Tire Rack.com

Installing Suspension Upgrades — When Fashion and Function Work Together

Suspension components tested:
BMW Original Equipment Springs, Struts/Shocks & Anti-Roll Bars
Eibach Pro-Kit Spring Set (w/ BMW O.E. Struts/Shocks & Anti-Roll Bars)
Eibach Pro-Plus Kit - Pro-Kit Springs & Eibach Anti-Roll Bars (w/BMW O.E. Struts/Shocks)
Eibach Pro-System Plus - Pro-Kit Spring Set, Pro-Damper Set & Eibach Anti-Roll Bars

Vehicles used:
2003 BMW E46 330Ci Coupe

History shows most drivers install performance lowering springs to enhance the look of their vehicle. Fitting a vehicle with larger wheels and lower profile tires can create a visual illusion that makes a vehicle with stock suspension appear lifted because of the gap seen in the fender well between the top of the tire and the vehicle’s bodywork. While the overall diameter of the lower profile tires doesn’t change significantly from the OE tires (when properly plus-sized tires and wheels are installed), the illusion occurs when the tire’s sidewall height is equal to or shorter than the visible gap between the edge of the fender and the top of the tire. (Take a look at lowering.) The illusion is eliminated by reducing or eliminating the gap seen in the fender well.

But there is also another side to lowering your vehicle – function. Along with the visual improvement a reduction in ride height offers comes an enhancement in vehicle performance. Performance lowering springs reduce the vehicle’s center of gravity, aiding stability. Lowering springs use increased spring rates engineered to cope with the reduction in travel, while still preventing bottoming of the suspension under most conditions found during normal driving. The increased spring rates help control side-to-side body roll during cornering, as well as the pitch and nosedive experienced during spirited acceleration and braking.

A vehicle’s suspension is comprised of many parts engineered to work together – including springs, dampers and anti-roll bars. Eibach Springs recognizes this, and now also offers Pro-Damper replacement shocks and struts and Anti-Roll Bars that are engineered to work in conjunction with their line of Pro-Kit lowering springs. For many applications, drivers can select components a la carte, or choose one of several pre-packaged combinations. The Pro-System package contains Pro-Kit springs and Pro-Dampers, while the Pro-System Plus adds upgraded Anti-Roll Bars to the package.

To get a better understanding of the enhancement upgrading the suspension can offer, Tire Rack conducted a Real World Road Ride and Performance Track Drive with four 2003 BMW 330Ci coupes. Our evaluation compared the Original Equipment BMW suspension, Eibach Pro-Kit Springs (with BMW dampers), Eibach Pro-System (Pro-Kit Springs and Pro-Dampers), and the Eibach Pro-System Plus (Pro-Kit Springs, Pro-Dampers and Anti-Roll Bars).

We equipped all four of our test cars with 205/55R16 Bridgestone Potenza RE950 High Performance All-Season tires, mounted on 16x7.5 alloy wheels designed specifically for use on the E46 chassis BMWs like the 330Ci coupe. Using the same wheel and tire combination on all four vehicles took the tire variable out of the equation, letting our team focus on the influence of the different suspension combinations. Both the road and track portions of our evaluation were conducted in dry conditions.

Stock BMW Suspension

The Original Equipment suspension fitted to the BMW 330Ci coupe at the factory already features a mild sport package suspension. The coupe rides somewhat lower than the sedan version, giving the car a fairly sporty look in the parking lot and taut, responsive feel on the road. BMW tunes the stock suspension to the average customer of the 2-door coupe, counting on a more sporting disposition than those choosing the sedan model.

Driving on the stock suspension as part of this evaluation reminds us of why we selected the BMW 3-Series as a test platform. The stock suspension works very well out on the road, where our team found the ride and handling qualities well suited to the intended purpose of the car. The stock suspension offered a comfortable ride, while still allowing the driver to feel connected to the road. The only portion of our road route that gave the factory suspension any trouble was when driving over the most-broken section. The vehicle with the stock suspension felt a little unsettled, tossing the vehicle and its occupants around more dramatically than the other combinations in this evaluation.

On the track, the stock suspension performed well, but felt a little sluggish compared to the other vehicles in this evaluation. Achieving quick laps required smooth input from the driver, and anticipation of each maneuver to give the vehicle time to respond. Rapid steering and pedal commands would upset the car, slowing lap times. Average lap times for the stock suspension were the slowest of the group.

Eibach Pro-Kit Springs

The Pro-Kit performance lowering springs were installed with the Original Equipment BMW dampers.

Whenever installing performance lowering springs, spring manufacturers recommend replacing the stock dampers, especially on higher mileage cars. Because the suspension has to be disassembled anyway to install the new springs, there is typically no additional labor cost to install new dampers at the same time. More importantly, aging factory dampers may not be up to the task of controlling the movements of the performance lowering springs, which can lead to a harsh, bouncy ride if not replaced.

The factory dampers on the BMW 330Ci are very capable to begin with, and our test vehicles have relatively low miles on them, so we opted to equip this vehicle with Eibach Pro-Kit springs and the stock dampers, simulating what owners of newer cars often elect to do.

Installing Pro-Kit springs on most vehicles results in approximately 1.25-1.6" lowering in the front and rear. Because the 330Ci coupe already sits somewhat lower than the sedan version, our coupe test car was lowered about half the usual amount.

Out on the road, the car equipped with Pro-Kit springs felt somewhat more nimble than the stock suspension. This vehicle had less body roll when carving around the off ramps, and steering response felt more crisp. The Pro-Kit-equipped car did ride more firmly over choppy pavement, but was not rated as being harsh by our team.

On the track, feedback to the driver was enhanced over the car equipped with the stock suspension. Steering response was improved, as was steady state cornering around the skid pad portion of our test track. Time and speed gains were made in all areas, with the average lap time improving nearly 0.250 second over the stock suspension.

Eibach Pro-System

Recognizing that there is more to a vehicle’s suspension than just springs, Eibach has also engineered a line of shocks and struts (dampers) for many applications. Pro-Dampers are specifically designed to work in conjunction with the revised spring rates and lowered ride height achieved with Pro-Kit springs, enhancing performance through the entire working range of the suspension. The Pro-System combines Pro-Kit springs with Pro-Dampers, all in one box, and at a modestly reduced price from the individual components. As with many applications, the Pro-System for the BMW 330Ci included new foamy rubber bump stops for the front dampers, further fine tuning the effective spring rates of the suspension when it gets to near full compression.

Out on the road, the Pro-System-equipped car drove much like the car with only Pro-Kit springs installed, providing crisp handling with a taut ride. Driving over the rougher portions of our road route demonstrated the advantage of the engineered combination of Pro-Kit Springs mated with Pro-Dampers. Here the car felt more connected, and less upset by the uneven pavement than the vehicles with the BMW dampers. There was never a moment where the driver didn’t know what the car was doing, or driving over, all while not feeling too harsh. This combination did seem to transmit a little more impact noise into the cabin than the vehicles with the BMW dampers, however.

Out on the track, we were surprised to find this combination did not lower average lap times more than it did vs. the car equipped with only Pro-Kit springs (there were only small improvements in all sections of the track). Subjectively, our team found this car somewhat easier to drive at the limit, with the steering response feeling more precise than the car with stock dampers and Pro-Kit Springs. Our test track is very smooth, possibly reducing the advantage the Pro-Dampers would have controlling suspension movements on a rougher surface.

Eibach Pro-System Plus

The Pro-System Plus package adds the third major component to the engineered suspension system, combining upgraded Anti-Roll Bars with Pro-Kit springs and Pro-Dampers. Eibach Anti-Roll Bars are designed to do exactly what their name implies – reduce side-to-side body roll (sway), enhancing handling and cornering power. Eibach engineers their Anti-Roll Bars to work as a matched set, usually upgrading both front and rear bars, with most applications including multiple adjustment holes for one or both ends of the car to allow drivers to tune the handling balance to their personal tastes. For the BMW 330Ci, because of the rear bar’s design only the front bar is adjustable, and we opted for the softest setting to minimize understeer.

On the road, straight-line, smooth road driving was found to be equivalent to the Pro-System-equipped vehicle. Anti-Roll bars are designed to work only during cornering, or when the vehicle encounters a significant one wheel bump, and do not play a role in ride quality or handling when the vehicle is traveling steady state down the road. This vehicle felt stable and had minimal body roll when taking off ramps and corners at all speeds, receiving good marks for handling from our team. The bumps and undulations on the two-lane country road portion of our route did upset this car more than the vehicles equipped with the factory Anti-Roll bars, but was rated as a modest trade-off for the improvements found in cornering stability and reduced body roll.

On the track, the Pro-System Plus package-equipped car received praise for its balanced handling and crisp steering response, feeling nimble through the slalom portion and around the tight turns on our course. Also, the addition of the Anti-Roll Bars further reduced body roll when traveling around the skid pad, helping this vehicle generate the fastest average lap times of the evaluation.

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