Honda Civic Si Coilovers & Suspension

Where to start

Modifications to the Honda Civic Si are extremely popular. While performance upgrades are nothing new, there are some critical building blocks that should be considered to ensure you unleash your vehicle’s maximum potential. Below are a few things worth doing to properly modify your car for horsepower and handling.

Suspension Set Up

Always make the suspension faster than the engine. Ensuring you can turn and stop will always be more important than knowing you can go fast. Getting your Honda Civic Si suspension dialed in can equate to you out-handling your competition, and depending on your type of racing, will even give you better times. If your vehicle came from the factory with softer suspension, it will almost always handle poorly until the suspension is replaced with a performance setup such as coilovers. Old, worn out suspension also has a very negative effect on the handling and should be replaced, especially if used for any spirited driving where handling is key.

Coilover Basics

Coilovers help to set up your Honda Civic Si height and damping, which allows you to lower your center of gravity and stiffen up your chassis for better cornering and control. Not only does your car look sportier (and better in our opinion), but it’s also a key step in allowing you to transform your car into a true performance machine, transferring your modifications into tangible wheel horsepower.

There are many different coilover brands and types on the market, so picking the right one can be daunting. Here are four key things you need to look for when buying Honda Civic Si coilovers.

Spring Rates

Springs are an integral part of your suspension set up. They control the vehicle’s ability to bounce, absorb bumps and create low body roll when loaded. Higher spring rates require more force to compress the spring, which reduces the amount of suspension travel. The body of your car moves when you accelerate, brake and turn. By reducing body movement, you make handling more predictable and effectively spread the cornering load across all four tires better leading to better grip. Most aftermarket coilovers use significantly stiffer springs than OEM suspension, which improves handling and gives the driver more feel for the road and their car when performing spirited driving.

Spring and Valving Adjustability

One of the many reasons anyone purchases a set of coilovers for their Honda Civic Si has commonly been to lower the car. The lower center of gravity will help reduce excessive body roll and improve performance. Having the adjustability for ride height, spring preload and damping are essential features of a high quality coilover. Adjusting your coilovers can help you fine tune how your vehicle handles and give it the perfect ride height for your application. The ability to replace the springs with stiffer springs is also an important feature as track cars need much higher spring rates than street cars to gain grip, improve handling and reduce body roll. If you swap to a stiffer or softer spring, it’s important to match your spring rate with your damping to avoid a bouncy ride which is ultimately detrimental to handling.

Top Mount

On top of the coilover is a mount that holds everything together and bolts the top of the coilover to the car. This mount is known as the “Top Mount” and between the mount and strut assembly are two different types of bushings, rubber or pillowball type. As you might expect, OE manufacturers use rubber bushings because it deflects more and is a primary cause for the failure of suspension precision. The rubber you’ll find on most OEM struts is soft and allows a lot of energy deflection. A stiffer rubber mount improves longevity and reduces energy deflection. A pillowball bushing is a metallic spherical joint which rather than deflecting from the cornering forces like a conventional rubber bushing, pillowball mounts do not move at all. This translates into a far more precise feel from the suspension and steering.

Monotube Design

Inside any coilover, there are two designs of dampers you will come across, monotube and twin tube. The twin tube uses an inner and outer tube, twins if you will. The inner tube holds the piston shaft, valve and oil. The outer tube holds damper oil and nitrogen gas. Here’s how it works; when the suspension is compressed, the piston forces oil out of the inner tube by its valve and into the outer tube. When the piston moves back into position, the oil is sucked from the outer tube back to the inner. Most OEM suspension utilizes the twin tube damper set up because it allows for more suspension stroke and improves ride quality.

Monotube dampers hold the gas and the shock in one tube, separating the liquid from the gas with a floating piston. The design pushes the damper piston through oil and pushes the oil through chambers through the valves in the piston itself. This design allows the gas to be compressed and react quicker, by compressing slowly over small bumps and more quickly through larger bumps. One incredibly important detail about the Monotube is its ability to be used either way up, unlike most twin tube dampers. Compared to the twin tube design, the Monotube holds more fluid, has better heat dissipation and improves the responsiveness of the damper.

For the best performance on the street or track, the Monotube design is a superior upgrade to the twin tube design.

Air Suspension

If you aren't needing Honda Civic Si Suspension options designed specifically for heavy track use, Air Suspension is another great choice. While the debate between those that prefer coilovers or air suspension can get pretty heated, the unmatched height adjustability of Air makes it a strong Honda Civic Si suspension option in our opinion.

Sway Bars

Another thing to consider when modifying your Honda Civic Si are sway bars. By default, almost all factory cars are tuned with an understeer bias. This makes them easier to drive at their limit, and much safer. For example, a stock Mitsubishi EVO 8 (AWD Turbo) comes factory with a 24mm front sway bar, and a 22mm rear. While there are many upgrades the EVO might need out of the box, the point is upgrading the rear bar should be one of the first mods you do to bring the car to a neutral state. On our EVO 8, we upgraded the rear bar to a 25mm bar and noticed that the bar itself nearly corrected all understeering issues with the car itself. A bar and its size can make the world of difference in handling. Keep in mind when lowering the vehicle it changes your vehicle’s suspension geometry, which can incorrectly preload the sway bars and cause unpredictable handling characteristics, or in an even worse case, damage. To cure this, use adjustable endlinks to correctly preload the sway bar.

Brakes

While going fast is fun, how well can you stop at your peak power? This is something that must be considered for every build. Whether you’re building a race car or a street car, how well you are able to brake and how often will make a notable difference. Big brake kits consist of larger calipers with more contact pins in the caliper to hold and compress larger brake pads. With more brake pad surface on the brake rotor, you’ll need less time to push the brake pedal to stop. This also helps stop brake fade, which is a buildup of energy and heat from the brakes that causes them to start slipping after an extended amount of time being used. Larger calipers also help dissipate heat from the braking process, which attributes to less brake fade. Being able to brake efficiently and safely, and in style, makes a Honda Civic Si Big Brake Kit a key component for your build!

Summary

The list of Honda Civic Si modifications is almost endless; however, we hope this helped give you a good idea of where to start.