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2G GST upgrade rear sway bar or both

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TehRiceBandit

Proven Member
317
52
Dec 12, 2013
Bay Area, California
Hey, I picked up some RM sway bars for cheap (2G FWD front + rear). I've read some conflicting information and was looking for some input. Would the best course be

A) Upgrade the rear only to reduce understeer
B) Upgrade both to decrease body roll

Thanks

Yes. I've used the search button.
 
I ran just a rear STRUT bar for a few weeks on my GST. (DC Sports hard bar)

It was really fun. You could feel the handling characteristics change for the better. I then threw on the front and it balanced the car.

The car is stable as hell but the "feel" that the rear only gave me had basically been relegated to a more all around car stability. Not a bad thing. I still have grip for days.

This is my STRUT bar first hand though. I have yet to do SWAY bars so I'm not totally sure my experience is completely relevant.

Your best bet would be to throw the rear on first, like I did, drive it around, see how the car is acting and then put the front on. You will be better able to feel for yourself how YOUR car likes it.

I say "your" car because even though I respect your inquiry of the topic at hand, there are so many suspension variables to even say THIS IS THE WAY IT WILL BE. Tires, bushings, shocks/struts, springs/coilovers, will all play a huge part in the out come of every individuals own conclusion.

So in the long short....your gonna have to play with your car :( I know right, sounds like a drag.

Have fun with it.
 
I say rear only, more fun. Car will obviously understeer less as you mentioned. Maybe more in regards to what the plans are for the car how often it sees track OR auto-x (stability vs tight corners and needing more rear slip comparatively). If it mostly sees street or auto-x I'd go rear only but if you are hitting Laguna seca or willow frequently I'd say both. Better yet, bring jackstands and a jack and try both and rear only on the track and see what YOU personally like.
 
Best advice (IMO) is to understand your goals. If your goal is arm-chair racing, then a nice RED sway-bar in front, and a GREEN one in the back will be best. Mixing colors for the urethane bushings F/R will also help tremendously.

Jesting aside, it takes a bit of "vehicle dynamics" understanding to know what you want. A SWAY-BAR = ROLL-BAR = STA-BAR... EXCEPT for the logic behind the language.

Sway-bars & roll-bars... These are terminology used... commonly for body-roll-control.
Sta-bar (Stabilizer-bar)... This terminology is much more precise (for the same chunk of steel) and might seem to indicate "stabilizing the vehicle."

Most people think of a BAR connecting suspension-corners left to right as a means to control vehicle roll... and to a sense it does. BUT as your BODY-ROLLs...during lateral-acceleration... that bar twists.... This "twist" will unload the front inner-tire AND add-load the front outer tire. And a similar game applies to the rear tires. (tires=contact patch in this case)

Since you have a "stiff" vehicle body connecting the front/rear suspensions... The "relative twist stiffness" between the F/R sta-bars will determine if the GIVEN-BODY-ROLL will load the OUTER-FRONT....OR....OUTER-REAR tire-contact-patch. Given-body-roll means the front-body-roll =equals= rear-body-roll.

Whoa there... Are we saying that BODY-ROLL can affect how loads are transmitted between Tire & ground? Yes.... Front to Rear? Yes.

COMMON KNOWLEDGE:
a. Relative stiffnesses of Front and rear stabilizer bars will affect F/R tire contact patch loading... Effectively modifying Under/Over-steer of a vehicle.
b. Perception of body-roll is most prevalent on the cover of Car & Driver Magazine.
c. Driver perception of body-roll is difficult to quantify... and is most accurate if the driver compares the dash/windshield intersection with road-horizon.
d. You don't feel 70mph... likewise... you don't feel vehicle roll... You DO feel acceleration... Likewise you DO feel roll-initiation and roll-termination.
e. Red sway-bars decrease lap times by 3.26581%
f. Hitting a pothole with your Right Front tire is now resisted by your RF-spring, RF-shock, and Front stabar-twist. (single-wheel-bump wheel-rate)
g. Really stiff ROLL-bars can lift an inside tire off the ground in a hard corner if improperly sized. (most likely not an issue for you)

If you are still with me... Controlling vehicle roll with BARS is not all that important, unless you want a cool picture on Road&Track cover. If you wish to control vehicle roll... consider lowering the CG or widening the vehicle-track. Huge bars bind-up suspension displacement, and increase single-wheel-bump-rate.

Bars between L&R suspension corners are used to balance the understeer/oversteer of the vehicle through relative F/R bar diameters, bar efficiencies, and bar-isolator/mount stiffnesses. Interestingly, BMW 335 uses a stamped stabar-bracket... and the M3 uses a cast bracket.... Hmmmm..... bar-efficiency... WTF...is he talking about? Forget it... Your only hope is bearings (or maybe a stiffer bracket....Hmmm)

My advise:

1. Measure the bar diameters.
2. drive your car through a ~40mph corner about 20 times at the same speed, same corner entry steering progression.
3. Swap the rear bar.
4. repeat 2 (above).
5. Take note of the steering wheel angle required for 2(above) and 4(above)
6. Sense the "glide," or "rotation" through the corner.
7. If 5 & 6 above make absolutely zero sense after completing the task... Paint the bars on the car RED and throw the others in the trash.
 
Best advice (IMO) is to understand your goals. If your goal is arm-chair racing, then a nice RED sway-bar in front, and a GREEN one in the back will be best. Mixing colors for the urethane bushings F/R will also help tremendously.

Jesting aside, it takes a bit of "vehicle dynamics" understanding to know what you want. A SWAY-BAR = ROLL-BAR = STA-BAR... EXCEPT for the logic behind the language.

Sway-bars & roll-bars... These are terminology used... commonly for body-roll-control.
Sta-bar (Stabilizer-bar)... This terminology is much more precise (for the same chunk of steel) and might seem to indicate "stabilizing the vehicle."

Most people think of a BAR connecting suspension-corners left to right as a means to control vehicle roll... and to a sense it does. BUT as your BODY-ROLLs...during lateral-acceleration... that bar twists.... This "twist" will unload the front inner-tire AND add-load the front outer tire. And a similar game applies to the rear tires. (tires=contact patch in this case)

Since you have a "stiff" vehicle body connecting the front/rear suspensions... The "relative twist stiffness" between the F/R sta-bars will determine if the GIVEN-BODY-ROLL will load the OUTER-FRONT....OR....OUTER-REAR tire-contact-patch. Given-body-roll means the front-body-roll =equals= rear-body-roll.

Whoa there... Are we saying that BODY-ROLL can affect how loads are transmitted between Tire & ground? Yes.... Front to Rear? Yes.

COMMON KNOWLEDGE:
a. Relative stiffnesses of Front and rear stabilizer bars will affect F/R tire contact patch loading... Effectively modifying Under/Over-steer of a vehicle.
b. Perception of body-roll is most prevalent on the cover of Car & Driver Magazine.
c. Driver perception of body-roll is difficult to quantify... and is most accurate if the driver compares the dash/windshield intersection with road-horizon.
d. You don't feel 70mph... likewise... you don't feel vehicle roll... You DO feel acceleration... Likewise you DO feel roll-initiation and roll-termination.
e. Red sway-bars decrease lap times by 3.26581%
f. Hitting a pothole with your Right Front tire is now resisted by your RF-spring, RF-shock, and Front stabar-twist. (single-wheel-bump wheel-rate)
g. Really stiff ROLL-bars can lift an inside tire off the ground in a hard corner if improperly sized. (most likely not an issue for you)

If you are still with me... Controlling vehicle roll with BARS is not all that important, unless you want a cool picture on Road&Track cover. If you wish to control vehicle roll... consider lowering the CG or widening the vehicle-track. Huge bars bind-up suspension displacement, and increase single-wheel-bump-rate.

Bars between L&R suspension corners are used to balance the understeer/oversteer of the vehicle through relative F/R bar diameters, bar efficiencies, and bar-isolator/mount stiffnesses. Interestingly, BMW 335 uses a stamped stabar-bracket... and the M3 uses a cast bracket.... Hmmmm..... bar-efficiency... WTF...is he talking about? Forget it... Your only hope is bearings (or maybe a stiffer bracket....Hmmm)

My advise:

1. Measure the bar diameters.
2. drive your car through a ~40mph corner about 20 times at the same speed, same corner entry steering progression.
3. Swap the rear bar.
4. repeat 2 (above).
5. Take note of the steering wheel angle required for 2(above) and 4(above)
6. Sense the "glide," or "rotation" through the corner.
7. If 5 & 6 above make absolutely zero sense after completing the task... Paint the bars on the car RED and throw the others in the trash.

So this is what the DSM community has become.
 
Sorry guy... The subject you brought up is NOT simple. And the easiest thing to do is swap parts.

EVERYONE can "feel" the difference after a part swap... UNTIL they encounter blind evaluations... Was a part swapped out?... or has nothing been swapped? change made to front... or rear suspension?... under what driving event can you feel a difference? People generally soften their opinions... because elaborating on "feeling the difference" is a good laugh when the instructor tells the driver no change was made to the vehicle.

The easiest way to decipher a change is to drive at the limit of tire-adhesion; then it is much easier to tell differences. Please do this on a track.
Consistency in driving is EXTREMELY important. Being off by 1-mph can make a huge difference when evaluating emergency lane changes.

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I apologize if you have been offended by humor. Installing a new turbocharger is easy to "feel" the difference (power). Vehicle dynamics is more complicated for evaluating differences and differences can crop up at different conditions... Wet/dry pavement, high-speed, low-speed, driver-only, fully-laden.

Some companies stopped blind evaluations for prototype test drives... Managers & Chief Engineers don't like to be embarrassed when they can't pick the vehicle with the part change.


As far as your question about "what the DSM community has become...." Have fun with your car, drive it, auto-cross it, take it to track days, work on it. Forget about the complexities. Do things that make you happy.
 
Last edited:
I run only the rear RM bar and stock front and there is a noticeable reduction in understeer (in autocross) from the stock setup. I've never had both installed though so I cannot offer any insight there.
 
I run only the rear RM bar and stock front and there is a noticeable reduction in understeer (in autocross) from the stock setup. I've never had both installed though so I cannot offer any insight there.

Great. I'm going to install just the rear for now and see how it goes, good to see some other FWD guys who are into turning.

Btw I checked out your profile, how do you like the tanabe tie bar? I was thinking about getting one
 
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