Installed Whiteline BHR93 Rear Sway Bar/review

Davep said:

...I still firmly believe that upgrading the struts/shocks will provide a better balanced solution over a rear sway bar.

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Changing the damping characteristics of the shocks (struts are shocks too) doesn't change the steady state balance of the car's cornering attitude. Damping changes change how the car reacts to DYNAMIC input, ie. sharp turn in moves and/or mid corner bumps. Damping has very little effect on a car's balance. Continued...

Davep said:

The problem with an aggressive rear sway bar is that there is a greater risk of being caught out with the car swapping ends unexpectedly. It could happen as easily as you cornering over a crest in the rain at 50 mph and you back off when the corner tightens up expectantly. Next thing you know you're travelling backwards.

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In order to change the car's cornering balance you need to change the TLLTD (Tire Lateral Load Transfer Distribution). Changes that affect the roll stiffness of the suspension affect TLLTD.

Assuming equal tire traction front and rear and steady state cornering, if the roll stiffness of the suspension front to rear is in proportion with the car's weight distribution front to rear, the car will have a neutral balance where the front and rear tires break traction at the same time as cornering loads increase.

If the front of the car has proportionally higher roll resistance the car will tend to understeer (front pushes wide), and if the rear has proportionally higher roll resistance the car will tend to oversteer (rear comes around).

What you're talking about is adding a significant amount of roll resistance to the rear suspension, creating suspension that's out of balance. Absolutely, this is a dangerous situation and should be avoided. Increasing the rear spring rates can have the same effect.

Having said that, most cars are set up from the factory to understeer quite heavily. This is safer since losing traction mid-corner will then result in the car going off the road nose-first where impact will be more survivable. This has been the case ever since the Corvair inspired the book "Unsafe at Any Speed"... now car companies err on the side of caution, and boredom. A little understeer is usually even found in high performance cars since it allows some dynamics mid-corner (on/off throttle, light braking) without failing into an oversteer condition.

Adding a little rear roll stiffness to a car can have a transformational impact on how it handles. The trick is not to add too much. A rear sway bar should be adjustable so you can set it up to have safe handling. Since spring upgrades often alter the front to rear roll stiffness of the chassis a rear roll bar needs to be able to compensate for that as well; just because it works well with the stock springs doesn't necessarily mean it will work with lowering springs or coil overs.

Any time a change in balance happens a car should be driven to an off-road facility for set-up, where the driver can push the car and see where its limits are and how it behaves.

Davep said:

I suggest you are better off upgrading the front sway bar end links, and perhaps the steering rack bushings. The endlinks are spaghetti thin and probably distort under extreme cornering.

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Yes, the front sway bar end links in the Cruze are a weak point. Someone posted part numbers for an all metal Moog end link from a Cobalt (IIRC) that fits the Cruze. Having said that, remember that increasing the effectiveness of the front sway bar in a car that already understeers will make it understeer more.

Davep said:

I disagree somewhat in that damping may have little affect on a car's balance, however IMO it does provide a more stable action/reaction to a steering or suspension input, if that makes sense. ie, it makes a car more predicable.

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Yeah, my examples are based on steady state cornering on smooth surfaces. In the real world damping has a HUGE effect on cornering stability and the car's ability to handle mid corner bumps and corrections. There's a TON of advancement in shock absorber technology all the time, unfortunately we as car enthusiasts get to play with relatively little of it.

The Magneto-Rheological (MR) shocks GM has been putting in cars since the '05 Corvette are a phenomenal piece of technology, literally able to transform a car's personality on the fly and adapt to individual road imperfections. One further, the Dynamic Suspensions Spool Valve (DSSV) shocks in the new Z/28 are literally race car pieces bolted to a production car... only the Astin Martin One77 shares this technology among road cars.

Having said ALL of that, a good understanding of roll stiffness and TLLTD is a big help when attempting to set up a car. Oh, and 30 Ounce isn't the first person I've heard admit that too much adjustability can give a guy a headache!

30 Ounce said:

I have built a completely adjustable suspension for my track car, a 1974 Datsun 260Z, and can tell you it is not something you want for daily street driven car. And the more adjustability you put into it the more you will be chasing your tail trying to get it right. The stock Cruze (mines an ECO manual) handles really well. The chassis is pretty stiff and the rear end (of the ECO) is pretty lively especially for a FWD which they usually tune in absurd amounts of understeer.

My Z is put on scales and corner weighted and aligned several times a year. The more adjustments you have the more you have to play with it.

Here a lap at High Plains Raceway.https://www.youtube.com/watch?v=wiNGjx-H-9U

If this is what you have in mind lets do it!

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Not quite what I have in mind, but it looks exciting!

I drive the car on highways frequently with lots of curves. I don't speed unless passing, but I like to maintain speed on the twisties. The rear sway bar seemed like the easiest way to improve the feel that I felt was lacking the most in the Cruze, and it worked. Now I see other shortcomings in the suspension highlighted, and I feel like I should improve them, too.

I appreciate all the conversation in the thread, it's very interesting and important to me to learn what all is involved and how it all works. It's hard to know what's lacking in the Cruze chassis besides what I can feel in daily driving since I have little experience with cars. I analyze most of what's going on from a physics standpoint, and things can function far differently than they appear to someone who is lacking the real world experience.

I understood that installing the rear sway bar could lead to potential oversteer and losing control of the rear end, and I took that risk when I installed it. I have had absolutely zero issues even pushing it in cold weather (below 32 is considered cold here) and in the rain, although I still hold some care from the years I spent only driving a motorcycle in San Diego. It probably also helps I got some significantly better tires to replace the OEM ContiProContacts, (Toyo Proxes 4 Plus) and they've been nothing but great for feel, handling, and traction.


Edit: I forgot to mention I had replaced the stock plastic front sway bar links with metal Moog links and removed the stock crap rubber bushings and replaced them with the blue thermoplastic moog bushings, lubricated with silicone lube. I think I'm getting about as much performance out of the front bar as possible without replacing it.

Justinus, another thing to consider is whether or not you plan to use lowering springs in the future.

If you do, consider that the Cruze's front suspension gains significant negative camber when lowered, which increases front end grip. I installed Eibachs and was amazed at how much more grip the front end had afterwards. True, the car rolls a little less because of the additional spring rate, but the majority of the grip increase is camber related. The rear already has quite a bit of camber.

My car is an otherwise stock '12 Eco. The car's balance isn't bad even with just the springs installed. On snow it is possible to get the rear end to come around if you do deliberate things with the steering mid corner, but other than that the car feels pretty good. A very slight increase in rear roll stiffness would probably give it all it needs to feel very balanced, though a sway bar might be too much... I'd then be into what you've done with the front sway bar to get the front end working more.

Installing the z-link is intriguing, but from what I can tell it's not a simple bolt on and requires a rear axle swap.

Blue Angel said:

Justinus, another thing to consider is whether or not you plan to use lowering springs in the future.

If you do, consider that the Cruze's front suspension gains significant negative camber when lowered, which increases front end grip. I installed Eibachs and was amazed at how much more grip the front end had afterwards. True, the car rolls a little less because of the additional spring rate, but the majority of the grip increase is camber related. The rear already has quite a bit of camber.

My car is an otherwise stock '12 Eco. The car's balance isn't bad even with just the springs installed. On snow it is possible to get the rear end to come around if you do deliberate things with the steering mid corner, but other than that the car feels pretty good. A very slight increase in rear roll stiffness would probably give it all it needs to feel very balanced, though a sway bar might be too much... I'd then be into what you've done with the front sway bar to get the front end working more.

Installing the z-link is intriguing, but from what I can tell it's not a simple bolt on and requires a rear axle swap.

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Negative camber does not necessarily increase grip. Lowering your cars center of gravity as well as it's roll center (note that those are 2 different things) in combination with an increase in negative camber can make the initial turn in feel better but unless you are cornering hard enough to make it roll enough to maximize tire contact patch then you may actually have less grip. I run between 2-3.5 negative camber and 4-5 degrees caster (which really helps turn in) but if i dial in too much camber it can really impact my braking because it literally has less tire contact to the road. All track tires have a triangular mark on the sidewall near the tread...it's there to help camber setup for the track. If your tires are rolling over enough to leave wear marks on them then you need to increase tire pressure or increase negative camber. Suspension setup is always a give and take. You can increase camber to increase cornering ability and possibly drastically increase braking distances. My Z is setup very well. I only have about 240 horsepower but am always put in the "A" group with cars that have 400-800 HP and the Lotus' that are always amazing. I don't think they ever touch the brakes.

I want to point out that the WTCC Cruze's do not use the Z-link rear suspension. They tested both setups and found that the ECO twist beam was lighter and actually performed better. I believe that they added reinforcements to the beam for the insane cornering loads they have.

Blue Angel said:

On snow it is possible to get the rear end to come around if you do deliberate things with the steering mid corner, but other than that the car feels pretty good.

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My car is all stock, and has the exact same behavior. Never had a front wheel drive car before that would do this, which if used to your advantage does improve handling. Much better than a typical FWD under-steering only with the ebrake being the saving grace.

Blue Angel said:

Installing the z-link is intriguing, but from what I can tell it's not a simple bolt on and requires a rear axle swap.

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I always hear this but can't believe from a manufacturing/profit stand point this makes allot of sense. I mean looking at the photo below why would they make a whole new axle just to add one bolt location(one each side)? I do remember a few threads on here that showed two different part numbers for axles, so your probably 100% correct. Again it just doesn't make much sense.

30 Ounce said:

Negative camber does not necessarily increase grip. Lowering your cars center of gravity as well as it's roll center (note that those are 2 different things) in combination with an increase in negative camber can make the initial turn in feel better but unless you are cornering hard enough to make it roll enough to maximize tire contact patch then you may actually have less grip.

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Absolutely, but if you look down the side of a Cruze with stock suspension you will notice that the rear wheels have a decent amount of camber (-1.4 deg nominal) while the fronts have almost none (-0.45 deg nominal), and since the rear camber is set simply by the wheel bearing mounting pads and the front relies on the assembly tolerance stackup of many welded sheet metal components as well as the subframe location and strut weldments, the front can vary quite a bit from there + or -. I doubt the camber curve of the suspension is agressive enough to compensate for body roll and keep the tires level to the road surface. All else equal I would expect adding a degree of negative camber to the front of a Cruze, even a Cruze with completely stock suspension, would increase front end grip.

Center of gravity and roll center changes will stack on top of that. I have always wanted to measure the suspension joint locations on this car to see what the effects of lowering are. After lowering with the Eibachs, my front wheels appear to have as much, maybe even a smidge more, negative camber as the rears do... somewhere between -1.5 and -2.0 degrees as a rough guess. With the narrow Eco 215's and zero toe I have not measured any camber related tire wear anomalies.

Here's a pic of a Cruze cornering on a wet surface:

And here's a crop of the right front tire, lightened up a bit to show some detail:

That front tire looks like it's rolling under pretty good, and on a dry surface with more grip that situation would likely be worse. Even though it's carrying less load, with an additional degree of camber the rear tire looks much more square but even it could probably benefit from a little more camber.

You're absolutely right in saying too much camber can do more harm than good. Look at the guys who add 4-5 or more degrees of camber to "stance" their cars... I realize they don't care about handling/braking but I doubt they know how bad it really is.

30 Ounce said:

I want to point out that the WTCC Cruze's do not use the Z-link rear suspension. They tested both setups and found that the ECO twist beam was lighter and actually performed better. I believe that they added reinforcements to the beam for the insane cornering loads they have.

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Interesting. Got any pics or a link to share? I'd like to see that.

I found a few pics but nothing really conclusive. The pic from this site:

2009 Chevrolet Cruze WTCC Images. Photo: 2009_Chevy_Cruze-WTCC_Image-020-1600.jpg

When shown at regular exposure doesn't show a lot of detail, it's too dark:

But if we lighten it up a bit:

It looks as though they have fabricated a trailing arm setup that pivots on the factory location as well as a point in the center. This looks far different than what you mention but this is from the 2009 season as well, it's very likely that rule changes or otherwise changed their suspension strategy since.

Since the Eco trailing arm setup basically locates at only the two "trailing arm" locations, I wonder if adding some triangulation supports between the lower spring perch and the center of the twist beam would reduce deflection any meaningful degree? I would imagine a large portion of the improvement on the racecar would come from removing the rubber busings at the locating points and replacing them with solid pivots... that wouldn't be an option on a street car, but urethane may be.