Today´s "tuner" market offers excitement for consumers and increased sales for retailers. In a word, we´re talkin´ "fun."
The phrase "tuner cars," though sometimes misused, primarily refers to sport and compact cars that have been altered to closely resemble low-slung European super-touring road race cars, at least in terms of appearance. The theme typically involves slamming the car to the ground, installing the biggest diameter wheels and lowest profile tires that can be fitted on it, and massaging the exterior with graphics and an array of body pieces such as air dams, lower side extenders, rear valance panels and rear aero wings.
For those vehicle owners who take this theme to the max, modifications also can include suspension upgrades, brake performance improvements, and layers of engine power frosting. These Hondas, Toyotas, Nissans, Acuras, Neons, BMWs, and even larger domestic brethren such as Mustangs and Stratus represent an evolutionary step in the performance world. In a nutshell, this group of cars is to today´s enthusiasts what the taller, bigger-bored domestic muscle cars were (and are) to the aging baby boomer crowd.
Instead of jacking up the rear and making use of mammoth displacement and big-gulp carburetors, these modern toys make use of aerodynamics, maneuverability, efficient electronic controls and air/fuel suppositories such as nitrous oxide injection, supercharging and turbocharging. The goal is to squeeze a bunch of juice out of a small package.
The size of the cars and the specifics of performance may have changed, but the overall theme remains the same: It´s all cars and all fun. And, it´s an exploding, fresh market that´s helping to further the performance aftermarket. We need to recognize that the "tuner" market is certainly not restricted to Hondas owned by 20-somethings alone. In terms of wheel and tire packages, the "tuner" concept also has spread to high-end, larger vehicles owned by 40- and 50-year olds. As an example, it´s not too uncommon to see a new Lincoln LS adorned with a set of whopping 20-inch alloy wheels. So, when you hear the term "tuner," try to maintain a broad perspective.
In this article, we´ll concentrate on the tuner market´s chassis package and the opportunities this represents to the progressive tire dealer and aftermarket business owner. The overriding constant of all tuner cars involves lowering and handling. Toward that end, let´s begin by discussing the vehicle support system.
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WHEELS AND TIRES
In a nutshell, this market wants the largest diameter wheels that will bolt to the vehicle, mated to the lowest profile/shortest sidewall tires that will fit the application. The current order of the day is to use 17-, 18-, 19- or 20-inch wheels shod with 45-, 40-, 35- or 30-series, ultra-high performance tires. The more the package looks like an almost-bare exotic alloy wheel with a hint of a black rubber band around the rim, the happier these folks are. Again, this is in-tune with the intention of emulating the "super touring" race car image.
As with any subjective choice regarding performance modifications, there are resulting pros and cons. The pros are two-fold. First, this type of extreme package looks cool. While an extremely large mass of wheel face and a ridiculously short tire sidewall would appear out of place on a 1960s-era American muscle car, this high-technocrat package is exactly what the late-model low-ride/tuner crowd desires.
Second, the wider-than-stock tread contact patch, coupled with a short, somewhat inflexible sidewall, provides a maximum bite area between the vehicle and the road surface (with a resulting assumption of increased handling and braking capabilities).
On the downside, this steroid-induced package can greatly contribute to a stiff ride and greater potential for a bent rim when driving in chuckhole territory. Also, while most owners who have dumped mega-dollars into their tuned rides wouldn´t think of driving their beasties in inclement weather, these owners must be reminded that due to the low ride height and predominantly ultra-wide, dry-weather-type tires, the vehicle probably should not be operated in conditions that present snow, ice and heavy rains. These low and wide performance tires provide a wide mass area, which is not always ideal for slicing through standing water. While several tire makers do offer tread designs that will handle wet weather, we´re simply making a broad generalization that wider isn´t necessarily better in deep water.
SPRINGS
Whether the vehicle owner chooses to stick with direct-replacement performance struts or specialty coilovers, performance coil springs may be selected that will provide both the desired ride height and stiffness rate. For the tuner market, coil springs may be available to provide anywhere from a one-inch to three-inch drop in ride height. Typically, performance coil springs from the major performance manufacturers will be CNC machined, heat tempered and shot-peened for superior fatigue resistance (the Eibach Sportline series is a good example of this).
If the vehicle owner opts to stick with the conventional MacPherson strut-type package instead of switching to coilovers, progressive rate springs are available that both lower the ride height and improve handling during acceleration, cornering and braking. A progressive rate spring will provide a more comfortable ride (softer rate) during minimal suspension compression, and will increase roll stiffness as the spring is further compressed, as during cornering, hard acceleration and braking. Progressive rate springs also can be ordered in reduced height profiles, allowing as much as a one- to two-inch drop. The specific amount of ride height reduction can be tailored simply by ordering the appropriate coil spring part number. Check with spring suppliers to determine what choices are available for a specific application.
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CONVERTING TO COILOVERS
A very cool change that easily can be made to any popular strut-equipped compact car involves converting to a coilover suspension system. A coilover unit features a shock fitted with a coil spring that is located on shock-mounted perches. The coil spring (smaller in diameter than a stock-type spring) is positioned over the shock body, hence the name coilover.
The lower area of the shock body features external threads. The lower spring perch rests on a threaded collar that engages onto the shock body´s external threads. This makes the spring adjustable, which provides easy ride height adjustability. Depending on the style, the threaded collar may be hand-adjustable, or a specialty "spanner" wrench may be required. In either case, a coilover unit is very easily adjusted on the car to tailor ride height. Another advantage of a coilover is space and weight savings, as compared to the original strut/spring package.
Aside from ride height adjustability, perhaps the most appealing benefit of a coilover for street applications is its appearance. It gives the wheelwell area a race car-like look.
Although adjustment ranges will vary depending on the specific vehicle and the coilover package selected, a set of coilover replacements will generally offer ride height drop in the range from one inch to as much as three inches. This makes it easy to obtain the "slammed" look without the need to perform extensive custom modifications to the suspension and/or uni-body structure. In addition, ride height can be increased when and if the vehicle owner needs additional ground clearance (naturally, wheel alignment in terms of camber and toe will require re-adjustment whenever ride height is changed).
Coilover suspensions are extremely compact, adjustable, and extraordinarily appealing from a visual standpoint. For a sport/compact tuner car, this is an excellent choice.
The aftermarket currently offers bolt-on coilovers that will directly replace the existing OE strut packages, so no custom fitting should be required. The vehicle owner may opt to install aftermarket performance struts paired with replacement performance coil springs, but in terms of visual enhancement and ride height adjustability, coilovers offer an outstanding modification option.
ANTI-SWAY BARS
Often incorrectly referred to as "sway bars," these laterally mounted torsion units connect the suspension´s left and right sides together via the vehicle frame. An anti-sway, or "stabilizer," bar is anchored to the frame at its midsection, and attaches to the left and right lower control arms.
When the vehicle enters a turn, weight is transferred from the outside of the vehicle to the inside (in a right-hand turn, the right side raises up, transferring weight to the left). The result: The outside spring (in a right-hand turn, this would be the left spring) compresses and the inside spring unloads. This places more weight on the left tire, mashing it into the pavement and causing the left tire´s outer tread shoulder to experience more abuse. At the same time, the right tire is unloaded, causing at least some of the tread to separate from the pavement. The most noticeable aspect felt by the driver is the amount of "body lean" as the car body rolls on its axis.
An anti-sway bar acts as a torsion spring when this side-to-side weight shift occurs. In a turn, where the outside wheel tries to move up toward the body, the torsional twist of the bar tries to force the inside wheel upward at the same time. The result is that both right and left tires are more evenly held in contact with the road, which prevents the body from leaning too far.
This is a simplistic explanation of how the bar works, but you get the idea. It´s a side-to-side spring that tries to keep both wheels on the same axle in a level plane. The result is reduced body lean, more contact between the tires and the road, and superior handling because there´s less body movement.
Always install anti-sway bars in matched sets, since they´ll be tuned to work together on a specific vehicle. For racing applications, adjustability is important to be able to tailor the car´s handling to a specific track. This is done with either an adjustable bar or by changing front and/or rear bars to accommodate the situation. For instance, if the car has too much understeer (the front doesn´t turn enough and it "plows" in a turn), increasing the diameter or tension on the rear bar will reduce understeer, or can even promote oversteer, depending on what the team wants.
If the rear of the car is too "loose," and the rear end swings around in turns, it has too much oversteer. Decreasing tension on the rear bar, or replacing it with a lighter rear bar, will reduce oversteer. For the street, stick with a matched set of bars from the same company. If your customer decides to go road racing, you can worry about tuning at that point.
The benefit of using thicker aftermarket anti-sway bars on the street is reduced body lean, quicker steering response and more overall driving fun. Keep in mind that an anti-sway bar only works hard in turns. When driving straight, it´s in a more relaxed state. Also, the addition of bars, or replacing original equipment bars with thicker units, will not stiffen the ride, again because they only noticeably come into play during side-loading in turns. Stiffer bars will not create a harsher ride!
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CHASSIS BRACES
In the context of this article, we´re primarily discussing late-model modified street vehicles as opposed to purpose-built race cars. As a result, we´re focusing almost exclusively on uni-body (the slang term for a "unitized" body) vehicles that do not feature separate-component chassis frames.
A uni-body car is constructed of varying thicknesses of sheet metal; the sheet metal itself is used to fabricate the entire body/chassis. In other words, the body substructure is the frame. This concept involves a civilian version of a "monocoque" design, wherein sheet metal is formed in sections and welded together to create a stressed "box" structure.
As opposed to a separate stamped steel or tubular frame component onto which a body skin is mounted, uni-body construction features a boxed body assembly whereby chassis stiffness and rigidity is created by the boxed-together body shell. As a result, the stresses created by driving on irregular road surfaces and during cornering are distributed not through a separate frame, but throughout the entire uni-body structure.
While a uni-body construction is perfectly adequate for normal street operation, depending on the specific make/model of vehicle, you may experience more chassis flex than desired, especially for performance handling applications. In order to minimize chassis and body flex on a uni-body vehicle, add-on chassis stiffeners or braces may be installed.
One of the most popular, and easiest to install, anti-flex bracing packages involves bars that connect the left strut tower to the right strut tower. Strut tower bars, which are available in both tubular steel, tubular aluminum or machined billet aluminum construction, reduce the frame twist commonly associated with uni-body cars. Depending on the vehicle, these brace bars are available for the front strut towers, and may be available for both upper and lower rear strut locations. If rear bars are offered for a specific vehicle, these help to further bolster the rear control arms for tighter handling.
Further chassis stiffening/anti-flex bracing might also involve lower braces that connect right and left sub-frames, and fore-aft braces that help stiffen the chassis during severe acceleration and braking. The specific bracing package will depend on the vehicle in question and its intended use. While some of these braces require a weld-on installation, the majority involve only bolt-on installation (with simple drilling required in certain applications).
Whenever a uni-body vehicle is used for competition, or when a street vehicle requires elevated handling capabilities, consider chassis bracing parts/systems as the first order of business. In order for the uni-body chassis to do its job, it needs to be reinforced properly for high-stress use. The addition of chassis stiffening add-ons provides the base onto which all other chassis improvements will depend. The braces will help transform a tack-welded uni-body structure into a more stable "hard box" to dramatically reduce unwanted flexing.
Remember: The more the uni-body flexes under stressful cornering or acceleration conditions, the greater the fatigue factor (i.e. welds and joints) becomes. Also, body/chassis flex equals wasted energy. If you reduce flex, the car will handle with greater precision. However, let´s be honest. The main reason street folks add strut tower braces, etc., is because the engine bay and rear trunk/hatch area looks so much cooler. If your customer is building a tuner car, he´ll simply gotta have this stuff.
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CAMBER ADJUSTMENT
The camber angle represents the wheel´s inward or outward lean from vertical. As viewed from the front or rear, if the top of the wheel leans inward, this is called negative camber. If the top of the wheel leans outward, this is called positive camber. If the wheel is positioned straight up, with no lean, this is zero camber.
For "normal" street operation, many vehicles feature a slightly positive camber angle. This provides easier steering and increased stability when driving in a straight line. However, most performance applications, where cornering forces will be extreme, require a negative camber angle. The reason is simple: Although the wheel may lean inboard at the top when driving in a straight line (which reduces the tire´s contact patch), a negative camber angle, when properly adjusted for the application, allows a full tire contact patch at the outboard wheel location during a severe cornering situation. In other words, for severe-duty use in which cornering forces will be high, a static negative camber angle can compensate for the expected lean, keeping more tread on the road where it belongs.
While high-profile tires with their taller and more compliant sidewalls are more affected by side loads, a lower-profile tire with stiff sidewalls may be less prone to rollover. As a result, the stiffer and shorter the sidewall is, the less negative camber angle may be required to maintain a maximum tread contact patch. The specific amount of negative camber, if any, will be dictated by the vehicle type, weight, type of wheels, tires, suspension/chassis stiffness and the anticipated driving style.
Remember: In terms of camber angle, our main objective is to keep as much tread on the ground as possible during the majority of driving operation. If the vehicle is street-driven only, the vehicle may require a minimal change in camber angle. If the vehicle is driven in performance situations only (autocross, race track, etc.), added negative camber may be needed to increase safety and decrease lap times.
Aside from the performance considerations, it´s important to note that camber angle has an enormous effect on tread life. If too much negative camber is selected for the application, the inboard tread areas will wear prematurely and the steering effort required during low speed turns will be higher. If too little negative camber, or too much positive camber, is used, the outer tread will wear faster. We can summarize this dilemma as follows: If your customer plans to drive the vehicle on the street, camber should be adjusted to promote even tread wear. If the vehicle will be raced or used in competition, camber angle should match cornering loads.
In a perfect world, a combination of wheel camber angle and tire inflation pressure can be used to obtain maximum cornering and tread life. While we can´t possibly provide specific camber angle recommendations for all applications, the rule of thumb is to follow, as closely as possible, the vehicle maker´s original camber specs for street-driven vehicles. For maximum cornering performance however, camber angles might be required in a range of -0.5 degrees to -3.0 degrees.
For street applications, you should stick with camber angles that approximate the OE specs as closely as possible. If the OE spec calls for +.5 - 0 degrees positive camber, for instance, moving to a 2- or 3-degree negative setting is definitely not recommended for daily driving. Naturally, each application will differ, so treat these numbers as a wide "ballpark" estimate.
If the vehicle is to be used in competition, tell your customer to monitor tread temperatures with a pyrometer immediately after full-bore speed runs. Using this all-important tread temperature information as a basis, wheel camber angle and tire inflation pressure can be adjusted in order to achieve uniform temperature across the tread face.
The camber adjustment, if any, that is provided on most production cars is woefully inadequate. In order to obtain true adjustability, an aftermarket adjustment system will need to be installed. Depending on the vehicle, this may involve the use of eccentric washers and bolt packages or bushings that will replace the OE strut-to-steering knuckle bolts and washers or control arm bushings. Other options include aftermarket control arms that may feature slotted holes for steering knuckle attachment, or upper camber plates at the top of the struts or coilovers.
For the greatest range of adjustment, easiest access -- and coolest appearance -- consider upper camber plate systems. These install onto the upper strut towers, and will either provide inboard/outboard adjustment for changing camber or may also provide fore/aft adjustment for caster.
Simply pop the hood, loosen the lock-down fasteners and make the needed adjustments. Many of today´s camber plates are beautifully machined and may be anodized in appealing colors, which will further enhance the underhood area when onlookers gawk at the car at shows.
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CHASSIS BUSHINGS
Production vehicles are designed for use on the street, and sold to a wide variety of consumers. As a result, noise, vibration and harshness (NVH) must be controlled to varying degrees in order to offer a comfortable, smooth and quiet ride.
The car makers don´t want their customers complaining about a rough ride, steering wheel vibrations, etc. As a result, the bushings used at key suspension points are made of compliant material such as rubber, urethane and other synthetic materials. The areas include pivot points where the front (and rear, depending on car design) control arms connect to the frame; the steering rack-to-frame/body mounting strut rod connections; control arms and frame; anti-sway bar mounts and end links; body-to-frame connections; and shock absorber mounts where applicable.
The use of a soft and compliant bushing is done simply in order to isolate the passenger compartment from buzzes, bangs and shakes that are transmitted from the tire´s impact with the road. However, the downside of soft bushings is a reduction in steering crispness and overall handling. While one person may want to float on a cloud while cruising down the highway, an enthusiast is likely willing to give up a degree of cushy comfort in exchange for superior vehicle control and steering wheel feedback.
The extreme modification would involve replacing all compliant bushings with solid connections using blocks of aluminum and spherical rod ends. However, that sort of approach is best left to dedicated race cars that are operated on smooth track surfaces.
For the street, a compromise is necessary. While it´s desirable to decrease bushing deflection in the pursuit of handling, we need to remember that the vehicle will be driven on public roads, which run the gamut from silky smooth to Baja-nasty.
We also need to recognize that the bushings and road shock isolators found in any street vehicle do not serve only to isolate passengers from annoying thumps, bumps and bangs. They also serve to isolate potentially damaging shocks and vibrations from the vehicle frame and body. This is especially important in a uni-body vehicle, since the entire structure is held together with thousands of small tack and pinch welds. If a uni-body car is bushed too stiffly, extended exposure to road shock can open a new chapter of buzzes, rattles and squeaks. The solution is to exchange OE marshmallow bushings for aftermarket urethane (or whatever other hooty-doo, high-tech synthetic is used) bushings. More road harshness will be transmitted to the occupants, but it will be to a tolerable level. This family of bushings and mounts typically feature a higher durometer (less compliance) than the OE counterparts.
Installing higher-durometer pieces will provide a number of benefits, depending on the area of application. When installed at control arm pivot points, these stiffer bushings will more precisely locate the control arm, which aids in holding the wheel alignment settings during cornering maneuvers.
While a softer bushing may allow the control arm to deflect, which can easily allow the camber and caster angle to randomly change, harder-durometer bushings will maintain a much more registered location for the control arm during vehicle dynamics. Harder (less compliant) anti-sway bar mount bushings will lock the bar in place on the frame or uni-body, eliminating wasted energy that is now transmitted more evenly through the bar. This allows the bar to do its job instead of wiggling around on its mounts.
Stiffer anti-sway bar end link bushings serve the same purpose, allowing the bar to more efficiently transfer loads without wasting energy via mushy rubber or soft silicone link bushings. When installed at the steering rack-to-frame mounting locations, stiffer bushings serve to lock the rack down, eliminating the slight movement that would otherwise occur with soft bushings. The result: a more positive and immediate feel in terms of steering wheel response and steering input.
By the way, these performance bushings are commonly available in colors other than black, which allows the vehicle owner to add color accents to an otherwise mundane undercar area; even color-matching urethane boots for ball joints and tie rod ends are available.
STREET TUNER MARKET: BY THE NUMBERS
How big is the sport compact market? It totals $1.2 billion in retail sales, according to the Specialty Equipment Market Association´s Research & Information Center (RIC). That´s up more than 300% since 1997. The RIC estimates further growth to $1.9 billion in retail sales in 2002.
Yokohama Tire Corp. estimates that tire sales in the sport compact, or "tuner" market segment totaled 775,000 units in 2000, up from 675,000 in 1999. The company estimates 930,000 units will be sold next year.
