Undercar upgrades: There are many ways to enhance handling and directional control

April 1, 2007

OK, so you've upgraded your customer's ride with a set of high performance rubber and snazzy alloy wheels. The vehicle looks great, steering response is quicker and it grips like never before.

But your customer now wants to take his car's handling and braking performance to yet another level. What can you do for him?

Here are some possibilities with regard to chassis upgrades.


The options here are many and varied, depending on what your customer wants to achieve. Lowering the vehicle (via replacement springs) will lower the vehicle's center of gravity and "tune" it for better steering response and handling.

Shock absorbers can be upgraded to provide superior vehicle control during acceleration, braking and turning. Moving to high-quality aftermarket shocks or struts can provide vastly improved chassis performance as compared to original equipment shocks.


Upgrading to thicker anti-sway bars, best done in front/rear sets, can provide an incredible boost in steering response and handling without sacrificing ride quality.

Two basic types of anti-sway bars are available, including "bent" bars and three-piece bar systems.

1. Bent bars feature anti-sway bars that are formed to adapt to a specific vehicle, allowing direct bolt-on replacement of the original bars.

2. Three-piece bar systems feature a straight (solid or hollow) torsion bar that connects to a pair of bar arms.

With three-piece systems, the bar ends feature splines that engage into splined holes in the arms. The opposite ends of the arms then attach to the frame, via stabilizer bar links. These links can be either bushed (traditional original equipment-style mounting) or can feature adjustable threaded rods fitted with spherical rod ends (often called heim joints).

Unlike bushing-equipped links, rod ends provide no cushioning effect, and may transmit unwanted noise in some cases, which may or may not be objectionable to the vehicle owner.

Always sell anti-sway bars as front/rear sets. Bar makers spend a great deal of time and testing to create a package that is tuned for a specific make/model of vehicle, so always follow the maker's advice in terms of front and rear bar upgrades.

If only the front bar is stiffer, you'll induce more understeer; if you upgrade only the rear bar, you'll induce oversteer. While that doesn't necessarily mean either condition will be objectionable compared to how the vehicle handled previously, the safest and best approach if you don't want understeer or oversteer is to sell a tuned pair of bars in order to take advantage of the bar maker's research. They know what works.


For any performance upgrade, you can't go wrong with quality aftermarket bushings that provide a higher durometer (stiffness) compared to the usually too-soft OE bushings. Applications include anti-sway bar mount bushings and end-link bushings, strut rod bushings and, where applicable, shock/strut mount bushings.

Reducing bushing compliance results in quicker energy transmission through suspension components, which translates into quicker/more responsive steering and crisper handling. Basically, stiffer, less-compliant bushings still provide a measure of cushion while providing superior handling response and tighter, more controllable wheel alignment angles during vehicle operation.

Brakes: upgrade basics

Anything that rolls must eventually stop. As far as a vehicle is concerned, it must be able to stop efficiently on demand.

For most performance-oriented folks, there's no such thing as having "too much" in terms of braking performance. However, moving to the largest disc available isn't necessarily a good idea.

If the disc is too large, you are adding unnecessary weight, which may not allow sufficient heat to be generated to make the pads work as efficiently as designed. Disc diameter must be tuned to the specific vehicle application. In other words, bigger isn't always better.

If the customer is fairly satisfied with the overall braking, he can consider a simple and inexpensive upgrade to high performance brake pads. Be aware that going to "race" pads could be a bad move for a street vehicle if the pad compound is designed to function best only when frictional heat is elevated, since a purebred racing pad may not be aggressive enough when cold. The good news is that several high-end aftermarket pad manufacturers offer outstanding pad compounds that are designed for the street, offering superior braking efficiency throughout the normal temperature range experienced in street driving.

Upgrading to high quality, performance-oriented brake pads can increase stopping power anywhere from 20% to 40% depending on the application, and also can result in low brake dust and reduced noise.


Brakes: the fun stuff

Now we get to the fun stuff. Consider installing larger diameter rotors (again, tuned to the application), which will offer greater surface area, along with aftermarket calipers that feature two-piston or four-piston operation.

As opposed to an OE-type sliding single-piston caliper, a fixed caliper (bolted in a fixed position relative to the disc) features multiple opposing pistons that spread the force applied to the pads evenly at each side of the disc and over a wider area, eliminating pad flex. This provides more even and stronger braking potential.

Many four-piston and all six-piston calipers feature different-diameter pistons, progressively small to large. The caliper is mounted to allow the smaller diameter pistons (the leading pistons) to apply pressure first, followed by the larger pistons. This progressive application of pressure stabilizes the pads, preventing uneven/tapered pad wear, and provides a smooth transition of minimal to maximum pressure application of the pads to the disc.

Calipers that feature pistons of varying sizes must be mounted with the smaller diameter pistons toward the rear and the larger pistons toward the front. Some aftermarket multiple-piston calipers feature a directional arrow to indicate rotor direction.

Also, moving to aftermarket alloy calipers will benefit the appearance of the vehicle, especially if the new custom wheels tend to expose more of the rotor/caliper area. Alloy calipers in powder-coated colors such as black, red, yellow, etc., provide far more eye-candy appeal than dull (and rusty) cast iron OE calipers.

As far as rotors are concerned, the popular trend is to go with slotted or drilled rotors. What's the reasoning behind the use of holes or slots? Aside from looking way cool, the edges of these holes or slots serve to sweep the pads clean, preventing residue buildup and making the brakes more efficient. Holes/slots also help to promote heat shedding (in conjunction with rotor vents) and provide more efficient release of heat and gasses that are generated between the pad and rotor during operation. This is critically important on a race car, but also of value on a street car.

By the way, slotted rotors may be directional, so be careful when installing them. If angled slots are featured, the end of the slot closest to the disc outer edge should attack the pads first during forward rotation.

To avoid potential rotor warp and cracking, your best bet is to install rotors made by established manufacturers. Sell calipers and rotors as a matched set from the same maker.


Don't forget about brake hoses! Rubber flexible brake hoses tend to expand slightly under hard braking due to the hydraulic pressure created as the system is pressurized during braking. Moving to stainless-steel braided reinforced brake hoses (these feature a flexible and expansion-resistant inner liner such as Teflon) allows more of the available hydraulic pressure to be transferred to the caliper where it's needed, instead of wasting pressurized fluid energy by running fluid through rubber hoses that can expand. And, like aftermarket rotors and calipers, stainless braided hoses offer a very tasty appearance as opposed to boring OE black rubber hoses.

Brake fluid and moisture

Finally, don't ignore the brake fluid. Glycol brake fluid acts like a sponge, attracting moisture from the air. As moisture enters the system, this lowers the fluid's boiling point. If the boiling point is compromised enough, this will result in a spongy pedal and/or brake fade.

Brake fluid in any street vehicle should be changed once each year. Realistically, we know that most people won't bother to do this, which is a shame. At the very least, as long as you're upgrading your brakes anyway, this is a good opportunity to flush the system and refill with fresh fluid.

This is a good time to mention silicone brake fluid (DOT 5). Silicone fluid has its place, but not in a performance street vehicle.

A common myth is that silicone fluid will prevent brake system corrosion because it won't attract moisture. In reality, while silicone doesn't act like a sponge, it nonetheless will transport and hold-captive any moisture in the system. And since moisture won't mix with silicone, it never has a chance to be "cooked" out.

Silicone fluid can result in a spongy pedal even when not contaminated, and it can promote brake system moisture damage. The best reason to use silicone brake fluid relates to its non-aggressive nature with regard to painted surfaces. Since silicone brake fluid won't damage paint (glycol can stain or even remove paint quickly), many street rodders and owners of vintage cars tend to use silicone simply to avoid any paint damage that might result from drips, splashes or leaks.

Never install silicone brake fluid in any vehicle that is equipped with anti-lock brakes. During severe or panic braking, the ABS actuator applies and releases hydraulic pressure in quick succession, which will cause silicone fluid to aerate (foam), resulting in temporary low or no pedal pressure.


Chassis reinforcement

Whenever a vehicle rolls down the road, and especially when the vehicle encounters uneven road surfaces and turns, the frame will flex. This applies to full-framed vehicles as well as those with unibody construction.

This flexing, regardless of the severity, degrades handling because a portion of the lateral energy that should be directed to the wheels and tires is wasted via frame flex. In order to maximize handling and braking performance, the frame may be "stiffened" with the addition of reinforcements.

For example, the front strut towers on a strut-equipped unibody vehicle can be tied together with the addition of a strut bar. This prevents the strut towers from flexing inboard or outboard. A strut bar can be even more efficient if the bar is also connected to the firewall/cowl area, which creates a triangulated bracing effect.

These bars are available for all popular applications and usually require a minimum of labor for installation.

In certain applications, subframe connectors may be added, which simply extends and braces the vehicle's existing subframe to reduce flex during maneuvering, braking and hard acceleration. This can involve either bolting on or welding on braces, depending on the vehicle and the design of the aftermarket braces.

A word to the wise

When it comes to "stiffening" the chassis for better handling, use caution.

While reducing compliance is a good thing in terms of performance, street vehicles can be turned into rock-hard beats that eventually shake themselves to death if you go too far in terms of reducing or eliminating compliance.

Street vehicles still need a measure of insulation/buffering to reduce the effects of road shock. Work with your customer to make sure he chooses the replacement parts wisely. Tell him over-stiffening a street vehicle can get downright nasty in terms of ride comfort and long-term frame or unibody life.

About the Author

Mike Mavrigian

Longtime automotive industry journalist and Modern Tire Dealer contributor Mike Mavrigian also is the editor of MTD’s sister publication, Auto Service Professional. Mavrigian received a bachelors degree from Youngstown State University in English literature with a minor in journalism in 1975.