Tech Tip: Uncovering Tire Noise

Tech Tip: Uncovering Tire Noise

By now you’ve probably become an expert at explaining the noise differences between a “mud” performance tire and one designed for "all-terrain" use. Tire lugs are dead giveaways. Even someone with trifocals can see the difference.

By Steve LaFerre

By now you’ve probably become an expert at explaining the noise differences between a “mud” performance tire and one designed for “all-terrain” use. Tire lugs are dead giveaways. Even someone with trifocals can see the difference. You’ve also become pretty good at explaining tread life differences between tires by using the UTQG. Or at least using treadwear warranties.

But what do you say to a valued customer who is complaining about noise? “I have a noise in my car and I want you to fix it,” they say.For decades, engineers have worked successfully in quieting down engines, exhaust systems, suspension parts, transmissions and isolating the passenger compartment from the rest of the vehicle. Consider it an all-out war against what engineers call noise, vibration and harshness. We’ve read volumes about NVH, to the point that when we see the acronym, some of us stop reading. That’s a mistake. An NFL quarterback reads the playbook every week, and those responsible for making the motorist’s life more tranquil are on the job everyday.

Thanks to vehicle engineers, today’s cars are very quiet. Vehicles have become unspoiled concert halls with super megawatt sound systems, or quiet places to repose after a long day at work. A Sunday drive with the radio off is as quiet as a … wait, what was that noise?Despite the best work of aerodynamists, who have even reduced the harmonics coming from the radio antenna, your customers are more likely now to complain about tire noise than ever before. Simply put, tire noise is, quite often, the only unusual sound they’re likely to hear.

START BY LISTENING
Here’s what you do about it. First, listen to what the customer is saying to you. One of the most effective treatments for an unhappy customer is to listen. When he or she is finished, it’s your turn. Ask questions.

“Are you hearing this noise on rough roads or smooth roads? Is the noise constant or does it vary? In what speed range does the noise occur? Is the noise more like a pulse or a buzz? Is it actually an audible noise or a vibration you feel? Where do you feel the vibration, through the steering wheel or the seat? Did it suddenly begin or did it develop over a period of time? Is there anything in the vehicle’s recent repair history that would provide a clue?”

Noise heard on rough roads leans toward vehicle suspension problems, like worn shocks or broken suspension components. Smooth road disturbances are more problematic. If your customer says the noise is prevalent in a specific speed range, you’re off to a good start. Even better, if a specific speed is mentioned. Test the vehicle on a smooth road within that speed range for a mile, if possible. Make some mental notes about what you hear – if anything.

Next, accelerate and coast through the problem speed range. By doing this you should be able to discern if the noise is exhaust- or engine-related. You’re not through.

Once again, accelerate up to the speed range noted by the customer. Take the car out of gear and coast. When you reach the problem speed, press the accelerator and match the engine rpms as if the car were in gear. This will help you determine if the noise is engine-related.

Continue your noise search by selecting a lower gear and again driving at the problem speed. Cycle the air conditioner on and off and note any noise. Also note any vibration when you apply and release the brakes.

These checks help you sort out if the noise is originating from the driveline, exhaust system, transmission, brakes or the tire/wheel assembly, to name a few.

A disturbance noted at 45 mph to 50 mph and increasing with speed (over a broad range of speed), indicates a balance problem. At the same time, a disturbance noted over a narrow speed range indicates other vibration sources, such as high runout or actual tire damage.

Noise pulses indicate balance or runout problems, while buzz-like disturbances are normally driveline or irregular tire wear issues. Vibrations felt only in the steering wheel indicate that the problem area is from the front of the vehicle. Conversely, vibration felt only in the seat indicates that the rear of the vehicle is the source of the problem.

A noise or vibration which occurs suddenly is generally associated with a mechanical problem, such as a bent wheel or a lost weight. A problem that develops over time could be blamed on imbalance due to wear or a progressively deteriorating mechanical or structural problem.

If your customer has been truthful with you about vehicle accident information (did they have one, and where was the damage?) look closely at what repairs were made and if new wheels were installed. This information may point to noise causes other than tires. Should your analysis indicate an out-of-balance wheel assembly, you know what to do. The same goes for radial runout, the bolt tightening sequence (also a noise causer), tire rotation and warped brake rotors.

Tires Are Not NoiselessDigging deeper into the mystery of unwanted decibels turns up some helpful information. For example, tire/road noise is made up of specific sounds that travel to the passenger compartment. “Boom,” “sizzle,” “tonal” and “roar” are some of the terms used to describe these sounds.

Much of this has to do with the relationship between tread blocks and the void areas of a tire’s tread. Tread elements provide the tire with the gripping edges needed for traction. In effect, they act like tiny hammers striking the pavement every millisecond causing the tire to radiate noise much like a drum.

At the same time, voids (grooves) also generate sound. As they approach and leave the road surface, the voids open wider, but are forced narrower on contact with the pavement. This widening and narrowing pumps air in and out of the groove, radiating noise in a manner similar to a siren.

Tread designs are developed to a deliver wide range of performance characteristics – hydroplaning resistance, all-season traction, wet/dry handling, etc. – in the same tire. These desirable safety features require a reasonably aggressive tread pattern that simply cannot be 100% “noiseless.”

For some of the more aggressive tires, engineers have been successful in reducing noise by using an interlocking tread block pattern and uniform void distribution. This allows for a more even transfer of load from tread block to tread block and a smoother orchestration of the tread blocks through the contact patch.

VEHICLE DETERMINES NOISE
On a scale of 0 to 10, with 10 being the quietest, owners of luxury cars like a Mercedes Benz, Cadillac and Bentley expect tire noise ratings in the 7.5 range, or higher. Their driving habits are more conservative, somewhat predictable. Not so for owners of high performance vehicles like the Corvette, Viper or even the Mazda Miata, who will settle for more noise because handling performance is a primary concern. Noise rating for tires on these vehicles is often in the 5.0 to 5.5 range.

Years ago, when cars were far noisier, tire noise blended into the white noise generated by the vehicle and disappeared into the cacophony. Not any more. The vast majority of new cars come with independent front and rear suspensions that require precise alignment of all four wheels, not just the front. Since many vehicle owners never align their vehicles, their tires wear unevenly – and unevenly worn tires make noise.

The change to FWD has also brought on noise complaints. Front tires on FWDs wear faster and more evenly while the rears can develop heel and toe wear issues. More noise. The solution: tire rotation every 6,000 miles at least.

Before leaving the subject, remember that sound (noise) is nothing more than waves of energy passing through a medium such as air, glass or metal. Like ripples that form when a stone is tossed into a pool, these waves radiate outward in ever expanding circles until they dissipate.

It’s this random collection of sounds coming from different sources that your customers are asking you to find and eliminate. Analyzing noise complaints can be a time consuming process. If done properly, it’s a substantive image enhancer, a constant reminder to customers that they’re dealing with a professional.

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