Friction and Automobile Tires The friction between the tires of your automobile and the road determine your maximum acceleration, and more importantly your minimum stopping distance. So the nature of that friction could actually be a matter of life and death. But like all applications of friction, it has frustrating ambiguities. Many years of research and practice have led to tread designs for automobile tires which offer good traction in a wide variety of conditions. The tread designs channel water away from the bearing surfaces on wet roads to combat the tendency to hydroplane - a condition which allows your car to "ski' on the road surface because you have a layer of water lubricant under all parts of your tire. Jones and Childers report coefficients of friction of about 0.7 for dry roads and 0.4 for wet roads. The tread design represents an "all weather" compromise. If you were an Indianapolis race driver, you would use "slick" racing tires with no tread. On dry surfaces you might get as high as 0.9 as a coefficient of friction, but driving them on wet roads would be dangerous since the wet road coefficient might be as low as 0.1 .

Sooner or later, most people have to deal with the tricky judgment of how hard to put on the brakes in an emergency stop. It is a difficult issue, and no final answers are given here. But the illustration below may point out some of the relevant physical principles involved. In the best case scenario, you should keep your wheels rolling while braking because the bottom point of the tire is instantaneously at rest with respect to the roadway (not slipping), and if there is a significant difference between static and kinetic friction, you will get more braking force that way. But you generally don't have the luxury of time to make a delicate judgment about how hard to put on the brakes. For good tires on dry surfaces, there is not much difference between rolling and sliding friction, and if you back off the braking force very much, you will get less braking than if you just locked them down. The other issue is that in an extreme emergency, the braking is instinctive and you tend to hit the brakes as hard as you can before you can even think about it.

Maybe locking the brakes is not so bad in good conditions on the dry road, and you may not be able to keep from doing so in an extreme emergency. But if you lock the wheels on a wet road, the results could be disastrous! I don't have anything like reliable estimates of the effective coefficient of friction, but I am guessing that it could easily drop to less than half of the "wheels rolling" braking because you are sliding on a surface which is lubricated by water. Delta Shower Faucet Doesn'T Get Hot EnoughIt may be that even with wheels rolling you might have in the neighborhood of 0.4 as a coefficient compared to 0.7 on the dry road, and it might drop down to the 0.1 of the slick tire. Cheap Ndt TiresThose scary scenarios are depicted below in a qualitative way - I don't have reliable numbers.Property For Sale In Azores Sao Miguel

Error - Page Not Found The page you requested cannot be found. The page you are looking for might have been removed, had its name changed, or is temporarily unavailable. Please try the following: As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction? Asked by: Mark Secunda This is a good question and one which is commonly asked by students when friction is discussed. that wider tires commonly have better traction. 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. narrow, soft tire would not be strong enough, nor would it last very long. Wear in a tire is related to contactHarder 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. Answered by: Daryl Garner, M.S., Physics teacher MacArthur High School, Lawton, OK Friction is proportional to the normal force of the asphalt acting upon the car tires. This force is simply equal to the weight which is distributed to each tire when the car is on level ground. Force can be stated asFor a wide tire, the area is large but the force per unit area is small and vice versa. force of friction is therefore the same whether the tire is wide or not. However, asphalt is not a uniformEven with steamrollers to flatten the asphalt, the surface is still somewhat irregular, especially over the with of a tire.

Drag racers can therefore increase the probability or likelihood of making contact with the road by using a wider tire. In addition a secondary benefit is that the wider tire increased the support base and makes it hard to turn the car over in a turn or in a mishap. Answered by: Stephen Scholla, B.A., Physics Teacher, Vienna, Virginia 'There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle.'Albert Einstein(1879-1955)A very nice question!Somewhere in your youth, you took a science course. And somewhere during that class, the teacher told you about friction -- that it is the resistance objects have when they rub against each other. Then, I'll bet, you were told to rub your hands and "feel the heat" of that resistance for yourself.It is also probable that your teacher told you that the force of friction depends on only two things: the weight of the object and the coefficient of friction. That is the force required to move the object divided by its weight, which varies according to the materials involved.

Further, you were told that surface area had nothing to do with the amount of friction force.On the other side of the coin, the first thing someone wanting to make his or her car handle better will do is put wider tires on it. "To get more friction."These two opposing answers can't both be true, can they? So which one is right?Both are, each in their own way; here's why:The first explanation -- that the force of friction only depends on the weight and coefficient of friction -- is correct most of the time, including almost all instances of two smooth, solid surfaces sliding past each other, like a hockey puck on ice or a coffee mug on a counter top. However, things are not so simple when it comes to tires.First, tires are not entirely solid. The tread is flexible, bending to conform to the road surface by sinking in to the open spots between grains of asphalt. This creates an interlocking effect, not unlike gear teeth meshing, or cleats on a football or soccer shoe digging into the turf.

Second, the whole tire, including the sidewall, flexes under load, both when weight is put on it and when it goes around a corner. All three of these figure into the amount of grip a tire generates and how width affects that grip. And tire flexing is the heart of the answer of why "Wide Tires Are Better."Here's an interesting fact: If you put the same load (weight) on two tires of similar construction and profile height (the distance from the road to the edge of the wheel), they will have the same size contact patch. Surprisingly, tire width doesn't affect this. Grabbing some numbers out of the air, let us say you have a six-inch wide tire (152 mm) and one that is 12 inches wide (305 mm); both of them will have the same number of square inches on the road. The six inch wide tire will have a contact patch 12 inches long, or 72 square inches. The 12 inch wide tire's contact patch will have the same area, but it will be only six inches, front to back. This, in case you've ever noticed it, is why an economy car's tires look "half flat," while a wider set of tires on a similar car look "fully inflated."

So, if the contact patches are the same size, why are wide tires "better"? It's because of what happens when you go around a corner.Try this experiment: Take a pencil eraser and rub it back and forth on a piece of paper. Notice how the leading edge (the side toward the direction you're erasing) "tucks under" and flexes away from the pencil. Then look at the trailing edge of the eraser and notice how it flexes, with the top (the part attached to the pencil) "ahead" of the bottom part, where it touches the paper.Now look even more closely. Assuming you're trying this with a new eraser, you will also notice that the "leading edge" is in contact with the paper, while the "trailing edge" has lifted clean off the surface! Believe it or not, tires do exactly the same thing when you put a side load on them as you go around a corner, though you have to look closely at photographs or video to see it happen.Next, repeat the eraser experiment with a big, wide eraser, the sort that is not attached to the pencil.

You will notice the same kind of bending, but you will also notice that the trailing edge of the eraser does not lift as readily from the paper -- basically, more of the eraser stays in contact with the paper.Here's where the difference between a narrow tread and a wide one becomes important. As you've noticed, both erasers flex, and by the same token, so do both narrow and wide tires; The difference is what happens at the tread.As a narrow tire rolls under, the inside edge of the tread lifts, leaving the outside edge to do all the work of keeping the tire from sliding. Since the tread "interlocks" with the road, that puts a lot of strain on the rubber. Sooner or later, the strain becomes too great and the rubber tears off. At this point,  you have sliding tires and black marks on the pavement.When you put the same side load on a wide tire, the sidewall will tuck under, but the tread will not lift as much on the inside edge. Thus, more of it stays in contact with the road and more of the rubber interlocks with the pavement irregularities.

That means that the load on each individual piece of rubber is less; thus, the whole tread can take more force before the rubber starts tearing. That's what makes wider tires hold the road better.Racing tire designers know this and take advantage of it. Since wider tires "share the load" of sideways grip better than narrow ones, they can make the tread compound softer -- sometimes so soft it gets sticky. This makes for still more grip before the tires let go. To enhance the effect still further, they make the tread "slick," that is to say, with no grooves or individual blocks of tread, at all. This converts the contact patch from a number of small erasers into one great big one, with each inch of the whole width of the tread supporting every other part, rather than being ground up individually.The one drawback to this is that slick tires have no place for water to go. That's what the grooves in the tread are for -- to channel water away from the rubber and allow it to stay stuck to the road.