Test Drive Techniques - Tire Review Magazine

Test Drive Techniques

Test drives on the surface can seem like one of the most unprofitable tasks a technician can perform. But, it can be one of the most profitable processes a shop can do to help sell more service. You just have to have procedures and training in place so a test drive is more than just seat time.

Today, a test drive is critical in spotting worn suspension and brake components on late-model vehicles. Unlike older vehicles, shocks and struts are shielded by a lot of plastic to protect the rods and seals. This can make looking for a leak more difficult. Even if there is not a leak, a lot of the wear on a modern shock and strut happens internally. The oil and valving inside a strut can wear out. Also, the gas chamber can leak and mix with the fluid.

Another issue test drives can help diagnose is problems with the bushings. Modern vehicles have larger bushings that are designed to isolate vibration and harshness. While they may look fine to the naked eye, deflection due to wear may only be experienced on the test drive.

Test Drive Tools

When you don’t perform a test drive, you are neglecting your most powerful inspection tool: the perspective of an expert. A technician or service writer behind the wheel of a customer’s vehicle brings fresh perspective to the vehicle’s ride that the customer may not notice.

A good test driver will be able to observe conditions or problems with the vehicle that may have developed so slowly that the owner is unaware of them, such as degraded shocks and struts. One of the keys to becoming a good test driver is to find a driving “loop” or route that has a variety of road conditions. A predetermined loop adds a consistency that helps you spot small problems.

Before the test drive, you should have a clear list of symptoms and related conditions the customer might be experiencing. On the test drive, you should have a clear and methodical checklist that will help gauge the need for ride control component replacement and other unperformed repairs.

The Loop

Before you get behind the wheel of a vehicle, make sure it is safe. Look at the gas gauge to make sure it has enough gas. Check the tires and make sure items inside the vehicle are secure. Last, make sure the lights work. Nothing is worse than getting pulled over by the police in someone else’s car.

For suspension road tests, your test loop should consist of sections: a flat and straight section; an area to test braking and acceleration; an area with a dip or bump; and an area that offers both left and right turns.

Avoid high-traffic areas and rush hour. Use a parking lot or rarely used section of road for the braking and acceleration section of the test. This test is used to detect brake pulls, torque steer and worn or loose suspension or steering components.

Developing a methodical and consistent test drive loop and procedure can improve your chances of coming back from a test drive with an understanding of the problem the owner is experiencing. Also, a plan and a loop can eliminate distractions that could lead to an accident.

What to Test For

Outside of the usual suspension noises and driveablity problems, you should be analyzing the performance of the ride control components. The typical shock or strut has two types of dampening forces: high- and low-frequency.

High-frequency dampening is rapid movement of the suspension. On the test drive, this type of dampening is required to deal with sudden bumps and dips. Inside the shock or strut, the rapid movement causes a valve to open quickly during compression and rebound. This allows the tire to stay in contact with the road and prevents the motion from being transmitted to the body and unsettling the vehicle. Too much dampening and the ride will be harsh because the energy can’t be absorbed by the spring. Too little of a dampening force will cause the inertia of the suspension to fully act on the spring, causing it to continue to travel. This will eventually cause the tire to lose contact with the road. On the flip side is high-frequency rebound. On the test drive, this can be tested on concrete seams and driveway turn-ins. Typically if this is an issue, it will feel like the suspension is still reacting to a bump even after it has passed over it.

The second type of dampening is low-frequency. This is a slower movement of the piston. Low-frequency dampening controls the movement of the body on the suspension and the transfer of weight on the tires. These are the forces associated with nosedive, acceleration squat, and body lean. If a shock or strut is worn or damaged, it will not be able to control suspension movement and weight transfer. This ultimately leads to an unstable vehicle. The low-frequency dampening can be tested with braking and acceleration.

If you have room, try performing a figure eight at close to full lock. Often a collapsed upper strut mount or a broken spring will cause binding and contact between the spring and tire on some vehicles.

There is an old proverb that says you have to walk a mile in another person’s shoes to understand them, and the same is true for vehicles. There are some things a customer will never tell you — either because the customer doesn’t know what’s wrong with the car or they fear being fleeced by mentioning something that may not need to be replaced. But, it often takes a test drive to reveal problems with a vehicle.

By not performing a proper test drive, you could be missing the most important part of the customer’s complaint.

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