Talk:Tire

Second Law of Friction

The following is false: "Dry traction increases in proportion to the tread contact area". It is absolutely mind boggling how many people believe this in spite of their high school physics classes which demonstrate its fallacy. Since the first introduction of the second law of friction by Guillaume Amontons in 1699, skeptics have attempted to debunk it without success. High performance tires are wider not for better traction. Better traction comes from stickier rubber. The tires are wider to get acceptable wear from the stickier, softer rubber. 192.249.47.196 (talk) 20:49, 27 August 2010 (UTC)

That's wrong, but so is the first statement. Reality isn't an high school experiment, and the "law of friction" isn't actually a general law, it is an approximative model. In reality the relationship of normal and lateral forces (the "friction coefficient") isn't linear (and therefore not really a coefficient). It is _approximately_ linear for the measurement envelope for the high school experiments and many applications, but then you don't get anywhere near for example contact area saturation where the model breaks down completely. Empirically what happens is that the "friction coefficient" decreases non-linearly with increasing contact area pressure, so for a given normal force you get a larger "coefficient" if you increase the contact area since the contact area pressure becomes lower. Which explains for example why wider tyres give more grip than narrower and lighter cars corner faster than heavier, all else equal. —Preceding unsigned comment added by 213.114.206.205 (talk) 22:51, 7 January 2011 (UTC)

Reality may not be a high school experiment, but if wider tires have more traction, then reality is also not what universities teach. If needed, I could list many references to university physics courses on friction in which variations from the model are discussed, better never a mention that increasing area increases the coefficient of friction. I have yet to see a reputable source make this claim. It comes down to this: show us the emperical data.192.249.47.196 (talk) 14:19, 14 January 2011 (UTC)

First, I have not yet found a suitable reference for the statement on the page - and I doubt that it is technically accurate. I want to do a bit more searching before I change the article.

But, tires do NOT behave according to classical friction theories. Amonton's and Coulomb's Laws apply to rigid and inelestic objects. A tire is not rigid, and rubber is elastic.

Why do tires not behave according to the classical laws of physics? Short version: Road surfaces have macro-texture and the tread rubber penetrates that surface. When tires slip relative to the road surface, bits of rubber are torn off - which results in higher levels of grip than normally obtained by friction alone.

In the meantime, I will leave the article as it is, but among the things I am looking through is "The Pneumatic Tire" as published by NHTSA. It has a whole section on friction and traction. I would suggest that anyone who wants to claim that tires are subject to the laws of friction should read the portions of this document pertaining to traction. Be forewarned: The document is 700 pages and it is just an overview of tires. — Preceding unsigned comment added by CapriRacer (talk • contribs) 14:28, 16 January 2011 (UTC)

I am very familiar with the NHTSA publication, and have used it as a teaching aid for this subject for years. Chapter 2 details the the physics of the coefficient of friction between elastic and hard surfaces... with no mention of the coefficient of friction varying as a function of contact area. Chapter 11 describes the factors that affect wet and dry traction, and includes details of testing performed to evaluate these effects, including the emperical data from the tests. These factors include temperature, speed, surface roughness, rubber polymer, and more. Best fit mathematical models are also provided. Once again, no mention of traction variation as a function of contact area. I have deleted the erroneous statement that "Dry traction increases in proportion to the tread contact area" from the article.192.249.47.196 (talk) 20:57, 21 January 2011 (UTC)

I'm no physicist or tire expert, but wouldn't temperature increase with contact area, since the tire would be absorbing more heat from the road across a wider surface area, or perhaps since there are more metal bands in a wider tire? If I rub my hand across a sheet of sandpaper, I notice much more friction than I do with one finger. Of course, that is a bit of a simplification and could be psychosomatic. However, my skin is also elastic and also has many ridges. — Preceding unsigned comment added by 173.55.117.56 (talk) 10:18, 14 March 2012 (UTC)

That's an interesting observation. It is true that a grippier tire will run hotter, but I think that is more to do with the work it generates as it creates the grip. The above two egos are having a fine time failing to persuade each other, it is a lot more accurate to say that the grip of a rubber tire on a typical road surface is so complex that any simple rule is an approximation at best. Fairly reliably, in the dry, up to a point beyond useful loads, increasing the vertical load on a given tire will increase its peak cornering or longitudinal force. Somewhat less reliably, increasing the size of the contact patch with the same construction etc will increase the maximum grip force for a given vertical load. Greglocock (talk) 10:54, 14 March 2012 (UTC)

Tires on wheeled armored military vehicles

Tires on wheeled armored military vehicles are vulnerable to small arms fire. Are these tires normal pneumatic ones? -- DavidJErskine (talk) 11:35, 8 February 2011 (UTC)

Yes, they are normal penumatic tires. Some (probably many/most by now) military vehicles like the hummer use runflat tires, and also have a CITS system. CITS is normally used to vary tire pressure for conditions (traction vs. fuel economy and wear), but in emergencies it can also be used to keep a punctured tire inflated for a short time.

Inaccurate skid mark image removed

Wrong.

I removed the "skid mark" image to the right from the article. Tread marks don't show up on actual skid marks because the tires are not rotating when a car skids. If you do not believe me, please take a look at images.google.com searching for "skid mark tire" for lots of evidence. This shows the danger of having editors create their own illustrations for articles. Comet Tuttle (talk) 18:08, 16 September 2011 (UTC)

Good call on removing the image. The dangers of having editors create their own illustrations, however, are probably no worse than the dangers of having editors create their own text. In both cases, we need to check the results against the sources. -AndrewDressel (talk) 18:30, 16 September 2011 (UTC)

Weather cracking

I have done a small amount of homework regarding the weather cracking of rubber trailer tires. I am not confident enough to post any information so I am writing to ask someone experienced with the subject of weather cracking of tires to add information about this subject. What I learned in a few minutes of "surfing" is that weather cracking is caused by U.V. (sunlight) or ozone and can be managed by covering tires or using a tire conditioner (of which there are varying ingredients which may be good or bad). Trailer tires are highly subject to cracking because when tires sit unused fresh oils (wax?) does not move to the surface to help protect the rubber. How can a consumer know if a tire is going to last two years or ten years? — Preceding unsigned comment added by Jim Derby (talk • contribs) 13:10, 18 October 2011 (UTC)

That's more of a how-to or consumer guide topic, which isn't appropriate for an encyclopedia. See WP:NOTHOWTO. It's fine to state the fact, with good sources that UV or ozone can cause deterioration, and you could state the fact, if you have it, of what tire manufacturers do to make their tires last longer. But advice on shopping for or maintaining your tires doesn't go on Wikipedia. --Dennis Bratland (talk) 18:10, 18 October 2011 (UTC)

"Summer" Tire

Under "Vehicle Applications", both "Mud and Snow" and "All Season" make reference to a summer tire, yet there is no summer tire application described in the article. Presumably, these refer to the high performance application. Should the language be harmonized? — Preceding unsigned comment added by 209.156.21.119 (talk) 19:48, 22 October 2011 (UTC)