Alignment on
Your BMW
Wayne R. Dempsey

Difficulty Level: 4
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

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     The BMW 3 Series cars are known for good handling and an excellent suspension system. Of course, precise handling and cornering are nonexistent if the car is not aligned properly. There are five suspension specifications that must be met to properly align the chassis: front-end caster, camber, and toe; and rear-end camber and toe. Unfortunately, on the stock 3 Series, all but front toe setting are fixed and nonadjustable. Aftermarket racing components can be substituted if you need additional adjustment, but the street cars don’t have this ability in their stock form. If the alignment of the suspension is slightly off, you may experience significant tire wear and a loss of power and fuel economy. The most common sign of a misaligned front suspension is the car pulling to one side of the road while you are steering straight.

     Although the home mechanic can adjust basic front-end toe-in setting, have a trained professional with an alignment rack make the other adjustments. It’s nearly impossible to determine the correct angles and settings for your car without an alignment rack.

     “Camber” refers to the tilt of the wheel as measured in degrees of variation between the tire centerline and the vertical plane of the car. If the top of the wheel tilts inward, the camber is negative. If the top of the wheel tilts outward, the camber is positive. On the BMW 3 Series, the camber should be slightly negative and within the standard stock settings. On some older BMWs, chassis deformation due to rust and age can cause the camber adjustments and measurements to be slightly off. If the car has been in an accident, the resulting chassis damage is often reflected in alignment values not within spec.

     With E30 cars, BMW makes an eccentric upper strut mount for the front suspension that allows you to subtract half of a degree from your camber setting (part number 31-33-1-139-484). This upper strut mount can correct the chassis camber when it falls out of factory specifications.

     Worn suspension bushings may also add to odd alignment measurements. As the bushings and suspension mounts age, they tend to introduce slop into the suspension system, which can result in poor alignment readings. Lowering your BMW will also change the alignment specifications from the factory defaults. If your alignment specialist says your car’s fixed specifications are outside the factory ranges, but your car has not been in an accident, it’s likely some of the suspension bushings are worn and need replacement (see Project 59). If you have difficulty achieving proper camber settings, a good-quality camber strut brace can help you tweak the chassis (see Project 64). Tightening or loosening the adjustment nut on the camber bar can move the upper strut towers in or out very slightly.

     The rear wheels should be set from the factory for a slight negative camber (about –1 to –2 degrees), as the trailing arms tend to bend slightly outward as the car accelerates under power. Since one-half of the wheel is mounted firmly on the ground, the top of the wheel has a tendency to twist outward. Setting the rear wheels for a slight negative camber means that under power they will be mostly neutral.

     “Caster” is the angle that the steering axis is offset from the vertical plane. On the 3 Series, the strut points toward the rear of the car, resulting in a positive caster angle. This angle varies over the model years from 3 to 9 degrees.  The amount of caster in the suspension directly influences the control and stability of the wheels when traveling in a straight line. Since the BMW rear suspension utilizes a trailing arm design, which has a tremendous amount of built-in caster, there is no specification for the rear caster. Front suspension caster is very good for high-speed stability because it helps to keep the wheels aligned and straight.

     “Toe” refers to the angle of the two wheels with respect to each other. If a car has “toe-in,” the front edges of the wheels are closer to each other than the rear edges. Toe-in is adjustable by changing the length of the tie rods (see Project 58). With rear-wheel-drive cars like the BMW 3 Series, the front wheels may try to move toward a toe-out position under power. Setting the wheels to have very slight toe-in can help neutralize this effect. “Toe-out” occurs when the front edges of the wheels are further apart than the inner edges. Some toe-out is necessary when turning, since the angle of inclination of the inner wheel must be tighter than the outer wheel. The rear toe should be set as close to neutral as possible.

     So how should your BMW be set up? If you plan to race your car, you will need aftermarket suspension components and as much negative camber as allowed by the racing rules. The car will tend to straighten out in turns, and you want the maximum tire patch on the road when cornering. When the camber starts to change to slightly positive through turns, a negative camber setting will help neutralize the effect.

     There’s a common misconception that a lot of caster is good for racing. While adding more caster to the suspension can indeed make it handle better, introducing too much caster into the suspension can negatively impact your track times. On a perfectly balanced rear-wheel-drive car, adding too much caster can transfer load from the outside front and inside rear tires to the opposite corners. This can upset the balance and cause a corner entry push.

     Seek professional help for alignment specifications and answers to questions you might have, and don’t accept blanket statements about suspension upgrades—they’ve led to many common misconceptions. Do your own research. Two books I refer to on these topics are Race Car Engineering by Paul Van Valkenburg and How to Make Your Car Handle by Fred Puhn.

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