the whiteline adjustable links for the front. Worth it or don't bother? I have spoken to quite a few people and it seems everyone just leaves it preloaded. I come from the euro tuning world and over there preload is definite no no but it seems no one has issues the same way for this particular chassis

Picture of springs I purchased and their rates below. You cna see the initial rate is less than stock and the upper rate is higher than stock. Almost a 3k differential to help control the body roll without use of stiff sway bars.
https://cimg0.ibsrv.net/gimg/my350z....5ff341efdc.png
https://cimg3.ibsrv.net/gimg/my350z....e83e5c34cb.png

It’s a standard progressive spring, only real way to get duel rate is to have separated springs

https://eibach.com/us/p-108-eibach-e...tem-guide.html

preload on a sway bar does little to nothing if you think of the dynamics. You can get it perfect, on scales , roll it off and back on, it will not be perfect. Adjustable endlinks will help, the main advantage more seems to be about strength with quality endlinks .

skating feel, could be tires, could be camber, could be a lot of issues. These cars don’t feel too planted till everything is worked on them.

Interesting writeup by eibach. Seems difficult to two springs in such a small stroke length in a road racing car.

I broke the acdelxo endkinks going off track with them the first time. I put some moog on and they are much beefier. Probabky spun out 6 times since then and they have held up.

Wouldn't have zero preload give the susepsnion more independence going straight? I live in Chicago so letting one side hit a pothole without it affecting the other side's suspension is desirable

https://www.jegs.com/i/Eibach/369/02...BoCXJ0QAvD_BwE

I could have run one of these up front to allow duel rate. 300 pound for small bump compliance, once compressed my 900 pound springs would take effect.

The middle of the sway bar is on a bearing/bushing. It’s impossible by design for a sway bar bot to affect the other side. It’s the part that directly links sides

What coilovers do you have? I was told those little springs are just helper springs to keep the spring loaded in long travel situations. Otherwise the spring would just come loose and bounce all around

https://www.summitracing.com/parts/h...BoC1b0QAvD_BwE

that’s what these springs are.I had to run them in the back on mine for that reason.

my car was on 2 way Moton dampers.

Interesting. I did not know there were two styles of them. I knew.

I contacted ARK to ask if they were progressive and they said they are actually dual rate. Since they are not sperated there is one coil that is technically a progressive coil and basically bridges the gap but, in effect, it performs the same way.

Here an article explaining the difference.
https://www.hypercoils.com/progressi...ngs-vs.-linear

terrasmak already said this but...

If you're going with Bilstein B6s, the best dual purpose (track days + street) that I have come across is to run with the OEM Nismo Coil Springs (Not the same as the S-tune coils). I just recently installed this combo on my 06 Enthusiast and I'm super happy with it. As a backup, I purchased a set of RSR Down Sus Coils (still in the box). I'm sure both options would be just fine. I tried the Nismo Coils 1st because they maintain the stock ride height which is more ideal when using B6 struts, while the RSRs lower the car slightly. I had a similar issue where the front end was sagging and the rear end seemed very bouncy, but I suspect more likely because the struts were worn out at all 4 corners (although none of the struts showed signs of blown seals) and my rear differential bushing was totally shot (also remedied). Now the car handles like a dream. I get solid feedback from the suspension, I feel all the bumps in the road, but it's not overly harsh or jarring. I let one of my Z buddies take the car for a spin after all the work I did, and he simply stated "This is how a sports car should feel." He owns a 94 Z32TT and wants the Bilstein B6s as well, unfortunately Bilstein has discontinued production on full sets for the Z32. Options are a bit limited these days for that chassis. In short, this setup has an excellent balance between performance and comfort while still maintaining the factory suspension geometry, I wouldn't have any concerns with using this setup on an open track day.

In the past I ran with the OEM non-Nismo (06+) coils on Koni Sport (yellow) struts. This setup was not a good match for street driving on poorly maintained roads. It was very harsh, even with the Koni's set on their softest setting, but the handling had improved a lot in the corners. It was still street-able, but very dependent on the road conditions in your area. I'm not a suspension wizard, so I can't explain the technical reasons for why this setup didn't work well for me.

I hope w/e you choose works out for you! There are so many options to choose from for the Z33s today.
Cheers!
-Icer

thats good to know. Then I will not regret going with my option. I wouldn't want the nismos if they ride any harsher. I think I am doing right getting the dual spring ARK.

​​​​​I had the same experience with Koni when I ran them on my old e46. The springs were only 10% stiffer but the yellows made the ride so harsh that it essentially ruined the car for driving in the city. The B6 are worlds better. I think I am done with any tein tube design on any sports car I own. Too harsh for the level of stiffness they provide.

If you go with the ARK coils, the drop is 1". You may want to investigate the Bilstein B8s. I'm not sure what the acceptable range for lowered coils is for the B6s vs. the B8s. I just recall the B8s being purpose built for lowered applications.
Cheers!
-Icer

I'm just going to run it and see what happens