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Pelican Technical Article:

Alignment on your 911

Tab:

$100

Talent:

*****

Tools:

Alignment rack

Applicable Models:

 
Porsche 911 (1965-89)
Porsche 912 (1965-69)
Porsche 914 (1970-76)
Porsche 930 Turbo (1976-89)

Parts Required:

-

Hot Tip:

Have a professional perform this job.

Performance Gain:

Better handling and better tracking of your front suspension

Complementary Modification:

Replace shocks, wheel bearings, tie rod ends, ball joints, lower front end, upgrade to Turbo Tie Rods
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

The 911 is known for its good handling and excellent suspension system. Of course, precise handling and cornering are nonexistent if the car is not aligned properly. There are five different alignment specifications that must be set in order to properly align the 911. These are front-end caster, camber, toe, and rear-end camber and toe. All of these may be set to the factory specifications, or tweaked slightly to give better performance when setting your car up for racing. If the alignment of the suspension is slightly off, then you might get some significant tire wear and a loss of power and fuel economy. The most common sign of a mis-aligned front suspension is the car pulling to one side of the road when driving straight.

Although the home mechanic can perform the basic front-end toe-in setting, it is suggested that you allow 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 the use of 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 inwards, the camber is negative. If the top of the wheel tilts outwards, the camber is positive. On the 911, the camber should always be set as close to neutral as possible, with a slight positive emphasis (about a sixth of a degree). On some of the older 911s, the chassis can sag due to rust and age, and it is sometimes difficult to get all of the negative camber out using the normal adjustments. The installation of a camber strut brace (Pelican Technical Article: Installing a Camber Strut Brace) can help prevent the sagging of the shock towers, but unfortunately it cannot help to undo damage that has already taken place.

On the rear suspension, the camber is set using an eccentric bolt that is rotated to change the angle of inclination. The rear wheels should be set for a slight negative camber (about 1 degree), as the trailing arms tend to bend slightly outwards 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 outwards. Setting the rear wheels to have 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 911, the strut points towards the rear of the car, resulting in a positive caster angle. This angle is typically set at about six and a half 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 911 rear suspension utilizes a trailing arm design which has a tremendous amount of built-in caster, there is no adjustment for the rear caster.

Toe refers to the angle of the two wheels with respect to each other. If a car has toe-in, it means that the front edges of the wheels are closer to each other than the rear edges. With rear-wheel drive cars like the 911, sometimes the front wheels try to move towards 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 farther 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 wheels also have a toe setting, and this should be set as close to neutral as possible.

So how should your 911 be set up? It all depends upon what you are going to be using it for. If you are planning on racing your car, then you will probably want as much negative camber as allowed by the racing rules. This is because the car will have a tendency to straighten out in turns, and you want the maximum tire patch on the road when you are cornering. Setting the camber to a negative value means that when the camber starts to change to slightly positive through turns, the negative setting will help neutralize this effect. Seek professional help for alignment specifications and any answers to questions that you might have.

Zero Camber.
Figure 1

Zero Camber. When the car is aligned with zero camber, it means that the wheels are directly perpendicular to the ground. The tires make even contact with the road, and exhibit a minimal amount of wear and friction when turning. The weight of the car is distributed evenly across the tire tread, but the steering control can be a bit heavy. Tire sizes are shown smaller than scale and camber angles are exaggerated for ease of illustration in these diagrams.

Negative Camber.
Figure 2

Negative Camber. The lower parts of the tires are angled outwards, causing tires to wear more on the inside edges. The 911 has an independent front suspension which creates a slight negative camber when traveling over bumps. As the suspension compresses upwards, the wheel tilts in slightly to avoid changing the track (distance between left and right wheels). Although this momentarily changes the camber of the wheel, it prevents the tires from scrubbing and wearing every time that the car travels over a bump.

Positive Camber.
Figure 3

Positive Camber. This can cause the outer edges of the tires to wear quicker than the inside. At factory settings, the 911 should have a slight positive camber (about a sixth of a degree). This is designed into the suspension in order to provide increased stability when traveling over bumpy roads, or through turns on the typical high-crowned roads.

Positive Caster.
Figure 4

Positive Caster. The concept of positive caster is best demonstrated by looking at the wheel of a shopping cart. The steering axis of each wheel is located in front of the point where the wheel touches the ground. The load of the cart is in front of the wheels, and as the cart moves forward, the wheels rotated on their axis around to follow the direction of the cart. This creates an inherent stability that tends to keep the wheels straight, unless they are forcibly steered in a different direction.

In a similar manner to the shopping cart, the 911 has a slight positive caster which creates an inherent stability when the car is moving in a straight line.
Figure 5

In a similar manner to the shopping cart, the 911 has a slight positive caster which creates an inherent stability when the car is moving in a straight line. With the angle of the strut tilted back, it places the steering axis and the load in front of the contact patch where the tire meets the pavement. Like the shopping cart, the 911 tends to move forward in a stable, straight line until the wheels are turned in a different direction. The rear trailing arm of the 911 by its design has extensive positive caster.

Toe In.
Figure 6

Toe In. The toe of the front suspension refers to the angle of the two wheels with respect to each other. Significant toe-in or toe-out will cause extreme tire wear, as the wheels constantly try to move towards each other (toe-in), or move away from each other (toe-out). The result is that severe friction is created on the tires, and at highway speeds, the tires will wear significantly, and power/fuel economy will suffer.

Toe Out.
Figure 7

Toe Out. The toe of the front suspension refers to the angle of the two wheels with respect to each other. Significant toe-in or toe-out will cause extreme tire wear, as the wheels constantly try to move towards each other (toe-in), or move away from each other (toe-out). The result is that severe friction is created on the tires, and at highway speeds, the tires will wear significantly, and power/fuel economy will suffer.

Toe-out through Turns.
Figure 8

Toe-out through Turns. When going around a turn, the inner wheels will turn at a tighter radius than the outer ones. This is so that both wheels will be able to turn around the same point without any tire wear. The outer wheel turns at less of a sharp angle than the inner wheel. This minimizes the amount of 'scrub' of the tires on the pavement as the car turns.

The only way to get the proper measurements for aligning your car is to have it professionally done on an alignment rack.
Figure 9

The only way to get the proper measurements for aligning your car is to have it professionally done on an alignment rack. The alignment rack shown here is owned by Alex Wong of Precision Tech Motorsports and costs in excess of $18,000. The proper alignment of your 911 is not something that the home mechanic can reliably perform. There are even a lot of incompetent alignment shops out there who are not familiar with the intricacies of aligning the Porsche 911. It's best to find an alignment shop that will be able to properly perform the alignment according to the factory procedures and settings. When purchasing new tires, don't necessarily settle for the tire shop's default alignment: it may be less that you pay for. The extra time and money spent taking your car to a professional will pay off in the long run.

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