2005 Acura RSX Chassis

9/1/2004 4:15:00 AM

Chassis

OVERVIEW

The RSX chassis was designed to achieve quick handling response, outstanding grip, a smooth and compliant ride, excellent stability, and exceptional packaging efficiency to help maximize spaciousness in the passenger cabin and engine bay.

For 2005, the goal for improving the RSX chassis was to simultaneously increase handling precision and enhance ride quality. The suspension, steering and braking systems of both models were substantially enhanced with that objective in mind.

The 2005 RSX features a Control-Link MacPherson Strut front suspension design. This advanced design provides the precise handling, stability and comfort of a double-wishbone layout with packaging efficiency that is difficult to achieve with a conventional front double-wishbone design. At the rear, a highly compact double-wishbone suspension improves handling, ride comfort, stability, and space efficiency. To deliver an even more high performance driving experience, the Type-S suspension features stiffer rear springs and more compression and rebound damping front and rear.

For 2005, the suspension geometry (camber and caster) on both models was optimized, damper, spring and stabilizer bar rates were changed, and bushings were retuned. In addition, inversely wound front coil springs were applied to minimize the affect of suspension compression on steering precision. Type-S models also receive a more rigid strut tower bar to further increase body rigidity.

The RSX wears standard 205/55R16 all-season high-performance tires on 16-inch, five-spoke alloy wheels. For 2005, the RSX Type-S gets enhanced traction with new 17x7-inch alloy wheels and Michelin 215/45R17 high-performance all-season tires.

Secure stopping power is provided by large-diameter disc brakes equipped with a standard Anti-lock Braking System (ABS). The RSX is equipped with 10.3-inch ventilated front discs, while both models use 10.2-inch discs at the rear. The high-performance Type-S uses 11.8-inch ventilated discs in front. The braking systems on both models were enhanced for 2005 to provide enhanced brake feel and improved performance. A larger master cylinder was applied to provide an upgraded brake pedal feel, the rigidity of the pedal itself was increased and the pedal stroke was decreased to supply a more immediate braking response.

The RSX utilizes a torque-sensitive, rack-and-pinion power steering system equipped with a variable capacity power-steering pump. For 2005, the flow of this pump was increased to provide greater hydraulic pressure and quicker catch-up during aggressive cornering. In addition, the steering ratio was retuned to provide quicker steering response and the rigidity of the steering column was increased for a more solid steering feel.

Chassis At A Glance

Ride and Handling

  • State-of-the-art Control-Link MacPherson Strut front suspension
  • Compact, high-performance double-wishbone rear suspension
  • 16-inch tires and alloy wheels for RSX
  • New for 2005, 17-inch tires and alloy wheels for RSX Type-S
  • High-mounted steering box with long control arms for improved toe control (tracking stability)

Braking

  • Large-diameter front and rear disc brakes
  • Superior pedal rigidity and higher braking force for enhanced feel

Steering

  • Quick-ratio power steering system for crisp handling
  • Variable-capacity power-steering pump for excellent driver feedback and improved fuel efficiency
  • Steering damper for more solid feel and enhanced straight-line stability

Safety

  • Standard four-sensor, three-channel Anti-lock Braking System (ABS)

FRONT SUSPENSION

The front suspension of the RSX combines performance-tuned handling (including superb grip and responsiveness) with positive feedback and road feel, a smooth and fluid ride, excellent space efficiency, and a reassuring level of safety.

After analyzing these objectives, the RSX engineers designed a state-of-the-art Control-Link MacPherson Strut front suspension with performance comparable to a double-wishbone system. Compared with conventional strut designs, this design provides superior suspension geometry and control by adding a control link to precisely vary toe change throughout the suspension's travel. This suspension helps increase the front tire's contact with the road-enhancing handling performance and stability, particularly during sporty driving. For superb refinement, the layout incorporates low-friction progressive-valve gas-pressurized shock absorbers that more effectively absorb bumps and other road shocks.

The compact design of the Control-Link MacPherson Strut front suspension helps to maximize packaging efficiency, providing added room for the RSX's high-output engines and increasing the spaciousness of the cabin. This layout also provides advantages simply not obtainable with a conventional front double-wishbone suspension, including the ability to incorporate a high-mounted steering gearbox. This arrangement uses 43 percent longer, high-mounted tie rods to steer the vehicle and provide improved toe control (the amount the tires angle in toward the body). The steering system also provides exceptional tracking stability during cornering.

For 2005, the front suspension was retuned on both RSX models to provide even more precise handling, improve cornering grip and ensure a smooth, compliant ride.

Because suspension geometry (caster, camber, toe, roll centers, etc.) has a tremendous affect on handling and response, both the camber and caster were optimized for 2005. The caster trail was increased by 65 percent from 9.9 mm to 28.6 mm, to enable more predictable steering, especially at speed. The camber angle was increased by 50 percent for maximized tire contact with the road during cornering

The new geometry and suspension settings lower the car's center of gravity by 7 mm, helping to reduce body roll and enhance stability. Spring and damping rates were optimized to match the new geometry while a new damper seal helps improve ride comfort by dramatically reducing static friction.

Construction of the front compliance bushings (used where the lower control arm attaches to the subframe) was adjusted (4 mm longer stroke and 20 percent lower spring rate) to improve handling while boosting ride comfort.

To provide even more agile steering for the Type-S model, front damper bushings (where the strut mount attaches to the body) were replaced by bearings to decrease friction, allowing the wheels to turn more easily in response to driver input and thereby increase steering feel.

On vehicles that utilize a strut front suspension design, since the strut is responsible for load bearing, drive forces during the suspension's compression stage can sometimes influence steering precision. As the springs compress, they exert torsional force in the opposite direction on the steering mechanism and sometimes make the car pull to the side. To neutralize this affect, Acura designers applied inversely wound (wound in the opposite direction) coil springs to the front struts. Because the two front springs compress in opposite directions, the torsional force they produce cancels each other out, minimizing their affect on steering.

The rigidity of the stabilizer bars was also changed on both models to reduce body roll during cornering. On the RSX, the diameter of the front stabilizer bar increased from 23 mm to 25.4 mm and the wall thickness went from 2.8 mm to 3.0 mm. Front stabilizer bar diameter on the Type-S went from 23.0 mm to 26.5 with wall thickness increasing from 2.8 mm to 3.5 mm.

Horizontal and vertical rigidity of the strut tower bar on Type-S models was reinforced by 13 percent and 26 percent respectively to minimize body flex and enhance traction during cornering.

REAR SUSPENSION

The RSX features a compact double-wishbone suspension designed to provide excellent handling, ride comfort, stability, and space efficiency. The geometry of this suspension arcs the tires rearward when compressing over bumps to reduce road shock and provide a smoother, more comfortable ride. By optimizing the rigidity of the body, bearings, control arms, and stabilizer bar, the rear suspension provides secure tire-to-ground contact for smooth, predictable handling. Rear toe-in during braking helps improve the vehicle's stopping stability.

At the same time, this highly compact design uses less space than conventional double-wishbone systems because there is no trailing arm alongside the fuel tank. Freeing up space in this manner allowed the engineers to place the exhaust pre-chamber in the rear-instead of in the cabin floor, enabling them to design a wider trunk and a flat floor in the interior.

Like the front suspension, the double-wishbone rear suspension of the RSX has been carefully retuned for 2005 to deliver even better handling, stability, and ride comfort.

The camber angle was increased by 30 percent and rear spring height was reduced, helping to lower the Type-S model's center of gravity.

Spring and damping rates were optimized for a more exacting combination of handling and ride comfort. The spring rate of the bushings at the suspension mounting points was lowered to minimize vibration without compromising suspension rigidity. The diameter of the rear stabilizer bar was increased from 19 mm to 21 mm to provide increased road-holding capability.

STEERING

The RSX uses a torque-sensitive, rack-and-pinion power steering system equipped with a variable-capacity power-steering pump. By incorporating a relief valve, which adjusts necessary power assist through oil-quantity control, the pump is able to achieve a linear injection volume. Unnecessary oil flow at 900 rpm and above is eliminated-increasing fuel economy by 0.5 percent. For 2005, pump flow was enhanced by seven percent, creating increased hydraulic pressure and allowing the steering to better "catch-up" during aggressive slalom-type driving. A kickback reduction valve has also been added to reduce steering kickback when driving over bumps or objects in the road.

Also, for 2005, a quicker steering ratio (14.9 vs. 15.1:1 for 2004) was applied for more nimble handling and this, combined with the stiffer stabilizer bars also enhances turn in. The steering column was also reinforced, increasing stiffness by 45 percent for an even more solid steering feel.

Steering smoothness and directional stability are enhanced with a vibration-reducing, oil-filled damper in the steering box.

Tracking stability is enhanced by the high-mounted steering box, which improves toe control (the amount the tires angle in toward the body) by using long, high-mounted tie rods to steer the vehicle.

BRAKING SYSTEM

For outstanding stopping power and excellent resistance to fade, the RSX is equipped with 10.3-inch ventilated front disc brakes and 10.2-inch rotors at the rear.

On the Type-S, the ventilated front rotors are increased in diameter to 11.8 inches. In addition, front caliper piston area has been reduced for improved rigidity, and braking force has been increased for a notably solid, linear pedal feel.BRAKING SYSTEM (continued)

For 2005, enhancements were made to the braking systems that are designed to improve braking feel and pedal responsiveness. The pedal stroke ratio was reduced by five percent for a shorter stroke and more linear brake feel. A flange was added to the pedal for a 50 percent increase in pedal rigidity and lastly, a larger diameter master cylinder was applied to increase brake fluid displacement and enhance brake pedal feel. The result is a 5.4 percent improvement in dry braking and a 9.7 percent improvement in wet braking according to internal testing.

ANTI-LOCK BRAKING SYSTEM

Standard on both RSX models is a three-channel Anti-lock Braking System with a speed sensor located at each wheel. The system modulates braking power to the front wheels independently and to the rear wheels in tandem-enhancing driver control during maximum-effort stops.

WHEELS AND TIRES

The RSX wears large wheels and tires in keeping with its race-bred, sports coupe breeding. The RSX features 205/55R16 Michelin MXM-4 all-season high-performance tires on strong, lightweight 16-inch, five-spoke cast-alloy wheels. For 2005, the RSX Type-S comes with new 17x7-inch alloy wheels and Michelin 215/45R17 tires.

FLAT FLOOR

The unique flat floor of the RSX-made possible by the compact rear suspension and such innovations as a high-efficiency exhaust system-helps make the cabin remarkably spaciousness and comfortable. To improve the floor's torsional rigidity, the RSX uses a "tunnel side frame" with a large, flat cross-section instead of the usual tunnel structure.

RESIN FUEL TANK

The RSX is equipped with a four-layer resin fuel tank that offers reduced weight, increased capacity, and reduced emissions. Capacity is maximized because the resin tank can be molded to fit around other components. For 2005, the shape of the fuel tank was optimized to reduce fuel evaporation. This reduction lowered evaporative emissions by 75 percent, enabling the RSX to achieve a LEV2 rating. The RSX also incorporates a returnless fuel supply system that helps reduce vapor generation.