Suspension Component Test Results

Good...Better...Best, the Eibach Pro-Kit Ride And Drive

Suspension Components Tested

Eibach Pro-Kit Spring Set (w/Lexus O.E. Struts/Shocks & Sway Bars) w/+1 Sized Tires
Lexus Original Equipment Springs, Struts/Shocks & Anti-Roll Bars w/+1 Sized Tires
Lexus Original Equipment Springs, Struts/Shocks & Anti-Roll Bars w/O.E. Sized Tires

Vehicles Used
1998 Lexus GS300 Sedan

Introduced in 1998 with 225 horsepower under the hood, a 5-speed automatic transmission, rear wheel drive and standard 16" diameter wheels and tires, the Lexus GS300 is one of the world's newest luxury sport sedans. But as always the real question is "How can it be improved for more enthusiastic drivers?"

Typically one of the first changes is to replace the vehicle's original wheels and tires. This allows the drivers to pick out their favorite wheel style and tire type, and often results in the installation of a "Plus Size" package which combines lower profile tires with larger diameter wheels. A correct Plus Size wheel and tire package has approximately the same overall diameter as the original wheels and tires and keeps the vehicle's computer controlled, speed sensitive functions operating as designed.

The next step is to lower the vehicle. It's important to note that modifying a vehicle's original springs almost always ends with unsatisfactory results. Cutting off coils or collapsing stock springs with heat will adversely affect the springs' rate and internal stresses and often prevent them from fitting the vehicle's suspension correctly. Properly engineered aftermarket sport springs are not only designed to fit the vehicle, but will enhance its appearance and its performance all at the same time.

Vehicle appearance is improved in two ways. Sport springs will typically lower vehicles to give them a more aggressive stance and reduce the vehicle's fender well gap (the distance between the top of the tire and the bottom of the wheelwell). When the vehicle is viewed from the side, the wheel and tire will appear to properly "fit" in the wheelwell when the tire's sidewall height is greater than the vehicle's fender well gap. But when the tires have less sidewall height than the vehicle has fender well gap, it may look out of proportion and even create the illusion that the vehicle has been "lifted." Sport springs help complete the vehicle's appearance by lowering the vehicle and reducing fender well gap.

Vehicle performance is also improved in two ways. Sport springs reduce the vehicle's ride height and feature higher spring rates that are carefully tuned to the vehicle. This not only assures sufficient load capacity, but lowers the vehicle's center of gravity for added stability and improves the vehicle's responsiveness by reducing body movement. This allows the tires to function more effectively when they are asked to perform at their limit.

Eibach is one of the world's leading spring manufacturers and supplies everyone from casual driving enthusiasts to professional racing teams. Their products are built to the highest standards and meet Germany's tough TUV standards. For most cars Eibach offers sport springs in two versions.

  • Pro-Kit spring sets typically lower vehicles about .75" to 1.25" and increase the spring rate just enough to provide an enthusiast's balance between ride comfort and handling.
  • Sportline spring sets typically provide increased vehicle lowering (as low as Eibach suspension engineers say you can realistically go on the street) of about 1.5" to 2.0" and further increase the spring rate to improve handling and help prevent the car from "bottoming out" over bumps and rough pavement. The Sportline spring set's goal is to make the car as low as possible.

Since a Lexus isn't a typical Sportline spring set candidate (you don't really expect to see many of them slammed to the ground, do you?) Eibach only offers a Pro-Kit spring set for our GS300 test cars.

In order to get a better appreciation of how a wheel and tire package, and a wheel, tire and spring package can improve an otherwise stock vehicle's looks and performance, we conducted a Real World Road Ride and Performance Track Test Drive using three Lexus GS300 test cars equipped as follows:

Car Springs Tire Type Tire Size Wheels/Size
Standard Goodyear Invicta GA "L" P215/60VR16 O.E. 16"
Standard Goodyear Eagle F1 Steel P245/45ZR17 +1 17"
Eibach Pro-Kit Goodyear Eagle F1 Steel P245/45ZR17 +1 17"

Lexus GS300 Stock - Good

As noted earlier, the Lexus GS300 is a good test vehicle in its stock form because of its combination of horsepower, rear wheel drive and 16" diameter wheels and tires. Our test car's Original Equipment Goodyear Invicta GA (L) tires were designed specifically for the Lexus GS300, and are unique because they combine a high speed internal construction (to match the car's top speed) with a traditional All-Season tread design (to match typical American driving conditions).

On the road the Lexus GS300's stock springs and Invicta GA (L) tires provided the most comfortable ride overall, although compared to the other cars some of our team members felt that they might be just a little "too" soft. And while the stock GS300's ride comfort ratings were the highest, it actually finished slightly behind the other two cars when combined with our real world handling ratings.

On the track the stock GS300 provided good cornering and braking traction but couldn't match the other two car's handling and responsiveness.

Lexus GS300 With Wheels and Tires - Better

Adding 17" diameter wheels and tires to the GS300 complemented its sporty personality without sacrificing much of its comfort. The new Goodyear Eagle F1 Steel used for this evaluation is the first ultra high performance tire to feature a single ultra-tensile steel radial carcass ply (which replaces the traditional fabric plies used in other performance tires). The ultra-tensile steel carcass helps the tire resist cuts and bruises while it enhances handling and improves treadwear. The Eagle F1 Steel radial's tread is further supported by 2 angled steel belts that are reinforced by spirally wound aramid cap plies to enhance handling, high speed capability and ride quality. The Eagle F1 Steel radial's directional tread design also features Goodyear's AATRAX tread compound and earns the highest UTQG grade of "AA" for wet braking traction.

It should be noted that while the Eagle F1 Steel shares ultra tensile steel carcass ply technology with Eagle Aquasteel tires, Eagle F1 Steel radials are NOT run-flat tires. They are designed to use standard wheels and do not require low tire pressure warning sensors.

On the road the 17" wheels and tires added real world handling and came surprisingly close to the stock GS300's ride comfort levels (however, remember that the GS300's Original Equipment Invicta GA (L)'s internal construction is stout enough to earn a V-Speed Rating). The Eagle F1 Steel also proved to be quiet on the road even though the P245/45R17 size tested was about 15% wider than stock P215/60R16 size.

On the track the wheel and tire package added traction, responsiveness and handling that was noticeably better than stock and produced quicker lap times.

Lexus GS300 With Wheels, Tires and Pro-Kit Springs - Best

Combining Eibach Pro-Kit sport springs with the wheel and tire package seemed to help complete the GS300's sporty personality. The Eibach Pro-Kit spring set lowered the GS300 by about 1.0" at all four corners and reduced the fender well gap far enough to allow the 17" wheel & tire package look just right. Like most Pro-Kit springs, the GS300's set features progressive rate springs (which as the name implies get progressively stiffer as they are compressed). This allowed the Pro-Kit equipped car to begin with near stock spring rates (for good ride comfort) which increase as the vehicle is driven hard and cornered at its limit (to enhance responsiveness and handling).

On the road the wheel, tire & spring combination provided very good ride quality, with the progressive rate springs absorbing small road irregularities and only becoming noticeable on larger dips and bumps.

On the track the wheel, tire & spring combination GS300 ran the quickest lap times by being more responsive during transitions and more stable in the corners. And while the Eibach Pro-Kit equipped car turned the fastest lap times, its Eagle F1 Steel radials showed less treadwear than the ones used on the car equipped with just the wheel and tire package at the end of our track day.

"Wheels, Tires & Springs"...they all go together!


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