Nissan 240sx Super Hicas Suspension

Imagine trying to parallel park a shopping cart. You steer the front wheels, but the back wheels stubbornly resist, making the whole process awkward and inefficient. Now, imagine if the shopping cart had rear wheels that could subtly steer themselves, working with your front wheel input. That's the basic concept behind Nissan's Super HICAS (Highly Integrated Capability Actuated Suspension) system, a technology that aimed to improve handling and stability, particularly during high-speed maneuvers, on cars like the iconic 240SX.

The Mechanics of Rear-Wheel Steering

Super HICAS, introduced in the late 1980s, wasn't just about slapping some extra steering linkage onto the rear axle. It was a sophisticated system that used sensors, a control unit, and a hydraulic actuator to precisely control the rear wheel steering angle. To truly understand it, let's break down the key components and their functions:

1. Steering Angle Sensor

This sensor, located in the steering column, measures the driver's steering input – how much the steering wheel is being turned. This is the primary input for the Super HICAS system. The information from this sensor is crucial for determining the desired rear wheel steering angle.

2. Vehicle Speed Sensor

Vehicle speed plays a vital role in how much rear steering is applied. At lower speeds, the system generally reduces or eliminates rear steering to avoid oversteer and instability. At higher speeds, the system becomes more active to enhance stability and responsiveness. This sensor provides the control unit with the necessary speed data.

3. Lateral G-Force Sensor

This sensor detects the lateral acceleration (side-to-side force) acting on the vehicle during cornering. This is a key indicator of how much the car is actually turning and helps the system fine-tune the rear steering angle to optimize the car's trajectory. A sharp turn will generate higher lateral G-force.

4. Control Unit (ECU)

The ECU is the brain of the Super HICAS system. It receives data from all the sensors (steering angle, vehicle speed, lateral G-force), processes this information using a pre-programmed algorithm, and then sends commands to the hydraulic actuator. This algorithm is specifically designed to provide optimal rear steering assistance under various driving conditions.

5. Hydraulic Actuator

This is the muscle of the system. Based on the signals from the ECU, the hydraulic actuator precisely controls the steering angle of the rear wheels. It uses hydraulic pressure, typically supplied by the power steering pump, to move the rear tie rods, which in turn steer the rear wheels. The actuator's precision is critical for achieving the desired handling characteristics.

6. Rear Suspension Linkage

The 240SX's multi-link rear suspension was modified to incorporate the Super HICAS system. Extra linkages and joints were added to allow the rear wheels to steer independently of the rest of the suspension movement. This requires robust and precise components to ensure the system operates smoothly and reliably.

How It All Works Together

Imagine you're entering a sweeping corner at highway speed in your 240SX. Here’s what happens:

1. You turn the steering wheel. The steering angle sensor detects the input.
2. The vehicle speed sensor confirms that you are traveling at a speed where Super HICAS should be active.
3. The lateral G-force sensor detects the lateral acceleration as the car begins to lean into the turn.
4. All this data is fed to the ECU.
5. The ECU calculates the optimal rear steering angle (typically a small angle, often less than one degree) based on its programming.
6. The ECU sends a signal to the hydraulic actuator.
7. The hydraulic actuator moves the rear tie rods, causing the rear wheels to steer slightly in the same direction as the front wheels. This is known as phase steering.

This subtle rear steering action helps the car rotate more smoothly into the turn, reducing understeer and improving overall stability. The system continuously adjusts the rear steering angle based on the changing conditions, ensuring optimal handling throughout the maneuver.

Pros and Cons of Super HICAS

Like any technology, Super HICAS has its advantages and disadvantages:

Pros:

• Improved High-Speed Stability: Super HICAS helps to reduce yaw and improve directional stability, especially during lane changes and emergency maneuvers.
• Enhanced Cornering Performance: The system can reduce understeer, allowing the car to rotate more easily into corners.
• Reduced Steering Effort: In some situations, the system can make the steering feel lighter and more responsive.

Cons:

• Complexity and Maintenance: The system is complex, with multiple sensors, actuators, and hydraulic components. This increases the potential for failure and makes maintenance more challenging and expensive.
• Weight: The added components of the Super HICAS system increase the overall weight of the vehicle.
• Potential for Unpredictability: If the system malfunctions or the sensors are inaccurate, it can lead to unpredictable handling behavior.
• Drifting Difficulty: The system is tuned for stability, which can conflict with the requirements of drifting. The rear steer correcting your drift angle can be a nuisance to maintain the desired angle.
• Added Complexity for Modifications: Aftermarket modifications to suspension or steering can be more difficult and require careful consideration to ensure compatibility with the Super HICAS system.

Use Cases and Manufacturer Examples

Super HICAS was designed for vehicles that prioritize handling and stability. While most famously found on the Nissan 240SX (S13 and S14 chassis), it also appeared on other Nissan models, including the Skyline GT-R (R32, R33, and R34) and the 300ZX (Z32). In the Skyline GT-R, the system was integral to the car's legendary handling prowess and played a key role in its success in motorsports. The 300ZX benefited from the enhanced stability it provided at higher speeds.

Other manufacturers have implemented similar rear-wheel steering systems over the years. Honda offered 4WS (Four-Wheel Steering) on models like the Prelude, and Mazda had its own system called 4WS on certain variants of the 626 and RX-7. While the specific implementations varied, the underlying principle was the same: to improve handling and stability through active rear-wheel steering.

Real-World Considerations and Recommendations

The Nissan 240SX is now a classic car, and many examples on the road today are modified or have aged Super HICAS systems. Here are some real-world considerations for owners and enthusiasts:

• Maintenance is Key: Regularly inspect and maintain the Super HICAS system. Check for leaks in the hydraulic lines, ensure the sensors are functioning correctly, and replace any worn or damaged components. Failure to do so can lead to unpredictable handling and potentially dangerous situations.
• Consider a Delete Kit: Many 240SX owners, particularly those who drift or track their cars, choose to remove the Super HICAS system entirely. Delete kits replace the system with solid links, effectively locking the rear wheels in a fixed position. This simplifies the suspension, reduces weight, and eliminates the potential for system-related issues.
• Upgrading Bushings: If you choose to retain the Super HICAS system, consider upgrading the bushings in the rear suspension. Worn bushings can introduce slop and play into the system, reducing its effectiveness and making the handling feel vague.
• Proper Alignment: After any suspension work, including Super HICAS maintenance or deletion, a proper wheel alignment is essential. Ensure the alignment is performed by a qualified technician who understands the nuances of the 240SX suspension geometry.
• Understand the System's Limitations: Even when functioning optimally, Super HICAS is not a magic bullet. It's a subtle enhancement that improves handling, but it doesn't fundamentally alter the car's characteristics. Be aware of the system's limitations and drive accordingly.

Ultimately, the decision to retain or remove the Super HICAS system on a 240SX depends on the owner's priorities and driving style. For those who value originality and appreciate the system's subtle enhancements, careful maintenance and upgrades can keep it functioning reliably. For those who prioritize simplicity, weight reduction, or have encountered persistent system issues, a delete kit may be the best option. Regardless of the chosen path, a thorough understanding of the Super HICAS system is essential for making informed decisions and enjoying the full potential of this iconic sports car.