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.
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
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.
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.
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.
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!