Tyre width- putting power to the ground vs. friction

[91eclipsegsx16boy]

I have a question.

Friction is no way related to surface area - just a misconception. kinda like the bottom spokes are what hold a wheel together (whereas its the top ones because they work under tension - a coil is useless uundercompression). so...

anyway, if friction is not relateed to surface area, and friction is "grip" by nature of resistance, why do you see higher torque cars runnin' fatter tyres (look im english :))?

All i could think was that it has somethign to do with the distribution of power - is torque affecteed by area/contact patch? Reasoning that more area, less "dense" - if you will - power. "Put the power to the ground" by means of distributing it so that you have however many ft/lbs divided up instead of more centralized, increasing your traction.

I askedd my physics teacher and she said ask someone and then i came to her with my theory and she just kinda blinked at me... so much for 20 year old high school teachers...

'lil help please?
thanks!
-aaron

[Edited by 91eclipsegsx16boy on 07-21-2001 at 09:29 PM]

[4G63Rydah]

Friction is in EVERY way related to surface area. The more rubber to contact the ground the more friction...

[Edited by 4G63Rydah on 07-20-2001 at 01:36 PM]

[Suryc]

please explain how friction is not related to surface area?

You also have to realize that when the tire begins turning the surface area is no longer flat because of the centrifigual force. The tire domes up in the middle. So a wider tire will give you a wider dome to make contact with the pavement. If you ever watch funny cars race their tires are really freaking wide till they step on the gas and you watch their tire get very tall.

[Edited by Suryc on 07-20-2001 at 11:21 AM]

[BatmanGSX]

Would you like some tea and crumpets with your "tyre"?

[91eclipsegsx16boy]

ok.. well sincee i dontknow how to do /sub and crap i cant really type the equations really well

can you find me and equation where surface area affect coefficient of friction or frcition?

thanks
-aaron

p.s.please pass the crumpets

[galntvr4]

In physics, there is a basic law which will enable you to compute the maximum theoretical friction force acting between two surface (with no slip). This equation reads:

Static Friction force = static coefficient of friction *
Normal Force

The static coefficient of friction depends upon the interface conditions between both mating surfaces and has a value anywhere from 0 - 1 (for relatively smooth surfaces). Different tire compounds can give you higher/lower values of this coefficient.

The normal force is typically the force exerted by the ground on the tire. This is the force which actually produces a contact path. Thus, theoretically, a tires width has nothing to do with traction. One might argue that a wider tire has a greater contact patch. If you look at the contact patch on a per unit area basis (just at every square inch of the tire), the wider tire will effectively have less normal force acting on each square inch. Just think about it.

Why do sports cars have fat tires then? Good question. I believe the answer to this question is to enhance a car's cornering, and road carving abilities. A "smaller" tire has a much smaller contact patch than a "large" tire. When a vehicle corners, the normal force acting on the inside tire is much greater than if it were traveling straight. This causes the vehicle to dip, increasing the size of the tire patch and tire pressure in order to support the vehicle. This happens to a lesser extent on the larger tire because the contact patch is so much wider. Remember:

Force = Pressure * Area pressure is acting on.


Hope this helps!!!!!

[4G63Rydah]

Are you guys serious??? PLEASE don't tell me that you guys actually believe that friction has nothing to do with tire size....Where are the moderators??? Shouldn't someone be deleting this thread?????

[BatmanGSX]

It's true, when the tire is spinning and there is no slippage it doesn't matter how wide the tire is, it could be 100feet wide, there is no friction. Duh. That is SIMPLE physics. IN THEORY...

But conditons would have to be perfect. The road would have to be perfectly level with no imperfections and the tire couldn't be made of rubber because it would have to be perfectly round and not EVER flex or give. The tires couldn't be under power, you would have to be pushed or pulled. There could be no gravity or air. Get the picture?

[Edited by BatmanGSX on 07-21-2001 at 12:48 AM]

[91eclipsegsx16boy]

i know about the contact patch and handling thing -

i said cars with high torque i meant like dragsters have huge ass slicks and little tires up front, cause they only go in a straigt line

keep the responses commin'
-aaron

[redgsturbo]

rolling friction (ie from tire... oops, tyre deflection) doesnt really play a major role until high speed (200+)

[99gst]

Aaron is right. Friction is independent of surface area. Take a piece of notebook paper and slide across a table. Now cut it in half and slide half across the table. The whole sheet did not have any more friction than the half sheet even though you cut the "surface area" by half. However, lets not forget that wider "tyres" are also heavier and friction is very dependent on weight. Since we are talking physics here let me drop another equation on you.

Fr=u*W

Fr is the force required to overcome friction

u is the coefficient of friction between the 2 surfaces. for example rubbing 2 pieces of sandpaper together would require more force than rubbing 2 pieces of notebook paper together. Therefore the 2 pieces of sandpaper have a greater coefficient of friction than the 2 pieces of notebook paper.

W is weight.

You can see by the above equation that any increase in weight would result in a proportionate increase in the required force to overcome the friction. Double the weight, then double the amount of force will be needed. Wider tires are heavier and will result in greater friction even though the surface area had nothing to do with it.

[redgsturbo]

that is not right because if i got much wider tires, i would still spin less than if I added the equivalent weight to the car

God please don't make me have to break out my big ass physics books

[4G63Rydah]

You morons (and yes i said morons) have forced me to bust out my physics book. And I definately didn't wanna look at anything school related on my summer vacation.... Here's a quote from Fundamentals of Physics: Sixth Edition by Halliday/Resnick/Walker...page 100. (look it up for yourself if you don't believe me).....


A frictional force is, in essence, the vector SUM of many forces acting between surface atoms of one body and those of another body. If two highly polished and carefully cleaned metal surfaces are brought together in a very good vacuum (to keep them clean), they cannot be made to slide over each other. Because the surfaces are so smooth, many atoms of one surface contact many atoms of the other surface, and the surfaces cold-weld together instantly, forming a single piece of metal. If a machinist's specially polished gage blocks are brought together in air, there is less atom-to-atom contact but the blocks stick firmly to each other and can be separated only by means of a wrenching motion. Usually, however, this much atom-to-atom contact is NOT possible. Even a highly polished metal surface is far from being flat on the atomic scale. Moreover, the surfaces of everyday objects have layers of oxides and other contaminants that reduce cold-welding.

When two ordinary surfaces are placed together, only the high points touch each other. (It is like having the Alps of Switzerland turned over and placed down on the Alps of Austria.) The actual microscopic area of contact is much less than the aparent macroscopic contact area, perhaps by a factor of 10,000. Nonetheless, many contact points do cold-weld together. There welds produce static friction when an applied force attempts to slide the surfaces relative to each other.]

Notice the very first line...it is "the vector SUM" of the forces acting between the atoms that are in contact. So it takes a pea size brain to realize that if for a X-size area you get a Y-amount of atoms touching, that if you increase the area to 3X you now have 3Y amount of atoms touching...resulting in MORE FRICTION. Hence the VECTOR SUM!!!!!.... Now will ANY moderator please DELETE this f*cking thread. These morons have forced me to pull out my physics book (and to type all this $hit) and they need to be banished to HELL for that. May you all burn in hell....

[Edited by 4G63Rydah on 07-21-2001 at 03:36 AM]

[BatmanGSX]

The guy who said "friction isn't relative to surface area" is wrong. But I know what he was getting at: We aren't sliding our tires over the road, we are rolling them (this means nothing in the practical world but let me get into that). A perfect circle can only contact a perfect plane by one point at a time. A point has no surface area. This is why the first dude assumes that the width of the circle does not matter, in that case it doesn't because a line made up of points still has no surface area. But tires are not perfect circles and the road is not a perfect plane. So in all practicality surface area still matters to us, as people with tires. Does this clear the matter up? The dude would be right if it was possible to have a perfect circle and a perfect plane.

[91eclipsegsx16boy]

i stil dont believe friction and surface area are related..

from my physics book:

Although friction forcesare complicated, a simplified model an be used to find solutions. the model assumes that friction depends on surfaces in contact, but not on the area of the surfacs nor the speed of their relative motion. in the model, the magnaitude of friction force is proportiona to the mgnitude of the foce pushing one suace against the other. that force, perpendicular to the surface, is the normal force, F*N.

F*f, kinetic=(cof fric*k)(F*N)

do you unnderstand what it means be sum of vector forces rydah?....................

-aaron

[galntvr4]

*** Notice the very first line...it is "the vector SUM" of the forces acting between the atoms that are in contact. So it takes a pea size brain to realize that if for a X-size area you get a Y-amount of atoms touching, that if you increase the area to 3X you now have 3Y amount of atoms touching...resulting in MORE FRICTION. Hence the VECTOR SUM!!!!!.... ***


You fail to realize that when a force is distributed over a larger area (e.g. a wider tire) the forces between the atoms on a per unit area basis (e.g. every square millimeter, square micrometer, etc...) becomes less. If you were however, to integrate the resulting stress/pressure distribution over the area of the contact patch, you would wind up with one number --- the weight acting down on the tire -- indepedent of the size of the tire. This is 100% true.

Just as an aside -- my group at the college I work at was building a robot for competition purposes -- the robot weighed 120lbs and one of the things it had to do was go over a ramp set at a 25deg incline. Needless to say the rear wheels kept slipping. Some of the students decied to add another two tires to the rear (bringing the total # of rear tires to 4). Did it help in the traction dept? Nope, not one bit. You see, instead of 80lbs of rear weight acting on two tires (40lbs/tire for perfect weight distribution), there was now 80lbs acting over 4 tires (approx. 20lbs/tire). What did help traction? The surfaces of the tire were roughien up and we redistributed weight/added ballasts to the rear of the robot.

[redgsturbo]

okay.. real world analysis.. I had stock 205s just like everyone else... i am now running 235's.. I have much more traction. BY YOUR RATIONEL AN AWD CAR WHICH HAS EXACTLY TWICE THE *POWERED* SUFRACE AREA AS MY FWD HAS NO MORE FRICTIONAL ADVANTAGE THAN MY CAR BECAUSE SURFACE AREA DOESN'T MATTER RIGHT???? WHO THINKS THERE EQUALLY MODDED AWD CAN'T OUTRUN MY FWD???????


Just because someone will try to despute it, an awd car running 205s has the same amount of fricion as a fwd car with 410's on the front (if it was possible) ie 2 410mm wide powered tires = 4 205mm wide powered tires ASSUMING A PERFECT 50/50 Weight distibution on the awd.

AND a 100% weight on the fwd's front axle (it ain't gonna happened but bare with me

[Edited by redgsturbo on 07-21-2001 at 04:10 PM]

[Suryc]

From reading everyones argument on this subject this is what I learned so far.

Given 2 surfaces, the ground and a tire, the coeffient of friction(CF) between the 2 will not change regardless of the surface areas of the 2 surfaces. The CF is a number generated by how well the 2 surfaces stick together at a molecular level. This is were I beleive 91eclipsegsx16boy came up with his first question. But CF is only part of the equation.
Now you also need to bring in normal force(NF). NF as stated earlier as being the force of the 2 surfaces exerted on each other. The tire pushing against the ground by the force of gravity.

Now multiple CF and NF and you get a number for Friction Force. Since the CF does not change give the 2 materials(cement and rubber) then the only way to get more friction force is to increase the Normal Force. One way to increase NF is by adding more rubber(weight). You could stack the rubber higher but we are limited by our wheel wells so the only option is to go outward, there by making the tire wider.

This is just my interruption of this thread.

[91eclipsegsx16boy]

so i talked to an engineer at GM right...

and he agreed with what i said.

it's point per load something i forgot the exact wording ill get back to you on it...

but anyway, the reason you want a taller contact patch is so that all the force is not on one point but spread. the greater the area, the more spread the power will be which will increase your traction - so assuming the the amount (coefficient) of friction of the tyre compound, simply increasing width will not only add weight to the normal forcee, but also increase the area which you are putting load on so that the load is distributed.

so why are the tyres so wide if you want a taller patch? so that they maintain there shape integrity under gross force. and the reason for smaller tyres up front is not 'cause they provide less friction, but they are more areodynamic and also have less rolling resistance/loss.

-aaron

[dsmdojo]

I never took a physics class, but I can seach the internet & find some answers. here's a good explaination:
http://www.physlink.com/ae200.cfm
In perfect world, wider tires wouldn't help, as friction does not depend upon surface area, but this isn't a perfect world, & there are other factors at work, & the wider tires do have traction advanages.(unless there is some definition of traction in the physics books I am no aware of.)

this site offers a quick explation of what happens when you stop & traction is dynamic & I assume it applies to when you take off quick & spin the tires:
http://www.cosm.sc.edu/~phys153/tirefriction.html

these results were found on google w/many more good results:
http://www.google.com/search?q=wider+traction+friction&hl=en&safe=off&start=10&sa=N

(ok, so what if I'm an internet racer? I admit it.)

[99gst]

Don't you love it when someone calls you a "moron" and it turns out they are the MORON. So, how does it feel MORON? I normally would not call someone out like this but you called several of us out in your post so its time for you to EAT CROW. You know who you are.

[FastGSXauto]

believe it or not, 91 eclipse boy is right. Traction should not theoretically depend on surface area. Think about the physics problems we always solve with weights sliding down ramps. They dont' give you surface areas because it doesn't matter. You assume the center of mass, and an infinitely small surface area and the force at the point is the entire objects weight. Surface area doesn't matter because if you increase or decrease it, the normal force just increase or decreases at the same rate the vector sums increase.

But in the real world, the reason wider tires is better is because the coefficient of friction is not constant at every point on the road.

The size of the contact area is very important in car tires because the traction is dynamic rather than static; that is, it changes as the tire rolls along. The maximum coefficient of friction can occur anywhere in the contact area, so that the greater the area, the greater the likelihood of maximum traction. Thus, under identical load and on the same dry surface, the wider tire has a greater contact area and develops higher traction, resulting in greater stopping ability.

[91eclipsegsx16boy]

:)

[roadpie4u]

I've taken quite a few physics/calculus courses in my day ~ try integrating irrational and non-real numbers. It's fun! Also I did a project where I proved 2=3. Mathamatically it's possible. It took 5 pages, but possible. Also I've seen a theorum that proves that ALL triangles are right triangles, and it works. Anyway!

You all must remember different things.
1)Why do we roll tires? Because the friction is less then if we slid.
2)so why if we lock our brakes on ice do we slide farther?

On ice, the friction creates beads of water between the tire and ice and acts all ball bearings. Alright try this. Make a toy car out of wood, and lock the rear axle. Let it go, face down, down a wooden plank. The rear ones, on dry wood, end up sliding around and going ahead of the rolling. It is merely the tendancy to roll vs the tendancy to slide. And in my work we've measured ways to break apart the 2 pieces of metal and the distance between them using capacitance probes. We deal with computer chip thickness. But back to tires. Watch indy car tires. The inside center cap rotates and the outside dosent for a fraction of a second, and tire deforms and wrinkles till it can expand to it's shape. Tires deflect in turns. Tires deflect when you apply pressure to them, gas or brake. Theoretically, if you made the tires 1" wide, you'd get great force on that patch of ground and great traction. In theory. But you dont, because the normal force pushing against the tire, and gravity on the car are so high, that it actually will tear at molecules of the tire and road, and leave rubber on the pavement, or if the normal/gravity are too low, you'll spin, but not leave marks, because there isnt enough force holding the tire down. We use wider tires mainly for cornering, because wider tires on a curve provide the force to keep the car moving in the direction it's being turned, vs sliding outward. The specifics do deal with that there are pits and groves in the road, just as the tread on your tire (hence why Indy tires are almost smooth, but smooth is bad, that'll slide, they have a very fine tread for more surface area)

But deflection is the key. If you could took an FWD with 4 front wheels and an AWD with the same HP and toruqe at their driven wheels, and we'll neglect the rear wheels on the FWD, they dont provide any friction for this example, and both have the same weight, and both let the clutch in at say... 6700rpms, and all their driven wheels stuck, they would go just as fast, just as far. It's complex physics by far. Just think of it this way

Grand Prix: Wider is better.

Now just accept it and stop giving me a headache, or I'll give you a 2100 page theoretical physics book!

(And normal/weight plays a huge role, hence in days of yonder why people put sandbags in the trunk!)

[99gst]

There are reasons why wider tires give you more traction. But as a pure matter of physics, friction is not related to surface area period. That is the point Aaron was trying to get across.

[redgsturbo]

Groovy, cause I was about to return my 235s for a set of 195s at half the price :D Really though.. avoiding all physics/calculus/abstract algebra, look around... Race cars have wider tires. It must provide more traction or why would a viper & F40 have rear tires as wide as my car

[shadow]

hehehe, fun stuff eh? :)

rub your hands together, and what do you get? - HEAT. Too much heat = bad for tires. You go for more surface area to spread the SAME amount of friction over more area, and at the same time, spreading the SAME amount of heat over more tire. Hence cooler running tires in the same situation. We all know what happens when our tires get too hot - we smoke 'em!

If you take heat out of the equation - then we would be running on 1" thick tires.

hope this makes some sense :)

[91eclipsegsx16boy]

redgs: thats why i was trying tfind out why wider gives more tration... read all the posts man, hehehe.

i was never say wider DOESNT give better traction.. i wanted to know WHY, because its NOT friction - as friction would make a simple answer if it were true.

thanks for all the info proffessor :) i wa waiting for someone with all the math/physics to explain it.

no more math/science for me ever...

thaks all
-aaron

[Edited by 91eclipsegsx16boy on 07-23-2001 at 12:10 AM]

[redgsturbo]

if you REALLY want my to dig out my physics books I will come up with a correct answer for you, as I have taken more college physics and mathematics courses than most people, and I have kept all of my books (damn bookstores.. sell me a book for $150 AND try and buy it back for $10, I'll be no part of your %1000 profit margin. I'll sooner burn it) sorry.. I'm a little bitter about that

[loreak]

Someone mentioned putting 410's on a fwd car it would have as much traction as an awd.
A fwd car with the same total tire width as an awd still would not have as much traction because when you accelerate the weight shifts to the back. In an awd it puts more force on the back tires aka more traction, and the front gets less. In a fwd the weight is shifted to the back and the front gets less traction, so all that extra traction on the back tires of an awd the fwd does not get. Thats why almost any rwd car can burn out in reverse even if it cant going forward. I used to have an 86hp 2.0L vanagon, i couldnt even burn out in 1st gear with just me in it, but i could burn out for 15-20 feet in reverse with just me OR one time i had 13 people in it =P

[redgsturbo]

go back and read that post again

[RyanV]

Not having taken any physics courses at all, I think the question is kinda obvious by common sense.

Funny/retarded question here.

Take a magnet and hang it under your car at the exact spot of 50/50 distribution.
Hang another magnet 1/3 the size bigger and reverse the polarity so they are pushing apart with the larger magnet on the bottom.
Would your car's weight be affected?
Would it even take away the extra (theorizing a 100pound magnet and a 150 pound one) 250 pounds you have already added?

Just curious

[firepower]

Wow guys, you have lots to say. I have read most of the posts and I think we have a few arguments going on here. First off for credibility I am a mechanical engineer.

I haven't heard slip plane brought up (didn't read every word of every post) and that is a big deal when talking about traction. Basically wider tires are used for cornering. They are also used for acceleraction, but that is secondary. The deformation that happens during these manuvers is why the wider tires are better than skinny tires at the same pressure. Now I don't care how wide or skinny your tires are if you are running both at the same pressure the contact patch will be identical in area (assuming similar sidewall stiffness).

For acceleration on dragsters (which was brought up) they run the lowest pressure they can w/o letting the wheel separate from the tire. This allows a larger contact patch when the car accelerates. The reason this happens has to do with static friction. The rear portion of the contact patch stays still and the front of the contact patch grows (ever see the wrinkles during a slow motion replay?).

For turning, you have a slip plane and you want that friction to be normal to the slip plane. The slip plane is (almost) normal (perpendicular) to the arc of the turn. The more friction that you place on the direct line the faster you can take the turn. So at 40psi (autocross pressure) you can turn faster on a 235mm tire than a 195mm tire, even though both have the same contact patch. This is assuming everything else is equal.

Have fun with your discussion guys. Hope my post wasn't just a lot of hot air for you.