Alignment (String Theory)

I’ve already measured the Camber, Toe, and Thrust Angle on the Lotus and have some thoughts about how to best achieve an alignment in a home garage using “ordinary” tools. I’m going to first describe two widely used methods and then generate some detailed postings showing the equipment I used as well as some enhancements that I think make wheel alignments go even better…

Reading through the literature on wheel alignment inevitably brings you to many different implementations of what is called the string method. Generally speaking this involves precisely setting a string around the perimeter of a vehicle to use as a reference for measurements taken from the wheels. The first photo below shows a typical setup using jack stands and conduit to support the strings strung along each side of the car. Notice that the car is sitting on leveling pads and has “slip plates” under the wheels. The two strings are set exactly the same distance apart on the conduit pipes at each end of the car. The conduit pipes are then positioned (slid back and forth) on the jack stands until the strings are equal distance from the center of the wheel hubs. This setup ensures that the strings are “perfectly” spaced equal distance (parallel) along each side the vehicle.

With the strings aligned you simply measure the distance from the string to a point on the face of the wheel (at both the front and rear of each wheel). You must (of course) also ensure that the steering wheel is set “straight” when measuring Toe at the front wheels.

A second, and I think improved version of the string method employs a pair of fixtures to support the strings that are attached to each end of the car. These systems have small grooves cut in the conduit pipes to ensure the strings are equally spaced. The pipes are then slid back and forth in the fixtures until the strings are set equal distance from the wheel hubs. It is much easier to keep the strings aligned to the car when they are attached in this manner. Once again measurements are made between the strings and wheels to determine the relative position of each wheel. A big advantage here is that the car can be moved back and forth to “settle” the suspension after adjustments removing the need for “slip plates”.

There are a few things to note about either of these string methods.

First… These string systems measure only Toe angle. Although the fixtures could (theoretically) be aligned to the “center-line” of the vehicle, therefore measuring thrust angel, this is very difficult to do in practice.

Second… Measurements from strings set in this manner are “secondary” measurements. That is; The accuracy of this system depends on the strings being “perfectly” aligned. It is nearly impossible to separate misalignment of the strings from the measured Toe angle.

last… The generally accepted “tolerance” for a wheel alignment on the Lotus is 1/2mm (.019”). That means the strings need to be aligned to something on the order of .010” or better. I’ve tried it and don’t believe it is realistic to expect that kind of accuracy.

One last observation… It needs to be said that F1 teams regularly set alignment using strings. As a matter of fact the image below shows team Ferrari employing strings and setup wheels in the pits at a recent race. So what I really mean to say about string alignment systems is that they are best used in “controlled” environments!