front sway bars

[mrmatto]

Great discussion as usual. A few thoughts as a relative newbie to this platform and just over a year of autocross on my GTI:

1. Pretty sure I would never do a stiffer FSB on this car I daily due to the impact on ride quality. Everything is a trade-off, of course, but one of the allures of the RSB is that it doesn’t negatively impact the ride. But everyone has to decide their priorities and what trade-offs they’ll tolerate.

2. Whether you’re inducing rotation via lifting a wheel or via toe, isn’t the net the same? The oversteer is due to reduced traction in the rear? I’m not positive the mechanics involved.

3. If you’re running stock bars, how much toe out do you need to get good oversteer characteristics, and does it ultimately affect highway speed stability?

 

[xXDavidCXx]

Great discussion as usual. A few thoughts as a relative newbie to this platform and just over a year of autocross on my GTI:

1. Pretty sure I would never do a stiffer FSB on this car I daily due to the impact on ride quality. Everything is a trade-off, of course, but one of the allures of the RSB is that it doesn’t negatively impact the ride. But everyone has to decide their priorities and what trade-offs they’ll tolerate.

I never noticed a change in ride quality with the FSB, but I had a noticeable change with poly bushings. It does change one tire bump stiffness, but based on my perspective and experience, nothing I've done so far has reduced my desire to drive the car daily except when I ran stiff springs (650/1000). Many changes in NVH can be learned to be dealt with over time.

2. Whether you’re inducing rotation via lifting a wheel or via toe, isn’t the net the same? The oversteer is due to reduced traction in the rear? I’m not positive the mechanics involved.

It's not the same. Less traction is slower. The OEM bar is already lifting the rear tire, so more is not better in this case.

Rear-toe out allows the rear tire to track a larger circle, the outside tire is pointed away from the direction of the turn like rear-steer and follows the front. In actuality, it's not dramatic, and you are not slinging or slipping the rear around, it just works.

3. If you’re running stock bars, how much toe out do you need to get good oversteer characteristics, and does it ultimately affect highway speed stability?

I suggest 1/8 in total rear toe out

 

[DerHase]

Everyone thinks in terms of just "body roll" but you need to look at what each corner is doing.

Of course the stock body roll is a problem (or at least not helping).

If you put just a ridiculous heavy rear bar, as @xXDavidCXx pointed out it'll compress the outer front even more.

The problem is that while this DOES help with understeer - I think the reason is because it's compressing the outside front about the same (or more?), but now the outside rear is NOT being compressed as much, with the same rough amount of overall body roll, it means the rear camber doesn't change as much (it gains camber in bump), so it makes the car oversteer more/sooner for the same input.

Admittedly the car feels really good with just a big rear sway bar. But IMO feels better with both. HOPING that some time this year I'll be able to test the front hard vs soft to see if there is any real difference there. I lack the desire to completely swap sway bars at the track (plus all the one-time-use bolts needed) to do "proper" testing. My only real motivation is to minimize tire wear more than anything FWIW. I need another set of RT660s and flash my stock tune back on to do as close to an "apples to apples" test on track.

 

[mrmatto]

It would be really interesting to experiment with swapping the stock rear bar back in and just running a bit of toe out. And compare that in back-to-back events to a bigger rear bar with 0 toe. Really hard to a/b test these things.

 

[tigeo]

Great discussion as usual. A few thoughts as a relative newbie to this platform and just over a year of autocross on my GTI:

1. Pretty sure I would never do a stiffer FSB on this car I daily due to the impact on ride quality. Everything is a trade-off, of course, but one of the allures of the RSB is that it doesn’t negatively impact the ride. But everyone has to decide their priorities and what trade-offs they’ll tolerate.

2. Whether you’re inducing rotation via lifting a wheel or via toe, isn’t the net the same? The oversteer is due to reduced traction in the rear? I’m not positive the mechanics involved.

3. If you’re running stock bars, how much toe out do you need to get good oversteer characteristics, and does it ultimately affect highway speed stability?

There isn't a change in the ride quality with the front bar UNLESS you are hitting uneven road surface/one wheel compression than yes, you are increasing your effective spring rate on that side. Rear does the same so saying it has no impact on ride quality isn't correct - I noted that issue when I did the rear bar under the same conditions.

 

[odessa.filez]

With an open diff, I've tried no front bar (disconnected) up front, making up for some of the lost roll control using spring rubbers on stock GTI springs. Unfortunately the front rate may only reach around 500# and this was not enough at AX, though it definitely was better than stock bar / stock springs.

Last year I added an h&r 26mm front and it made a positive difference to grip on full soft. I plan to try full stiff this season to see if it improves or worsens, noting David's experience.

I haven't given up completely on the no bar, but I need to figure out how I would supplement the spring rubber approach (possibly bump stop / spring tuning) before trying again. I do this in the back and it works well, but there's more off the shelf product for shocks than struts, and the rear shocks have more shaft travel to work with.

 

[mrmatto]

Am I wrong in interpretating this thread as ultimately less about FSB and more about balancing front and rear roll stiffness?

 

[El_bigote_AJ]

Am I wrong in interpretating this thread as ultimately less about FSB and more about balancing front and rear roll stiffness?

My Freudian interpretation of this comment is that it’s loaded and bias due to your current justification (probably not intentional) of why you only have a rear bar

 

[mrmatto]

My Freudian interpretation of this comment is that it’s loaded and bias due to your current justification (probably not intentional) of why you only have a rear bar

No I’m literally just trying to understand and distill it down to what this is about. I even posed a/b testing so clearly I’m not married to anything. If it’s mainly just about balance, then perhaps stock bars and some rear toe-out is better and faster than just a fat rear bar (like I have). And/Or it opens up the conversation to additional ways to achieve that roll balance.

Either way. Just seeking to understand. I have a rear bar only because it’s cheap and easy and gave me more confidence and fun at autox.

 

[scrllock]

Am I wrong in interpretating this thread as ultimately less about FSB and more about balancing front and rear roll stiffness?

That's the point of the FSB, no? I'd guess what, 75% of guys who are "suspension-curious" change their rear sway, especially guys who don't wanna screw with toe plates or extra tire wear.

https://www.motortrend.com/how-to/ctrp-0408-big-sway-bar-and-soft-spring-setup/

Interesting article, essentially what folks are doing on stock-ish springs (big bar, soft spring). A balanced setup is likely faster (i.e. the effective grip change in the rear should be matched in the front) but driver confidence is even better (and the car feeling settled due to less body roll gives that).

 

[mrmatto]

That is interesting. Thanks.

 

[xXDavidCXx]

Am I wrong in interpretating this thread as ultimately less about FSB and more about balancing front and rear roll stiffness?

It is, and given the restrictions of GS autocrossing, I think having more front roll stiffness is better because rear looseness can be achieved in another ways.

Given the choice, I'd get both bars and stiffer springs.

 

[odessa.filez]

Am I wrong in interpretating this thread as ultimately less about FSB and more about balancing front and rear roll stiffness?

Ultimately, how do you preserve some amt of front negative camber and does daily ride quality and AX classing effect your choices? FWD has no power on oversteer capability, so front camber is precious as car turns.

Front bar checks boxes for both for the daily ride quality sensitive and stock classes.

Rear bar only is still an improvement over stock but for stock class, you must choose one or the other as mentioned by David.

Entering STH opens up the whole spring vs bar debate which may still be influenced by daily ride quality for some.

Balancing the car will include the driver confidence / experience level / aspirations. My car has stupid rear bias for now but it's helping me learn how to drive(?)

 

[mrmatto]

It is, and given the restrictions of GS autocrossing, I think having more front roll stiffness is better because rear looseness can be achieved in another ways.

Given the choice, I'd get both bars and stiffer springs.

If it’s about balance, given the choice, is stock bars better than a rear bar?

 

[tigeo]

Great info/convo here folks!