B arry's T ire T ech

This is a series of articles on the technical aspects of tires, their care, and usage.

My primary purpose in these articles is to help people understand tires and thereby reduce the risks we all face every day.

..........and since tires is just about the only thing I know about..........

Please drop me a note if you have a topic you want to see:

Barry@BarrysTireTech.com

Tire Noise and Noise Testing:
  • If you came here to find a list of brands/models of tires that are quiet:
    • I suggest you read the reviews available at Tire Rack, or some other websites to make your determination. Please note that the EU requires a noise rating on tire labels, but I am not aware of anyone who complies a list.
    • I am not aware that anybody actually does testing for noise (at least testing that involves good science) and publishes the the results. Even Tire Rack doesn't always evaluate noise, and when they do, it's subjective.
  • If you came here to help guide you in selecting a quiet tire by its visual appearance:
    • It's more complex than that. I will give you some guidance below, but there's only a small amount you can get from looking at the tread pattern.
    • Again, I suggest you go to Tire Rack or some other websites to help make your determination.
  • If you came here to find out what to do about worn tires that are noisy:
    • First suggestion is to get an alignment and rotate tires. Sometimes a new wear pattern on top of an old one will be quieter. Please note that it may take several hundred miles before you'll be able to tell if the rotation made a difference.
    • If that fails, you'll have to replace the tires.
    • Below, I'll give you some advice as to what is causing the noise.
  • Sometimes tires generate vibrations that will cause a body panel to make noise.
    • There are sound deadening materials that can be applied to the panels in a car. They involve removing upolstery, but they are effective.

I am going to talk about how tire manufacturers try to reduce the noise that tires generate. That may help you select a tire that doesn't generate as much noise as others.

The operative word here is boring. Boring tread patterns generate less noise than exciting, futuristic looking patterns. And it's the tread pattern that is making the noise. The casing doesn't play a significant role in noise generation (except if it sets off a body panel.)

EXCEPT that a few more psi will tend to reduce the noise by stiffening up the entire tire.

HOWEVER, The road also contrubutes to noise - and worse, the tread pattern can interact with the macro texture of the road surface in unpredictable ways.

A side note: This has been the most difficult article I have ever tried to write, because there are sooooo many exceptions, and sooooo little actual data available to the public. Plus it is sooooo difficult to describe.




What you should get from this page:

  • Noise is just a high frequency vibration. That is, you sense noise using a different part of your body than you do with a vibration, but in essence, they are both part of a continuous spectrum.
  • There are 2 players when it comes to tire noise.
    • The tires
    • The pavement
    • A tire can interact with the pavement and not only will an otherwise quiet tire be less quiet, but different tires will react differently to different road surfaces - and maybe even change which one is worse!
  • There are a lot of techniques employed by tire manufacturers to reduce the noise in new tires.
  • Alignment can generate irregular tire wear which in turn can generate noise.
    • Irregular tire wear mostly generates vibrations - and those vibrations tend can manifest themselves as noise by vibrating various parts of the car - usually body panels. Sound deadening material works wonders here.
    • Most people are sloppy when it comes to identifing irregular wear patterns. Those descriptions lead many to false conclusions as to the cause. Do NOT take the description of the name of a wear pattern as gospel.


The photo above is of a semi-anechoic chamber. Semi (not complete - notice the smooth floor) and anechoic (without echo). The wedges on the ceiling and floors are sound absorbing material. Obviously you can't drive a car onto those wedges and it is common for there to be a dynamo wheel imbedded in the floor.

A chamber such as this one is used to research all kinds of noise generating things, including tires, without the influence of the wind or the pavement.

Please note: This photo seems to be testing car noise. Tire noise usually is done with a tire holding rig, not a vehicle.

To the right is an outdoor setup. It's a smooth pad instrumented with microphones. This is a common set up for vehicle testing where even the driver's head is instrumented as noise can come through the vehicle and it is important to know exactly what the driver is experiencing.

It should be noted that the EU (European Union) requires tires to have a label that indicates the results of an external, engine-off, pass-by test on a test surface that meets certain standards. A sample of the label is to the left.

There is no noise requirement for the US, but there appears to be a tire noise regulation (limitation) in Japan. However, the EU is currently (Nov. 2022) the only place where tire noise values are published and available to the general public.

Please note: This is a moving target and likely to change. I'll update the webpage as I find out about those changes.

The Science:

You would think that a smooth tire (aka a slick - one with no tread pattern) would produce little or no noise - but you would be wrong. Partially because of the texture of the road surface - and partly because moving air makes noise. That means that even a slick on a smooth surface is going to make noise. Look at the image to the right and observe that the air (yellow arrows) has to move out of the way of the rolling tires - and what I didn't show you is that the air has to return back behind the rolling tires. All of that makes noise.

Further, the texture in the road surface produces pops and hisses as the tire rolls into the surface, and wooshes and smacks as the tire rolls off.

But if there were a way to allow the air to more easily move out of the way, the noise would be less, right?

Yes, and interestingly, the way one designs such a feature into a tire can also allow water to more easily move out of the way, too! And that is with grooves - smooth ones would be better than more complex ones.

And the less sipes and cross grooves the better! Unfortunately, cross grooves and sipes improve wet and snow traction - as does non-straight sided and crooked tread grooves - so using as few of each as possible is key to making a quiet tire.

What that means is that tread patterns that excel in wet or snowy conditions are going to be noisy!

The more broken up the tread pattern, the worse the noise.

In other words, boring is beautiful when it comes to noise!

Noise is a high pitched vibration. So what you feel in the steering wheel is similar to what you hear with your ears. The difference is the frequency and where you sense it.

Large tread elements produce low frequency noise - and if the frequency is low enough, you can feel those.

Small tread elements produce high frequency noise - and here's the kicker:

If you mix large and small elements, it fools the ear into thinking the noise level is lower. (Neat, huh!)

Put a different way, if you can somehow vary the size of the tread elements, it sounds less noisy, even though the amount of energy being generated is the same.

Look at the image to the right and see that principle in action. A tread can be designed with different "pitches" - That is, different repeatable elements of different size - and the net effect is that not only is the noise perceived to be lower, and if done correctly, the tread pattern doesn't reinforce a given vibrational frequency.

There is also another way to do this: Make the tread pattern have a variety of different sized elements. This is particularly useful if the tread pattern doesn't lend itself well to different pitch sizes.

The photo to the left illustrates this.

There are a lot of techniques tire manufacturers use to reduce noise, while still making interesting tread patterns.

To avoid generating noise, it is common for tire manufacturers to avoid sharp, acute corners that are less supported - meaning less rigid. Obtuse corners are better.

One of the ways to turn an acute corner into an obtuse corner is to cut off the corner. See the illustration to the right. Both started out the same size.

Another way is to put a piece of foam inside the tire. The principle is that the air chamber inside a tire tends to develop echos and can reinforce certain frequencies.

But what I find interesting is that this has been done repeatedly by different tire manufacturers and always for a vehicle manufacturer (not always the same one), and as soon as that particular make/model tire is no longer being supplied to the OEM, it gets discontinued.

Makes me think the buying public isn't interested or that this doesn't work as well as advertised! I wish there were some test statistics to show how much that foam actually reduces the noise level.

Update Nov, 2022: Here's a link to a Car and Driver Test where they concluded the noise reduction with a foam insert wasn't very much. Car and Driver: Tested: Do acoustically insulated tires really hush road noise?

There are sound deadening materials that can be applied to body panels to reduce noise. The photo to the right is a sample.

There are 2 ways this insulation reduces noise:

  • Insulating the car interior from external noise.
  • Dampening the vibration in sensitive body panles.

Sound insulation materials require getting access to the body panels - and that means removing a lot of upolstery.

However, it is effective.

And I can't leave this subject without showing the most interesting bit of equipment I have ever seen - the Aachen head (to the left).

It is named after the city in Germany where it was developed. It simulates what a person hears to a remarkable degree - plus it looks really cool!

Noise in worn tires:

In my opinion, this is almost exclusively caused by irregular wear - and irregular wear is mostly caused by misalignment - typically toe.

Yes, there are tires that are more suseptible to this than others, but it doesn't happen if the aligment is good.

I am of the opinion that the published vehicle manufacturer's alignment specs are too wide - by half. In order to get good tire wear and avoid noise, the alignment has to be within the inner-half of the allowable range.

I came to this conclusion during a dispute between a major vehicle manufacturer and the tire company I worked for. We developed data showing that if the alignment was within the inner half of the allowable tolerance, there were no customer complaints.

This also means that the alignment tech has to be willing to do the work that this might entail. Not every tech is willing to do this. Some techs even go so far as to think that if the vehicle manufacturer didn't provide for adjustment, then they shouldn't (or can't) - opting for a "Toe and Go" approach. They are wrong!

For this reason, I recommend that consumers ask BEFORE:

  • That the alignment tech agrees to put all alignment settings in the inner half of the allowable range.
  • That if there needs to be additonal parts - like a camber plate, or an eccentric bolt (both added cost), that the tech is authorized to do such an install. It is OK to ask what those will cost.
  • That there be a printout showing the before and after values AND the consumer should look at that BEFORE leaving the shop.

The consumer needs to be prepared to pay for those additional parts.

But one of the problems with trying to fix irregular wear is that you can't undo what is already there - that is, you can't do anything to reverse the wear. Any new wear pattern will be on top of whatever is already there.

So generally fixing the alignment only fixes the source of the irregular wear and prevents the tires from getting worse, but only replacing the tires will get rid of the noise.

And that's not quite true. Sometimes rotating the tires will allow noisy tires to develop a different - and less noisy - wear pattern.

HOWEVER, this doesn't often work.

Irregular wear names:

For some reason, many otherwise knowledgeable people seem to misidentify the type of irregular wear - and therefore, the cause. This is particularly true for "Cupping".

While it is true that cupping wear is caused by out-of-balance and out-of-round tire and wheel assemblies, as well as bad shocks, it is common for many people to misidentify other types of wear and call it cupping wear.

This is because bias tires used to be really susceptible to cupping wear - AND - back then tire balance, out-of-round conditions, and bad shocks were pretty common.

Not only are radial tires less susceptible to cupping wear, but balance, out-of-round, and bad shocks are much, much less common nowadays.

What I am trying to say is to be aware that some folks have bought new shocks unnecessarily - and since vehicle alignment is usually part of the shock install, the problem could have been fixed with just the alignment. This is speculation on my part, because I have never been directly involved in such situations.




Barry's Tire Tech - Main Page