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      02-09-2018, 05:49 PM   #23
Ginger_Extract
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Quote:
Originally Posted by bbnks2 View Post
I don't understand this mentality. Increasing the rear spring rate by 114lb/in is only an EFFECTIVE wheel rate change of ~40 lb/in. You're talking almost an imperceptible difference.

By my math, that's still about a 15% increase in wheel rate, not insignificant at all, IMO. My philosophy is to use the least of spring rate/bar possible to get the right results. A bit of roll doesn't bother me, the car acting like a rollerskate does.

Additionally, the rear struts themselves have a separate motion ratio from the springs since they are mounted separately. I believe I saw the motion ratio of the strut put at around .7 vs the spring being only .3x? Therefore, my guess would be that the actual impact of increasing the rear spring rate by such a marginal amount would have only a marginal impact on valving. Put the rear struts 1 click stiffer?

Unsure about "stiffer," but at the track, I have my rebound maxed out in the back. It's proven to be the fastest way around, but it still feels like insufficient spring/wheel control. Hence my valving-related hesitations.


800lb/in is still relatively soft compared to spring rate people are running up front in the 400-500lb/in range. The car will still squat HARD under acceleration. I have 900lb springs out back and the car still squats on acceleration quiet a bit.

Also worried about chassis fatigue with such heavy duty spring rates. No one has really determined the long term effects of almost tripling the spring rates on these cars. I don't want to be the one to find out what breaks when I'm bouncing curbs (the fastest way around several tracks here) with such high rates.
Answers in bold.
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      02-09-2018, 10:27 PM   #24
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Quote:
Originally Posted by Ginger_Extract View Post
Answers in bold.
Your concerns are completely unfounded thus far. If roll resistance exceeds chassis stiffness then yes you'll have failure points pop up like the subframe welds on older generations. However, that doesn't seem to be a concern on our cars.The spring itself being 1000lb doesn't cause any more "stress" then adding roll resistance with a sway bar does... And if you run the springs so soft that you're riding the bump stops then think about how much stress that puts on the chassis since nothing is damping load... if you were concerned about failure points then I'd look at the upper strut mounts since they have been known to blow through to the trunk.

The rear springs are not 100% effective because they mount closer to the chassis where they get leveraged less. For ever 1" of wheel movement- and you've only got about 4 1/2" to play with as dictated by your strut stroke- the spring only compresses 1/3". Hence why a 1000lb spring is only as effective as a 300lb spring in the rear.

I remember from another thread that people are running longer rear springs than I do... at full droop (car in the air) do you have preload on the rear springs to achieve your current ride height? That might be the source of your damping issue... Or, inadequate damping. Take all preload off the rear spring, if present.

I keep getting told ycw probably aren't all that great, yet, the spring rates, spring lengths, and damping all appear to be more ideal than everything else people are paying more money for. If I set my rear dampers to max damping the car will completely jack down even with 900lb springs

Last edited by bbnks2; 02-09-2018 at 11:08 PM.
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      02-10-2018, 11:50 AM   #25
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Quote:
Originally Posted by bbnks2 View Post
I keep getting told ycw probably aren't all that great, yet, the spring rates, spring lengths, and damping all appear to be more ideal than everything else people are paying more money for. If I set my rear dampers to max damping the car will completely jack down even with 900lb springs
This statement is nothing more than basis and personal preference. There is no analytical data backing this up, nor any results or anything else to confirm this. So it is what it is. I can jack down my car with MCS shocks. So what does that prove exactly?

TCK is a great damper. It should be a concern if you're rebounding is maxed out on a TCK damper, because they have quite a bit of rate in there. FWIW - After a rear bar I settled to about mid-setting on my rebound and it was very happy within that range.

Maxing out rebound trying to force rotation is a sign that something is up - And I don't agree that forcing more spring is ultimately the solution.

OP - Do what you want, but in the end there are people that do calculations on a computer and math and will disagree until they’re blue in the face that say you're wrong....and others that tend to throw away and setup cars based on feel and times.

Last edited by Kgolf31; 02-10-2018 at 04:35 PM.
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      02-12-2018, 07:28 AM   #26
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Everytime i read your Posts here in the track area i am just confused.
I wrote my thoughts concerning spring rates etc. last year because i was having crazy Problems with my car...

In the end it came out that the PU Bushings were to blame.

Still i don´t understand that it seems so Different in what spring rates most of the german guys here run and what spring rates you american guys run:

The KW Clubsport e.g. for the 135i AG Model has spring rates of 70N/mm in the front, 80N/mm in the rear (same as my ST XTA).

The same Setup for the 1M is 110N/mm in the front and 120N/mm in the rear.

Concerning the results from the different Setups you guys drive that should result in massive understeering, because the front axle is way to hard.

I had both Setups already in my car (With OEM Roll bars and ST XTA Dampers (similiar to V2)) and both worked really well (besides the Problems going straight because of the PU Shit)....

Also the most Setups from race Shops around the nordschleife do not use this 1:2 front to rear measurement for their spring rates...
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      02-12-2018, 09:49 AM   #27
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Quote:
Originally Posted by frontside0815 View Post
Everytime i read your Posts here in the track area i am just confused.
I wrote my thoughts concerning spring rates etc. last year because i was having crazy Problems with my car...

In the end it came out that the PU Bushings were to blame.

Still i don´t understand that it seems so Different in what spring rates most of the german guys here run and what spring rates you american guys run:

The KW Clubsport e.g. for the 135i AG Model has spring rates of 70N/mm in the front, 80N/mm in the rear (same as my ST XTA).

The same Setup for the 1M is 110N/mm in the front and 120N/mm in the rear.

Concerning the results from the different Setups you guys drive that should result in massive understeering, because the front axle is way to hard.

I had both Setups already in my car (With OEM Roll bars and ST XTA Dampers (similiar to V2)) and both worked really well (besides the Problems going straight because of the PU Shit)....

Also the most Setups from race Shops around the nordschleife do not use this 1:2 front to rear measurement for their spring rates...
If you're trying to say we run our front axle way too stiff, you do realize that 70 N/mm is 400 lbs correct?

You're setup with a car running 400 lbs in the front, and 457 lbs in the rear.

The rear is crazy soft - like, not even remotely close on wheel rates compared to the front. That setup is like trying to copy cat a E36 spring rate setup - They are COMPLETELY different cars.

My car drove fine:



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      02-13-2018, 10:35 AM   #28
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Lots of different points being made within this thread so I’ll to stick to debating one thing at a time. First I’ll address the side conversation taking place. Then, I’ll get back to the OP.Please skip to the the end of this post now for my suggestions to the OP if you don't feel like participating in the side conversation...

Quote:
Originally Posted by Kgolf31 View Post
If you're trying to say we run our front axle way too stiff, you do realize that 70 N/mm is 400 lbs correct?
I think he was replying to me lol. And, I think what he is trying to say is that SOME people in the US run their front springs relatively softer than-- and their rear springs relatively stiffer then-- SOME people in Europe. To that, I'd say that I have never seen or heard of anyone running the rates he is suggesting. At least... not since 2007-2008 when people (yes even TCKLINE) were using common E36 or E46 spring rates on the E8x/E9x chassis despite all 3 cars having significantly different suspension needs (early trial and error)…

Quote:
Originally Posted by Kgolf31 View Post
This statement is nothing more than basis and personal preference. There is no analytical data backing this up, nor any results or anything else to confirm this. So it is what it is. I can jack down my car with MCS shocks. So what does that prove exactly? .
Biased? I try to be impartial. I was just poking fun at you since you once again inserted YOUR bias into the conversation with another backhanded comment about my coilovers. I've given data points such as spring length, spring rate, spring usable stroke, usable strut stroke, ride height, and many other data points. All you have provided us with is a video of your car and I am the one making biased comments without data?

OP stated he does not appear to have enough rear rebound damping to run a higher spring rate. I was pointing out that I can run a 900lb spring at 3/7 damping without issue. It makes me wonder, is the damping really that poor with TCKline valved coilovers, or, does OP just have too much damping dialed in and he is riding on springs basically once the strut has been compressed? Or, does he have the rear springs preloaded? That would cause the return rate of the spring to be higher necessitating more rebound damping to control droop travel.

Quote:
Originally Posted by frontside0815 View Post
Everytime i read your Posts here in the track area i am just confused.
I wrote my thoughts concerning spring rates etc. last year because i was having crazy Problems with my car... Still i don´t understand that it seems so Different in what spring rates most of the german guys here run and what spring rates you american guys run:

The KW Clubsport e.g. for the 135i AG Model has spring rates of 70N/mm in the front, 80N/mm in the rear (same as my ST XTA). The same Setup for the 1M is 110N/mm in the front and 120N/mm in the rear.
I cannot find a single vendor of 135i KW Clubsports that provide a ~400lb (80N/mm) rate as the stock rear rate offered. They all list the rear rate as 600-800lb/in (105-140N/mm).

BC coil-overs are the only ones I know of that come with a stock spring rate like what you mention 10k/11k (98/107 N/mm) and it rides awful.

Quote:
Originally Posted by frontside0815 View Post
Concerning the results from the different Setups you guys drive that should result in massive understeering, because the front axle is way too hard.
In general, the people replying in this thread are all running between 300-450lb/in springs up front (52-78N/mm) which is a relatively softer range than the 400-570lb/in you quote as being used over in Germany (70-100N/mm)… A 300-450lb/in front spring rate puts a coil-over that has 4-5” of available stroke in a much more ideal compression stroke at ride height than the higher rates that you quote would… This was covered in another thread.

The car doesn't just under-steer because the front wheel rate is higher than the rear. You have to exceed the tires ability to maintain grip first. Driving style is the #1 contributing factor to causing ANY kind of traction loss. If you just cornered slower the car wouldn't break traction, right? Whether or not the aforementioned springs rates are “stiff” can be a bit subjective and is completely relative to the rest of the cars setup… ride height, tires, track width, alignment, damping, etc…

Quote:
Originally Posted by frontside0815 View Post
Also the most Setups from race Shops around the nordschleife do not use this 1:2 front to rear measurement for their spring rates...
Every spring manufacturer in existence talks in terms of spring frequency, wheel rate, motion ratio, and suspension geometry when spec'ing springs rates for a chassis. That is not to say that KW, or any other coil-over manufacturer, actually re-tools their manufacturing process for each specific chassis to produce an ideal product. You are in-large just getting a generic length and valved strut body with modified pickup points.

A quick google:
Hypercoil: https://www.hypercoils.com/spring-rate-calculator/
Koni: http://www.truechoicekoniracingservi.../worksheet.pdf
Eibach: https://eibach.com/america/p-101-sus...worksheet.html
Eibach: https://eibach.com/de/sites/default/...rings-EN_0.pdf

As a reference, spring rates for the E82/135i are:
BMW M sport = 120/350 lbs/in.
Dinan = 144/490.
Cobb = 148/457.
BMW performance = 160/420.
Swift Spec-R springs = 201/ 503.
Moton SS kit comes with 360 front and 620 rears
E92/M3 specific Swift Spec-R springs are 279/670.
F82/M4 specific Swift Spec-R springs are 279/726.

Seems to me that spring manufacturers have all spec’d springs to provide a ratio of at 1:2-1:3 to achieve a neutral effective wheel rate. Literally every car manufacturer in existence does the same. The question that you might be able to answer for us is... what do the German track bros know that BMW, Porsche, Mercedes, Eibach, swift, hypercoil, and others all don't? The math is just meaningless anyway, right?

Quote:
Originally Posted by frontside0815 View Post
I had both Setups already in my car (With OEM Roll bars and ST XTA Dampers (similiar to V2)) and both worked really well (besides the Problems going straight because of the PU Shit)....
NOTHING I SAID above means that I am saying you can’t mismatch the front and rear springs. Plenty of people do it and then work backwards to find ways to re-balance the chassis… What doesn’t make sense to me is that people aren’t willing to stiffen their rear springs but they are willing put in a stiffer sway bar to achieve the same goal. It makes 0 logical sense and goes against all conventional RWD traction wisdom. Not only is it harder to change the rear bar but you are also increasing the likelihood of lifting a drive wheel.

Ok, so let’s go back to OP’s issue. His car is understeering which means he is exceeding the grip available at the front tires. The answer here is not USUALLY to stiffen the rear (unless we are talking on-power exit understeer), as others have already stated and I never suggested he do that. That was a side conversation. What we really need to know from the OP is where in the corner is the understeer occurring?

OP can try the following (I am no expert, but this is based on what I have learned):

Some generic things:
• Lower the front ride height modestly if not already done so. A lower ride height = lower roll center = greater distance between COG and RC = more roll torque = more grip.
• Run stickier front tires
• Reduce the front track width (remove spacers) = lower roll center = more roll = more grip
• Increase rear track width (opposite of above). Less rear roll = more front load distribution. This is one of those “don’t take grip away from the opposite end” things though…
• Reduce front toe-in
• Decrease front tire pressures (I run 26-28psi cold and aim for <34psi hot).
• Decrease front spring rate (not suggested as you’ll introduce bind without making the springs longer and the ride height will be slammed).
• Decrease front sway bar rate. If OP has the stock sway bar in, he should do what I did and remove the stock sway bar mounts from the sway bar. With the mounts glued to the stock bar the bar can't pivot and it is also contributing to compression rate and not just roll rate.

Corner entry understeer:
• *Decrease rear rebound damping – Less rear damping = more weight shifting forward more quickly over the front wheels = more grip.
• *Decrease front Compression damping – More dive = more weight shifting forward more quickly over the front wheels = more grip.

*These recommendations assume weight transfer IS NOT already happening fast enough (OP stated he is running max rear rebound damping). If Weight transfer is already happening too fast, and under-steer is being caused by overloading the front tires, then you would want to do the opposite of this and INCREASE rear rebound to prevent the front tires from becoming overloaded under heavy braking.

See page 24/26 for a more in-depth explanation here: http://www.kaztechnologies.com/wp-co...ak-Updated.pdf

Corner exit understeer:
• Increase front rebound damping – Less rearward weight transfer = more front grip = less corner exit understeer.
• Increase rear compression damping – Less rearward weight transfer = more front grip = less corner exit understeer.

There are plenty of things that can be done to balance the car… Which one is best for OP will depend on his setup…
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Last edited by bbnks2; 02-14-2018 at 01:41 AM.
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      02-13-2018, 07:58 PM   #29
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Quote:
Originally Posted by bbnks2 View Post
OP stated he does not appear to have enough rear rebound damping to run a higher spring rate. I was pointing out that I can run a 900lb spring at 3/7 damping without issue. Does OP just have too much damping dialed in and he is riding on springs basically once the strut has been compressed? Or, does he have the rear springs preloaded? That would cause the return rate of the spring to be higher necessitating more rebound damping to control droop travel.

My rear springs are TCK 700lb-in 10" springs. I measured them last night, and at my specified ride height, there is MAYBE a 1/4" of pre-load on them. I measured just a hair under 10".

My comment about damping is gut instinct/reaction to the car's balance when playing with the shocks on track. I'll give 800lb, 10" springs a shot and see how it feels.


The car doesn't just under-steer because the front wheel rate is higher than the rear. You have to exceed the tires ability to maintain grip first. Driving style is the #1 contributing factor to causing ANY kind of traction loss. If you just cornered slower the car wouldn't break traction, right? Whether or not the aforementioned springs rates are “stiff” can be a bit subjective and is completely relative to the rest of the cars setup… ride height, tires, track width, alignment, damping, etc…

Agree to disagree here. Front traction, turn-in and balance all improved notably moving from a 400lb front spring to the 336lb spring. Obviously, if I just chuck the car into a corner and pray, that'll overload the front tires, but beyond that, if the general tendency of the car is understeer, it's a settings issue. This isn't my first track car, never had understeer issues with my Miata, 240sx, etc.


As a reference, spring rates for the E82/135i are:
BMW M sport = 120/350 lbs/in.
Dinan = 144/490.
Cobb = 148/457.
BMW performance = 160/420.
Swift Spec-R springs = 201/ 503.
Moton SS kit comes with 360 front and 620 rears
E92/M3 specific Swift Spec-R springs are 279/670.
F82/M4 specific Swift Spec-R springs are 279/726.

Ok, so let’s go back to OP’s issue. His car is understeering which means he is exceeding the grip available at the front tires. The answer here is not USUALLY to stiffen the rear (unless we are talking on-power exit understeer), as others have already stated and I never suggested he do that. That was a side conversation. What we really need to know from the OP is where in the corner is the understeer occurring?

Mid-corner, steady-state understeer. I can mitigate it on entry by slowing down (shocker), but understeer is the predominant cornering characteristic, right up until the very end of the exit where it'll oversteer on power out. Being a steady-state hanlding characteristic, that leads me to believe it's a suspension setup issue.

If OP has the stock sway bar in, he should do what I did and remove the stock sway bar mounts from the sway bar. With the mounts glued to the stock bar the bar can't pivot and it is also contributing to compression rate and not just roll rate.

Can you elaborate on this? During my many times pulling the bar, I've had to move the mounts around. They certainly aren't glued on/fixed on my bar. Additionally, I've shimmed the bar mounts to minimize binding.

There are plenty of things that can be done to balance the car… Which one is best for OP will depend on his setup…

This is a very Socratic discussion: the more I learn about suspension setup, the less I know.
Answers in bold. I know you've moved around to a bunch of different spring rates, however, when you tried the 4K and 5K front rates, how tall were your springs? Did you try an 8" spring? I bet it would have alleviated bind issues...
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      02-14-2018, 12:50 AM   #30
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Quote:
Originally Posted by Ginger_Extract View Post
Answers in bold. I know you've moved around to a bunch of different spring rates, however, when you tried the 4K and 5K front rates, how tall were your springs? Did you try an 8" spring? I bet it would have alleviated bind issues...
The stock springs were 4k and 240mm I think... So close to 9.5". That was fine. The issue was that I couldn't fit my 17x9 wheels. So, I then moved to a 4k 7" spring and the coil would bind just rolling around town. It was not driveable. The car was also sitting at around 4.125" ground clearance which was too low to get up on to a standard alignment rack. No good. Therefore, I moved to a stiffer 6k spring which gained back some bump travel and ride height. Moving to a longer than 7" spring in order to run a softer spring rate is out of the question for me since the spring perch would then be into the tire.

As for the sway bar, the mount bushings were molded to my sway bar. I had to heat them up and cut them off. Now the bar is free from bind for me...

Last edited by bbnks2; 02-15-2018 at 10:47 AM.
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      02-14-2018, 04:02 AM   #31
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Sorry for Offtopic, hope it´s ok since it is still somehow connected to the original Topic.

Quote:
Originally Posted by bbnks2 View Post
I cannot find a single vendor of 135i KW Clubsports that provide a ~400lb (80N/mm) rate as the stock rear rate offered. They all list the rear rate as 600-800lb/in (105-140N/mm).…
I don´t know where you are looking, but KW is a german Company and after i had that much Problems with my car with the PU Bushings in the toe arm i called almost every german coilover Producer to have a talk with them what spring rates they use.

I am 100% percent sure, that the spring rates for the 135i KW Clubsport 2 Way with Uniball Camber Plates in the front are:

Front 70N/mm, Rear 80N/mm (in the rear there isn´t a linear spring but a progressive one, so the 80N/mm is the middle value of the spring).

The Setup for 1 M-Series and M3 from KW for the Clubsport is 110N/Mm in the Front and 120N/mm in the rear (here the rear has a linear spring and a helper spring).

I know a lot of cars which got a Setup from Raeder Motorsport, which is a famous Workshop around the Nurburgring.
On one 335I for Example they installed 110N/mm in the front and 80N/mm in the rear (with KW Clubsport Dampers). So almost exactly the other way around most of you guys are stating.

Also Öhlins uses 60 and 70N/mm F/R for their Road & Track Version for the AG Model 135/335i.

Bilstein Clubsport have the same odd rates...

I will try to install a 120N/mm spring in the year just to see how the car will behave with them installed.

What i just don´t get ist how can most of the cars here in Germany (and i talk about most n54 powered cars, not e36 or others) run in your opinion such a wrong spring rate Balance?
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      02-14-2018, 09:17 AM   #32
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Quote:
Originally Posted by frontside0815 View Post
What i just don´t get ist how can most of the cars here in Germany (and i talk about most n54 powered cars, not e36 or others) run in your opinion such a wrong spring rate Balance?
I asked you for that answer... you give me one logical reason for doing it. I've already spend hours typing out the logical reasoning for NOT wanting to do it. Your only rebuttal appears to be "but all the cool kids in Germany do it."
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      02-15-2018, 03:36 AM   #33
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You Sound so offensive, i don´t want to offend anybody just to say :-)!

I really don´t know any reason for it, what i know is that the most cars using this Balance are really fast (07.30 NOS BTG) and that KW theirself uses this rates. And i highly doubt that KW uses These rates without a reason or because they drive so bad?

I just want to understand why
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      02-15-2018, 09:20 AM   #34
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Quote:
Originally Posted by frontside0815 View Post
You Sound so offensive, i don´t want to offend anybody just to say :-)!

I really don´t know any reason for it, what i know is that the most cars using this Balance are really fast (07.30 NOS BTG) and that KW theirself uses this rates. And i highly doubt that KW uses These rates without a reason or because they drive so bad?

I just want to understand why
I don't know, but maybe that is why so many people complain about under-steer on this chassis

Maybe they run a really staggered tire setup? Maybe they've just compensated for it with driving style? Maybe they run a lot of rake? Too many variables to say... Like I already said, you can combine 20 different other tweaks to get the car balanced back out. Tweaks you wouldn't have to do if you just started with a neutral base...
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Last edited by bbnks2; 02-15-2018 at 09:47 AM.
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      02-17-2018, 04:41 AM   #35
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UUC has a weekend sale going on, so I bit the bullet and ordered the 19mm rear bar. It's going to suck to install, but hopefully it fixes the issue.
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      02-17-2018, 05:06 PM   #36
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This is the most peculiar thread. I wonder how many people actually drive their cars competitively / at the grip limit versus just reading other people's posts and regurgitating the same bad information.
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      02-17-2018, 08:18 PM   #37
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Originally Posted by RyanDavies View Post
This is the most peculiar thread. I wonder how many people actually drive their cars competitively / at the grip limit versus just reading other people's posts and regurgitating the same bad information.
None of us. We don't even own cars at all. Thank god you're here.
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      02-17-2018, 10:17 PM   #38
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Originally Posted by RyanDavies View Post
This is the most peculiar thread. I wonder how many people actually drive their cars competitively / at the grip limit versus just reading other people's posts and regurgitating the same bad information.
So, where is all this good information that you can provide in response to the op? Did you even read the thread?
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      02-18-2018, 12:57 PM   #39
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Originally Posted by bbnks2 View Post
So, where is all this good information that you can provide in response to the op? Did you even read the thread?
There's a littany of information all around the internet about target suspension frequencies for balance.

I ran the car on several different rates. I started with 400/850 w/stock rear bar and a reasonable front (27mm adjustable). It was such horrific push I can't possibly describe. Those who aren't experiencing it are simply underdriving the car, period. Kyle warned me about it when I mentioned wanting to try it (he ended up at 400/700 with a 19mm rear bar and slightly softer front than me), but it was still there, very badly. I switched to 575/1200 (because the car was rolling well out of its camber curve up front as well), and went to a 20mm rear bar). It was much, much better. I've switched shocks and don't campaign the car very much anymore. I'm at 450/850 with a 20mm rear bar and 27mm front bar.

Even at 575/1200, the car rolls a LOT because of how bad the motion ratio is in the back, it's hardly any wheel rate at all. The stock spring rates for the car are biased nearly 3x (160/420). Yet it still pushes pretty badly. Just adding a mountain of camber does not solve this. It's a wheel rate of 150/135, because of the motion ratio. I would use as a starting point a similar wheel rate target if you want to keep the stock rear bar. So, starting with a 400lb spring, you're looking for a wheel rate of around 320lbs, or a 1000lb spring. Of course, after going to a larger front bar, you'll want to add the requisite rear rate to compensate for it. I ran the numbers to keep my balance on 450 fronts with a stock rear bar, and it required (I think) around a 1350lb spring. That's why people add bar / run a lot of spring. Look up the OEM M3 rear sway bar size and you'll see that a lot of the justification on here makes very little sense unless you're keeping the open diff. It's substantially larger than what either of us ran.
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      02-18-2018, 04:24 PM   #40
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Originally Posted by RyanDavies View Post
There's a littany of information all around the internet about target suspension frequencies for balance.

I ran the car on several different rates. I started with 400/850 w/stock rear bar and a reasonable front (27mm adjustable). It was such horrific push I can't possibly describe. Those who aren't experiencing it are simply underdriving the car, period. Kyle warned me about it when I mentioned wanting to try it (he ended up at 400/700 with a 19mm rear bar and slightly softer front than me), but it was still there, very badly. I switched to 575/1200 (because the car was rolling well out of its camber curve up front as well), and went to a 20mm rear bar). It was much, much better. I've switched shocks and don't campaign the car very much anymore. I'm at 450/850 with a 20mm rear bar and 27mm front bar.

Even at 575/1200, the car rolls a LOT because of how bad the motion ratio is in the back, it's hardly any wheel rate at all. The stock spring rates for the car are biased nearly 3x (160/420). Yet it still pushes pretty badly. Just adding a mountain of camber does not solve this. It's a wheel rate of 150/135, because of the motion ratio. I would use as a starting point a similar wheel rate target if you want to keep the stock rear bar. So, starting with a 400lb spring, you're looking for a wheel rate of around 320lbs, or a 1000lb spring. Of course, after going to a larger front bar, you'll want to add the requisite rear rate to compensate for it. I ran the numbers to keep my balance on 450 fronts with a stock rear bar, and it required (I think) around a 1350lb spring. That's why people add bar / run a lot of spring. Look up the OEM M3 rear sway bar size and you'll see that a lot of the justification on here makes very little sense unless you're keeping the open diff. It's substantially larger than what either of us ran.
So you agree with everything said in the thread lol...

Is the M3 rear sway hollow like the front?
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      02-19-2018, 08:26 AM   #41
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So you agree with everything said in the thread lol...

Is the M3 rear sway hollow like the front?
I will say that I think the posts *you* have made are fine.

Suggestions like running mega-soft front rates and unhooking the front bar on a car with a miserable camber curve to begin with. Suggestions that "OMG these consumer level coilovers for the street have softer rear rates so that's optimal!" Suggestions that because a shock can jack down a spring it's great for a given spring? Come on...

And for some reason people here continue to suggest mega-soft rates. I'm sure I know why, because they're running pretty awful cheap dampers without even bothering to look at a shock dyno, and wonder why the car rides poorly, so soften the springs as a band-aid.

The way I see it, there are two reasonable options to balance the car, run a lot of rear spring (which again, looking at wheel rates, isn't that much), or run something like the 20mm bar I have, the 19mm UUC bar Kyle has, or an OEM M3 rear bar (the route I'd go now if I were developing the car). The vert bar is larger than the sedan/coupe bar.

Given the front camber curve, I would run as stiff as one reasonably could up front for a given surface while still maintaining some semblance of compliance. The front of the car is also really limited on static camber (the highest numbers I'm aware of were in the mid/high-3s for Kyle, and I don't know that many others have been able to get there. When I had the JRZ plates, I also had offset bushings and was at mid-3s. Still not really enough. It was okay on RE71s as they don't seem to want as much camber as other tires, but if I'd run BFGs or a Hoosier on the car, I'd be doing everything I can to maintain camber in roll / increase static camber. The rear of the car is basically the exact opposite, in that it gains a ton of camber in roll, so you really don't need very much back there (especially with these soft rear rates, the rear will compress a ton, I know Kyle has some picture of the rear wheel totally buried in the well in Pittsburgh).

This picture was on 575/1200, and it is still rolling a ton, and you can see the deflected front tire going positive even with ~3.4 degrees of camber.

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      02-20-2018, 08:35 AM   #42
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Oh, you mean this one? Granted, this was cause of a massive dip/bump...but yea, that shock did compress probably to it's full extent lol



I like this one as well.

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      02-20-2018, 09:34 AM   #43
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That looks like exactly the type of parking lot that I would want to run big sway bars in
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      02-20-2018, 11:00 AM   #44
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That looks like exactly the type of parking lot that I would want to run big sway bars in
Yea, you know running on 50 acres of concrete padding next to an active runway really sucks.
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