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Cortex coilovers - softening the spring rate - how far?

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My cortex dampers are excellent under most conditions but i'm finding that I need a softer spring to deal with very harsh bumps.

Its perfect on smooth roads but on these Michigan roads my system is so stiff its crazy. This is exactly what I asked for - race setup - however I'm having so much fun street driving my car the ratio of race to street has tilted a lot more toward the later.

Current Rates for the Cortex / Jri setup:
500 lbs / in front 300 lbs / in rear. Front sway bar is factory bonded 34mm tube, rear is 18mm solid.

How soft should I go for street mode? I was considering going to 400 front 175 rear and then bumping up to the 20mm bar. What part numbers do you suggest? I didn't write down the eibach coil numbers before I installed them.

Thanks, Jeff Check
 
I have 450/225 on mine. I've also wondered how soft you can go. Mine aren't too bad driving around town and I have the dampers set pretty soft. I suspect the roads around here in NorCal aren't as bad as your Michigan roads though.
 

Wingrider

'11 GT500, 99% Track Car. Lots of mods & I coach
NFSBOSS said:
I have 450/250 on mine. I've also wondered how soft you can go. Mine aren't too bad driving around town and I have the dampers set pretty soft. I suspect the roads around here in NorCal aren't as bad as your Michigan roads though.

What do you set them to for the track? Do you dial them differently for Laguna vs say THill?
 
401
0
Op, where in Michigan are you located? I am in Troy, Oakland County, I was wondering if I could see your setup, have been thinking about the Cortex coilovers, but I was hesitant in spending 4 g's on something I havn't seen, never mind driven.
 
sadil said:
Op, where in Michigan are you located? I am in Troy, Oakland County, I was wondering if I could see your setup, have been thinking about the Cortex coilovers, but I was hesitant in spending 4 g's on something I havn't seen, never mind driven.

I'm in Dearborn give me a PM. The cortex are works of art and the car handles like a different machine.

1. Don't even think about street driving 500 / 300 spring rate setup.
2. With the shorter high rate coils I recommend the helper spring setup (just like the one in back).
3. I put in a note to Filip asking what street rate is ideal. at this point I've found the upper bound now lets find the lower.
 

ArizonaBOSS

Because racecar.
Moderator
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Arizona, USA
TMSBOSS said:
Coil overs are likely in my future. Curious what "Helper Springs" are.

Sorry to hijack the thread. ;D

A "helper spring" is an extremely-low rate, flat-wound spring that is placed in the system to take up the slack when the working spring does not have enough height to reach the spring perch at full droop with the desired ride height. Due to the extremely low rate they have (virtually) no effect on spring rate itself but just keep the working spring in-place at full extension of the shock.

The upper spring in this picture:
helpers.jpg


Separately:
HelperSprings1.jpg
 

Grant 302

basic and well known psychic
ArizonaBOSS said:
A "helper spring" is an extremely-low rate, flat-wound spring that is placed in the system to take up the slack when the working spring does not have enough height to reach the spring perch at the desired ride height. Due to the extremely low rate they have (virtually) no effect on spring rate itself but just keep the working spring in-place at full extension of the shock.

The upper spring in this picture:
helpers.jpg


Separately:
[ im g]http://www.twinenginemini.co.uk/images/HelperSprings1.jpg[/img]

It's normally collapsed in the normal working range and at ride height, but keeps the spring seated at full droop.
 
OK everyone here are pics of my current front and rear springs - 500 rate front 300 rate rear. Help me pick out some softer ones!

Part numbers:

front: 0800.250.0500
rear: 0800.250.0300

eibach.jpg


BTW, what does the acronym A/P on front and A/N mean on the back coilovers. You can see this adjacent to the Eibach logo on the springs.

Here are the front and rear coils as found on the Eibach site using the part numbers listed. Ignore the ES prefix coils those are Extra short solid height in case you don't have enough compression travel in your application. Eibach call solid height "block height". Also ignore the S suffix that's for a sliver colored coil.

catalog.jpg


http://eibach.com/america/en/motorsport/application-look-up/ers-coil-over-2-50


My goal is to make a softer setup for bumpy tracks with a little more ride height much like the Roush setup a couple seasons ago.. I'll be verifying this with Dean Martin of Rehagan first and will let you all know what he says. Since the front coils are identical to rear except for load and rate, I have a simple task of choosing a softer set from these available rates:

rate (lbs / in)
475
450
425
400
375
350
325
300
275
250
225
200
175
150

A straight lowering of spring rate by 25% takes me to 375 front 225 rear. However, i'm in the mood for something a little softer than that with these Michigan roads and tracks so I'd probably go down to 350 lbs / in front and 175 rear. Then upsize the stabar from 18mm to 19mm or 20mm depending on any extra understeer created. Let me know if that's a sound decision. I already can hear a bearing creaking noise coming from the driver side strut stack, these things are getting beat to death on Michigan roads I've only driven 1500 miles on them. There is also a touch of darker oil collecting in the first two threads of the passenger front strut meaning they are getting way to much of a workout and leaking a touch. Good thing JRi's are fully rebuildable many times over!

FYI - Eibach also sell the HELPER250 helper spring that's 0.5" solid stack height. I recommend the helper spring on front if you are doing street driving, to keep the coil in place over chatter bumps I get some noises from that now. Cortex already supplies us with that same helper spring setup on the rear. The part SPACER250 is used to connect the helper spring to the main spring.

New top mount thrust bearings TRB250 are $45 each with spacers. I'd also grab four new ISOLATOR250 spring isolators while i'm there :)

FYI - when I pulled off the wheels to put my drag radials on at Milan Dragway on Friday you could hear some ohhs and ahhs about the Cortex setup. That was cool! Its good to put a Gucci part on your car every once in a while. Not only that they significantly improved my drag launch - no more leaning to one side or inconsistent traction.
 

Grant 302

basic and well known psychic
I've been considering adding some of the same isolators and maybe the bearings. I also noticed a LOT more noise from the top hat when I changed from max neg. camber for the road trip to Laguna Seca. Made a even more around the crappy roads in Salinas.

I'm surprised you're considering going down to 175 in the back, since that's softer than stock Boss/LS or Track pack rates in the 186-191 range. And if going back to similar rates, I think a bar in the 24-25-26mm range would be more appropriate. Otherwise I think you'd be hitting the bumpstops pretty hard when cornering at the track. Just a guess though.

I think you'd get more comfort on the street by dropping the front rate more. It's hard to guess how much when I have no idea about your roads... But if they're anything like Salinas, I'd even consider going down to 225 to 300 range. If you just buy the 175 for the rear, try the 300 up front?
 
Grant 302 said:
I've been considering adding some of the same isolators and maybe the bearings. I also noticed a LOT more noise from the top hat when I changed from max neg. camber for the road trip to Laguna Seca. Made a even more around the crappy roads in Salinas.

I'm surprised you're considering going down to 175 in the back, since that's softer than stock Boss/LS or Track pack rates in the 186-191 range. And if going back to similar rates, I think a bar in the 24-25-26mm range would be more appropriate. Otherwise I think you'd be hitting the bumpstops pretty hard when cornering at the track. Just a guess though.

I think you'd get more comfort on the street by dropping the front rate more. It's hard to guess how much when I have no idea about your roads... But if they're anything like Salinas, I'd even consider going down to 225 to 300 range. If you just buy the 175 for the rear, try the 300 up front?

This is exactly why I posted my question on the board. I agree now looking at the LS rear spring rates. I'll probably go 375 from 225 rear now.
 

Grant 302

basic and well known psychic
twistedneck said:
This is exactly why I posted my question on the board. I agree now looking at the LS rear spring rates. I'll probably go 375 from 225 rear now.

Also make sure you get more spring length when you go softer. Your current rear springs compress about 2.5"+ for the static ride height, and the 225 rate springs will compress at least 3.5"
 
Grant 302 said:
Also make sure you get more spring length when you go softer. Your current rear springs compress about 2.5"+ for the static ride height, and the 225 rate springs will compress at least 3.5"

Excellent point. i'm almost out of threads already anyway in back and the front is about midway down. I will get the 10" versions. I wont need the helper springs in the front with the longer spring anyway and they should just about fit.

Guessing 1000lbs per front coil at curb height assuming the fronts compress to about a 1000lb curb load, going from free zero load 8" height to curb height, that means curb height would be would generate 4.4" of compression with the 225 rate vs. 3.3" with the 300 rate.

Meaning to get the same ride height i'd have to dial the higher rate coils down another inch! That's exactly what you came up with Grant.

Here are the new part numbers:
1000.250.0375
1000.250.0225
 
Well for what its worth, I should be able to provide some better insight into how my rates work out with proper damper settings and shitty roads by the end of this weeked. I've got 425 lb Front & 225 lb Rear on my car using the JRi DA setup.

Also, I ran the same spring rate before I purchased the Front JRi's when I was using Koni Race inserts up front and my Penske's out back. I didn't find it too bad on the roads here in PA which is why I opt'd to use the same spring rates this time around when I bought the JRi's up front.

Lastly, I'm not sure if you saw my post the other day in your "CorteX JRi Double Adjustable Front & Rear Damper Adjustment Settings" thread but by accident I ended up running the front JRi DA's on -25 Compression & 2 Sweeps for Rebound and it was damn smooth using the above mentioned spring rates with those damper settings.

Understandably though I know some people perception of ride is very different than others so my smooth may be considered rough to others so take it with a grain of salt.
 

Grant 302

basic and well known psychic
^That does remind me...I forgot to ask: What were the softest settings you ran on? It really makes a difference for comfort. I probably need to experiment more on the front at softer Low Speed settings myself.
 
Grant 302 said:
^That does remind me...I forgot to ask: What were the softest settings you ran on? It really makes a difference for comfort. I probably need to experiment more on the front at softer Low Speed settings myself.

Right now I'm 5clicks softer than neutral in front of 15-5 = 10 (out of 30), rear I pulled 10 clicks out. Both low speed. Front high speed rebound still at factory setting.
 

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