Common Sense Counterfactuals - Tire Width

[DTLarca]

Did you know that the width of a tire has no effect on a car's ability to stick to the road on turns or on accelerating or breaking?

[Quality]

Stop talking rubbish

There are many factors to what you mentioned

you may know your stuff (or somebody else s)

but you are gettin boring

[monkey spanners]

I had some Counterfactual Vanco's on my van, my favourite tyre pattern but Continental replaced them with the Vanco 2 which has a horrid tread pattern so i am trying some Bridgestone Duravis R410's on there at the moment.

Nice,

http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=Vanco-8

Nasty,

http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=Vanco+2



New,

http://www.firststop.no/first_stop_produkter/bridgestone/bilder/dekk/varebil/r410_duravis.jpg

[nevgee]

Did you know that the width of a tire has no effect on a car's ability to stick to the road on turns or on accelerating or breaking?


Of course! ... it's perfectly common sense anyway, why would anyone think differently except the dippy woman down the street?

But .... what was the point of asking? Why don't you just get to your point without the charade?

[DTLarca]

Of course! ... it's perfectly common sense anyway, why would anyone think differently except the dippy woman down the street?

But .... what was the point of asking? Why don't you just get to your point without the charade?

But why is it so? :)

[DTLarca]

I had some Counterfactual Vanco's on my van, my favourite tyre pattern but Continental replaced them with the Vanco 2 which has a horrid tread pattern so i am trying some Bridgestone Duravis R410's on there at the moment.

Nice,

http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=Vanco-8

Nasty,

http://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=Vanco+2



New,

http://www.firststop.no/first_stop_produkter/bridgestone/bilder/dekk/varebil/r410_duravis.jpg

You're pointing to two different tires thefore two different profiles and rubber etc. I'm requesting the principle of Ceterus Parabus :)

[nevgee]

I had some Counterfactual Vanco's on my van, my favourite tyre pattern but Continental replaced them with the Vanco 2 which has a horrid tread pattern so i am trying some Bridgestone Duravis R410's on there at the moment.

Nice,



I prefer Pirrelli Scorpion ST ..... really good in the crap stuff ..... regardless of the width. ;)

[Quality]

You're pointing to two different tires thefore two different profiles and rubber etc. I'm requesting the principle of Ceterus Parabus :)
Why did you not say this ????

Try slicks with your theory

[monkey spanners]

You're pointing to two different tires thefore two different profiles and rubber etc. I'm requesting the principle of Ceterus Parabus :)

I'm making a play on words with counterfactuals/continental but i guess humour is a personal thing :)

[DTLarca]

Why did you not say this ????

Try slicks with your theory

My question makes it quite clear that I am talking only about width - not radius, not profile, not rubber, not road, not temperature, not pressure etc etc etc - just width.

[nevgee]

But why is it so? :)


Hook line and sinker ........

We all know the amount of frictional is proportional to the area of contact, also proportional to the pressure by which the two surfaces are "held" together.

increasing the surface area decreases the pressure therefore a change in surface area will counter the effect, the only thing left is the weight of the vehicle acting downwards.

larger tyres are used to allow softer compounds to be utilised.

It was always a point with the older Quattros they were useless in the wet and ice .... AWD or not, they just had too wide a tyre config.

Thin tyres are crap on corners as the compound and or the wall fails ... so a wider tyre lower profile overcomes this problem.

SO the lack of stick (friction) is not tyre width but tyre compound.

[nevgee]

I'm requesting the principle of Ceterus Parabus :)


If this is the case then why are we having this debate ....? If nothing changes then everything, surely, will remain the same, et ceterus parabus?

[DTLarca]

Hook line and sinker ........

We all know the amount of frictional is proportional to the area of contact, also proportional to the pressure by which the two surfaces are "held" together.

increasing the surface area decreases the pressure therefore a change in surface area will counter the effect, the only thing left is the weight of the vehicle acting downwards.

larger tyres are used to allow softer compounds to be utilised.

It was always a point with the older Quattros they were useless in the wet and ice .... AWD or not, they just had too wide a tyre config.

Thin tyres are crap on corners as the compound and or the wall fails ... so a wider tyre lower profile overcomes this problem.

SO the lack of stick (friction) is not tyre width but tyre compound.

All true - doubling the width halves the area the weight is distributed across thus halves the downward force upon which the traction is directly proportional to. So increasing the width just reduces the wear on the tire per area but not the mass of tire wear. Increasing the width just has no effect on traction.

But you must admit that it is not intuitive - If you approach people in the street asking the question you will find that most will get it wrong.

[DTLarca]

If this is the case then why are we having this debate ....? If nothing changes then everything, surely, will remain the same, et ceterus parabus?

I am suggesting width be considered a variable in relation to a possible dependent variable called traction but on the implicit basis of "all other things being equal or held constant" (Ceterus parabus).

[nevgee]

Sorry I really don't know what planet you're from ..... I'm out of this.

[DTLarca]

Sorry I really don't know what planet you're from ..... I'm out of this.


The amount of eccentricity in a society has generally been proportional to the amount of genius, mental vigor, and moral courage it contained. That so few now dare to be eccentric marks the chief danger of the time ~ John Stuart Mill

Beware those who do not realise that their idea of liberty is in effect just their freedom to agree between one another without challenge - where, by their perverse notions of liberty, all alternative ideas are stifled in order that they may be free to stagnate without interruption :)

[chilliwilly]

Ceteris paribus, an interesting metaphore that might suggest that a latter may be superior to the former. What has that actually got to do with turning into a bend at high speed with nice fat tires. Or skinny ones made from the same compound that will screech like buggery, and will probably increase your chances of skidding?

Some earth moving equipment have large ballooned fat tires on them, instead of tracks. The principle is to do with increased surface area. That will be equal to or greater than that of a laid track that gives limited traction on a non viscous but dense and maybe loose surface. Despite its tread pattern or compound.

[mad fridgie]

whats the difference between a rough road and a prositute
One Knackers your tyres
The other tires your knackers

[chilliwilly]

Ha Ha very good, a jeovial way of saying I'm a sh!te speller, lol.

[mad fridgie]

Ha Ha very good, a jeovial way of saying I'm a sh!te speller, lol.
I am "an excellent shyte speller"

[chilliwilly]

eye wunt a thort it misen!

[mikeref]

I have wider than average tyres for weight distribution and pothole avoidance handling among other things. Feel safer with more meat on the ground, also find it easier to mow down toads.

[mikeref]

kinetic energy involved.http://www.bing.com/videos/search?q=cane+toad&docid=309003944345&mid=FB589406B5A6EE61CDE4FB589406B5A6EE61CDE4&FORM=VIRE8

[DTLarca]

Did you know that the width of a tire has no effect on a car's ability to stick to the road on turns or on accelerating or breaking?

So, what this means is, that, for instance, with the journal bearings of a compressor, the friction factor is purely related to the force (mass x acceleration) experienced by, say, the con rod or the shaft.

Increasing the width of the bearing does not increase the bearing resistance but it does help reduce the load-bearing duty of the oil film (hydrodynamic bearing) and the bearing metal itself by distributing that friction load.

[chilliwilly]

But yet a conveyor belt thats only a foot wide will struggle to convey materials or goods that are four feet wide. Especially on an incline, whatever the torque capabillity of the drive system.

A slotted headed screw of say 7/16-11mm head width, can't be tightened by a screwdriver blade of 3/16-4/5mm blade with damaging the screw head.

The rollers inside a printer need to have a certain amount of surface area of purchase/grip to feed the sheet of paper. So they have a series of small rollers of a certain width, if the rollers were any narrower they would require more rollers.

If a timing belt on an engine were half its width, it would more than likely break before it was due to be replaced.


If I was walking through snow with stillettos on, I would sink into the snow. :o If I wore snow shoes I wouldn't sink any where as far.

[lowcool]

run 4" tyres on a v8 super car lots of weight run em on an F1 not much weight,either of them would not make it through a corner let alone get their.

my 2 bobs worth anyway

[nevgee]

It is important to note that tyre shear forces depend on tyre load. This dependence is usually nonlinear, where for increasing tyre load, the absolute slope of the tyre force versus tyre load reduces. This is the reason why during cornering, the average lateral tyre force per axle reduces due to force redistribution from inner to outer wheel. Consequently, as we shall see later, the steering performance of the vehicle is changed which might even lead to yaw-instability (oversteer conditions).

Extracted from ....

http://www.tut.fi/plastics/tyreschool/moduulit/moduuli_10/hypertext/3/3_1.html

[r.bartlett]

Having taken advice from professional auto engineers they confirm the statement is false.



Tyre width does have an effect on adhesion and performance.

Summary: if the width is not important, why slicks? You could use rain tyres and get the same grip. So, get a grip... ha, ha.

Now, one of my legendary short posts. I disagree with Tim in one thing: it's not "horribly" non-linear, it's beautifully non-linear. What's going to be horrible is this post, because of its length, but I honestly think that any aspiring racer in the XXI century should know this. In short, the best graph I could make of the data available to me is this one:

https://sites.google.com/site/cirospictures/TyreRoadContactArea2.jpg

Why? Well, kep reading.

The weight of the car is not the only thing that limits the adherence, but the interlocking and sticking you get between tires and asphalt. If you could develop a perfect interlocking (think of a "funicular" with gears) you would, in theory, get infinite "friction factor". Same consideration applies if you could develop perfect "stickiness" between the asphalt and the tire. This is not as farfetched as you could think, there are new materials based on gecko's feet that help to develop this "microeffect" of fractal grip.

In the end, friend, F1 and dragster tires "work" mainly by adhesion. Therefore, slicks.

I give some links again:

Why Tires Grip The Road: New Theory Reduces Testing (http://unisci.com/stories/20022/0612023.htm)


..dry-weather tires in Formula One racing ... exude resins and actually even out irregularities in the asphalt, thus considerably improving the area of contact... Racing tires are literally sucked dry.

As you can imagine, the wider the tyre, the largest the amount of fluid the tyre "sweats".

So, what you try to do with a racing tyre is to "fill" the spaces among the irregularities in asphalt. There is a new theory, some years old by now, that has completely superseded Coulomb's. If you wish, read here.

Elastoplastic Contact between Randomly Rough Surfaces (http://prola.aps.org/abstract/PRL/v87/i11/e116101)

As, in my experience, NOBODY follows links around here, there you have my explanation. I do not doubt many people will point out my errors... sigh. http://www.refrigeration-engineer.com/forums/images/smilies/icon_cool.gif

Essentially, what Bo Persson (blessed be his soul!) proved is that if you see the asphalt as a fractal surface (remember fractals?) the area of contact between tyre and asphalt increases proportional to the force you put on the tyre. This image shows how small is the real contact area under regular loads:

https://sites.google.com/site/cirospictures/TyreRoadContactArea.jpg

There are several "modes" of developing friction, from an "interlocking" mode to a "sticky" mode. The interlocking works at macroscopic scales, the stickiness work at molecular scales.

This means that the tyre "grabs" the small rocks in the asphalt and also "sticks" to the smooth parts of the tarmac. In the following image, which I also repost, the "interlocking" occurs when you see the tyre at the 5 mm level (macrotexture) while the "stickiness" happens at the microtexture level.

https://sites.google.com/site/cirospictures/TyreRoadContactArea1.jpg

Therefore, the references to the "physics of smooth bodies" don't apply: the smoother the surface, the more adhesion you can develop by chemical, electrostatic or even dispersive or diffusive mechanisms (and less macroscopical interlocking or "mechanical adhesion"), which are the five mechanisms developed to explain adhesion.

There is an optimal asphalt-and-rubber texture where the sum of the five modes of adhesion reach a maximum.

Finally, slip angle is what makes the tyre grip. An infinitely narrow tyre has no slip angle... This is the image from "The Racing and High-Performance Tire", that shows how slip angle works. For the non mathematically inclined, the idea is that a tyre works by twisting. So, a wider tyre has a more "gentle" twisting, so the erosion (wear) is smaller.

http://www.insideracingtechnology.com/Resources/bhvrdrvbrkslip.gif

So, why are not infinitely wide tyres used in racing?

Well, the problem is aerodynamic, as you can imagine. So, the width of a tyre is a compromise between the aerodynamic drag you "pay" and the "stick" rewards you get from a wider tyre.

What are the rationals? Here you have a "small" history of tribology.

The first known theory of friction was written by Leonardo Da Vinci around 1450. He studied a lot of things about friction, including wear, bearing materials, plain bearings, lubrication systems, gears, screw-jacks, and rolling-element bearings. Almost two centuries before Amontons' Laws of Friction were introduced, he had discovered them.

Unfortunately his writings were lost and unread for two centuries. After Leonardo, the first guy (and almost the last...) to explain friction was Amonton, around 1650. He rediscovered Leonardo's principles of:

- friction proportional to weight and
- friction independent of the area of contact

Coulomb, around 1750, introduced the idea of:

- kinetic friction independent of speed of displacement

These three laws can be summarized in this graph, which, unfortunately is most of what the majority of people learn about friction:

Some engineering courses never go beyond this graph. Sad.
https://sites.google.com/site/cirospictures/AumontonCoulombLaws.jpg

Then after another century, Reynolds (and a russian guy whose name I cannot remember) came up with an equation (unchanged since 1880 or so) of:

- friction in fluids proportional to sliding velocity and bulk viscosity and inversely proportional to thickness of film

A few years later Stribeck (not sure about the name) came up with the Stribeck curve that explains that when the film is very thin, Reynolds equation fails. He stated that:

- the area enlarges because the contact surface deforms elastically and the film, with a larger area, can support the weight.


Then, after 50 years (we're getting some speed here... ), Hardy, around 1920, came up with the idea of very thin films like this:

- asperities coming in contact, breaking and then reacting chemically with the lubricant, thus creating a tenacious layer of lubricant and small chips of material that supports the weight and prevents further wear (I swear I'm not making this up... ).

Hardy findings about films inspired some people to try to understand what happens in dry friction. Finally, a few years later, a guy named (I think) Bowden came up with the concept of friction by adhesion. Another guy called Desangulier in Coulomb's time had the same idea but nobody heard him because of Aumonton 2nd law (friction independent of area), so people devoted to purely geometric explanations (interlocking of asperities). Bowden discovered that Tim is right and:

- friction is created by adhesion of solids because of electric charges.

It might sound incredible, but asperities in solids deform above a critical shear strength, which depends on the adhesive forces of the two surfaces in contact. That adhesive force, the one that "crushes" the asperities, is created by electric charges.

Yes, I know, it sounds like science fiction, but I'm dead serious. The relationship with the load is not lineal but is, as showed in the first graph of this "summary": http://www.refrigeration-engineer.com/forums/images/smilies/icon_e_wink.gif

F = L^2/3 (that is, friction is proportional to load elevated to two thirds)

The inconsistence with Aumonton's first law (friction proportional to load) is explained because the real contact area varies under load. Why nobody noticed in five centuries beats me.

Once electronic force microscopes were developed, around 1950, Bowden (and Desangulier) were vindicated, because measurements were precise enough to validate their theory. Thus, Tim is right. That's most of what I know about friction. and you can stop reading now.

If someone is interested in visualize (that's what distinguishes engineers!) what's going on, please, come with me for a couple more paragraphs and imagine what happens if you become really tiny: your weight decreases as the cube of your height does (a person half as tall, half as wide and half as deep, weighs eight times less!), right? However, if you're half as tall, your surface is only one quarter of the original one. For example, let me tell the story about Gauss famous observation on the size of things.

Gauss teacher told the class (in primary school, according to legend) that the Universe could grow slowly to one million times its actual size and nobody would notice. Gauss answered that it was not true, because all the picture frames would fall from the walls. Their weight would increase to the cube, but the area of the strings holding the pictures would increase to the square and they would not be resistant enough to hold the pictures to the walls. Incidentally, that's why ants and spiders have such thin legs and elephants have sturdy ones, but I digress.

So, if you're a really small asperity, you have a very large surface compared with your weight. If your ten thousand times (2^13) smaller than a person (around 0.2 mm), your weight/surface relationship is 10.000 times larger (I think). Persons are taller than wider: this means that electric charges migrate to the pointy parts (by electromagnetic laws: that's why lightning rods are pointy). Like this:

Small clay particle with positive electric charges in the pointy parts
https://sites.google.com/site/cirospictures/SmallClayParticle.jpg

Thus, any point in a microscopic asperity of the tyre (charged positively) adheres to the sides of the microscopic asperities of the track (charged negatively). Its weight is ridiculously small compared with the surface, thus the electric forces are immense compared with gravitational forces at these scales. Tyres adhere to asphalt by electricity. QED.

Finally, in the last ten years friction has been explained by quantum theory. In the improbable case that someone is interested in "The Master Equation" of friction, there you go: http://www.sbfisica.org.br/bjp/files/v27_214.pdf

Friction Quantum Theory Master Equation. If someone can explain it in simple terms, be my guest!
https://sites.google.com/site/cirospictures/FrictionQuantumTheoryMasterEquation.jpg

[lawrence1]

bloody riveting stuff

[Gingerair]

I wish someone would let the air out of you know who's tyres...

[nevgee]

So amazing and no animals were hurt in the process. ;)

We all should aspire to being an asperity .... awsome powers. :D