Honda S2000 -- Chassis

OVERVIEW
A front-engine/rear-wheel-drive configuration was chosen 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 -- especially when approaching the chassis and tires' adhesion limit.

Since optimum weight distribution and balance are such important factors in achieving excellent handling characteristics, 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 an all-new double wishbone suspension for the S2000 with optimum geometry.

Steering is by an all-new electrically assisted, power rack-and-pinion system, similar to the system used on the NSX. The braking system uses 4-wheel discs and ABS. The system has been specially engineered for optimum efficiency, feedback and control.

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 Honda-designed 3-channel ABS
  • Limited-slip differential

50/50WEIGHT 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 RIGID BODY AND 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.

Designing such a strong structure for the S2000 posed additional 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 light weight 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.

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.

Neutral cornering response can be improved through increased roll stiffness and quicker weight transfer. The stabilizer bar's effectiveness, and thus roll stiffness is increased here through the adoption of ball-jointed lower arms. At the rear, changes in lateral force, as tread (track) varies with suspension movement and the accompanying jacking effect, are used to increase weight-transfer speed and aid in neutral cornering power pickup.

WHEEL ALIGNMENT VALUES:
Front: Toe Angle: 0*
Camber Angle: -0* 30'
Caster Angle: 6*
Rear: Toe Angle: 0* 17'
Camber Angle: -1* 30'

A 1.11-inch diameter front stabilizer bar and 1.07-inch rear bar contribute to the S2000's flat cornering and enhanced steering linearity. The bars connect to their respective suspension arms via ball-jointed links.

The rear dampers, which feature large remote reservoirs, are attached to the lower wishbones, leaving more space available for the folding top and space-saver spare tire.

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.

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.

Steering kingpin and caster angles have been optimized for better steering feel, and a quick 13.8-to-1 gear ratio also contributes to the car's nimble and direct steering characteristics.

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 their rear discs are solid. Brake material is 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 pad material is a high-performance, fade-resistant type. 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, single-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.

HONDA-DESIGNED 3-CHANNEL ABS
The anti-lock braking system (ABS) is a new 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.

Increasing the memory capacity of the system's Electronic Control Unit (ECU) 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.

WHEELS AND TIRES
The S2000 features 205/55R 16 89W front tires, mounted on 16" x 6.5" jj aluminum-alloy wheels.

The rear tires are 225/50R 16 92W and are mounted on 16" x 7.5" jj aluminum-alloy wheels.

A space-saver spare tire is in the trunk.

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