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Old 09-18-2020, 09:20 AM   #1
GothamDrew
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Default 2020 STI Swaybar Size and Recommendation

Hi all, I read though the stickies and searched but most of the info I found on sway bars were on 2017 STI's and older and I want to make sure I'm getting this right as I have a 2020 and don't know if things and sizes got changed. I'm looking to dial out some of the sway (lean) on my STI when turning. I don't autocross but do like to have a more flat car when cornering in daily driving.

1) Does anyone know the exact sizes of the front and rear sway bars on the 2020 STI?

2) Which aftermarket rear sway bar size will provide the most neutral handling on stock suspension on the 2020 STI? Why didn't Subaru include a larger rear sway from the factory if the car Under-steers? Is it to allow the car to rotate better into a turn?

3) Can you recommend brands for an upgraded rear sway?

Thank you all for taking the time!
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Old 09-18-2020, 09:25 AM   #2
JP Chestnut
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The car under steers because about 60% of the weight hangs over the front axle. A stiffer rear bar doesn’t change that dynamic. It just lowers rear grip so you notice it less.

Messing around with sway bars for a street only car is a bad idea.
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Old 09-18-2020, 09:31 AM   #3
standardtranny
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I've got the 24mm whiteline rear swaybar, endlinks, and bracing set on medium stiffness. I quite like it but I've also got other stiffer bushings etc
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Old 09-18-2020, 11:13 AM   #4
gtsilver944
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Front sway is the same for all years on the VA at 24mm. Rear was originally 20mm then was reduced to 19mm.

While 24mm rear bars felt balanced with the same size up front on pre-2015 cars, it causes inner rear wheel lift on 15+. Consider an adjustable 22 mm.

Whiteline rusts. I'd go with any other brand.
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Old 09-18-2020, 03:10 PM   #5
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Quote:
Originally Posted by JP Chestnut View Post
Messing around with sway bars for a street only car is a bad idea.
This may be applicable to you, but is not a true statement at all.

Even if you keep with the standard OEM suspension bits ( struts, bushings, etc. ) a change in sway bars can have a dramatic positive improvement in handling.

It all depends in the appropriate choice in matching sway bars for the particular car.

Adjustable bars give you the option of buying multiple bars in one.
- Try one setting and if that doesn't get you what you want, try another setting.
- Something like a 22mm adjustable rear sway bar will allow you to have a 20mm / 22mm / 24mm all in one. You just change the position of the endlink in the sway bar.

As was mentioned, stiffer bushings and better endlinks / endlink mounts will also improve your handling.
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Old 09-18-2020, 03:13 PM   #6
murrdogg24
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that's like your opinion man...
Quote:
Originally Posted by JP Chestnut View Post
The car under steers because about 60% of the weight hangs over the front axle. A stiffer rear bar doesn’t change that dynamic. It just lowers rear grip so you notice it less.

Messing around with sway bars for a street only car is a bad idea.
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Old 09-22-2020, 01:55 PM   #7
GothamDrew
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Thanks all!
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Old 09-22-2020, 02:06 PM   #8
JP Chestnut
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Quote:
Originally Posted by Samurai Jack View Post
This may be applicable to you, but is not a true statement at all.

Even if you keep with the standard OEM suspension bits ( struts, bushings, etc. ) a change in sway bars can have a dramatic positive improvement in handling.

It all depends in the appropriate choice in matching sway bars for the particular car.

Adjustable bars give you the option of buying multiple bars in one.
- Try one setting and if that doesn't get you what you want, try another setting.
- Something like a 22mm adjustable rear sway bar will allow you to have a 20mm / 22mm / 24mm all in one. You just change the position of the endlink in the sway bar.

As was mentioned, stiffer bushings and better endlinks / endlink mounts will also improve your handling.
If you're messing around with sway bars before optimizing your choice of tires and front/rear alignment, then you're putting the cart before the horse. That might be popular with the vaper crowd, but nobody who's serious and knowledgeable about getting a car to handle messes with sway bars on a bone stock car.

Even some highly competitive stock class AX racers don't swap their sway bars (though lots do, after sorting out the suspension). Boubly so if it's a dual purpose car that gets driven on the street.

Here's a decent thread talking about this from the point of view of people who actually care about performance, not "feel":
https://grassrootsmotorsports.com/fo.../127524/page1/
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Old 09-22-2020, 04:09 PM   #9
Samurai Jack
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Quote:
Originally Posted by JP Chestnut View Post
If you're messing around with sway bars before optimizing your choice of tires and front/rear alignment, then you're putting the cart before the horse. That might be popular with the vaper crowd, but nobody who's serious and knowledgeable about getting a car to handle messes with sway bars on a bone stock car.
That's not what you said.

You said, " Messing around with sway bars for a street only car is a bad idea. "
Totally incorrect statement.

And, you are still incorrect when you say you have to optimize your tire / alignment settings BEFORE you upgrade sway bars. Totally untrue.

We are talking street cars here, not optimized track cars.

That's why companies make adjustable sway bars.
Adjustable sway bars allow you to change the sway bar characteristics, if necessary, when / if you change tires and / or alignment. You can make them softer or stiffer or combination of both.

You actually need to know how to drive a car to make appropriate changes to get the most out of your suspension bits.

From personal experience:
I chose adjustable front and rear sway bars.
I set the bars at the settings I determined were best for my set up. Major handling improvements.

Years later, I upgraded wheels / tires. Never had to change settings.
Years later, I upgraded to coil-overs. Never had to change settings.
Changed additional suspension pieces to adjust for proper alignment with lowered car.

Never had to change settings.
The whole time car was very neutral and, if I wanted, I could easily bring the end around in a controlled manner.

Reading only gets you so far. Actual hands-on is where it's at.

Last edited by Samurai Jack; 09-23-2020 at 08:52 AM.
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Old 09-23-2020, 09:15 AM   #10
Norm Peterson
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Quote:
Originally Posted by JP Chestnut View Post
The car under steers because about 60% of the weight hangs over the front axle. A stiffer rear bar doesn't change that dynamic. It just lowers rear grip so you notice it less.
This much is kind of a half-truth.

Understeer is a 'balance' concept that considers far more than a car's static weight distribution. Mathematically, it's the difference between front and rear tire slip angles, where the front tires are operating at higher slip angles than the rear tires are.

You can shift this balance by any of several means, but tinkering with sta-bar stiffnesses is one of the more effective methods. No matter whether it's a race car, or a dual purpose street/HPDE or street/autocross car, or just a regular old street-only car.

Keep in mind that pretty much by definition, an understeering car has a surplus of rear tire grip. Meaning that there's rear grip you just can't get at because the front tires will have limited you before you could get there. So yeah, you're throwing away some potential rear grip (this is the part you sort of did get right) . . . grip that's theoretically there but not usable. So there's no harm in trading grip you can't even get at, for a little more rear slip angle that'll reduce the understeer.


Quote:
Messing around with sway bars for a street only car is a bad idea.
No, messing around with bars (or anything else in the suspension) is a bad idea when you don't understand the tech behind what you're doing. Or when you don't even suspect that real engineering tech is involved.


Norm

Last edited by Norm Peterson; 09-23-2020 at 09:22 AM.
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Old 09-23-2020, 09:57 AM   #11
Ferretts
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I would venture a guess that 95% of y'all would crap your pants and crash if you encountered oversteer on the street.
Honestly money spent on a sway bar, bushings, coilovers, etc... would go 10x as far if spent at dirt fish, boundurant, or any other reputable driving school.
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Old 09-23-2020, 10:37 AM   #12
Norm Peterson
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Quote:
Originally Posted by Ferretts View Post
I would venture a guess that 95% of y'all would crap your pants and crash if you encountered oversteer on the street.
Oversteer on the street will definitely get your attention. Best be on your A-game to keep it from doing any more than that.


Quote:
Honestly money spent on a sway bar, bushings, coilovers, etc... would go 10x as far if spent at dirt fish, boundurant, or any other reputable driving school.
Probably true, though outside the expense of decent coilovers and having to pay somebody else to install everything I'm not sure how much Bondurant/Skip Barber/etc. that same money would buy.

Performance driving schools are the best (and fastest) way to learn performance driving. Not the only way, but clearly the best way. For us older guys, instructed performance driving wasn't nearly as available early-on in our driving lives as it is for today's crop of younger drivers.


Norm
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Old 09-24-2020, 09:22 PM   #13
Denver1357
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I used the SuperPro sway bars and their end links along with their stiffening kit.
The front bar is a 26 mm diameter and the rear is a 24 mm diameter with the front set on soft and the rear on medium. That is the end hole on the front and the middle hole on the rear for the mounting points of the end links.

The quality of the kit is excellent! Nice, heavy coating with quality fasteners all around, you won't be disappointed. I purchased them from Geoff at Cygnus Performance and I was pleased with his service and price.

Word of caution, if you go this route, take care on the first drive as the handling is much improved and quite different from what it was. Work your way up to the max level.

Post back with your observations.
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Old 09-25-2020, 07:23 AM   #14
Norm Peterson
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Quote:
Originally Posted by Denver1357 View Post
Word of caution, if you go this route, take care on the first drive as the handling is much improved and quite different from what it was. Work your way up to the max level.
Good advice no matter what you do to your car's suspension. Or its wheels and tires, for that matter.

Better for any surprises to be little than . . . not so little.


Norm
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Old 10-07-2020, 01:11 PM   #15
GothamDrew
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Quote:
Originally Posted by Samurai Jack View Post
That's not what you said.

You said, " Messing around with sway bars for a street only car is a bad idea. "
Totally incorrect statement.

And, you are still incorrect when you say you have to optimize your tire / alignment settings BEFORE you upgrade sway bars. Totally untrue.

We are talking street cars here, not optimized track cars.

That's why companies make adjustable sway bars.
Adjustable sway bars allow you to change the sway bar characteristics, if necessary, when / if you change tires and / or alignment. You can make them softer or stiffer or combination of both.

You actually need to know how to drive a car to make appropriate changes to get the most out of your suspension bits.

From personal experience:
I chose adjustable front and rear sway bars.
I set the bars at the settings I determined were best for my set up. Major handling improvements.

Years later, I upgraded wheels / tires. Never had to change settings.
Years later, I upgraded to coil-overs. Never had to change settings.
Changed additional suspension pieces to adjust for proper alignment with lowered car.

Never had to change settings.
The whole time car was very neutral and, if I wanted, I could easily bring the end around in a controlled manner.

Reading only gets you so far. Actual hands-on is where it's at.
Great info, thanks!
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Old 10-07-2020, 01:14 PM   #16
GothamDrew
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Quote:
Originally Posted by Denver1357 View Post
I used the SuperPro sway bars and their end links along with their stiffening kit.
The front bar is a 26 mm diameter and the rear is a 24 mm diameter with the front set on soft and the rear on medium. That is the end hole on the front and the middle hole on the rear for the mounting points of the end links.

The quality of the kit is excellent! Nice, heavy coating with quality fasteners all around, you won't be disappointed. I purchased them from Geoff at Cygnus Performance and I was pleased with his service and price.

Word of caution, if you go this route, take care on the first drive as the handling is much improved and quite different from what it was. Work your way up to the max level.

Post back with your observations.
Awesome, thanks!
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Old 10-07-2020, 05:57 PM   #17
Norm Peterson
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'08 Mustang GT (the toy)

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Quote:
Originally Posted by GothamDrew View Post
Hi all, I read though the stickies and searched but most of the info I found on sway bars were on 2017 STI's and older and I want to make sure I'm getting this right as I have a 2020 and don't know if things and sizes got changed. I'm looking to dial out some of the sway (lean) on my STI when turning. I don't autocross but do like to have a more flat car when cornering in daily driving.
What are you comparing your 2020 against, as far as the amount of roll goes? Are you driving your 2020 harder in the corners than you did in whatever came before it?

What I'm getting at here is that you're likely to be noticing the difference from before rather than any absolute amount of roll.

There's nothing wrong with a street driven car letting its suspension move when you pick up the pace through a curve. Truth is, reducing roll rapidly gets into the land of diminishing returns, where each additional drop of 0.1° per g of roll requires increasing amounts of added roll stiffness. About here, you need to start thinking about how much deterioration in ride quality you're really willing to accept.

Even on the track at 1+ g cornering, a basic roll rate of around 2°/g is not unreasonable and if you're focused on your line and your driving you might not even notice it most of the time. That may take a bit of acclimatization, which probably comes easier to some than to others.

Even this much roll doesn't have to be bothersome, although I did at least notice it.




A 2°/g car looks more like this. There's about another half degree per g coming from changing tire deflections as load is transferred off the inside tires onto the outside ones that no amount of additional roll stiffness can reduce. There isn't much load on either right side tire.





Quote:
2) Which aftermarket rear sway bar size will provide the most neutral handling on stock suspension on the 2020 STI? Why didn't Subaru include a larger rear sway from the factory if the car Under-steers? Is it to allow the car to rotate better into a turn?
Like all OEMs, Subaru has to tune the handling of their sedans to be at least mildly understeerish. It's a little extra designed-in safety margin mainly for the benefit of less skilled drivers that can potentially benefit most of us at one time or another under unusual circumstances. Even Randy Pobst (a nationally recognized professional race car driver) prefers light understeer to oversteer.

A truly neutral car would most likely feel too "loose" (circle track-speak for oversteer because that's what it feels like) for most people, certainly initially. And if you're careless or un-smooth with the pedals, you'd be likely to find out what oversteer is like.


Norm

Last edited by Norm Peterson; 10-08-2020 at 07:01 AM.
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