Measuring a wheelbase

Part 1. Preparation and safety

Objective

• Identify and measure the wheelbase.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• Make sure that you understand and observe all legislative and personal safety procedures when working around vehicle chassis components. If you are unsure of what these are, ask your supervisor.

Points to note

• The vehicle chassis is the platform to which all the operating components and systems of the vehicle are attached. It is important that the chassis is straight and square so that steering and suspension components can operate in the intended manner.
• Manufacturers specify dimensions in relation to the location of the wheels. Two particular dimensions are:
  • Wheelbase
  • Track

• The wheelbase is the distance between the center of the front wheel and the center of the rear wheel and is normally the same on both sides of the vehicle.
• Some vehicles may have different wheelbase measurements from left to right. This is the exception rather than the rule. Always check the manufacturer's specifications before you take the measurements.
• The track is the measurement between the center of the left wheel tread and the center of the right wheel tread. It is common for the front track and the rear track to differ.
• If the dimensions differ from the manufacturer's specifications, refer to your supervisor.
• Two other dimensions should be noted:
  • The overall length of the vehicle. This is the distance between the front and rear extremities.
  • The overall width of the vehicle. This is the distance from the extreme right side to the extreme left side of the vehicle, but not usually including the external mirrors.
• These measurements are particularly important for legislative purposes. A vehicle's overall length and width can determine the roads where it can legally operate.
• The majority of service departments will have some form of electronic equipment to measure the axle alignment. When there is no specialized equipment, a basic method of checking axle alignment or the wheelbase can be carried out with simple tools. We have outlined this procedure in this module. The procedure shown here is not the only measuring method, but shows how to carry out these checks if no specialized equipment is available.
• Carry out this procedure with specialized equipment if it is available and you have been trained to use it.

Part 2: Step-by-step instruction

1. Prepare the vehicle
   Position the vehicle on a flat surface with the road wheels pointing straight ahead. Engage the emergency brake and place the transmission in neutral or park, then turn off the ignition.
2. Select appropriate measuring equipment
   You will need to prepare a measuring device. Such as a straight length of wood or steel with two moveable pointers attached.
3. Compare distances between axles on both sides
   Place the length of steel, with the two moveable pointers attached, next to the front and rear wheels on one side of the vehicle. Align the two pointers to the centers of the front and rear axles. Tighten the pointers to the position of the axle centers. Alternatively, use a mechanic’s set-square to align the front and rear axle centers with the length of steel, and mark the steel with chalk or marking pencil. Move the measuring device to the other side of the vehicle and check to see if the pointers align with the axle centers on this side. Compare the two; they should be the same. If one side of the vehicle has wheels significantly closer together or further apart, refer this to your supervisor.
4. Measure the wheelbase between marks
   Remove the length of steel and measure the distance between the two marks. This will give you the distance between the two wheel axles.