1989 Nissan 240sx Coilovers: Suspension Setup

The Nissan 240SX, specifically the S13 chassis produced from 1989-1994, enjoys legendary status in the world of drifting, time attack, and spirited street driving. A key component in unlocking its potential is the suspension, and for many enthusiasts, that means upgrading to coilovers. But what exactly *are* coilovers, and how does their setup affect the 240SX's handling characteristics? This guide delves into the technical details of 240SX coilovers, providing a deep dive into their components, adjustments, and implications for vehicle performance.

Understanding Coilovers: Form and Function

The term "coilover" is a portmanteau of "coil spring over strut." In essence, it's a suspension assembly where the coil spring is concentrically mounted around the shock absorber, or strut. For the 240SX, this represents a significant departure from the factory setup, which utilizes separate springs and shocks. The key advantages of coilovers stem from this integrated design:

Adjustable Ride Height: Coilovers allow for precise adjustment of ride height, a crucial factor in achieving the desired stance and lowering the car's center of gravity. Lowering the center of gravity reduces body roll and improves handling.
Adjustable Damping: Most aftermarket coilovers offer adjustable damping, controlling the rate at which the shock absorber compresses and rebounds. This allows for fine-tuning the suspension to match the driving style and road conditions.
Improved Performance: The combination of adjustable ride height and damping allows for a more responsive and predictable handling experience compared to the factory suspension.
Increased Spring Rate Options: Coilovers typically use stiffer springs than stock. This can reduce body roll and improve responsiveness.

Component Breakdown: Deconstructing the Coilover Assembly

Let's break down the individual components of a typical 240SX coilover:

The Shock Absorber (Strut)

The heart of the coilover is the shock absorber, also known as the strut. Its primary function is to control the movement of the suspension and dampen oscillations. Inside the shock absorber is a piston that moves within a cylinder filled with hydraulic fluid. As the suspension compresses or rebounds, the piston forces the fluid through small orifices, creating resistance. The size and number of these orifices, as well as the viscosity of the fluid, determine the damping characteristics.

Damping Adjustment: The ability to adjust these damping characteristics is a key feature of many coilovers. This is typically achieved through an external adjuster that modifies the size of the orifices or the bypass flow of the hydraulic fluid. Common adjustment types include:

Single Adjustable: Adjusts both compression and rebound damping simultaneously.
Double Adjustable: Allows independent adjustment of compression and rebound damping. This provides a higher degree of fine-tuning.
Triple Adjustable: Offers independent adjustment of low-speed and high-speed compression, as well as rebound damping. This is typically found on high-end coilovers for track use.

The Coil Spring

The coil spring provides the primary support for the vehicle's weight and determines the ride height. The spring rate, measured in pounds per inch (lbs/in) or kilograms per millimeter (kg/mm), indicates how much force is required to compress the spring one inch or one millimeter, respectively. A higher spring rate means a stiffer spring.

Spring Rate Selection: Choosing the right spring rate is crucial for achieving the desired handling characteristics. Stiffer springs are generally preferred for track use, as they reduce body roll and improve responsiveness. However, they can also result in a harsher ride on the street. Softer springs offer a more comfortable ride but may allow for more body roll.

The Coilover Body

The coilover body houses the shock absorber and provides a mounting point for the spring. It also includes the threaded portion that allows for ride height adjustment.

The Spring Perch

The spring perch is the adjustable collar that sits on top of the coilover body and supports the spring. By rotating the spring perch, you can compress or decompress the spring, effectively raising or lowering the ride height. This adjustment must be done carefully to ensure equal spring preload on each corner of the vehicle.

The Lower Mount

The lower mount connects the coilover to the vehicle's suspension. It typically consists of a clevis or fork that bolts to the lower control arm. Some coilovers also feature adjustable lower mounts, allowing for further fine-tuning of suspension geometry.

Setting Up Your 240SX Coilovers: A Step-by-Step Approach

Proper coilover setup is critical for maximizing the 240SX's handling potential. It's not just about lowering the car; it's about achieving a balanced and predictable suspension.

1. Initial Ride Height Adjustment

Start by setting the initial ride height. A good starting point is typically around 1-1.5 inches lower than the stock ride height. Ensure that the ride height is the same on both sides of the car. Use a measuring tape and measure from a consistent point on the chassis to the ground. *Precision is key*.

2. Corner Balancing

Corner balancing involves adjusting the ride height at each corner of the car to distribute the vehicle's weight evenly across all four tires. This is best done on a set of scales specifically designed for corner balancing. The goal is to achieve a specific weight distribution (e.g., 50/50 front/rear or slightly more weight on the rear for better traction). Corner balancing significantly improves handling, especially in cornering situations.

3. Damping Adjustment

Once the ride height is set, you can begin adjusting the damping. Start with the dampers set to the middle of their adjustment range. Then, test drive the car and observe its handling characteristics. Here's a general guideline:

Too much rebound damping: The car will feel "bouncy" or "jumpy" over bumps.
Too little rebound damping: The car will feel unstable or "floaty" over bumps.
Too much compression damping: The car will feel harsh and jarring over bumps.
Too little compression damping: The car will feel like it bottoms out easily over bumps.

The Importance of Incremental Changes: Make small adjustments to the damping, one click at a time, and test drive the car after each adjustment. It's crucial to feel the difference that each adjustment makes. Keep a log of your adjustments so you can easily revert to a previous setting if needed. This approach ensures you are not drastically changing the behaviour of your car.

4. Addressing Suspension Geometry

Lowering the 240SX's ride height can negatively impact suspension geometry, leading to bump steer and reduced tire contact. Bump steer occurs when the toe angle changes as the suspension moves up and down. This can cause the car to steer unexpectedly when going over bumps.

To correct these issues, consider the following:

Roll Center Adjusters: These correct the roll center, which is the point around which the car rolls during cornering. Lowering the car can lower the roll center, potentially leading to increased body roll. Roll center adjusters raise the roll center back to its optimal position.
Adjustable Tie Rod Ends: These allow you to correct bump steer.
Adjustable Control Arms: These allow you to adjust camber and caster. Camber is the angle of the wheel relative to the vertical axis. Negative camber (where the top of the wheel is tilted inward) is often used to improve cornering grip. Caster is the angle of the steering axis relative to the vertical axis. Increased caster improves steering feel and stability.

5. Fine-Tuning and Track Testing

The final step in coilover setup is fine-tuning and track testing. If you plan on using your 240SX for track days or competitive events, it's essential to test the suspension on the track and make adjustments based on the car's performance. This may involve adjusting damping, spring rates, or suspension geometry. Consider working with a professional suspension tuner to get the most out of your coilover setup.

Conclusion

Installing coilovers on a 1989 Nissan 240SX is a common and effective way to improve its handling and performance. However, it's crucial to understand the components of the coilover assembly, the principles of suspension setup, and the potential impact on suspension geometry. By following a systematic approach to ride height adjustment, corner balancing, and damping adjustment, you can unlock the full potential of your 240SX's suspension and achieve a balanced and predictable handling experience. Remember that suspension tuning is an iterative process. Be prepared to experiment and make adjustments based on your observations and driving style. With careful attention to detail and a thorough understanding of the principles involved, you can transform your 240SX into a true handling machine.