What causes *tire chirp*?

Factual Questions
1

Quick question: I always thought “tire chirp” was caused by under-inflated tires. If you start hearing a little chirp when you go around a corner, you need to add some air to a tire.

However, I’ve got somebody here at this end who maintains that tire chirp is caused by the fact that Detroit has supposedly changed the composition of tires and there’s nothing you can do about it. (And yes, there’s more than a hint of “things Detroit doesn’t want you to know” here.)

Is he right? Or is he just too lazy to go out and put some air in his tires?

2

Um, friction? Just my guess…

3

In what manner would Detroit be able to change the composition of tires?

Personally, I think your supposition about under-inflated tires is right.

4

Your tires chirp or squeal because there is a higher force applied to them than there is friction between the road and the tire. If the tire is under-inflated than the friction is less and you hear the squealing sooner. I don’t know if there is a new tire with less friction i doubt this is the case people want better tires not worse. My thought is you hear more tire squealing now is because people are driveing faster cars more aggresivly so there is more force between the car and the road therfore more squealing.

5

I’m with you, under inflated tires. I have a 97 Toyota Tacoma Pickup and i’ve only ever heard the “tire chirp” if the pressure was low.

But that’s not really counting the times i come flying around a corner doing twice the normal posted speed limit. :smiley:

6

that sound is the rubber sliding on the pavement and many factors contribute. faster speed is the main contributor but also other things like tire width. The wider the tire the sooner it will do it as the outer part of the tire has to travel longer distance than the inner part.

7

This vaguely rings a bell with me. I recall there being some legitimate, useful reason for changng the composition. I could also be remembering something completely unrelated. not a very useful response, but there ya go.

8

I drive an SUV and have a right front tire that has a slow leak. When the tire starts to squeal or chip as I go around the corner, It’s time to add some air. It’s usually down 10 pounds or so before it makes any noise.

It’s also most noticeable when that tire is on the “outside” of the turn.

Gary

9

qualifications, a caveat and disclaimer:

I’m a car guy. I know a fair bit about motor vehicles generally. The disclaimer is that I am not an engineer. The caveat is that the answer to this question is known, but not by me. However, it’s a lot of fun to guess.

First of all, “tire chirp” is the same phenomenon as the “tire squeal” effect heard when you spin your tires accelerating away from a light (or whatever).

Yes, tires squeal more readily when underinflated than when they’ve got enough air pressure. The tire casing deforms a lot more when the tire is underinflated, and my best WAG is that what you’re hearing is the rubber squirming around (and slipping) beneath a quivering casing. In technical terms, the casing is quivering because the shear loads produced by the lateral acceleration of the vehicle is causing the rubber to squirm, slipping against the pavement.

However, tires almost never squeal because they are wide, as suggested by a previous poster. I once saw a street-legal drag car make a slow, squealing u-turn, but in that case the tires squealed (in other words, they were slipping) because they were connected by a locked differential. The differential keeps the tires from moving at different speeds, a necessity when turning. I would be hard-pressed to believe that a sufficiently-inflated single tire would squeal at super-parking-lot speeds.

Now: tire compound. That has something to do with it, but Detroit does not. Generally, tire compounds squeal in inverse proportion to their coefficient of friction. If you go to an autocross event, you will hear cars with fairly hard-compound tires squealing away, but the ones with sticky tires (i.e., DOT-legal slicks and stickier) will squeal very little or not at all. I suspect this is because cars with stickier tires are sticking to their chosen line better and sliding laterally to a lesser degree.

Detroit has very little say about what goes into tires. Michelin (and others) recently began putting silica into tires to increase their wet traction, but I don’t believe that this increases squealy noises.

One minor note: if your tires are squealing going around corners at normal speeds, they’re not just underinflated; they’re dangerously so. Pump up those tires!!

Anthros

10

Regarding the different tire composition aspect, I’ve heard (on Car Talk so it must be true) that the reason that nowadays you often get a static shock from your car while getting out of it is that tires are no longer electrically conductive, due to their being reformulated (to reduce rolling resistance and get better gas mileage IIRC).

Regarding your main question, I can’t imagine that you would use the term “chirp” to describe tires squealing, so I don’t think I know what you’re talking about. “Chirp” to me describes something that is short and quickly repeats itself, like the sound a tricycle with a rusty axle might make.

So what do you mean by “chirp”?

11

Curtc, I do not believe tires were ever conductive and I have been getting those shocks all my life.

Anthros, I do believe a wider tire will squeal before a narrower one does. Many years ago I changed cars and noticed the new car would squeal when I cornered much sooner than the old car and I did not know why. Later I read in a specialized source the explanation that wider tires tend to squeal sooner and I remembered the new car had wider tires so it made sense. The explanation is that the outside of the tire has to go more distance than the inside (I am talking when cornering, of course). My new, small car with wide tires would squeal like crazy in tight turns even at very slow speed and I cannot think of any other reason.

12

<<Anthros, I do believe a wider tire will squeal before a narrower one does. Many years ago I changed cars>>

<snip>

This is important. When you change cars, you change a LOT of variables, not the least of which are the tires. Suspension geometry (caster, camber, etc) is also important.
<Later I read in a specialized source the explanation that wider tires tend to squeal sooner>

I do not dispute this…I am perfectly willing to believe that wider tires tend to squeal sooner…e.g. the street dragger example in my earlier post.

<and I remembered the new car had wider tires so it made sense.>

Hmm…correlation is not causation…

Corvettes have, IIRC, 335-mm wide tires in back. That works out to more than a foot. They tend not to squeal too much when going around corners. What kind of car was your new, smaller one? The old one? What kind of tires did they have?

Anthros

13

Hey, also, if your tires squeal alot when you’re turning, and inflating it doesn’t help much, and you don’t have bias-ply tires (for the love of God, why would you?), then you should get your alignment corrected NOW, before you need four new tires, a steering rack, new shocks and struts, et al.

–Tim

14

The wider the tire, the more difficult to lose traction(break out).

Dragsters use monster tires because the wider they are, the more surface area, hence the more difficult it is to spin.

Think about it, will a 4-inch wide tire spin before a 15 inch wide tire? No way, there’s lots of property on the asphalt, and lots more area “grabbing” the pavement.

I think a hard rubber tire would spin easily, but a wider performance(they’re usually much softer and pliable) tire would definitely not cause it to break tractiuon easier.

-Sam

15

As another car guy, race fan and all around gear head, I think I can make an educated WAG.

In a sense, you are right in that changes have been made in the way most tires are constructed that make them more prone to “chirp”. The driving factor here is the desire to improve gas mileage. One way to improve fuel economy is to reduce rolling resistance (fancy name for friction). A consequence of decreased rolling resistance is less “grip” between the tire and the road, leading to a greater probability that the tire will “chirp”. In fact, Autoweek likes to refer to these types of tires as “eco-squealers”.

There are several ways to lower rolling resistance. You can make the tire narrower, you can use a harder compound or you can increase the air pressure. Making the tire narrower decreases the area of the contact patch (the actual area where the rubber meets the road), which in turn decreases rolling resistance. Using a harder rubber compound or increasing the air pressure does the same thing, with the added benefit of stiffening the tire itself. This way, the tire will flex less as it rotates. Flexing the tire generates heat, which translates into lost energy.

[aside]
Contrary to statements by others, lowering the air pressure will increase the amount of grip available by increasing the area of the contact patch. A common trick in drag racing is to run as little air pressure as possible on the drive wheels to increase traction. However, lowering the air pressure can cause problems in cornering because it can allow the sidewall of the tire to flex excessively.
[/aside]

gEEk

16
      • Uh, -
      • No, no, no, no, no, no, no, no, no, no, no, no, no and no.
      • The reason that the tires chirp when going slowly around a turn with the steering wheel fully turned either to the left or right (you hear this happening in parking lots all the time now) is that because of the toe-in of the front wheels and the geometry of cheap steering linkages & suspensions, one wheel ends up turned at a greater angle than the other. The outside tire is turned “more” than the inside tire, so the chirping is because of friction but it’s because the tires are pointed in different directions and one is slipping sideways, not that either tire isn’t free to rotate at the speed it should.
  • Old cars didn’t used to do this, for at least one reason: they used giant balloon-style low pressure tires. High-profile tires give a cushy ride, but they squirm very badly around turns (you can get the same effect at about 20 PSI); that’s why modern cars tend to use lower aspect ratio tires. Balloon tires didn’t make the noise because there was enough play in their “squirm” that you never heard it, but low aspect ratio tires are firmer [sideways] and so end up making the noise.
  • Corvettes may not do it though, no matter what kind of tires they have: normally, toe-in is used to try to make up for a simple (read CHEAP) steering geometry/suspension that doesn’t track well over bumps. Expensive cars may be less likely to do it, and cheaper cars more so. - MC
17

**

I’ve never heard tires chirp in parking lots (unless some guido who thought he was cool was showing off his new 5.0 mustang). I’ve heard a lot of squealing from the power steering pump when the tires are turned to full lock, but this is because the flow of fluid is blocked and the pump runs dry. Besides, I think the OP was talking about normal driving conditions.

In addition, the outside tire actually turns at a slightly smaller angle than the inside tire, because the radius of the turning circle is greater for that tire than the inside tire.

Also, in cornering, the tires always slip sideways. This is how they turn the car. The relevant turn is, aptly enough, slip angle and refers to the difference between the direction the tire is pointing and the direction it is actually moving. Check out this site for a definition of slip angle. Excessive slip is what leads to chirping. Excessive slip is caused by excessive speed entering a corner. The tire cannot generate enough force to turn the car and so continues to slide sideways (understeer). At low speeds, it would be difficult to generate the required loads to get the tires to chirp this way.

gEEk

18

Sam wrote to Sailor:

<<The wider the tire, the more difficult to lose traction(break out). Dragsters use monster tires because the wider they are, the more surface area, hence the more difficult it is to spin.>>

Sam, I think you may be missing Sailor’s point here. You’re right; a wide tire generally has more traction than a narrower one. However, we were talking the tendency of the inside edge of tires to slip relative to the inside edge when following extremely small-radius curves. An extreme case would be this:

Take the 15-inch-wide drag slick you were talking about. Spin it on a vertical axis dropped through the inside sidewall. The outside of the tire must scrub the pavement since it is trying to follow a 15"-radius curve while the inside is trying to follow a 1"-radius curve. Sailor was discussing a much less-intense version of the same effect. While I do not doubt that this effect exists, I also do not believe that it plays a significant role in tire squeal.

<<Think about it, will a 4-inch wide tire spin before a 15 inch wide tire?>>

I don’t think anyone was claiming that. If we were, you would be right to protest.

Anthros

19

Okay, I just want to clarify that I’m not talking about the power steering squeal, nor am I talking about rally car driving, peeling rubber around a corner.

I’m talking about a gentle little “chirp” from what sounds like a single tire when I turn a corner at normal speeds. Sometimes it even does it when cruising slowly through a parking lot. Yes, I know it’s caused by friction, but my question is, is it because a tire is under-inflated (which is what I was told way back in the 1970s as a newly fledged car owner), or is it because Detroit has changed the way they make tires, so they’re just more likely to chirp at normal turning speeds?

20
      • That’s just it; the noise the tires will make is very much like the noise from a power steering-pump cranked against its travel stop. It’s only if you’re driving the car, that you know that isn’t so. You don’t have to turn the steering wheel all the way until it stops for this noise to occur, just most of the way. - I do note that I only hear it happen on asphalt parking lots, however.
  • And this isn’t paticularly addressed to gEEk, but lowering the pressure of tires increases traction; increasing the air pressure decreases traction. - MC