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ncorrect alignment con- ditions affect wear and can cause and/or pulling during cruise, acceleration and PERFORMANCE braking, plus poor directional PERFORMANCE control. For the performance- minded customer, the need for precise Iwheel alignment becomes more pro- nounced, due to a number of factors: •He expects crisp handling and maxi- mum grip/. WHEEL •Aftermarket upgrades—such as WHEEL moving to wider , different wheel offset, shorter sidewall due to plus-siz- ing—are common. •Common upgrades to ride height as a result of installing lower, stiffer springs and possibly aftermarket arms with raised spindle locations. ALIGNMENTALIGNMENT The goal, regardless of any potential aftermarket upgrades, is to retain the original specifications, as closely as possible for street-driven BY JIM GIBSON . If a is intended only for off- use, deviating from stock set- tings will be necessary in order to maxi- Performing a precise mize the tire during hard cornering and to enhance turn-in re- wheel alignment sponse. However, since the majority of assures maximum alignment jobs, even those termed “per- formance,” will involve street driving, tire life, vehicle stability we’ll focus on this aspect. The majority of your alignment jobs and control. Alignment will involve daily street drivers and un- modified vehicles, in which case you want assumes even greater to align the (within manufacturer specs) for maximum tire life and direc- importance as vehicle tional stability. For the performance- performance increases. minded driver, a performance alignment is preferred, which simply means that you should take advantage of the vehicle maker’s tolerance range of wheel angles to choose the settings that will maximize Photoillustration: Harold A. Perry; images: Hunter Engineering & Thinkstock the tires’ performance. This would in- volve using the manufacturer’s maximum A -in condition (also referred to as ally offer rear wheel toe adjustment. negative camber, maximum positive cast- a positive toe angle) is present when the The toe angle is critical in terms of er and preferred toe settings. In this way, two wheels on the same are closer life. Ideally, the front steer you enhance handling without wander- together at the front and wider apart at wheels need to be parallel while cruis- ing beyond the vehicle maker’sspecs. the rear. A toe-out condition (also called ing to avoid tread scrub. However, toe Toe angle compares the distance be- a negative toe angle) is present when the can also be used to alter a vehicle’s han- tween the center of the front of the wheels are farther apart at the front and dling traits. An increased toe-in setting tires to a distance between the centers closer together behind the axle center- can help to reduce an oversteer condi- of the rear of the tires on the same line. All front suspensions, regardless of tion in turns, and will improve a vehi- axle. A zero-toe angle exists if the dis- design, feature toe angle adjustment, at cle’s high-speed directional stability. An tance between the front of the wheels a location on the steering tie rods/tie rod increase in toe-out can reduce an un- (ahead of axle centerline) is identical to ends. Live rear will feature no toe dersteer tendency and will enhance ini- the distance between the wheels be- angle adjustment, since this is a fixed an- tial turn-in during cornering. But, a toe- hind the axle centerline. gle. Independent rear suspensions usu- out can also result in a darty, less deci-

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likely won’t change as much, so you may be able to set front toe closer to zero, or a bit toward the preferred side, depending on driver requirements. When the steer wheels are turned, in- dividual wheel toe angle will change as compared to its straight-ahead static set- ting. For example, when the steering wheel is turned to the left, the left front wheel will exhibit greater toe-out as com- pared to the number of degrees that the right front wheel toes in. This design fea- ture reduces the tendency of tire scrub during turns and reduces the turning ra- dius of the outboard wheel, reducing the ’s tendency to turn-in too quickly, while providing reduced recovery effort when the vehicle direction changes. The inside wheel must turn in a tighter radius than the outside wheel to allow a smoother turn and reduce tire scrubbing. While static toe (with wheels aimed straight ahead) allows both front wheels to rotate at the same speed and parallel to each other, during a turn the individ- ual wheel toe angles differ when the steering wheel is turned more than 20°. This is referred to as the Ackerman principle, allowing the inside wheel to turn in a tighter radius while the outside wheel turns at a larger radius. refers to a wheel’s an- gle from top to bottom when viewed from the front or rear of the vehicle, as compared to a true vertical. If the wheel leans out at the top, this is positive cam- ber. If the wheel leans inward at the top, this is negative camber. If the wheel is set at a true vertical, this is zero camber. For high-performance driving, a neg- ative camber angle is preferred, to com- pensate for the lateral experi- enced in cornering. Dialing in more negative camber serves to compensate, sive straight-ahead condition at speed, Commonly, a rear-drive vehicle will placing the load more evenly across the especially in wet or slippery conditions. call for a slight toe-in setting, and a front- tire’s tread area. With an excessive toe setting (in or drive vehicle will call for a slight toe-out For a performance setting, you need out), each front tire is pointed in a di- setting. This is intended to compensate to consider how the vehicle is to be rection other than straight ahead. When for front tire and front suspension bush- driven (re the driver’s expectations) to the tires encounter a with ing deflection as the vehicle is driven for- achieve an acceptable balance between diminished traction (water, snow or ice), ward. As a rear-drive vehicle moves for- cornering traction and tire tread wear. the tire that hits the less tractive side of ward, the front wheels may tend to try to As you increase negative camber, the in- the road loses its grip, favoring the op- crawl away from each other, while a side tread area will tend to wear faster posite tire on the same axle, which can front-wheel-drive vehicle’s front wheels than the rest of the tread when the ve- tend to pull the vehicle in the direction may try to crawl inboard. If the suspen- hicle is driven in a straight line; but if of the toe angle. For the street, it’s best sion has been modified with the use of the driver is aggressive in turns, insuffi- to stay within the limit range specified stiffer, less compliant bushings, the cient negative camber will allow the tire by the vehicle maker. amount of toe change under acceleration to “roll” excessively, reducing the tire

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contact patch. The goal is to manufacturer’s caster spec to create an acceptable com- Toe-Out obtain the best compromise promise between tread wear between tight-turn and high- and cornering grip. In simple speed control. terms, we dial in more nega- Front may or tive camber to allow the tire may not be readily ad- to “stand up straight” during justable, again, depending on hard cornering. suspension design. If the Factory camber specs are front suspension features up- usually biased toward overall per and lower control arms, tire tread life for so-called the upper arm will likely be normal driving. The perfor- Toe-In adjustable, either via the ad- Illustrations courtesy Hunter Engineering mance-minded driver will During turns, the inside wheel turns at a greater toe-out angle, dition or removal of shims benefit from a setting that’s turning the wheel to follow a tighter radius than the outside (between the upper arm and negative. Keep in mind that wheel. This reduces tire scrub during a turn, allowing the wheels frame) or via eccentric bush- excessive negative camber to rotate during the turn with less resistance. ings. If an upper/lower con- (excessive for the street, that trol arm system is featured, is) can result in reduced straight-line er . A more positive caster an- the two anchoring locations (where the high-speed stability and make the vehi- gle contributes to directional stability at upper arm attaches to the frame) can be cle a bit darty. speed, and aids in steering wheel re- adjusted (again, with shims or ec- Caster angle settings for street-driven turn, helping the steering to return to a centrics). To alter camber, the adjust- vehicles should provide a good compro- straight-ahead position after a turn. A ment must be performed equally at mise to achieve an acceptable steering zero caster angle, where the lower pivot front and rear attachment points, to effort, confident high-speed stability is directly below the upper pivot, would move the upper arm pivot inboard or and turning/cornering performance. In- result in reduced directional control outboard. If caster is to be adjusted, only creasing positive caster improves high- and poor steering wheel return, which one end would be adjusted. speed stability but increases steering ef- would require the driver to manually If the front suspension features fort. In the case of a vehicle without drag the wheels back to a straight-ahead MacPherson , the upper steering, this can cause an issue, direction following a turn. mount serves as the upper locating point, depending on the vehicle weight and The steering axle’s caster angle has a which is usually a fixed point on most driver preference. major influence in directional control. production vehicles. To achieve front- The caster angle (steering axis angle) Reduced caster angle may suit an appli- rear adjustment of caster, an aftermarket involves the relationship of the upper cation where the car is being driven in a adjustable top mount is usually required. ball joint (or top of the strut mount) to series of tight, twisty turns, but would Viewed from the front of the vehicle, the lower ball joint as viewed from the likely be twitchy and darty at high speed. steering axis inclination (SAI) is a non- side of the vehicle. Using a true vertical A car driven primarily at high speeds on adjustable angle between a true vertical drawn through the hub center as a ref- straightaways will favor a more positive drawn through the center of the tire erence, caster angle is represented by a caster angle. With that said, for street and a line drawn through the upper and straight line drawn through the upper driving, even on a performance vehicle lower ball joints. The SAI is determined ball joint/pivot location through the low- application, it’s best to follow the vehicle at the point in which these two lines in-

Caster angle refers to the angle created by the location of the up- per ball joint or strut top relative to the lower ball joint. As shown on the left, if the upper point is ahead of the lower, this is nega- Camber angle refers to the lean of the wheel, viewed from the tive caster. If the upper and lower follow a true vertical, this is zero front. Performance alignments should bias the front wheels to- caster. If the upper is behind the lower, this is positive caster. In- ward the maximum tolerance of the factory’s negative camber creased positive caster aids in directional control at speed and su- range to maximize the tire contact patch during hard cornering. perior steering wheel return following a turn.

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tersect. In simple terms, SAI is the fac- road surface, this condition is known as Commonly, a front-wheel-drive tory-designed “camber” angle of a spe- negative scrub. When the lines intersect MacPherson strut front suspension fea- cific wheel’s suspension system. below the road surface, the condition is tures a negative , which aids Another fixed angle is included angle called positive scrub. An excessively in minimizing the steer effect (IA), which is the combination of SAI negative scrub radius tends to increase that’s a common trait of front-wheel- and wheel camber. Both SAI and IA are steering effort, while excessive positive drive systems. measured to verify that the fixed-by- scrub radius (where the load of the A vehicle’s thrust line represents the design angles are correct. If either the tread is moved moves further outboard) “aim” of the rear axle, as viewed from SAI or IA are outside of the OE specifi- can not only affect handling and ease of above. The thrust line effectively di- cation, this indicates that damage has steering, but can overstress wheel bear- vides left and right rear wheel toe. The occurred, such as a bent , ings as well. thrust line may or may not follow the bent strut, dislocated strut tower, etc. Scrub radius is affected when after- geometric centerline. Scrub radius represents the point of market wheels featuring a different off- The thrust angle refers to difference greatest load on the tire tread area, pri- set from stock are installed, which between the geometric centerline and marily during turns. As viewed from the moves the tire’s tread center from the the thrust line, measured in degrees. As front of the vehicle, this is determined original location. A wheel offset that viewed from above, if the thrust angle by considering the distance between the moves the wheel further outboard aims to the right (passenger side), this is center of a front tire tread and the imag- places greater stress on wheel bearings. a positive thrust angle. If the thrust an- inary SAI line, when measured at the In the case of front-drive systems, this gle aims left (driver’s side), this is a neg- road surface. Since these two lines will can also lead to overstress and wear on ative thrust angle. eventually intersect, it’s this intersection the outer CV joints. Centerline steering refers simply to a point that we’re really interested in. In most cases, a short-arm/long-arm “straight and level” steering wheel clock When the two lines cross exactly at suspension (upper and lower control position when the vehicle rolls in a the road surface, this is known as zero arms where the lower arm is longer) straight line. If the steering wheel is not scrub. When the lines cross above the will exhibit a positive scrub radius. centered, this may indicate a possible thrust angle deviation. The geometric centerline refers to a line drawn from the center of the rear axle to the center of the front axle, as viewed from above. Types of Wheel Alignment The age-old method of centerline two- wheel alignment does not consider the rear wheel positions, and should not be employed because it ignores the thrust direction of the rear axle. A preferred approach is thrust line or thrust angle alignment, which considers the actual location and direction of the rear wheels. This allows you to adjust the front wheel angles relative to the rear wheel angles, regardless of the geomet- ric centerline. If a vehicle features rear wheel toe adjustment, we can achieve optimum wheel alignment using the total four- wheel alignment, which includes adjust- ment of all four wheels, allowing toe ad- justment to bring the thrust angle to ideal zero, or as close to zero as possible. If the thrust angle is off zero, this can contribute to vehicle dog-tracking (crooked body relative to direction of travel), increased tire wear and unequal left/right turning. Total four-wheel Circle #23 alignment allows you to adjust and hopefully correct rear axle thrust angle,

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then adjust the front wheels parallel to camber and caster angles. In addition to the rear wheels. dealing with bent suspension compo- Whether the rear toe is adjustable or nents or a damaged resulting not, always use a four-wheel alignment. from pothole impacts or crashes, where This approach allows you to refer to and replacing parts and straightening the consider the rear, while a total four- substructure are required, if the cus- wheel alignment allows adjusting of both tomer has lowered the vehicle or simply front wheel angles as well as rear toe. desires an increase in negative camber Note: While loading a vehicle in the and you’re out of the range of factory manner in which it will be driven adjustment, aftermarket kits are readily should be done with any wheel align- available that provide an increased ment job, it can be especially important range of camber (and often caster) ad- for the performance-minded driver. To justment, as well as rear toe adjustment obtain the optimum wheel alignment in certain applications. angles for someone who expects maxi- Depending on suspension design, mized performance, the weight of the upper and lower control arms may be driver should be considered (as well as adjustable for camber and caster via one or more passengers, depending on spacer shims between the upper arm

IA Camber

Kingpin or Steering Axis Inclination SAI

Scrub or Pivot Angle Radius Steering axis inclination (SAI) is the fixed angle established by a line drawn through The pivot/load point scrub radius of a tire upper and lower ball joints (or center top considers the angle created by the wheel of a strut to lower ball joint), with refer- camber and the SAI. An aftermarket wheel ence to a true vertical at the lower joint. with greater offset from OE that places the Out-of-spec SAI indicates suspension dam- wheel centerline further outboard results age. Included angle (IA) considers both SAI in a more positive scrub radius, which can and the hub and wheel camber angle. place excess strain on wheel bearings.

how many people will be riding in the and frame, or by rotating an eccentric vehicle for the majority of its operation). shaft or washers on either arm. If the Whenever possible, place the driver of front suspension is strut-equipped, the vehicle (or another technician of the camber may be adjustable (via an after- same weight) in the driver’s seat during market kit) by adjusting the top of the the entire alignment process. This will strut mount inboard/outboard at the allow you to better tune the wheel an- upper towers or, again, depending on gles in a loaded condition as the car will design, by adjusting an eccentric at the normally be driven. This becomes more lower mount at the strut-to-steering of a factor if the driver tends to be on arm connection. the heavy side. If a vehicle is equipped with an inde- Today’s production vehicles tend to pendent rear axle, camber should be ad- offer a limited range of adjustment for justable via either eccentric bushings at

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the inboard control arm pivot points or original and in other cases, slightly more. one wheel at a time encounters a longi- an eccentric at the strut-to-rear upright. Usually the amount of offset change is tudinal rut and/or groove. Even if all the To aid in maintaining chassis rigidity, kept to a minimum, and vehicle tracking tires are aimed straight ahead when the aftermarket strut tower braces can be in- remains relatively unchanged. However, vehicle is in , a wheel that’s cam- stalled to tie the left and right struts to- if the offset is significantly different, it bered naturally wants to turn. gether, preventing the unibody from will alter the way the road forces are is generated by a flexing during hard turns. This will help transmitted through the tire and wheel leaning tire. A vehicle suspension using to avoid camber changes during spirited to the suspension. Therefore, large excessive negative camber (for example, driving. Depending on the make, model changes in wheel offset will increase the when wheel alignment is adjusted for and year of the vehicle, these bars may likelihood of . competition) will naturally tend to expe- or may not be available. Adding these Also consider the condition of suspen- rience more tramlining when the vehi- brace bars won’t degrade ride (won’t re- sion components such as bushings, ball cle is driven on the street. When a chas- sult in a stiff ride), but they will prevent joints and mounts. As the sis is set up for competition use, it’s unwanted chassis flex, allowing set cam- miles pile up, coupled with age, suspen- common to adjust for greater toe-out in ber angles to remain more constant. sion components gradually wear and/or order to achieve more immediate turn- You’re probably all too familiar with deteriorate. Control of the tire path de- in on corners. This added toe-out will the phenomenon known as tramlining— creases, making the vehicle more suscep- also contribute to tramlining because it the tendency for a vehicle to follow irreg- tible to following road irregularities. will reduce vehicle straight-line stability. ularities on the road surface such as un- Imagine a worn suspension that al- It should be obvious at this point that even pavement or severe rut- adjusting wheel alignment for ting. Drivers in the snow belt the will be detrimental region of the country com- for street driving, and vice monly experience this when versa. For daily street driving, they upgrade to a plus-size Thrust Line & following factory specifica- tire and wheel package, or Geometric Centerline tions is preferred to enhance when they change over from both stability and directional winter tires to summer tires. control and to reduce tire Upgrading to a set of higher wear. Track settings are for performance tires can also re- the track, street settings are sult in a more pronounced for the street. Period. tramlining issue. A final word about infla- The more “sensitive” the Thrust Line tion pressure: While tire in- tire, the more susceptible the Geometric Centerline flation pressure must be ad- vehicle is likely to become to justed for any competition road irregularities, since application to obtain maxi- wider tires with shorter side- mum tire contact patch, es- walls and/or tires that feature pecially under severe lateral stiffer sidewalls have a greater Top: The geometric centerline of any vehicle refers to a line drawn (during turns), using tendency to “track” the road from the center of the rear axle through the center of the front higher tire pressures than axle. Above: The thrust line refers to the angle at which the rear surface. The wider the tire, axle is aimed. The thrust angle is the difference between the geo- recommended by the vehicle the greater the contact patch, metric centerline and the measured thrust line. manufacturer for street driv- which results in increased ing will unnecessarily stiffen surface area to react to more of the road lows a front wheel and tire to swing be- the tire and make it even more willing 1 surface. It’s simple physics: Contacting tween the recommended ⁄16 in. of toe- to cause tramlining. Always adjust tire 1 more surface area and/or using a high- in and ⁄16 in. of toe-out when it encoun- pressure prior to performing any wheel 1 performance tire with greater grip and ters a rut in the road. This ⁄8-in. differ- alignment, and always follow the factory stiffer sidewalls means that the surface of ence in the direction that the tire is inflation specs for any street-driven ve- the road will have a greater influence in pointed will result in the vehicle - hicle. If the vehicle owner intends to terms of feedback to the suspension and lining. This is a perfect example of why use the vehicle for occasional autocross steering systems. it’s important to inspect suspension and events, you can increase tire pressure to Wheel offset has a direct bearing on steering components prior to perform- suit track conditions, but he must drop tramlining as well. Installing wider tires ing any wheel alignment. pressure to factory spec before driving or a plus-size tire and wheel package Wheel camber and toe settings com- on public . usually requires using wheels with a dif- bine to affect a vehicle’s tendency to ferent offset than the vehicle’s original tramline. Extreme positive or negative This article can be found online at wheels. In some cases, the new wheels camber settings will make a vehicle www.motormagazine.com. will have slightly less offset than the more sensitive, especially when only

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