TECHNICAL GUIDE / 04

Reference, Rigidity, and Measurement Conditions that Affect Measurement Results

Even when using dummy wheels, measurement results are not solely determined by the tools.

Alignment values are influenced by what is used as a reference for measurement, whether the tool can maintain its reference under vehicle load, and whether the vehicle and work environment are consistent during measurement.

To ensure that measurement results can be compared, you need to check the following three points:

01Reference
02Rigidity
03Measurement Conditions

1. What to use as a reference for measurement

To measure alignment, you need a reference point for angles and distances.

When measuring camber, the horizontal mounting surface and the measurement surface where the angle gauge is applied serve as references. When measuring toe, a string is stretched using the vehicle's hub as a reference, and the difference in distance from the string to the front and rear of the tire is checked.

If the measurement position or the location where the angle gauge is applied differs each time, there will be differences in the measured values even if the vehicle's condition has not changed.

Points to check

  • Height and inclination of the surface where all four wheels are placed
  • Surface to which the angle gauge is applied
  • Position where the string is stretched
  • Position for reading toe
  • Installation method of measuring instruments

It is important not only to have a reference but also to be able to use the same reference repeatedly.

2. Can the reference be maintained under load?

Dummy wheels bear the vehicle's weight individually when mounted on the vehicle.

Even if the shape is correct under no load, if the tool deforms under the vehicle's weight, the measuring surface and position used for measurement will also change.

This is where rigidity becomes important.

Strength is the property of not breaking under load. Rigidity, on the other hand, describes the resistance to deformation under load.

Not breaking and being able to maintain the measurement reference under load are not the same. Therefore, in addition to the maximum load specification, it is necessary to check whether the structure is designed to account for deformation during use.

Difference between static shape and deformation under vehicle load
In addition to the shape under no load, check whether the measurement reference can be maintained under vehicle load.

Points to check

  • Designed load per plate
  • Path of load transmission to the ground
  • Positional relationship between the measuring surface and the load-bearing part
  • Approach to deformation under load

For details on the shape of the product itself and items to check when selecting, please refer to "7 Items to Check When Choosing a Dummy Wheel."

3. Are the measurement conditions consistent?

Even if the same vehicle and tools are used, differences in the mounting surface, vehicle condition, and work procedures will result in different measurement results.

Especially in camber measurement, the inclination of the mounting surface is included in the angle gauge reading. Therefore, a laser level and leveling table are used to adjust the height and inclination of the four wheels.

Alignment measurement environment using a leveling table, laser level, and angle gauge
Prepare the measurement environment, including the mounting surface for all four wheels, the measuring instruments used, and the measurement positions and procedures.

For the vehicle and work procedures, make the following conditions as consistent as possible:

  • Fuel load
  • Method of settling the suspension before measurement
  • Order of measurement and adjustment
  • Position for reading each value

When comparing before and after adjustment, it is more important to understand what was kept consistent and what differed, rather than making all conditions perfectly identical.

Recording the measurement date and time, tools used, fuel load, and adjustment details will make it easier to confirm differences in values later.

Differences in values due to measurement methods will occur

Alignment values will differ depending on the equipment and measurement method used.

Measurements using dummy wheels, measurements with tires and wheels installed, and measurements with a shop's alignment tester each have different measurement references and procedures.

Just because values measured by different methods do not match does not mean that one is incorrect.

When checking for setup changes, it is important to compare before and after changes using the same tools, the same references, and the same measurement conditions.

Consider the three factors separately

When there is a difference in measurement results, check not only the vehicle but also the following three points separately:

  • Has the reference changed?
  • Can the tool maintain its reference under load?
  • Have the measurement conditions or work procedures changed?

Even if only the tool's shape is checked, if the mounting surface or work procedures differ, the measurement results will not be consistent. Conversely, even if work procedures are standardized, comparison will be difficult if the measurement reference is vague.

For alignment measurement using dummy wheels, the tools, measurement environment, and work procedures must be considered as a single measurement system.

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