Why do fat tires offer better grip on the road than thin tires? *SOLVED*

[TechnoKid]

Originally posted by: jntdesign

Originally posted by: Skoorb

Originally posted by: MrColin

Wrong, you will not get increased traction because the tire is smaller in width, why ?

In the snow you will have very poor traction on wider tires btw, compared to narrower ones. on asphalt however wider tires (all other things constant )will give better traction in that the wider tire has increased opportunity for friction in imperfect conditions, particularly with sideways movement.

OK mr. smartie pants - why do wheels seem to spin backwards on cars when you look at them?

:evil:

I thought they only "spun backwards" in movies...and I thought it was due to the capture rate of film

Yes, this depends totally on the light source reflecting off the wheels, and the device caputring the movement, be it your eyes in real time, or via the screen from a camera. This is most noticable at night when many of the street lights are shining on the wheels.

Also, to address the wider tire thingy, does it not also have to do with lateral grip?

I think that, say you have a 4" wide tire with a "20" traction. If you make the tire double its contact width, then would you not get double the traction, "40"?

And this goes to say, tires cannot grip the road if there is no friction between the tires and the road surface. If there were no friction, then the cars would slide all over the place.

 

[Howard]

Originally posted by: Roger
Skoorb;
If I ever have the chance to meet you in person, remind me to sucker punch you in the face, you made my brain hurt and question my own beliefs.

Roger's not omniscient? :Q

 

[WinkOsmosis]

I asked this question months ago and everyone said it was the bumps. No one said stupid stuff like they are doing in this thread. "Not controlled blah blah" "Tires flexing blah blah" "Sidewalls hydroplaning blah blah".

 

[Apathetic]

It's because the tires have more surface area which touches the ground. The tires actually try to grip the pavement (unless you have slicks). Remember, tires ROLL across the road. What you're saying would probably be true if you tried to push the car while it's in park.

Dave

 

[Savij]

Skoorb, the problem with the direct application of your equation is that it assumes two static surfaces sliding across each other. Rolling friction is not the same as kinetic friction.

When the tire is rolling on pavement (two fairly rough surfaces) it "grips" the road. Think of it like velcro. With a wider tire, you have a large surface area "gripping", or your velcro has more hooks attached.

 

[911paramedic]

 

[TechnoKid]

Originally posted by: Savij
Skoorb, the problem with the direct application of your equation is that it assumes two static surfaces sliding across each other. Rolling friction is not the same as kinetic friction.

When the tire is rolling on pavement (two fairly rough surfaces) it "grips" the road. Think of it like velcro. With a wider tire, you have a large surface area "gripping", or your velcro has more hooks attached.

Yea, just had a thought, get a regular pink eraser. Now, find a glass surface and run in on the "pointy" side, and then drag it on the flat of the eraser. One's easier to move than the other. I don't think that slicks offer less traction than treaded tires, for the reason that many drag cars and race cars use slicks, more of the tire is contacting the road at any given time versus a treaded tire.

This goes to say that the road cannot be too "textured" because than it would act the opposite as to why race cars use slicks; /\/\/\/\/\ <------think of it as the circulon idea.

 

[madthumbs]

I know a guy that claims to have drag raced a lot with narrow tires and he won consistantly. However, professional drag racing uses wide tires. This may be due to the wear normal tires would take under those circumstance. I believe that the weight on the tires makes a difference. The width should be according to the weight.

 

[StormRider]

I think it's the same reason that a fat woman is harder to get off of you when she's on top.

 

[FrustratedUser]

Originally posted by: Skoorb

Originally posted by: Roger
It has more surface area, your analogy does not work with rolling traction Skoorb.

But with kinetic friction the same equation applies for the brick as it does when the brick is not moving (static friction).

It has more surface area. Just deal with it.

 

[WinkOsmosis]

Originally posted by: FrustratedUser

Originally posted by: Skoorb

Originally posted by: Roger
It has more surface area, your analogy does not work with rolling traction Skoorb.

But with kinetic friction the same equation applies for the brick as it does when the brick is not moving (static friction).

It has more surface area. Just deal with it.

I think it's already been established that more surface area doesn't increase friction force but more bumps sunk into the rubber does.

 

[WinkOsmosis]

Actually I think I asked this question on HardForum, not here.

 

[FrustratedUser]

Originally posted by: Skoorb

Originally posted by: MrColin

Wrong, you will not get increased traction because the tire is smaller in width, why ?

In the snow you will have very poor traction on wider tires btw, compared to narrower ones. on asphalt however wider tires (all other things constant )will give better traction in that the wider tire has increased opportunity for friction in imperfect conditions, particularly with sideways movement.

OK mr. smartie pants - why do wheels seem to spin backwards on cars when you look at them?

:evil:

You mean on TV and under street lights. That fenomenon will never happen in daylight.

 

[LethalWolfe]

Originally posted by: Apathetic
It's because the tires have more surface area which touches the ground. The tires actually try to grip the pavement (unless you have slicks). Remember, tires ROLL across the road. What you're saying would probably be true if you tried to push the car while it's in park.

Dave

I'm confused, are you saying that people running slicks aren't trying to grip the pavement?


Lethal

 

[Brutuskend]

Larger patch.

 

[FrustratedUser]

OK, see it like this. Lets introduce a field of science, Tribology.
Note that I am not a physics major and have limited knowledge about this.

Tribology is defined as the science and technology of interacting surfaces in relative motion, and embraces the study of friction, wear and lubrication.
The word tribology is based on the Greek word tribos, and translates as "the science of rubbing".
Friction is the force of resistance encountered when one body moves relative to another body with which it is in contact. We can all agree on that.
Surfaces in contact with eachoter are not flat (Tire / road). The microscopic peaks of a surfaces topography are called asperities. Understanding this we know that the true contact area of two surfaces is the area formed by the contacting asperities.
So it means that the true contact area is a very small percentage of the apparent contact area.
The normal force is the load pushing two bodies together, as normal force is increased, taller asperities deform bringing shorter asperities into contact. We can now say that the true contact area is proportional to the normal force.

Now introduce the term Adhesion. Adhesion is defined as the force of molecular attraction exerted between two bodies (asperities) in contact.
Adhesive irreversibility is the degree to which the force of molecular attraction between two bodies becoming stuck (interfacial adhesion) is irreversable in their becoming unstuck. Basically the force that forced the two surfaces together is not enough to separate them (Does it make sense?)
Frictional force is proportional to adhesive irreversibility and true contact area.

In the original question the adhesive irreversibility was left out.
Since the true contact area of a surface is such a small a percentage of the apparent contact area, and load has such a large impact on the percentage of true contact area, it makes changes in the surfaces apparent contact area inconsequential when compared to changes in load when determining friction at anything greater than microscopic levels.

 

[ebaycj]

Originally posted by: DuallyX
Fat Tire= GOOD BEER!

so unbelieveably true.

 

[FrustratedUser]

Daumn, I actually spent some time on my latest post and the reply is about beer. LMAO!
But yeah, Fat Tire = great beer.
Just had one myself.

 

[Caanon]

From the link earlier in thread.

The main reason why this is so does not relate to contact patch, however, but to composition. Soft compound tires are required to be wider in order for the side-wall to support the weight of the car. softer tires have a larger coefficient of friction, therefore better traction. A narrow, soft tire would not be strong enough, nor would it last very long. Wear in a tire is related to contact patch. Harder compound tires wear much longer, and can be narrower. They do, however have a lower coefficient of friction, therefore less traction. Among tires of the same type and composition, here is no appreciable difference in 'traction' with different widths. Wider tires, assuming all other factors are equal, commonly have stiffer side-walls and experience less roll. This gives better cornering performance

This is what I remembered being true too...basically softer tire = more traction, but if you had a thin soft tire...it would wear out very fast.

Think of a smooth surface, with say a smooth plate of metal...if you push down and too the side on it....its not that hard too move the plate to the side, if you did the same thing with smooth, soft rubber....it's alot harder. Similar thing with hard vs soft tire.

 

[MikeMike]

well, tir balloning, is just caused by the tire wanting to travel in a straight line.

slicks are only good for certain occasions where you are not cornering, they do a burn out to get the tire sticky (yes rubber melts when hot LOL) and also, the wider tires will also allow more surface area (yes i said it) when the tires begin to ballon. imagine how little surface area there would be if a skinny tire was spun at 200mph. now as to the different compounds for f1 vs gt? it probably has to do with the cars themselves. and how they handle, and their weight distribution.

MIKE

 

[lowtech1]

Not only we have surface area to deal with but there are such thing as heat that come into play in. The coeficiency of the tire compound changes as it heat up, and once the threshold of the material is overcome...you then loses traction. Thin tire with less surface area would have more force apply to a smaller area compare to the same mass with larger area, therefore thin tire would heat up more quickly and loses it traction.

 

[Nebor]

Alright.... how about this.... It's been established that surface area, according to the fancy formula, does not itself increase friction. But tires aren't a consistent object, that is, they aren't uniform across the surface (except for slicks.)

Thus, when you increase the surface area, you also get more treads, and more bumps, which DO increase friction.

So basically, it's because of more surface area. You just have to take into account that the surface area of a tire isn't entirely flat, or uniform.

 

[DrPizza]

I got in on this thread too late....
Skoorb's question was an excellent one.

Friction has NOTHING to do with surface area. His example, sliding a brick on it's side will require an equal force as sliding it on its end (which has about half the surface area). Somewhere in this thread, someone was trying to calculate coefficients of friction, based on the tire size... Coefficients of friction:

..........................................Kinetic...Static
Rubber on concrete (dry)...0.68......0.90
Rubber on concrete (wet)..0.58
Rubber on asphalt (dry).....0.67......0.85
Rubber on asphalt (wet)....0.53
Rubber on ice.....................0.15

At this point in the discussion, the size of the tire DOES NOT MATTER AT ALL..
Now, I'll add that this is at the physics 1 level. The physics that likes to ignore all the extra factors that cause the real world to deviate from the nice equations.... such things as air resistance, etc.

Hopefully I can provide a decent explanation, slightly different than those above.

Skoorb... do you remember doing a lab on friction in high school? You would have noticed that rough sandpaper has a higher coefficient of friction than smooth sandpaper. Take two identical masses, one with rough sandpaper on the bottom, and the other with smooth sandpaper on the bottom. The rough one is harder to push. But why? The sandpaper is made out of the substance... (silicon carbide, or aluminum oxide, or garnet, or alumina-zirconia, or whatever). It's not just a matter of the coefficient of friction of the silicon carbide against the surface of the table......

In both cases, the surface area of the bottom of the block was the same, but the actual amount of surface in contact with the table changed. In the case of the rough sandpaper, the surface in contact decreased, causing an increased pressure per unit of area, increasing the degree to which the grit "dug in" to the table surface. At this point, the contact surfaces were not parallel to the direction of motion.

Now, I'm going out on a limb here, but I think in the case of the tires, there's a limit to the degree that the weight of the vehicle can "force the tire into the pavement." Increasing the pressure (decreasing the surface area with narrower tires) will not cause the rubber to be pushed farther into the irregular surface of the road. Thus, by making bigger tires, you can cause more of the coarse sandpaper analogy type of pushing into the road. I would have to guess that it is the edge of the treads that is doing the actual "digging in".

signed,
DrPizza, physics/math teacher.

p.s. I doubt that my explanation is perfect. But, at least to the degree that my students have to understand friction, in an ideal world that limits the amounts of extra interactions, I succeed in getting them that far.

 

[cavemanmoron]

More tire on the road,

less sidewall height allows less sidewall flex,
keeping even more of the wider tire in contact with the road/pavement/dirt,etc.

too wide of a tire sucks in snow tho!

My 1967 Camaro has 255/60/r15 on the rear
and 205/70r15 front, If i ever buy new tires for the front i will consider 225/65r15

My Camaro prob came with 14x7 rims,new,with e70x14 tires,

I have 15x7 front wheels,and 15x8 rear.

A wider rim allows more total tread width.

Look at a race car,if the wider tire did not help,why spend the money?

 

[StageLeft]

Thanks for all the responses

I think I can safely conclude that there are two reasons why the simple physics equation is not adequate and why, as we all know, in practical application wider tires are better:

1) Inconsistencies in the tire and road allowing them to "lock" together. The sand paper example makes it fairly easy to understand, as does frustrated user's post and the one before it about the cogs of a train and how more force would be required to break a wider cog hooked in to the road than it would be required to break a smaller one. In the case of a tire a thinner tire will result in more downforce from the car in any one area which may allow SOME additional "locking" (I mean each lock is more significant) to take place over any given area than in a fat tire, but I think this is more than offset with wider tires by the fact that their mountains and the mountains on the road lock in on more numerous ocassions and so, as with that example of the cog, there is more shearing force required to rip the locks apart.

Another way to look at it would be gears on a car. If the gear is very thin - like a very thin plate - the gear is going to wear out a lot quicker than if the teeth are the same dimensions but the gear is a thicker plate. In fact in this case friction isn't a factor at all.

2) Perhaps to some degree tire materials are made with a softer compound as you get wider. Although a person could theoretically - if this was the only factor - make a thin high grip tire, due to the weakness of the rubber it would wear out quickly.

I think a combination of the above two probably will allow me to sleep at night now. Thanks all