2004 Honda S2000 -- Chassis

Chassis

Overview

A front-engine/rear-wheel-drive configuration is used for the S2000. This "classic" layout is widely regarded for its excellent handling characteristics and direct, linear response to control inputs from steering, brakes and throttle.

Steering is by an electrically assisted, power rack-and-pinion system. The braking system uses 4-wheel discs and ABS. The system has been specially engineered for optimum efficiency, feedback and control.

New for 2004

Objectives for enhancing the 2004 S2000 chassis included simultaneously improving both at-the-limit track performance and the street performance during everyday driving conditions. Honda engineers re-visited the performance of the tires and suspension to improve overall handling of the S2000 and enhance "limit controllability." To accomplish this, the tire size was increased, body rigidity improved, rear suspension bump steer qualities minimized, and the rear roll center was lowered.

Significant changes include:

  • Revised spring, shock absorber and stabilizer bar rates
  • 17-inch wheels and tires (increase from 16-inch)
  • Optimized rear toe settings
  • Enhanced suspension bushings
  • Revised Electrically Powered Steering (EPS) programming with optimized steering gearbox ratios and enhanced steering bushing rigidity
  • Body rigidity increased
  • Brake pedal rigidity and build-up feel increased
  • Brake pads upgraded to enhance brake fade durability and master cylinder power ratio optimized

2004 S2000 Suspension Features

The following Honda-designed chassis features contribute to the S2000's exceptional handling and response:

  • 50/50(front/rear) weight distribution
  • Entire drivetrain located behind the centerline of the front axle (front mid-engine layout). This helps lower the vehicle's center of gravity and helps to centralize vehicle mass, resulting in a low yaw moment and more responsive vehicle behavior
  • Wide track (57.8 in. front/59.4 in. rear) contributes to vehicle stability and chassis rigidity
  • Highly rigid "high X-bone frame"
  • Compact, highly rigid 4-wheel "in-wheel" double wishbone suspension allows for low hoodline
  • Mono-tube shock absorbers
  • Electric power steering system
  • Four-wheel disc brakes (11.8-in. vented front/11.1-in. solid rear), with 3- channel ABS
  • Limited-slip differential
2004 Honda S2000 vs. 2003 Honda S2000 Suspension Specifications
Suspension
2004 2003 Change/Notes
Wheels (inches) Front: 17x7.0
Rear: 17x8.5
Front: 16x6.5
Rear: 16x7.5
Front: + 1x0.5 (new wheel design)
Rear: + 1x1 (new wheel design)
Tires Front: P215/45R17
Rear: P245/40R17
Front: P205/55R16
Rear: P225/50R16
+15/10R1
+20/10R1
Springs New Setting
-
Front: Increased spring rate 6.7
Rear: Decreased spring rate 10%
Shock Absorbers New Setting
-
Tuned for new suspension settings
Stabilizer Bars (mm) Front: 26.5x t4.5
Rear: 25.4 x t4.5
Front: 26.5x t4.5
Rear: 27.2 x t4.5
Front: Same
Rear: -1.8
Brake Pads Jurid632(front) NF71 Solid pedal feel and increased resistance to brake fade
Steering Gear Ratio 14.9:1 13.8:1 Tuned to match new tire size

Benefits from Suspension Changes

  • Improved cornering grip
  • Body torsional rigidity increased for enhanced vehicle stability
  • Greater stability over road disturbances
  • Enhanced stability on wet surfaces
  • Linear steering feel increased with reprogrammed EPS system
  • Dynamic braking qualities improved

50/50 Weight Distribution

Honda engineers wanted the S2000 to have a balanced 50/50(front-to-rear) weight distribution, considered ideal for a front-engine rear-wheel-drive roadster. To accomplish this, and also lower the center of gravity, Honda engineers placed the engine and transmission low in the chassis and behind the front suspension.

Centralized Mass, Low Yaw Moment

Five decades of designing and building racing cars and motorcycles has taught Honda engineers the value of centralizing a vehicle's mass-placing as much weight as possible close to the center of the vehicle. The result is what engineers call a "low polar moment of inertia," which gives the vehicle a lower yaw moment-or less steering delay-which translates into quicker, more linear steering response.

Since light weight is a performance asset, Honda engineers also took great pains to design the S2000's various chassis components to be as light and as compact as possible.

Highly Rigidity Body and X-Bone Frame

The S2000's highly rigid body and frame are major contributors to its excellent handling characteristics. In fact, the S2000 exhibits bending and torsional rigidity (especially important for good handling) better than many closed-top sports cars.

For 2004, S2000 torsional body rigidity has been further increased by 10-percent in the front and 9-percent in the back through the use of four strategic sets of new reinforcements on the body and chassis.

  • Reinforcements have been added to the rear wheel house bulkhead
  • Reinforcements have been added to the front cross members
  • Brackets have been added to the front upper A-arms
  • A performance rod has been added to the front cross member

Benefits from the increase in body rigidity include decreased response lag during steering input, improved steering linearity through enhanced rigidity, and reduced body flex, which can diminish handling qualities.

Designing such a strong structure for the initial S2000 posed challenges because open-topped vehicles have inherently less bending and torsional rigidity. This problem can best be illustrated by removing the lid of a shoe box, and then twisting both its ends in opposite directions. The box twists easily. However, if you repeat the operation with the top in place, you immediately notice how much stiffer the enclosed box has become.

Similarly, unless an open-topped vehicle's body and frame are reinforced, cornering grip and handling control will be compromised. A torsionally weak frame will store, then release suspension energy in an uncontrolled manner, resulting in less tire contact with the road and less steering precision and control.

In order to achieve the desired level of frame stiffness, Honda engineers designed a new monocoque body with a centralized backbone frame for the S2000. This backbone tunnel is enclosed by the floor and runs down the center of the cockpit, between the driver's and passenger's seat. Large side sills provide additional strength. Diagonally braced front and rear bulkheads contribute to tying the frame members together into a strong beam-like structure that resists bending and torsional forces. Crossmembers running under the driver's and passenger's seat add additional stiffness.

The front and rear portions of the central frame and the side sills tie into diagonal braces (X-braces) at the rear of the cockpit and at the front cowl. These X-members connect directly to the front and rear suspension subframes.

Despite the front subframe's lightweight and compactness, its overall lateral rigidity is quite high. In addition, the engine mount structure has been designed so as to minimize the effect of lateral movement in the frame, when cornering.

The rear subframe is a three-dimensional structure consisting of hollow steel pipes that connect the rear side members and floor tunnel to the upper and lower arms of the rear suspension. A deep-section, rear crossmember ties the beams together and anchors the rear of the differential.

Compact (In-Wheel) 4-Wheel Double Wishbone Suspension

The 4-wheel, double wishbone suspension system used on the S2000 contributes greatly to its exceptional handling. The system consists of upper and lower wishbone arms at each wheel, with coil-over spring/damper units and anti-roll bars.

Since optimum weight distribution and balance are such important factors in achieving excellent handling characteristics for 2004 S2000, Honda engineers set the S2000's engine and drivetrain as low and close to the center of the chassis as possible. Suspension geometry (toe, caster, camber, roll centers, etc.) also have a tremendous effect on handling and response, so Honda engineers designed the double wishbone suspension for the S2000 with optimum geometry in mind.

For 2004, modifications have been made to enhance performance at the limit, improve control and reduce unwanted sensitivity to internal and external forces during acceleration and braking. Overall suspension geometry has been enhanced by changing the initial rear toe and bump steer settings, lowering the roll center, and optimizing the shock absorbers, spring rates, stabilizer bar and body rigidity.

The system boasts many features found on road-racing suspension systems, including a compact layout, highly rigid construction, minimal unsprung weight, a low center of gravity and ideal geometry.

The entire S2000 suspension system is very space-efficient. Honda calls it an "in-wheel" suspension (the same design is used on the NSX). The S2000 "in-wheel" system contributes to assuring higher rigidity, as well as allowing for a low hoodline.

The suspension's ductile iron wishbone arms are connected to the body via special rubber bushings, designed to minimize vibration without compromising suspension rigidity.

From a handling standpoint, the 2004 S2000 features improved steering response and accuracy with a more linear overall feel. At-the-limit controllability has also been enhanced along with vehicle stability under heavy accelerator on/off situations.

Wheel Alignment Values:

x 2004 2003
Front:
Toe Angle: 0 0
Camber Angle: - 0 30' - 0 30'
Caster Angle: 6 6
Rear:
Toe Angle: - 0 10' - 0 19'
Camber Angle: - 1 30' - 1 30'

A 1.04x0.18-inch (26.5x4.5mm) front stabilizer bar and a 1.00x0.18-inch (25.4x4.5mm) rear bar contribute to the S2000's and enhanced steering linearity and quality. The bars connect to their respective suspension arms via ball-jointed links.

Mono-Tube Shock Absorbers

The S2000's mono-tube shock absorbers help minimize body roll and contribute to rapid weight transfer, resulting in more neutral cornering behavior and improved power transfer characteristics. They are also less harsh and better damp body vibration, which gives the chassis a more rigid feel. The rear shock absorbers, which feature large remote reservoirs, are attached to the lower wishbones, leaving more space available for the folding top and space-saver spare tire. The 2004 S2000, with the improvement of damping forces, reduces the feel of road disturbance while maintaining ride quality.

Electric Power Steering (EPS) System

The S2000 uses an electrically assisted power steering system in place of the more commonly used hydraulically assisted system. The electric system (first used on the high-performance Acura NSX), offers numerous advantages. The S2000 system is simpler and more compact (there is no need for a pump and hoses) and the power loss is minimized. The system's compactness and simplicity also offer more design freedom. The system is also smoother and more responsive to driver input, and more communicative to the driver.

The system consists of a toothed rack and pinion gear, with a microprocessor-controlled, coaxial electric motor assisting the rack. The microprocessor senses vehicle speed and steering torque and is programmed to vary boost accordingly, providing more boost at low speeds and progressively less at higher speeds. Failure warning, self-diagnosis and self-protection functions are built into the system.

To achieve higher performance, enhancements have been made to the steering system that match the new tire sizes, suspension settings and body rigidity specifications. Also, the rigidity of the steering mount bushings have been increased and the EPS computer has been reprogrammed, resulting in a more linear steering feel.

High-Performance, 4-Wheel Disc Braking System

Honda engineers designed the S2000's brake system to deliver braking performance consistent with the vehicle's other high-performance capabilities. In addition, they wanted the system to be very direct, with a firm pedal feel that enhanced the driver's braking control.

The heart of the system is its four large-brake disc brakes. Front rotor diameter is 11.8 inches (300 mm) and the rear diameter is 11.1 inches (282 mm). The front rotors are also vented for added cooling, while the rear discs are solid. Brake rotors and calipers are cast iron.

The brake calipers are large, highly rigid, cast-iron units. Front piston diameter is 54 mm, and the rear pistons are 40 mm in diameter. The front pad material is Jurid632, a high-performance, low steel, fade-resistant type that enhances the brake pedal's solid feel and helps increase resistance to brake fade. Brake-pad area is 42 square centimeters for the front pads and 27.9 square centimeters for the rear-brake pads.

A 7.8-inch, tandem-vacuum servo-assist unit is used because it offers the best

balance between pedal feel (stiffness) and assist. Braking bias-front-to-rear-has also been optimized so that the front and rear brakes operate at maximum braking efficiency during heavy braking.

Anti-Lock Brake System (ABS)

The anti-lock braking system (ABS) is a compact type that incorporates the solenoid valve, motor and ECU into the modulator body, thereby saving both space and weight. The ABS system is a four-sensor, three-channel system with a speed sensor located at each wheel. There is a separate channel for each front wheel and the rear wheels share a common third channel. This is a "select-low" system, meaning the system controls both rear-wheel slave cylinders together when it senses incipient wheel lockup in either wheel.

The system uses the memory capacity of the system's Electronic Control Unit (ECU) and allows the system to better estimate vehicle speed, which gives it better control in the lower-slip range. This contributes to superior braking efficiency and stability. For the 2004 S2000, with improvement of both hardware and software in the compact ABS modulator, memory capacity has increased and new program logic has been added which enhances braking efficiency and reduces the weight of the system.

Wheels and Tires

Larger wheel and tires for the 2004 S2000 improve overall grip and cornering performance. The S2000 features Bridgestone Potenza RE 050 215/45R 17 87W front tires, mounted on 17 x 7.0 jj aluminum-alloy wheels. The rear tires are 245/40R 17 91W and are mounted on 17 x 8.5 jj aluminum-alloy wheels. A space-saver spare tire is in the trunk.

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