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Suspension choices analyzed: Should I upgrade springs, sway-bars, or both? And more...

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
The number one question I see on these forums and the VW racers FB page I'm on is, "should I get a rear sway bar?".

The answer is, it depends.

First, read this thread, it's long, based on a Mk4 Golf, but much of what is discussed is applicable to the MK7 Golf.

https://www.golfmk6.com/forums/index.php?threads/ultimate-suspension-thread.239344/

Thread overview

1. What is Understeer?

2. Five Categories of the Suspension Enthusiast

  • A. Track-Based Suspensions: Autocross
  • B. Track-Based Suspensions: Road Course
  • C. Street-Based Suspensions: The 'Darter'
  • D. Street-Based Suspensions: The GT's
  • E. Street-Based Suspensions: Driving a Slow Car FAST
3. The Stock Suspension

4. The Autocross Suspension

5. The Road Racing and the Shine Real Street Suspension

6. The Grand Touring (Turismo) Suspension

7. Roll Centers and Weight Transfer

8. European Road Tests and Engineering

--------------------------------------------------------------------------------------------------------------------------------------
If you made it through that thread, congratulations!

Here is what I did about the issue of springs/bars and how to get my car to "handle"

When faced with what to upgrade to reduce body roll, you have essentially three options.

All of these options allow for reduced body roll but have different side effects.

1. Combination of bars and springs
2. Mostly springs
3. Mostly bars

Here is what these three options would look like on my car.

*** I used my specific corner weights, modifications and suspension measurements. I used an Excel spreadsheet to calculate these values for my car. Your results may vary. ***

My goal was to find the nominal bar or spring rate for options 2 or 3 that matched the front and rear wheel rate (WR) and front roll couple % of option 1. I find that for me and my setup/driver preference, I like 63% front roll couple. I could not find my online about what % is best for autocross, so your results may vary, but testing is required.

Front
Opt 1 (current setup)​
Opt 2​
Opt 3​
Spring rate in/lb
400
850
250
Spring WR
249​
530​
156​
Spring WR (body roll)
499​
1061​
312​
Swaybar rate
312 Hotchkis on soft
160 OEM
360 Hotchkis on hard
Swaybar WR
295​
151​
340​
Spring WR (body roll)
590​
303​
681​
Rear
Spring rate in/lb
650
1200
575
Spring WR
203​
376​
180​
Spring WR (body roll)
407​
752​
360​
Swaybar rate
842 O34 on soft
333 OEM
912 O34 on hard
Swaybar WR
139​
55​
151​
Spring WR (body roll)
279​
110​
302​
Front WR/Side
840
833
837
Rear WR/Side
482
486
482
Roll couple % front
0.635
0.631
0.635

1. Combination of bars and springs (This is my daily setup for autocross)
2. Mostly springs (If I go back to OEM front and rear bars, I have to dramatically increase spring rates to keep the same wheel rate (WR) and keep the same roll couple %)
3. Mostly bars (If I max my current front and rear bar, then I can go down on spring rates to keep the same WR and roll couple %)

#1 is a good balance between relative comfort with the selected spring rates and body roll control,
#2 is tough to live with on the street and my shocks can't dampen the body with such large energy stored in the springs, but provides the most "independent" suspension
#3 is generally more comfortable on the street, but one wheel bumps are harsher and the front may lift a tire on corner exit causing issues with power down for non-PP GTIs, the rear bar won't help much either because of the soft front springs, the rear inside tire will be off the ground all the time in corners

Keep in mind these are not the only options for spring and bar rates, I just used what I have for this comparison. Also, I have additional modifications to take advantage of reduced body roll (more front camber) and an autocross alignment to increase rear rotation. Not everyone will want this level of rotation, but rotation is easily modified with less rear toe-out if required.
 
Last edited:

grantpab

Ready to race!
Location
Minneapolis, MN
Thanks for sharing that link. That's a really well written and informative post.

Correct me if I'm misunderstanding, but your roll couple depends on the lowering height of the suspension. What assumptions are you using to determine the roll couple from the wheel rate?
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
Here is what a 034 rear bar upgrade looks like for a stock GTI.

Front
Opt 1​
Opt 2​
Spring rate
175​
175​
Spring WR
109.2​
109.2​
Spring WR (body roll)
218.4​
218.4​
Swaybar rate
160​
160​
Swaybar WR
151.5​
151.5​
Spring WR (body roll)
303.0​
303.0​
Rear
Spring rate
230​
230​
Spring WR
72.1​
72.1​
Spring WR (body roll)
144.3​
144.3​
Swaybar rate
333​
912​
Swaybar WR
55.2​
151.1​
Spring WR (body roll)
110.3​
302.1​
Shock Rate
177.5​
486.0​
Front WR/Side
412.2​
412.2​
Rear WR/Side
182.5​
374.3​
Roll couple % front
0.693​
0.524​

The roll couple is nearly even, which is why there is less understeer, usually.
 

JackRabbitSLIM

Go Kart Champion
Location
OHIO
Car(s)
MK7 GTI

JackRabbitSLIM

Go Kart Champion
Location
OHIO
Car(s)
MK7 GTI
I think the stock + 034 bar setup reduces understeer for the same reason as the large rear bar in the snow example of the thread. Basically shocks the rear tire into giving up early. Just my opinion, I have never driven a GS GTI.
 

jmblur

Autocross Champion
Location
Massachusetts
Car(s)
2017 Golf R
Got some numbers from Superpro on their AWD MQB 26mm front bar. I imagine they're probably near identical to the FWD 26mm bar.

Looks like roughly 15% stiffer on soft, 30% stiffer on hard than stock golf R bar (which I believe is stiffer than the GTI bar). So overall a mild change. Maybe not worth the effort of dropping the subframe but the adjustability is nice. And after all that work it ain't coming off again 🤣

SuperPro RC0052FZ-26 vs. OEM Rate Chart.jpg
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
Got some numbers from Superpro on their AWD MQB 26mm front bar. I imagine they're probably near identical to the FWD 26mm bar.

Looks like roughly 15% stiffer on soft, 30% stiffer on hard than stock golf R bar (which I believe is stiffer than the GTI bar). So overall a mild change. Maybe not worth the effort of dropping the subframe but the adjustability is nice. And after all that work it ain't coming off again 🤣

View attachment 214684
Better up your springs to compensate 😉
 

jmblur

Autocross Champion
Location
Massachusetts
Car(s)
2017 Golf R
Better up your springs to compensate 😉
You sharing your spreadsheet by chance? (understand if not). Gotta figure out where I'm gonna land with the coilovers... I'm thinking 400/600 to start and then ramping rear springs up if needed, or swapping the stock 450 springs to front.
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
You sharing your spreadsheet by chance? (understand if not). Gotta figure out where I'm gonna land with the coilovers... I'm thinking 400/600 to start and then ramping rear springs up if needed, or swapping the stock 450 springs to front.
I’ll share it with you later today, PS, pick springs for ride comfort, add toe out for rotation. Otherwise you will end up with huge rear springs if you keep the OEM toe settings.
 

jmblur

Autocross Champion
Location
Massachusetts
Car(s)
2017 Golf R
I’ll share it with you later today, PS, pick springs for ride comfort, add toe out for rotation. Otherwise you will end up with huge rear springs if you keep the OEM toe settings.
Yeah rear toe reduction is in store for next autox. Gotta set up a string box to make sure all my trials and tribulations with LCAs didn't screw up front toe too.
 
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