Eibach is 10%. i have them with collars on mine. Rides like factory really.

1.5" drop on all 4 fenders. (I have the collar spacers installed, so it could got 1/4 inch lower but its LOW now ha)

 

Looks really good . I have the factory coilovers but front lift also so i dont want to mess with front collars with all the warranty denials so ill have to settle for 1.1 drop im front. 10% is really doable for me. Thx !

 

Same my car is a Z51, with Front lift. I use the lift now haha.

 

My car is Mag Ride with front lift. This is Eibach springs only. No collars or coil over adjustment. Rides fantastic.

 

For my curiosity. what do you measure at the fenders to ground? with just springs. I debated that vs both. split the difference with both but with spacers ha

 

In the front it is 25.5” on the drivers side and 25 7/8 on the passenger side. This is on a 275/35/18 tire with -3 degrees of camber.

 

So I just heard back via email from the R&D at Eibach and they provided much different spring rate numbers for their springs on C8 Z51.
It is 32% front stiffer and rear is 17% ...Hyperco is supposedly, according to Paragon 30% stiffer front and rear. Front is same but rear is somewhat softer for the Eibachs.
Here is a summary:
OEM Front = 207lb /in. Rear 235. makes sense, engine in the back etc.
Eibach Front = Progressive 183-275 lbs/in. Rear =275.
I guess the front is progressive and not linear the like the rear and unlike the Factory setup?
Maybe Perhaps that is why ppl like the ride on the Eibachs more? adjusts as needed. Idk i might be completely off.

 

Interesting that their own R&D department and there sales documentation don't match haha. Companys now days do not communicate

As i post this I went to find the link to the 10% in their own adds. and can't find one... I swear I read it as I canceled my paragon order and swapped to them once I read up on it... oh well, rides and looks good ha.

New wheels will be here soon.

 

Dual rate springs are not very good especially since it affects what damping rates you target. +/- 10% isn't too bad without changing the damping. 30% is potentially massive.

The c8 does not have a McPherson strut. The front spring/shock is a coilover so the motion ratio is the same for both, and the shock is inclined inboard a fair amount. This makes the spring and shock less effective since the MR is less than 1:1. Now I don't know what the total piston travel is for either the passive shock or the MSRC shock but it will decrease with lowering springs. You will end up in a situation where there is not enough damping force in either bump or rebound and possibly even both regimes.

All of that said, and I'm guessing since I have not measured everything. It would appear the front MR is something like 0.6-0.8:1

Let's assume 0.8:1
Car weight 1662kg(z51)
Car weight dist: 40% fr
Quick math - 333kg front corner weight
Z51 front spring rate is 225lbs
OE z51 front ride frequency ~ 1.4hz
If Eibach is truly 30% stiffer that means 292lbs
Eibach front frequency ~ 1.6hz

Which results in an overall 15% stiffer ride rate at the front. Which is again depending on total shock travel either just within acceptable tolerances, or there isn't enough total shock travel to control wheel travel in an acceptable way. What is or is not acceptable is of course subjective based on use case / personal preference. For instance I like a medium -soft setup to use less ARB and more tire/ mechanical grip for a street car. Also lowering a car without preserving total shock travel is objectively bad for performance and comfort in a street car.

 

Nice write up ! Over my head all that engineering and mathing.
I listed exactly what I was given by the "Team Eibach" tech advised in an email when I inquired. Basically says 32% stiffer in front but it is progressive apparently in front. Rear is 17% stiffer allegedly. Stock 235 lb/in. Eibach 275 lb/in. Hyperco/Paragon 270-350 lb/in. in rear progressive lol.
Paragon's is 300 lb/in. in front linear.
All I know is that Paragon's website says 30% stiffer rates all around and EIbach says 32 up front and 17 rear. Your math is better looking though! So who knows im not educated on this matter enough to say lol.

Based on what I see and understand from the numbers provided to me, Eibach should ride a bit softer which is what I am looking for even if its just 10-15% softer. I am right on the edge right now with comfort and of course depends on how bad the road surface is too but im ok with stock z51 levels and could probably do a bit harder but would prefer to keep it stiffness down much as possible.

So looks like Paragon and Eibach for some reason decided they wanted to do opposite ends on progressive springs.
.
OEM Front 207 linear
Eibach 183-275 progressive with 275 being the active rate.
Paragon 300 linear

OEM Rears 235
Eibach 275 linear
Paragon 270-350 progressive

 

"The base Corvette has 180-lb coil-over springs in the front and 217-lb springs in the rear,

The Z51 gets 226-lb coil-over springs in the front and 263-lb springs in the rear."

The numbers you are getting from Eibach do not match what I am finding for OE c8 specs.

275lbs is not 32% stiffer from 226

226*1.32 = 298

I'm not sure what you mean by the "active rate" if Eibach is progressive you will experience both rates and that will work against any control trying to be provided by the shock. Basically the shock needs more damping for less spring rate and less damping for more spring rate since the shock shaft speed varies based on total wheel deflection.

Because of the rear weight bias the rear of the car will be less sensitive to the spring changes especially with so little rate change. The front though will be and more so if you lower the car. I wish we knew what the full soft shock curve looked like for the MSRC piston. It would tell us way more what the ride will feel like vs a particular spring change. My guess is it's linear for both bump and rebound. When I talked with Jim Miller, he didn't answer how or even if MSRC has a defined knee speed. To my knowledge there is no shim stack and so no blow off happens. The shocks 'could' digress a small amount but without knowing what the full soft shock looks like I can't tell you for sure if they are ever digressive and if they are, by how much. There are also to my knowledge no bleed circuits and I do not know what effect the ferro fluid has on when the shock oil cavitates but my best guess is there is not much gas force OR the piston can flow a ton of fluid at full soft.

TL DR

Aftermarket springs that are stiffer will make the ride more stiff. IF you care more about how the car looks, you do you make it the best version of what is cool to you. If however you care about how it rides too, I would ask Eibach why they chose what they did. I'm willing to bet the just took a general rule of thumb and went with a scientific wild *** guess (SWAG).

You could always just measure the spring dimensions and purchase one that most closely fits what you want. It's ok to get a spring that's +/- 1" give or take.

 

Right on 👍 not sure where they got the numbers they gave me in the oem springs either , probably assumed i wasn't going to check or they are confused. I do have the z51 with no magneride but has front lift. Just dont want to go 30 stiffer all around if e8bach is going to guve me slightly softer ride and most on this thread appear to be for eibach, does cost $150 more for the set though vs. hyperco

 

I like both brands. Paragon's hyperco offering is best since the springs are linear AND the numbers match what we would expect. Remember "30%" stiffer spring doesn't mean anything by itself. Making an educated guess it will make the front of the car 15% stiffer. I don't think the rear will be affected much either way but it could be slightly more than 15% stiffer based on the suspension geometry. Thus is my caution to people do not get caught up in brand wars, or more is better. You need to understand what "more" is getting you.

 

Eibach been laking springs for a lot of cars a ling time....

 

Yes and they are my first choice. I usually measure and then order the correct size spring with the rate I want. It is rare that an OTS rate is at all good.

 

Yeah ive had Eibach on at least 2 other cars as well and no issues. Also, Paragon's isn't linear both ends. It is linear in front but rear is progressive and goes up to 350 and front is 300 linear. Opposite for Eibach, front progressive and rear is linear for them at slight lower rates

 

Just checked paragon's site, you are correct

"300lbs/in Front Spring Rate - Linear
270lbs/in Rear Spring Rate - 350lbs/in Final Rear Spring Rate - Progressive "

That does also match +30% spring stiffness

 

I’ll add this, I have owned both the paragon and the Eibach’s The car sits better and handles better on the Eibachs, they do actual R&D and it shows in how they perform.

 

Thank you I was looking for someone to chime in who may have used both and could give an honest opinion on it. Eibachs also appear to be a bit softer, albeit not by much, on rates then the Hypercos , not knocking them just stating number wise. Ill go with Eibachs. For ride comfort the extra $150 might be worth it.

 

I got them from summit for less then 150 more.

414 on amazon. I got from Summit for 411 and 30 shipping