RSB: Eibach 22 mm vs. OEM 18 mm Si

Which rear sway bar?

  • Si OEM 18 mm

    Votes: 23 35.9%
  • Eibach 22 mm

    Votes: 41 64.1%

  • Total voters
    64

hobby-man

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Which do you guys think is best for a daily driver who has opportunities for more "spirited" bits along his commute? I'm leaning towards the Eibach but wondering if it's too aggressive for daily driving (I'd use the soft setting).

I also plan to install Eibach pro springs along side the RSB upgrade.
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hobby-man

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@gtman thoughts on this? You seem to be our resident expert on strut bars / sway bars :p
 
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hobby-man

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herox

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I thought the Si/Type R bar was solid vs Eibach which is tubular? I imagine the sizes don't correlate. Or am I mistaken?
TBH I have no clue how the Eibach compares to the SI/R bars. On this forum the FK7 owners with the SI bar are happy and a couple people with the R bar have said it was too much. Since you mentioned this is for your daily driver with no mention of autocross I voted for the SI bar. It's a safe choice and you'll get better performance.

https://www.onallcylinders.com/2017/04/25/video-strength-testing-hollow-vs-solid-sway-bars/
 


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I ran the Si RSB for about 10 months and recently switched to a Progress RSB (20.6mm) and while the Si difference was nice and a little sportier the Progress is the one I should've went for from the beginning. The 20mm sway bar gives a solid amount of rear rotation which makes the car feel more balanced during harder turns rather than pushing through the turns (understeer). Honestly for daily driving the Si bar is a perfect mix of performance and usability but if you want the extra edge a Type R or Progress size bar is a great choice
 
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hobby-man

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I ran the Si RSB for about 10 months and recently switched to a Progress RSB (20.6mm) and while the Si difference was nice and a little sportier the Progress is the one I should've went for from the beginning. The 20mm sway bar gives a solid amount of rear rotation which makes the car feel more balanced during harder turns rather than pushing through the turns (understeer). Honestly for daily driving the Si bar is a perfect mix of performance and usability but if you want the extra edge a Type R or Progress size bar is a great choice
TBH I have no clue how the Eibach compares to the SI/R bars. On this forum the FK7 owners with the SI bar are happy and a couple people with the R bar have said it was too much. Since you mentioned this is for your daily driver with no mention of autocross I voted for the SI bar. It's a safe choice and you'll get better performance.

https://www.onallcylinders.com/2017/04/25/video-strength-testing-hollow-vs-solid-sway-bars/
OK guys...math time. Found this info on another forum combined with a sway bar thread here. I think I have this right.

To find the stiffness factor (SF) of a solid swaybar you take the 4th power of the outer diameter of the bar. This means the SF of the Si bar (19mm)^4 = 130321 and SF of the hatchback bar (16.5mm)^4 = 74120.

Simple ratios tell us that the Si bar is therefore 76% stiffer than the hatchback bar.

Now, the Eibach is a 22mm tubular bar. With these, the SF is the bar's inner diameter (ID) to the fourth power subtracted from the bar's outer diameter (OD) to the fourth power. To do this you need the thickness measurement of the bar wall. We'll guess it at 1 mm, 1.5 mm, and 2 mm. Because I have no idea. The ID is simply the OD - 2*wall thickness.

This gives us OD = 22 mm and potential IDs of 20mm, 19mm, and 18 mm.

So the SF range for the Eibach would be (OD)^4 - (ID)^4 = (22^4) - (18^4) and (22^4) - (20^4) = 74256 - 129280.

At the low end (1 mm wall), it is pretty much exactly as stiff as the stock hatchback bar. This is unlikely. At the high end (2 mm wall), it is 74% stiffer than the hatchback bar and actually 1% less stiff than the Si bar.

All this being said, it seems like there's very little difference between a 19 mm solid bar and a 22 mm tubular bar, depending on the thickness of the tubular bar's wall. I'd like to find out what the wall thickness is from Eibach. The OEM Si bar may just be the safer choice then rather than all this guessing :p
 
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JO3L

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@hobby-man Thank you for the analysis. Upon reviewing your math you forgot to multiply the wall thickness by 2 when calculating ID and also the OEM Si bar is 18mm not 19mm so (18mm)^4 = 104,976 SF. Feel free to check my math.

Base= 16.5mm solid = 74,120 Stiffness factor
Si= 18.0mm solid = 104,976 Stiffness factor
CTR= 20.5mm solid = 176,610 Stiffness factor

Eibach 22mm tubular bar - using 1mm wall thickness
22mm^4 = 234,256 SF
(1.0mm) x 2 = 2.0 mm
22mm - 2mm = 20mm

20mm is our inner diameter so...
20^4 = 160,000 SF

Putting it all together
234,256 SF - 160,000 SF = a stiffness factor of 74,256 for a hollow bar of a 22mm outer diameter and 1mm wall thickness. This represents a 41% DECREASE in stiffness for the Si and a 0.1% increase in stiffness for the base models.


Now lets look at this again with a different wall thickness.

Eibach 22mm tubular bar - using 1.5mm wall thickness
22mm^4 = 234,256 SF
(1.5mm) x 2 = 3.0 mm
22mm - 3mm = 19mm

19mm is our inner diameter so...
19^4 = 130,321 SF

Putting it all together
234,256 SF - 130,321 SF = a stiffness factor of 103,935 for a hollow bar of a 22mm outer diameter and 1.5mm wall thickness. This represents a very slight 1% DECREASE in stiffness over the Si bar and a 28% increase for the base models.

I think this is very informative for people, because most people just jump to conclusions thinking bigger diameter = more stiffness and not realize they are comparing two completely different products in the OEM solid rear sway vs. aftermarket tubular bar. Most companies making tubular bars will use the thinnest wall thickness possible to maximize the weight savings of a tubular bar over solid. That is why I only used 1.0 and 1.5mm wall thickness in my example. Without knowing the true wall thickness of the Eibach bar it is hard to say with certainty, but to me it looks like it was designed for the base model Civics only.

Did you ever end up upgrading your rear sway?

I am running the 22mm Whiteline solid bar on my Si and think it still isnt a big enough bar. Using their sway bar stiffness chart this represents a 123% increase for the Si guys and approximately 257% increase for the base models.
https://www.whiteline.com.au/docs/bulletins/Update BL-281.pdf

People complaining about the FK8 20.5 mm rear bar giving them oversteer on their lower level Civics I think need to get their alignments checked that they arent running any toe out in the rear first. Or step up to a grippy low tread wear tire with a way higher slip angle and stop trying to be a street racer on 500+TW all season tire.

EDIT: So after review I found out a popular Mazda shop, Racing Beat, sells tubular bars for Miatas with wall thickness of 0.125"/3.175mm and also 0.188"/4.77mm. I would be surprised if Eibach's tubular bars were any less than 2mm wall thickness. This exercise was to point out the fact that when it comes to tubular bars you really don't know what you are getting unless the manufacturer is stating these types of things from the start. To avoid confusion sometimes its best to just stick to a solid bar if that is the type that is equipped from the factory.
 
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hobby-man

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@hobby-man Thank you for the analysis. Upon reviewing your math you forgot to multiply the wall thickness by 2 when calculating ID and also the OEM Si bar is 18mm not 19mm so (18mm)^4 = 104,976 SF. Feel free to check my math.

Base= 16.5mm solid = 74,120 Stiffness factor
Si= 18.0mm solid = 104,976 Stiffness factor
CTR= 20.5mm solid = 176,610 Stiffness factor

Eibach 22mm tubular bar - using 1mm wall thickness
22mm^4 = 234,256 SF
(1.0mm) x 2 = 2.0 mm
22mm - 2mm = 20mm

20mm is our inner diameter so...
20^4 = 160,000 SF

Putting it all together
234,256 SF - 160,000 SF = a stiffness factor of 74,256 for a hollow bar of a 22mm outer diameter and 1mm wall thickness. This represents a 41% DECREASE in stiffness for the Si and a 0.1% increase in stiffness for the base models.


Now lets look at this again with a different wall thickness.

Eibach 22mm tubular bar - using 1.5mm wall thickness
22mm^4 = 234,256 SF
(1.5mm) x 2 = 3.0 mm
22mm - 3mm = 19mm

19mm is our inner diameter so...
19^4 = 130,321 SF

Putting it all together
234,256 SF - 130,321 SF = a stiffness factor of 103,935 for a hollow bar of a 22mm outer diameter and 1.5mm wall thickness. This represents a very slight 1% DECREASE in stiffness over the Si bar and a 28% increase for the base models.

I think this is very informative for people, because most people just jump to conclusions thinking bigger diameter = more stiffness and not realize they are comparing two completely different products in the OEM solid rear sway vs. aftermarket tubular bar. Most companies making tubular bars will use the thinnest wall thickness possible to maximize the weight savings of a tubular bar over solid. That is why I only used 1.0 and 1.5mm wall thickness in my example. Without knowing the true wall thickness of the Eibach bar it is hard to say with certainty, but to me it looks like it was designed for the base model Civics only.

Did you ever end up upgrading your rear sway?

I am running the 22mm Whiteline solid bar on my Si and think it still isnt a big enough bar. Using their sway bar stiffness chart this represents a 123% increase for the Si guys and approximately 257% increase for the base models.
https://www.whiteline.com.au/docs/bulletins/Update BL-281.pdf

People complaining about the FK8 20.5 mm rear bar giving them oversteer on their lower level Civics I think need to get their alignments checked that they arent running any toe out in the rear first. Or step up to a grippy low tread wear tire with a way higher slip angle and stop trying to be a street racer on 500+TW all season tire.

EDIT: So after review I found out a popular Mazda shop, Racing Beat, sells tubular bars for Miatas with wall thickness of 0.125"/3.175mm and also 0.188"/4.77mm. I would be surprised if Eibach's tubular bars were any less than 2mm wall thickness. This exercise was to point out the fact that when it comes to tubular bars you really don't know what you are getting unless the manufacturer is stating these types of things from the start. To avoid confusion sometimes its best to just stick to a solid bar if that is the type that is equipped from the factory.
Hey man, great work. I took a long break from the forum but am back now with a vengeance :headbang:

I've not yet upgraded my RSB, but it is imminent. Still weighing all these options!
 

Fit2Hatch

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For my Hatch, SI RSB improvement was slight, so it was a waste of money!

Now, I found Whiteline 22mm more suite my taste.

Both combo ran with Rays 57CR + Michelin PS4S.
 


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Wondering if the Eibach type r rear sway bar could be a good option.. 25mm tubular design?
 

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Hey man, great work. I took a long break from the forum but am back now with a vengeance :headbang:

I've not yet upgraded my RSB, but it is imminent. Still weighing all these options!
Thanks to you also for starting this. I was led deep down the rabbit hole as you can tell.
 

Josehern10

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Wondering if the Eibach type r rear sway bar could be a good option.. 25mm tubular design?
I am also wondering the same thing! Did you ever end up getting the bar? I actually just ordered one today.. found it at a great price, so went ahead with it. If you don't have it yet or haven't heard any feedback, I will let you know!
 

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I ran the stiffer setting on the eibach rsb and it was hardcore. Snap overstear and rotating on corners easily. I was shocked. On the B hole it's just right. I wonder what the lbs raiting on the 2 holes. There was a thread that had all the sway bar specs OEM and aftermarket I can't find...
 

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One factor is the rear sway bar binding, which momentarily increases rear spring rate and results in oversteer. I have a Type R bar on my SI and for autocross, it’s perfect. For track cross or track work, I swap back to the factory SI bar.

I bring this up because the factory end links don’t really work well for other RSBs. I like the loose rear end for autoX, but it’s too loose. Definitely budget for adjustable end links for you can fully tune the bar.
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