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. To meet the demands of today's discriminating drivers, both RSX models boast a sport-tuned suspension system, which has been substantially retuned for 2005 to make the RSX even more fun to drive. An increase in front and rear body rigidity result in even more responsive handling while at the same time enhancing ride comfort.
New for 2005, the Type-S model receives standard 17-inch alloy wheels (up from 16-inch) fitted with Michelin 215/45R17 all-season high-performance tires, which provide enhanced traction and a more substantial appearance under the wheel wells.
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. 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. Type-S models also receive a more rigid strut tower bar to further increase body rigidity. 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.
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.
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. 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.
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.
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.
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.
Source: Honda PR