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Old 02-25-2013, 05:40 AM   #1
bako
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Default 7K/5K vs 6K/5K spring rates

suspension gurus, I have one little question:

in 2 weeks I will have cusco zero 2R in my garage. right now I'm riding on vacanza. Vacanza has front 6k, rear 4k springs, zero 2R from factory has 7k/5k.
I think to change springs and to install on Zero2r springs front spring from vacanza, so I will have 6K/5K instead of 7k/5k. I think this can increase grip for front tires? or I'm missing some ideas? wont' that cause even more mid corner oversteer?

the car is DD, but I do not care about comfort.
my main concern is corner exit understeer.
main interest is track, not AutoX...

my setup is:
cusco vacanzas without damping adjustment 6k/5k springs;
rear 22mm sway;
alk;
F -2.4 0toe, caster 6. R -1.3 0tore (going to encrease up to -1.5, I often have mid corner oversteer)
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Old 02-25-2013, 10:45 AM   #2
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7/5 is a great combo for street with occasional track, BUT if comfort it not a concern and you want more rotation then do the 6 in the rear.
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Old 02-25-2013, 10:49 AM   #3
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Originally Posted by Turn in Concepts View Post
7/5 is a great combo for street with occasional track, BUT if comfort it not a concern and you want more rotation then do the 6 in the rear.
As inappropriate as that sounds, it's what I'm running and I love it. I'd even consider 8-7 instead of 7-6. Although I auto-x not track..
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Old 02-25-2013, 11:23 AM   #4
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I used to have 7/6 springs, it was ok with oem tires and wheels. When I used Michellin PS2 255 35 R18 tires, I felt my rear is kneeling when I do some fast turns.
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Old 02-25-2013, 11:24 AM   #5
bako
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I do not have locally available springs here, only have: f7k, f6k r5k,r4k.

by the way, front and rear springs in cusco coilovers are interchangeable?
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Old 02-25-2013, 06:06 PM   #6
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Quote:
Originally Posted by bako View Post
I do not have locally available springs here, only have: f7k, f6k r5k,r4k.

by the way, front and rear springs in cusco coilovers are interchangeable?
I.D." wise I'd imagine they would be the same, but the front's and rear's will probably be different lengths i.e. rears are typically longer. Also some manufacturers run progressive springs in the rear of the street oriented set up's for the GD's. Not sure if the Cusco's listed do or not, I doubt the 2r's would be, but the vacanza may.

I'd say start fresh with a set of Swift springs in the size's and rates you want/need. Plenty of vendors online here that could help you out with that (myself included)

-Anthony
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Old 02-26-2013, 05:28 AM   #7
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thank for advice, thanks for interest in helping me, but I'm in the middle of Euroasian continent shipping the springs in way too expensive.

yes, Vacanza has linear springs too. I will check diameters of springs on both setups, if they can be fitted in each anothers place.

do you think that length of the spring can be an issue on full threaded strut? (installing shorter spring in the rear instead of long one)

so I hope my english is enough for you people to understand: I want to put front 6k spring from Vacanza on the rear strut of Zero2r.
if that can't be possible, or this will issue some additional problems I think to put 6k front springs from Vacanza in front sturts of Zero2r, instead of it's original 7k ones.
I'm sure one of this combination can lead to more balanced car. (but won't this be too much? I already have neutral car in mid corner, my concern is corner exit understeer)

Last edited by bako; 02-26-2013 at 05:34 AM.
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Old 02-26-2013, 01:59 PM   #8
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From the way you describe your current setup I'd try the 6K front and 5K rear. Any weight reduction on your car?
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Old 02-26-2013, 08:09 PM   #9
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It's somewhat counter intuitive. Higher spring rate allows for higher tire loading. Also dampers follow springs, so higher spring rates also mean higher damper rates. In the end, this will offer higher normal loading of the tire and faster response. You will get more grip and turn faster.

Now this seems odd right? Well, there is a limit. At the end of the day you can still only load the tire so much before there isn't any more grip. Also adding more stiffness to the front without balancing it with the rear will eventually make the front end work too much and generate understeer. Understand that sway bars can be used to adjust balance beyond the spring rates, so for cornering handling, you will be looking at a mix of spring and sway bar to create the steady state balance of the car. The spring and dampers will more so control the dynamic behavior.

You will drive with the side that is stiffer and more responsive. A front stiff car will have a lot of steering feel. This is to say that you will most notice the front end of the car when maneuvering. The rear end will feel loose and sluggish in comparison. You can add a bigger rear sway bar to neutral out the balance. This sway bar is a moderate spring force that will not be well damped. This is to say a soft rear end with a sway bar will be "springy" side to side. You will find that you can toss the back end around more, but too much uncontrolled spring can cause snap oversteer if you manhandle the steering too much. You can stick to smaller sway bars all around to maintain relatively high damping control side to side since much of the force will be from the springs which are in turn controlled by the damping set to them.

You will naturally drive more so through the steering wheel. If you go rear stiff, the rear end of the car will be more responsive. The front end will comparably feel sluggish and squishy. You will naturally pay more attention to the rear end of the car and drive more so through throttle. You will add a bigger front sway bar to neutral out the handling. Again, a big sway bar will be more springy side to side. The rear end will feel more stable even if the car oversteers. It is reactive and well damped, so you will find it easier to rotate the car with the back end. You can find it harder to toss the car around though. Because the back end sets up faster, it takes more effort to break the rear end loose through feint maneuvers unless the car is set up with oversteer to begin with. In this sense, it's a nicer setup for a person who manhandles the steering wheel because the front end will be comparatively sluggish to inputs and be more forgiving. This option can also be better for high powered cars as the stiff rear end will not introduce as much understeer on corner exit during acceleration, more so for the 50/50 WRX owners. The STI owners have the torque split to counter on-throttle balance change.

What's best is relative to the individual. I'm a personal fan of a more even setup where the front and rear are at the same frequency. Realistically you can go either way from there and mix and match springs and sway bars to retain neutral handling or understeer or oversteer depending on preference and generate different dynamic behaviors for the car as one may prefer. As a note, a lot of aftermarket spring sets are rear stiff, but most stock cars run bigger sway bars on the front which in turn necessitates stiffer rear springs to balance out the handling. Some of the choice may also have to do with auto-x rules that previously only allowed bigger front sways in lower classes, forcing a need for stiffer rear springs.
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Old 02-26-2013, 09:35 PM   #10
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I would want 7/6 or even a little higher if you are on track a lot.
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Old 02-27-2013, 07:11 AM   #11
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Quote:
Originally Posted by Vaughn Performance View Post
I.D." wise I'd imagine they would be the same, but the front's and rear's will probably be different lengths i.e. rears are typically longer. Also some manufacturers run progressive springs in the rear of the street oriented set up's for the GD's. Not sure if the Cusco's listed do or not, I doubt the 2r's would be, but the vacanza may.

I'd say start fresh with a set of Swift springs in the size's and rates you want/need. Plenty of vendors online here that could help you out with that (myself included)

-Anthony
KW do this.
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Old 02-27-2013, 04:40 PM   #12
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Quote:
Originally Posted by bako View Post

do you think that length of the spring can be an issue on full threaded strut? (installing shorter spring in the rear instead of long one)

I want to put front 6k spring from Vacanza on the rear strut of Zero2r.
if that can't be possible, or this will issue some additional problems I think to put 6k front springs from Vacanza in front sturts of Zero2r, instead of it's original 7k ones.
Aside from having to min/max the spring perch up or down to get the height you want, you don't want the spring to be the wrong length or it will run out of travel before your damper does, which is what you don't want.

Honestly, your best bet with the springs you have there is to just run the 7/5k set up that is coming on the zero2r's. Should be fine, especially considering it looks like you have a stock front bar.

Also, don't forget to keep track of the one of the most important suspension adjustments..........tire pressure. A little nudge up or down at either end can really change things, especially at the track. Folks tend to want to jump straight to the bigger adjustments, sometimes this is all that's needed.

-Anthony
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Old 02-27-2013, 06:09 PM   #13
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What diffs are you running?
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Old 02-28-2013, 06:43 AM   #14
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I'm running front open, central stock 4kg, rear Suretrack (from 98 JDM GC STI)
about tire pressures I use CO with F-2.3 bar R-2.3 bar.

so you think rear shoks have much more travel then front ones and spring bottoming out will be a concern?

and I have another question, does those inverted shock really need dust covers? one is ripped...
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Old 02-28-2013, 06:49 AM   #15
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how about an ALK to help with corner exit??
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Old 02-28-2013, 07:10 AM   #16
bako
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alk gave me the biggest difference in corner exit, I was amazed.
by the way, can I move alk housing even lover with some spacer? will that give some additional benefits for front traction?

what else can I be suggested?

- increased rebound on front dampers
- move battery to the trunck ( but I already have lightweight one whcih anyway does weight 10kg);
- remove AC (do not want because of DD);
- roll center kit > go lover;
- front aero splitter;
- some better central diff...
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Old 02-28-2013, 07:32 AM   #17
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hd cowl stays that some, mistakenly, call 'fender braces' really help stiffen the front end and moving the battery will also help a LOT
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Old 02-28-2013, 07:38 AM   #18
bako
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so the factory ones are such a real junk?
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Old 02-28-2013, 10:31 AM   #19
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yes..
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Old 02-28-2013, 04:43 PM   #20
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Quote:
Originally Posted by bako View Post
alk gave me the biggest difference in corner exit, I was amazed.
by the way, can I move alk housing even lover with some spacer? will that give some additional benefits for front traction?
No, I don't think that will gain you much. There's the "free caster mod" and the ability to put spacers in the control arm but you already have a sufficient amount of caster. Roll center kit will probably be good, plus on track a little more camber all around should help.

As far as a splitter goes, yeah, a little aero is good to have, but you want to get the chassis sorted out before you start adding downforce.
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Old 02-28-2013, 05:02 PM   #21
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If the corner exit understeer is basically wheelspin then look at a mechanical (plated) front diff, should make a huge improvement.
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Old 02-28-2013, 07:27 PM   #22
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If the corner exit understeer is basically wheelspin then look at a mechanical (plated) front diff, should make a huge improvement.
that's a much more difficult install dropping & cracking the box open though. i think he's trying to do what he can before getting to that point.

though what JD said is correct. put a TBD in and be amazed.
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