Part II - Suspension & Brake Basics:

In Part I of this series, we discussed the basics of getting more performance out of your car's engine with the typical bolt on modifications. Now that you have tweaked some extra power out of your engine, it is time to look at the parts that help you put that power to the ground. Altering the suspension for performance and aesthetics is right at the top of most import enthusiasts' wish list. This often includes new wheels, tires and a change in ride height. More performance savvy drivers put high performance shocks, anti-roll bars and performance brake upgrades on that list as well.

Wheels, Tires and Plus Sizing:

Probably the most visually obvious change to the appearance of a car is custom aluminum alloy wheels. There is a dizzying selection of custom wheels that can be added to replace the, often mundane, stock wheels.

Most people who opt for new wheels select rims with a larger than stock rim diameter. Referred to as plus sizing, rims may be selected that are one, two and sometimes three inches larger than the stock rim diameter. A 17-inch wheel is the largest "practical" wheel for Honda cars. Hondas can accommodate 18 inch wheels, but the 17-inch wheel is still far more popular.

The actual wheel diameter selected is a matter of personal preference, but the conditions under which the car is driven should be considered. In regions where the roads are in rough condition, or if you have a problem with striking curbs occasionally, then a 17-inch wheel may be a bad choice. If you are planning on racing, live in an area with good roads and/or plan on showing your car at car shows, then a 17-inch wheel would be perfectly appropriate. Be forewarned though, as rim diameter increases, the costs of both rims and tires increases substantially.

A common question that arises when discussing plus sizing is the concern over larger diameter rims causing the tires to rub the fenders. The goal of plus sizing is to increase the size of the rim while decreasing the height of the tire sidewall (profile), such that the overall tire diameter does not change. This ensures that the wheel will have the same clearance as the stock wheel and the speedometer will not need to be recalibrated to read correctly. The difference in tire height is achieved by selecting a tire with the same (or slightly larger) width but a lower aspect ratio. Tire widths are measured in millimeters. The actual width will vary depending on tire manufacturer and tire brand, but in general the tread width is around the given size. The aspect ratio is given as the second number in the tire specification. In this case, the 65 indicates that the sidewall height of the tire is 65% of the section width (126.75 mm). Since the aspect ratio is a function of the tire width, the aspect ratio cannot be the sole indicator of sidewall height. Increasing the section width of the tire and lowering the aspect ratio can result in a tire with the same sidewall height. Many people mistakenly assume that a lower aspect ratio means a lower profile tire. However, if a tire with an aspect ratio of 55, for example, is substantially wider than another tire with an aspect ration of 60, is slarger then that is not necessarily true.

When plus sizing the goal is to select tires with a lower aspect ratio, but with the same (or slightly larger) width and a larger rim diameter. For example, a stock wheel/tire size of 195/65 R 14 can be replaced by a 205/45 R 16 (plus two) and maintain the exact same overall wheel diameter. Similarly, a 205/40 R 17 is the correct plus three size.

Aside from the obvious aesthetic improvement, the low profile tire provides much more responsive handling.

Springs:

Another popular trend in customizing the appearance of a car is to lower the ride height. This may be done for a variety of purposes. Many do it purely for appearance sake. Stock ride height is intended to prevent the car from bottoming in a variety of "worst case" scenarios. This often results in large gaps between the fender openings and the tires. Lowering the car gives it a more aggressive, racecar like stance that fans of import and performance cars find much more appealing.

Another goal for lowering ride height is to improve handling performance. Lowering the ride height serves to lower the center of gravity, which can have a dramatic impact on cornering and braking performance.

Lowering the car is most often accomplished by changing the springs on the car. Aftermarket springs typically lower the ride height from 1 to 2.5 inches and increases the spring rate (stiffness of the spring) to improve handling. The spring rate is increased either by reducing the number of coils in the spring or by using a heavier wire in the construction of the spring.

Often people try to lower their ride height by cutting coils from their stock springs. This trick has been used to lower cars for years, but it is not a recommended practice. As mentioned above, reducing the number of coils increases the spring rate. By cutting the spring you effectively increase the spring rate, but the new spring rate cannot be predicted and probably won't be correct for the new ride height. For a car that is only used for daily driving and cruising around town the effect of this is usually minimal, but in a performance driving or racing environment cutting the springs is considered heresy.

Shock Absorbers:

When lowering a car with a set of performance springs, the natural progression is to install a new set of performance shock absorbers at the same time. The shock absorber's job is to control the motion of the spring. When you replace the spring with a stiffer spring the shock may no longer have sufficient enough dampening to control the spring. People who replace the springs without a stiffer set of shocks often complain of a bouncy ride.

Alignment Issues:

A side effect of lowering your car is the wheel alignment is changed. The greater the change in ride height, the more drastic the change in alignment. There is usually a small change it toe, and a larger change in camber. The camber change for a moderate change in ride height is usually not drastic and can often be corrected using the stock alignment adjustment. For more aggressive changes in ride height, some sort of camber correction device may be necessary to return the car to OEM specifications.

Anti-roll bars:

A less popular modification to the suspension is to change one or both of the stock anti-roll bars (often referred to as sway bars). The anti-roll bars are designed to increase the roll stiffness (the chassis' resistance to leaning to one side or the other) of the car. The anti-roll bars increase the roll stiffness by offering no resistance to the motion of both control arms in the same direction (the bar just hinges up and down), but when one arm tries to move independently of the other it must twist the bar to do so. The stock bars are a compromise between ride comfort, compliance and keeping the handling balance on the side of understeer (considered safer for street cars and uninitiated drivers with suspect skills). While just the front or just the rear bar can be changed, aftermarket anti-roll bars are usually designed to work as a pair to make the handling neutral. Typically the rear roll stiffness is increased more than the front. By increasing the rear roll stiffness, the stock tendency to understeer can be dialed out so the car handles more neutral.

High Performance Braking:

Now that you have increased the power and handling of your car, you must also give some consideration to making sure you can stop your car. Properly maintained stock brakes are adequate for normal everyday driving, and Honda brakes are better than some, but for more spirited driving and occasional race track excursions the stock brakes may need a little help. Other than a good quality brake fluid, basic braking improvements are usually made at three points.

Braided stainless steel brake flex lines are often used to replace the stock rubber flex lines. When stepping on the brake pedal the pressure in the brake system is extremely high. Under this high pressure the rubber flex lines may have a tendency to expand. This results in a slightly soft or spongy brake pedal. With the braided stainless lines that expansion does not occur. This results in a firmer pedal and much better feedback from the brakes.

High performance brake pads are also a good way to increase brake power and fade resistance. Semi-metallic, metallic and carbon fiber composite pads are popular. These pads are far more resistant to heat and provide better pad friction. At the extreme end of the performance brake pad market are racing pads. These pads are made of materials designed to handle extreme temperature conditions without fading. These pads are not necessarily practical for street driven cars though. These pads typically do not provide much braking effort until they are hot. Under normal street driving conditions there is never enough heat generated to get sufficient braking effort.

Stock brake rotors can substituted for a high performance rotor that is either cross-drilled, slotted or both. Cross-drilled rotors use a pattern drilled into the rotor braking surface. This serves several purposes. It creates more rotor surface area, which increases the rate of heat dissipation. It also releases gasses created by the brake pad at extreme temperatures. These gasses can hold the brake pads away from the rotor surface and reduce brake effort. The holes also sweep the surface of the pad to keep it clean. One drawback is the holes decrease the surface area where the pad contacts the rotor. Also, rotors of substandard quality can be prone to cracking.

Slotted rotors accomplish many of the same goals of cross-drilled rotors but do so with a slot etched into the surface of the rotor. This negates the problem of rotor cracking, but still maintains the benefits of pad cleaning and allowing the gasses to escape. Slotted rotors also typically give up less contact area than cross-drilled rotors do.

In some extreme cases there are rotors that incorporate both options. The choice between cross-drilled and slotted rotors is mostly a matter of personal choice, since both do a good job of increasing the brake's fade resistance. The slotted rotors are great insurance against cracking. Though, from an aesthetic perspective there is no denying the appeal of a set of cross-drilled rotors inside a large open aluminum racing wheel.

Conclusion:

This article certainly isn't the last word on brake and suspension upgrades. There is much more that can be said about coil-over suspension, custom alignment, suspension bushings and tuning your car for the track. However, this article touches on the major issues that confront someone new to modifying their car.

As with Part I, there is an unending trail of development and performance upgrades you can perform. These articles will give you somewhere to start, and help you avoid costly mistakes. Key to this process is a comprehensive, well-researched plan. Once you have addressed and mastered the issues in these articles you are ready to move on to more complex modifications.

Good luck in your pursuit of performance motoring!