I'd like to provide a brief (relatively) write-up on suspension modifications for those of you who are interested. It seems that there's a great deal of misunderstanding regarding some suspension modifications, so in an effort to help you guys actually improve how your car handles (as opposed to just how it looks), I'm going to walk you through some modifications and their direct effect on your car's handling ability.
Let’s put our assumptions on the table before we begin. First, it is assumed that you are driving this vehicle on the street, and that your interest is in improving the car’s handling ability, stability, and/or performance not just on the track, but on the street. You’re the kind of person who likes to push the car’s limits on a highway on/off ramp, and you are not building a dedicated track car. Second, it is assumed that you have a basic understanding of automotive mechanics and know what your suspension components are.
Our first assumption is critical because a street-driven vehicle requires a vastly different approach than a track driven vehicle. You can’t get away with some of the shortcuts you might perform on a track, in a daily driven vehicle. The difference can be summed up with one term; chassis stability. This is the reason a slammed car will work well on a track, but will not work well the street. Let's not kid ourselves here, most of us rarely take our cars to road racing events, if ever.
If you want to actually improve the handling of your vehicle, you must first forfeit any images in your head of slammed suspensions or even drastic reductions in ride height unless you have coilovers that allow you to adjust suspension travel as you lower the car, and even then, you’ll have to be conservative with just how much you lower the car. There’s a very simple reason for this. On the street, the roads are not perfectly smooth.
Try to picture this scenario: you have to make a right turn and you’ve got a green light, no traffic in any direction, and you start to throw your car hard into the turn. Halfway through the turn, you hit a 2” bump in the road caused by some pothole repair. If you have stock ride height, your suspension compresses and absorbs the impact. If you have a slammed car with drastically reduced ride height, you are already riding on your jounce bumpers during the turn (even if you don’t know it), and the moment you hit that bump, the energy of that force transfers directly into the chassis. You’ve now destabilized the chassis, and the back end shifts as you lose the force the tire had with the pavement.
I can’t stress enough the importance of chassis stability. Any time you hit a bump bigger and faster than the suspension can fully absorb, that energy is transferred into the chassis, which results in a loss of stability. A loss of stability has a direct result on how much traction you have. I would not recommend lowering more than an inch over stock ride height. This concept is even more important when you hit a bump or road anomaly during a turn. During a turn, your car will have some body sway (lean), which will naturally cause the suspension on the outside of the turn to compress under the weight of the car. Because the suspension is already compressed, you have even less suspension travel under these conditions. The fact that you're in a turn makes any destabilization of the chassis that much more dangerous, as you could lose control of the vehicle.
Next, we need to talk about body sway. Some people think their car handles better around corners when lowered because of the reduction in felt body sway/roll, and they would be correct were it not for often unpredictable road anomalies. The only primary reason is that, as noted earlier, you are effectively resting on jounce bumpers in a hard turn, which affords you zero flexibility in absorbing road anomalies. Great concept for dedicated road racing, not so great for spirited street driving. Since we need some suspension travel for the purpose of absorbing road anomalies without destabilizing the chassis, we need to minimize body sway. Reducing body sway has at least two benefits. One, it improves the amount of suspension travel you have while conducting a hard turn, so your suspension is better able to absorb road anomalies while already under more weight. Two, the physical reduction in body sway improves tire contact with the road and therefore traction. In cars like the Cruze, where we have relatively little dynamic camber on suspension compression, this keeps the front tire on the outside of the turn flatter, which reduces understeer and provides more grip. Your first improvement should be a rear sway bar, since our cars don’t have one and the rear axle is far too flexible to effectively serve that purpose. Understeer is a big problem with FWD cars.
On the topic of understeer, we have another modification available; Whiteline front control arm bushings. In a hard turn, force on wheels is applied to a direction. The outer wheel is pushed inward, and the inner wheel is pulled outward. The control arm has bushings where it mounts to the subframe, and the factory ones are fairly soft for ride comfort. Soft bushings means that when you are in those turns, you have more of an undesirable camber change as force is applied to the wheels. Upgrading to stiffer control arm bushings reduces the camber change caused by force against the control arm, which directly reduces understeer by keeping the tire flatter to the pavement. There is a very significant increase in traction to be obtained here.
Next is chassis bracing. On everyone’s list should be at least a set of upper (front and rear) strut tower braces. From the factory, the chassis is fairly soft and allows the front of the car to twist relative to the rear, and vice versa. Chassis twist means your car feels like it functions as two separate parts as opposed to one unit. A soft chassis is more likely to flex during suspension compression. Suspensions operate best when the chassis remains stable. Chassis bracing stiffens the chassis and forces the suspension to do the work. A stiff chassis paired with a suspension that can absorb all road anomalies effectively will allow you to glide over road anomalies without destabilizing the chassis, thus maintaining traction. You’ll be able to turn harder, faster, and will be able trust your car more doing so. A stiffer chassis makes the car more predictable.
Next is the discussion of shocks. The stock shocks are soft, and the vehicle relies heavily on the jounce bumpers. Jounce bumpers are big blocks of soft rubbery foam. When you go over a hard bump, the force of the bump applied to the wheel causes the suspension to compress. If the bump is hard enough, the unsprung weight of that suspension, using inertia, will cause the suspension to bottom out. This vehicle uses some pretty large jounce bumpers in order to soften the blow of the suspension bottoming out so you don’t even notice with the exception of extreme cases. The soft chassis aides in this, but you ultimately trade some chassis stability and traction for that comfort. Remember, the purpose of the shock absorbers/dampers is to control the rate of suspension compression and decompression (jounce and rebound). A stiffer shock transfer more of the small bumps on the road in to the chassis (the car will feel much stiffer), but will absorb large road anomalies much more effectively without destabilizing the chassis. The end result is very positive for enthusiasts; it allows you feel more of the road, while at the same time allowing your suspension to deflect large road anomalies without destabilizing the chassis and keeping constant tire pressure to the pavement. The first thing you notice when upgrading shocks is that the car feels much more glued to the road, especially at high speeds.
Next, I will briefly touch on wheels and tires. Remember that when going over bumps, inertia causes our wheels to travel upward, compressing the suspension. As a result, heavier wheels and tires will run contrary to your goals. Reducing unsprung weight is a very important goal as it allows the suspension to keep the tires planted firmly on the ground as opposed to allowing them to bounce upward and compromise traction. The heavier the wheel/tire combination, the worse your handling will be. A cheap and easy upgrade is to get Eco wheels, which are much lighter than any stock wheel and many aftermarket wheels, with the only compromise being sidewall height. Specific tires are out of the scope of this article.
Let’s get back to ride height as our last topic. Reducing ride height has the benefit of lowering your center of gravity, which is a positive thing. However, for the reasons I mentioned above, too much of a drop can reduce your performance on the street. I will only touch on this briefly, but the suspension geometry of a McPherson strut design is such that significant lowering of the suspension causes a widening of the control arm-to-strut angle, which results in a loss of negative dynamic camber while cornering. This is opposite of what you want and will directly increase understeer. In my opinion, lowering your car is the last thing you should do after you’ve addressed all of the above concepts, and should be done with a conservative approach that considers the road quality in your specific area. Ride height tuning will require you to know when you have reached the limits of your suspension in a turn and will require you to be well aware of what your chassis is doing when going over road anomalies. I don’t want to offend someone, but many people don’t have that ability. Always remember that lowering your car requires stiffening of your shocks. You need to compensate for the reduced suspension travel by reducing how easily your suspension compresses.
If you are actually looking to improve your car's handling on the street, focus on what will actually improve your vehicle’s suspension as opposed to simply what will look “fast.” You can make additional improvements by tweaking the static camber of your wheels, but that’s outside the scope of this article.
I have a separate article written for the specific products you can add to your Cruze to achieve the above goals: http://www.cruzetalk.com/forum/12-g...ving-2011-2016-cruze-handling-suspension.html