Suspension Component Test Results

Eibach Lexus IS300 Pro-Kit Springs and Anti-Roll Sway Bars

Suspension Components Tested

Lexus Original Equipment Springs, Struts/Shocks & Anti-Roll Bars
Eibach Pro-Kit Spring Set (w/ Lexus O.E. Struts/Shocks & Anti-Roll Bars)
Eibach Pro-Plus Kit — Pro-Kit Springs & Eibach Anti-Roll Bars (w/Lexus O.E. Struts/Shocks)

Vehicles Used
2001 Lexus IS300 Sedan

Eibach Springs... it's a name that no longer fully describes the company's capabilities. Their expanded product line now includes an array of high performance street suspension components. And by engineering sport springs, anti-roll bars, shock absorbers and bump stops that can be integrated into complete suspension systems, Eibach's "harmonized suspension" philosophy allows them to deliver their best blend of vehicle appearance, performance and comfort.

The primary tasks of a vehicle's suspension haven't changed. Suspensions help absorb irregularities in road surfaces, and at the same time help prevent unwanted vehicle body movements and vibration.

A suspension is a group of components that have different, yet interactive functions:

Springs - the load bearing component and heart of the suspension helps determine properties such as ride quality, load capacity and handling balance. In order to provide the best possible performance, the other suspension components have to be "matched" to the springs.

Bump Stops - their common name belies their full function. In addition to preventing the suspension from "bottoming" as the vehicle hits large road irregularities, many bump stops are also progressive acting elastomer springs that combine both springing and damping properties. Under certain conditions bump stops act as "supplemental springs" to help optimize and fine-tune a vehicle's ride and handling.

Shock Absorbers - while often called "shock absorbers" they act as "motion dampers" that help control the suspension's movement by restricting the rate at which energy is stored and returned by the vehicle's springs.

Anti-Roll Bars - also called "sway bars," they reduce body roll when cornering to further improve tire grip, handling balance and vehicle stability.

All together, these components become an integrated suspension system.

Most vehicle manufacturers design their vehicles with a suspension that is tuned to suit the needs of the average driver. Unfortunately, if you're not the average driver, the original suspension may not be best for you. If you desire to take your vehicle to a new level of control and handling, a sport suspension may be just what you need.

The Tire Rack Team conducted a "Real World Road Ride" & "Performance Track Test Drive" comparing a stock 2001 Lexus IS300 to a second IS300 equipped with Eibach Pro-Kit Sport Springs, and a third IS300 equipped with both Eibach Pro-Kit Sport Springs and Eibach Anti-Roll Kit Sway Bars. While an Eibach sport suspension system would typically includes Pro-Kit Sport Springs, Pro-Control Dampers, bump stops (where appropriate) and an Anti-Roll Kit, Eibach currently only offers Pro-Kit Springs (which include new bump stops) and an Anti-Roll Kit for our 2001 model year Lexus IS300 test cars. Rather than wait for the Pro Dampers to become available during the winter of 2001, we elected to compare Eibach's current suspension components to those used to equip a stock IS300.

All three cars were equipped with a wheel and tire package that consisted of Dunlop SP Sport 9000 Hydro Max Performance tires in the 215/45ZR17 size mounted on 17' x 7' alloy wheels. The Dunlop SP Sport 9000 radial's most immediately recognizable feature is its unique tread design. It has a distinctly directional pattern that is comprised of many relatively narrow 'fingers' of varying lengths. In Dunlop's testing this design was shown to spray water to the sides of the tire enhancing hydroplaning resistance and wet traction. The SP Sport 9000 also features a tread compound that has a very high silica content to further enhance wet traction while improving wear and reducing rolling resistance. The SP Sport 9000's internal construction features the latest technology to enhance ride comfort as well; single strand beads provide a more uniform fit to the wheel while JointLess Bands (JLB) of nylon enhance high speed durability and tire uniformity while minimizing weight.

Stock Lexus IS300 Springs and Sway Bars

The Lexus IS300 sport sedan is equipped with either 17' x 7' alloy wheels fitted with 215/45ZR17 summer tires, or 16" x 6.5" alloy wheels fitted with 205/55VR16 All-Season tires as a no-cost option. Since these tire and wheel sizes reflect a Plus Size type application right from the factory, the overall diameter of the car's 16" tire's diameter must remain close to the standard 17" tire's diameter (comparing these two sizes reveals that the 205/55VR16 tire is just 1/4" (about +1%) taller than the 215/45ZR17 tire).

As a rule of thumb, if a tire's visible sidewall height is equal to, or less than the vehicle's wheelwell gap (the distance from the lower edge of the wheelwell to the outer circumference of the tire) it will create an optical illusion that may make the vehicle appear 'lifted.' However, while both tires have equivalent overall diameters, the visible sidewall height of the 205/55R16 sized/55R16-sized tire is 3.75', while the visible sidewall height of "Plus One" sized 215/45R17 tire is only 3'. In the parking lot, we measured the silver IS300's stock wheelwell gap and found it to be about 2.5' in the front, and about 2.25' in the rear. Then we compared the relationship of wheelwell gap to visible tire sidewall height and confirmed that while the IS300 would appear "normal" with the 16" tire's visible sidewall height of 3.75', it looked a little 'lifted' with the 17" tire's reduced visible sidewall height of 3'.

On the road, the stock IS300 equipped with the Dunlop SP Sport 9000 tires was praised for its low noise level, good ride comfort and responsive handling.

On the track, the Dunlop SP Sport 9000 tires allowed the Lexus to run fast lap times, but compared to the other two cars, the stock suspension felt 'slower.' The stock car's motions (squatting during acceleration, diving during braking and leaning in the corners) weren't controlled as precisely or completely. This resulted in less ultimate cornering power and slower vehicle response during transitions. The car with the stock suspension turned in the slowest lap times of the three combinations tested.

Eibach Pro-Kit Springs and Stock Sway Bars

Our next test car was equipped with Eibach Pro-Kit Sport Springs. Pro-Kit springs are designed specifically for each vehicle, and are engineered to properly lower the vehicle and its center of gravity. This helps reduce the amount of vehicle movement during quick acceleration, cornering and braking maneuvers. Eibach Pro-Kit springs typically use progressive rates to maximize improvements in handling while minimizing disturbances to the vehicle's ride quality. This allows them to offer close-to-stock rates during normal driving for ride comfort, yet increase stiffness when the vehicle leans as it's pushed to the limit. Eibach Pro-Kit sport springs are engineered to remain securely in the vehicle's spring perches at all times to prevent them from shifting or rattling around (even when the vehicle is lifted off of the ground on a hoist) and maintain the vehicle's load capacity with little additional risk of 'bottoming' the suspension.

Vehicles equipped with higher performance wheels and tires benefit from the additional suspension performance provided by Eibach Pro-Kit Sport Springs. Performance tire and wheel packages usually generate more traction that often results in additional body movement when the vehicle is driven hard. The Eibach Pro-Kit is designed with overall higher than stock spring rates to control this additional body movement at the limit.

In the parking lot, the addition of Eibach Pro-Kit Sport Springs on our black Lexus IS300 also caught your eye. However this time, the second look revealed that the Eibach Pro-Kit equipped car with the 17' wheel and tire package looked hunkered down on its suspension. The Pro-Kit springs reduced the front wheelwell gap by about .5' resulting in a wheelwell gap of only about 1' (which is much less that the 3' visible sidewall height of the factory 17" wheel and tire package). Rear wheelwell gap was reduced to about 1' from the approximate 2.25' gap with the stock suspension.

On the road, the Eibach Pro-Kit Sport Spring equipped Lexus IS300 was praised for its low noise level, and provided ride comfort that was considered to be equivalent to the stock suspension. However, this combination provided more responsive handling.

On the track, the Eibach Pro-Kit Sport Spring equipped Lexus felt well 'matched' to its tires. More of the SP Sport 9000 tire's traction could be used, and this combination allowed the Lexus to run lap times which were about 4/10 of a second faster than the IS300 with the stock suspension. The Eibach Pro-Kit Sport Spring equipped Lexus's lower center of gravity and higher than stock progressive spring rate controlled the vehicle's motions (squatting during acceleration, diving during braking and leaning in the corners) more precisely and completely. This resulted in more cornering power and faster vehicle response during transitions. The car with the Pro-Kit suspension turned in the middle lap times of the three combinations tested.

Eibach Pro-Kit Springs and Eibach Anti-Roll Kit Sway Bars

Our next test car was equipped with both Eibach Pro-Kit Sport Springs and Eibach Anti-Roll Kit Sway Bars. While springs and sway bars both help control the motions of the car, the job of the sway bars is to help balance the vehicle's handling by distributing the work load between the front and rear tires by resisting body lean when the vehicle is cornering. Eibach Anti-Roll Kits are designed specifically for each vehicle and may contain a front and/or rear sway bar depending on the needs of the vehicle. Eibach Anti-Roll Kit sway bars come complete with all required hardware and many have multiple mounting holes at their ends to allow fine-tuning the bar's stiffness and the vehicle's handling.

Sway bars run from one side of the vehicle to the other, and are typically mounted to the vehicle's frame in the center, and to its suspension control arms at the ends. One of their advantages is that they don't adversely affect ride quality during most driving conditions. When the vehicle hits a dip or a bump with both tires on an axle at the same time, the sway bar doesn't resist the up and down movement of the suspension. For that matter, the only time sway bars influence ride quality is when only a single wheel hits a pothole or bump.

In the parking lot, since sway bars don't affect ride height, the look of our blue test car didn't change from that of the black Pro-Kit equipped car. It retained an aggressive stance and a hunkered down look.

On the road, the Eibach Pro-Kit Sport Spring and Anti-Roll Kit equipped Lexus IS300 was also praised for its low noise level and good ride comfort. This combination provided even more responsive handling which was quick to transmit the driver's inputs. However, when traveling on our rough, two-lane country road, the single wheel bumps were more noticeable.

On the track, this combination added a little more "sport" to the IS300 sport sedan's theme. Body roll was reduced allowing faster speeds around the skid pad portion of our track, and driver input was quickly rewarded with changes in the vehicle's direction during the transitions. The Eibach Pro-Kit and Anti-Roll Kit equipped Lexus turned in the fastest laps of the day. It was an additional 2/10 of a second faster than the Pro-Kit equipped car and almost 7/10 of a second faster than the stock car. This car was the easiest to drive at the limit and its tires showed the least wear at the end of the day, a rewarding combination.


Need help choosing the right products for your vehicle? Our team of highly trained experts has
the knowledge and passion to help. Just pick up the phone and give us a ring.

Or let's chat via email. We love solving problems and lending a hand (or an ear).

Contact Us