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Discussion Starter #1 (Edited by Moderator)
Hello,

The idea here is to post all the spring rates of your suspension you've tried, so we'll build a database reference for future track focused users. Spring rate units calculator is here: http://www.numberfactory.com/nf torque.htm

OEM SUSPENSION - NON SPORT

  • unknown spring rates
  • 23mm front sway bar
  • no rear sway bar
Good for street and OK for basic track use. A lot of body roll, brake dive and acceleration squat, becoming even more noticeable with stickier tires.

NITRON NTR R3 (adjustable low speed compression, high speed compression, rebound) - 300/620
  • 300 lbs/in front (52 N/mm)
  • 400 lbs/in rear (70N/mm)
  • 23mm front sway bar
  • no rear sway bar
Very good all around setup with decent track capabilities. Brake dive and acceleration squat greatly reduced. Some amount of body roll is still present, but can be solved with sway bars, but with only adding a rear sway bar and keeping front OEM, the rear end would be too stiff, causing an excessive oversteer. I tend to find this spec solid with non sport 4C package (no rear sway bar) and in case a car is equipped with rear sway bar, I'd recommend a softer rear spring rate at about 375 lbs/in.
 

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Fixed your first post as requested, left the conversion link because it is helpful, and also added a link to this thread in the Technical Reference Index thread.

If any of this is not correct, please let me know.

Good info!
 

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Do you mind if I put this here?


Kind of an interesting primer to stiff vs soft.
Obviously, it depends on what your goals are, and mostly what the surface you drive on is like!
 

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Just curious, what tires are you running with this setup on the street? Would this work well to balance larger rear tires or offsets/spacers that would have more understeer?
 

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Discussion Starter #7 (Edited)
Fixed your first post as requested, left the conversion link because it is helpful, and also added a link to this thread in the Technical Reference Index thread.

If any of this is not correct, please let me know.

Good info!
NITRON NTR R3 (adjustable low speed compression, high speed compression, rebound) - 300/620
300 lbs/in front (52 N/mm)
400 lbs/in rear (70N/mm)
23mm front sway bar
no rear sway bar

Please correct this one aswell. Thank you!

Do you mind if I put this here?

http://www.youtube.com/watch?v=hGZRairqHNI

Kind of an interesting primer to stiff vs soft.
Obviously, it depends on what your goals are, and mostly what the surface you drive on is like!
Good explanation.

My suggestion:

FAST STREET + OCCASIONAL TRACK: Medium spring rates + stiff adjustable swaybars (this way your suspension soaks up all the imperfections of the road, yet the body roll is kept low with swaybars. Going too stiff will make your car slower on the street)

FREQUENT TRACK + RACE: Stiff spring rates + medium/stiff adjustable swaybars (it will be slower setup on imperfect and bumpy surface, but it will provide better results on a race track where surface is optimal. You can also run high downforces without affecting body pitch and you can run slick tires without causing too much bodyroll. For the rainy conditions however, you can usually get a good results with simply disconnecting the swaybars)

Just curious, what tires are you running with this setup on the street? Would this work well to balance larger rear tires or offsets/spacers that would have more understeer?
On the street, I'm running semislick 235/265 and I set the swaybars to soft. For the track I set the swaybars to stiff.
 

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Rudy, how about attacking kerbs on the track? do you consider this while deciding on suspension setup.
i stay away from them for the most part as they can launch the car and usually - both on the apex and on the exit - they upset the rear end causing it to step out.

my suspension is a stock non sport.
so far with stock rear bushings.
next track day will be with yours :grin2: - from what i've felt so far on the road the rear end will be more planted and help with the kerbs.

Gennady
 

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Discussion Starter #9
High speed compression affects the ability to drive over the kerbs. You need to keep high speed compression low if you want your suspension to take kerbs well, on the other hand you can quickly bottom out suspension this way, so it's up to you to find the setting and decide whether you'll drive over the kerbs or not. I try to avoid them in most cases, especially on high speed corners as they usually upset the car's balance more than you gain with cutting the corner. I do however drive over the kerbs on some tight twisted tracks, where speed is not that high and I can gain some time by cutting the corners. This also depends of the kerbs height of course.

Report back you you find the handling after the uniball mod at the rear.
 

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Do you mind if I put this here?

http://www.youtube.com/watch?v=hGZRairqHNI

Kind of an interesting primer to stiff vs soft.
Obviously, it depends on what your goals are, and mostly what the surface you drive on is like!

The video simplifies a bit too much. I suggest to look at the suspension as a two mass problem with two springs and one damper. This model suits better for ground contact/grip questions (not for ride comfort). Form the bottom up it would be: tire = spring with almost no damping, unsprung mass = everything between the ground and the sprung mass (moving parts), spring and damper and finaly the sprung mass.
Here a little picture of the situation:




The tire and rim:


Sidewall stiffness is the "spring rate" of the tire. If you drive a street, semi or slick the sidewall will have very different spring rates. Even between the manufacturors are differences when you just look at one category of tires. The rim diameter has also a huge impact - the difference between a 17/18" and 19/20" setup is for everybody noticeable. With a bigger rim you reduce the range of spring and increase the spring rate of your tire. The rims may add some extra weigth to the unsprung mass.


Besides where you drive it's also about what you drive :)

It would be helpful to add tires and rims specs to the initial post.



A personal example:


I mounted 18" instead of 16" rims on my daily fwd (147). They are wider 10% and can generate more lateral acceleration. But now - when I accelerate out of corners - the inner front wheel starts to trample on bumpy surface (more unloaded, less sidewall and heavier wheel). I would need harder springs and stronger dampers now to unleash all the performance which is in the tire. My lsd (and gta anti-roll bar) reduces the negative effect a bit.
 

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Discussion Starter #11
I got the spring rates for:

OEM SUSPENSION - SPORT
125 lbs/in front (22N/mm)
200 lbs/in rear (35N/mm)
22mm front sway bar
23mm rear sway bar

It would be helpful to add tires and rims spec to the initial post.
I agree.

F: 17x8.0 235/40/17 Federal RSR TW140
R: 18x9.5 263/35/18 Federal RSR TW140
 

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Discussion Starter #12 (Edited)
Hello,

I have tested the new spring rates I must say I'm not happy. Car feels stiffer, but it's still way too much proned to oversteer. Also tires temps front/rear still differ too much.

SPRING RATES:
FRONT:
370 lbs/in front (65 N/mm)

REAR:
456 lbs/in front (80 N/mm)​

DAMPING:
FRONT:
R-3
LC-1
HC-5

REAR:
R-1
LC-18
HC-10​

TIRES:
Semislick TW140 235/265

ALIGNMENT:
FRONT:
Camber: -2°30'
Caster: 5°00'
Toe: 0°00'

REAR:
Camber: -2°00'
Toe: 0°22' per wheel / 0°44' total​

SWAYBAR:
FRONT:
Stock 22mm

REAR:
none​
 

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@Gale I saw the most recent video you uploaded. You are definitely driving that car on the edge. I do completely see why you say the car still wants to oversteer as it is a COMPLETE handful. What are your tires pressure hot? I usually try to aim for 30/32 psig (2.06/2.2 bar) for hot pressures. You start to dance on marbles if its higher. I wonder if some of has to do with no rear swaybar. I am still convinced that once you install aftermarket shocks, then you should be able to put on rear swaybars easily. (I suspect that they didn't delete the hole that the sway bar screws into)

How far off your laps times are you from your BMW?
 

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Hello,

I have tested the new spring rates I must say I'm not happy. Car feels stiffer, but it's still way too much proned to oversteer. Also tires temps front/rear still differ too much.

SPRING RATES:
FRONT:
370 lbs/in front (65 N/mm)

REAR:
456 lbs/in front (80 N/mm)​

DAMPING:
FRONT:
R-3
LC-1
HC-5

REAR:
R-1
LC-18
HC-10​

TIRES:
Semislick TW140 235/265

ALIGNMENT:
FRONT:
Camber: -2°30'
Caster: 5°00'
Toe: 0°00'

REAR:
Camber: -2°00'
Toe: 0°22' per wheel / 0°44' total​

SWAYBAR:
FRONT:
Stock 22mm

REAR:
none​
Do we have the motion ratios for the front versus the rear. Because of those are different I can give you an effective spring rate to be different than the actual spring rate in comparison to the front vs rear.
 

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Same 50nm front and 70nm rear on the Novitec Black Series coilovers. Great weekender/trackday balance. The dampers is more compliant and actually more comfortable on the street.
 

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such a big difference between front and rear compression settings probably suggests that front/left spring rate balance is not correct.
but i guess you already know this :laugh:
 

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now i see that your rates are 370/456 f/r while Inokinetic sales them with 342/456.
Assuming he has long experience and know what he is doing - you're already have stiffer front and still you're oversteering.
and no rear sway yet.
and still you're oversteering.
why is that?
 
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