Tire contact patch area equation

Tire properties such as compliance and inertia are ignored. This includes the weight resting on the tire contact patch plus any aerodynamic downforce. Tire contact patch shape length vs width post wed aug 01, 2012 4. If the tire pressure is held constant, the width of the tire can only change the shape of the contact patch. This equation says that the friction is a percentage of the total weight on.

Jun 29, 20 when you install wider tires without changing anything else, the size of the tire s contact patch i. During a cornering maneuver, however, the tire contact patch slips laterally. This page focuses mainly on the normal direction, i. Tire contact patch lowering pressure gain traction. Prints of the contact patch may be obtained by using ink or carbon paper. Getting a grip examining the elements of tire traction. Assuming your 930 loader has a wheel load of say 8000 lb and it has standard tires, you probably have a contact area of about 70 to 80 square inches.

Whats the best way to calculate tire contact areas. This is part 6 of my 10 part series on how race car tires tyres work. Since the puncture is outside the permitted repair area, this tire. Vertical load is the load actually seen at the tire contact patch. The contact patch of a tyre is the section of the tyres tread that is in physical contact with the road surface. Manipulating this equation, we can get a formula for area, which we will use to calculate contact patch. To calculate the overall diameter of a tire, the sidewall height must be multiplied by 2 remembering that the tire diameter is made up of 2 sidewalls, the one above the wheel and the one below the wheel touching the ground and add the diameter of the wheel.

Calculating the contact area of trailer tyres in the field. The tire contact patch all vehicles are supported by a cushion of air contained in four flexible rubber tires. With the tire 15 cm wide, the contact patch is 6 cm. Town fair tire tire contact patch also known as tire footprint. The longitudinal force arising from this interaction is given by the magic formula, an empirical equation based on four fitting coefficients. The acceleration signal was processed to obtain the contact patch length created by the tire on the road surface.

Estimation of vertical load on a tire from contact patch. This part covers the dynamics of a tires contact patch. The contact patch of most tires is about the size of your hand and has to handle a lot more weight and force than those big reeboks do. To show that the contact area load pressure formula was wrong you could just show it in the slopes of the lines. Jul 02, 2016 this is part 6 of my 10 part series on how race car tirestyres work.

The two laws can be combined into a single equation. Harder compound tires wear much longer, and can be narrower. W, where f is the friction between two given surfaces, w is the force pressing them together the weight, in most of our examples, and. Estimating tire contact area and volume of displaced soil are important factors in determining. The problem with this is thats its a model, and it assumes a perfectly flexible tire, something like a balloon. Narroe will have longer contact patches and wide tires will have shorter. If the tyre pressure was 30 psi, the contact area would be 30 square inches, and if the pressure was 90 psi, the contact area would be 10 square inches. In fact, a typical tire contact patch is about the size of your hand.

The first part of this paper presents the results of experimental estimation of the contact patch area depending on the normal wheel load and inflation pressure for different car tires. Contact patch is the portion of a vehicles tire that is in actual contact with the road surface. The tyres of your car may seem imposing to you, as if solidly anchored into the ground, but in reality the contact with the road is very often no more than a few squared inches of rubber. Believe it or not, most tires have a fairly small contact patch a little larger than the size of your hand. Then an appropriate equation relating the patch length to the vertical load is used to calculate the load. If you had an infinitely rigid carcass and tread youd have a line of contact patch with nearinfinite unit pressure. High aspect ratio tall and narrow contact patch short aspect ratio chort and wide contact patchwhat does this. Contact area at 6psi is listed as 9 square centimeters. The tire carcass has some stiffness and the tread is even more stiff, so there has to be some deflection starting well before the tire rotates into the contact patch. If a person of mass 82 kg gets into the car by how much will the total area of contact between the tyres and the ground increase assuming that the tire pressure. Notice tire size, width, nor wheel size enters that equation.

May 28, 2017 for example, a 10% change in load or inflation pressure usually does not result in a 10% change in the contact patch area. Pressure, surface area and force in tire physics forums. That size is based on a tires overall diameter, inflation pressure, and the weight acting on it. Me en 7960 precision machine design contact stresses and deformations 78 spheres in contact vertical stress distribution at center of contact area plot shows material with poissons ratio. Truck tire types and road contact pressures by pedro yap the. The force from the weight on the tire must be equaled by the tire in terms of pressure x area. It is most commonly used in the discussion of pneumatic tires, i. The design of the contact patch is an engineering feat that is specific not only to each manufacturer, but for each individual tire. Does car tire pressure change with weight of car load.

Then estimate the total load, this is truck tare weight plus rock or dirt being hauled. If a slick tire and a treaded tire were made with the same. Imagine the contact patch as a matrix of discrete elements. Only contact patch area, length, width and measured load are considered in this paper. As an engineer, i know that friction does not depend upon. However, these two properties are not linearly proportional to the area of the contact. It should distinguish between the tire contact area and the nominal touch patch because of the tread pattern.

That internal pressure means that each square inch of area can support 10lb, so, in this case, the contact patch will be 90 square inches. Approximate tire contact patch lengths wheel type, tire designation wheel load kn inflation pressure or deflection kpa or % approximate tire contact patch length mm 40 690 310 550 330 690 310 wide single 38565 r225 r194 50 550 360 dual wheel 690 220 29580 r225 m840 40 20% 280 kpa 290. Best of all, costco offers all these professionalgrade tires, car accessories, and tools at our famous wholesale price. An effective rectangular contact area may be defined with an area equal to that of the envelope of the actual print. Contact mechanics is the study of the deformation of solids that touch each other at one or more points. Hopefully steve can answer this in a much better way but here are my thoughts, for what they are worth. Considering this, and the 7inch slab thickness, the vertical deflection in the soil will be about 0. A wider tyre reduces the contact pressure at each element for a given vehicle weight which increases the cof. The maximum width of the contact patch or footprint is determined by the tires tread width.

For instance, if you measure the area of the contact patch in square inches of each tire in in2, times the pressure in the tire in lbsin2 youre left with pounds, which should be very close to the weight of the car. This is the reason why it comes with a contact patch wider than an allseason tire. Higher tire pressure results in a smaller contact patch. Most modern passenger car and light truck tires feature size designations that indicate the tire s dimensions in a combination of metric, mathematical and english systems.

After more than 50 years working in the automotive field as engineer, owner of tire and repair dealerships and having sold millions of tires in multistate, multistore tire repair chains i would summarize as follows. Think extremecontact sport and extremecontact dws06. The variation of the contact patch according with tire air pressure knowing the total and effective area of the contact patch it can be determined the influence. As a result, not much of the tire s surface area is touching the ground, so the amount that does touch the ground must handle. Given this alone, the contact patch area should be constant for a given tire pressure and load. That is a lot of force from those four tire contact patches. Difficult is an understatement when describing driving in snowy conditions. Regardless of whether knowing what the actual contact patch area might be useful, thats at best only a crude approximation. What this means is at the same pressure, a narrower tyre will deform more than a wider tyre to achieve the same contact patch. May 24, 2017 a wider tire results in a contact patch better suited to handling lateral loads less percentage deformation of the contact patch due to lateral loads, and the total surface area of the tread is a factor in dissipation of heat in a tire. The point here is, even if the calculated contact patch data was wrong, the trend is still obviously in the direction that contact patch pressure and air pressure are not very intimately related at all. Word tire pressures, truck tires, contact area, contact pressure. Measured tireroad contact stresses tire type, wheel load. The omission is intentional, because the area of the contact patch does not depend on the width of the tire.

Tires with weak sidewalls called wrinkle wall tires, combined with lower pressure provide more contact. So for the same tire drop of 6% the 29 wheel has a 2. An ordinary differential equation the lumped model for the friction force is developed, based on the patch boundary conditions and the normal force distribution along the contact patch. When the vehicle is at rest, the distribution of normal contact pressure is symmetrical fore and aft, with the centre of pressure directly below the axle centreline.

It differs for different types of tyres and sometimes under different road conditions. I had this argument with my high school physics teacher. This report also proposes mathematical models for 1 estimating the tire contact area based on the relative area value ratio of wheel load over inflation pressure and 2 estimating the tire vertical stiffness based on the tire contact area. Light truck and passenger tires are viewed as high profile tires.

Calculate the surface area of the part of the tire that touches the ground by multiplying the length and width of the footprint. Truck tire types and road contact pressures by pedro yap. If you could place a car on a glass floor and look at it from below, you would see four patches of rubber, most folks are surprised at the size of these four patches, depending on the vehicle each patch is a little smaller than a hand. Drain out the air and the tire center sits lower past 24 psi anyway. Jan 27, 2015 homework statement a car has four tires in contact with the ground each of which is inflated to an absolute pressure of 3. Tire width intuitively, increasing the size of the tires would also, in theory, increase the size of the contact patch. The shape of a tire s contact patch or footprint greatly influences its performance and is dependent on its profile or aspect ratio. The area of tire surface contact is the crucial parameter in analyzing the influence of various surface and vehicle parameters on contact friction processes. Slip ratio is a means of calculating and expressing the slipping behavior of the wheel of an automobile. Additionally, the calculated contact patch pressure rises from 6.

In the cases where the tire is overloaded or underinflated, the vertical contact stresses maximize towards the edges of the tire contact patch typical mshape, while lower loads and overinflated conditions result in maximum vertical stresses towards the center portion of the tire contact patch typical nshape. A wider tire results in a contact patch better suited to handling lateral loads less percentage deformation of the contact patch due to lateral loads, and the total surface area of the tread is a factor in dissipation of heat in a tire. That in itself would have made the point and done it with a lot less rambling. The contact patch of the tire changes shape by becoming shorter and wider. Speedo reading tire 1 is assumed accurate tire susp. Correct pressure ensures correct contact area preventing wear on the tire, and keeping rolling friction low.

Inflated to 90 psi and fitted to a bike under the same rider, a supernarrow 700c x 19 clincher would have the same contact patch area as a mediumwidth 700c x 25 or a 700c x 32 loaded touring tire. Many performance tires are considered low profile tires and have a short and wide contact patch. Dynamic friction models for road tire longitudinal. A short and wide tire contact patch, which is usually found on low profile or performance tires, can provide you with more control, corner stability and tire traction.

This part covers the dynamics of a tire s contact patch. Tire pressures, tire widths, wheel widths, and contact. The tire road interaction magic formula block models the interaction between the tire tread and road pavement. While this unusual combination of millimeters, percentages and inches is a byproduct of the evolution of global tire. A tire s contact patch is the area of the tire that comes in contact with the ground, much like a footprint.

Longer and narrower tire contact patches are most often found on passenger vehicles. These forces are produced by the deformation of the tire where it contacts the road during acceleration, braking, and cornering. Back to contact patch, you can safely assume that contact patch stays roughly the same area with wide or narrow tires as long as the load stsys the same. Bring your bike into your garage, wetting the tire with a inert liquid that and lifting the tire off of the floor. A central distinction in contact mechanics is between stresses acting perpendicular to the contacting bodies surfaces known as the normal direction and frictional stresses acting tangentially between the surfaces. With the loaded truck sitting still on flat level ground, go measure the tire contact patch, ie the width and length of each tire contact patch. Lift the bike again and you will see the contact patch of the tire. In the absence of side forces, a rolling tire travels straight ahead along the wheel plane. Tire tech information calculating approximate tire. Tire width intuitively, increasing the size of the tires would also, in theory, increase the size of the contact patch and thus improve traction. Tire pressures and contact areas heavy equip tires. Jan 22, 2009 id say thats got to depend entirely on the amount of reenforcement in the tire, which is going to vary, potentially pretty significantly.

High aspect ratio tall and narrow contact patch short aspect ratio short and wide contact patch what does this. The shape appears to change from an oval shape at very low normal loads to a more rectangular shape at higher values of the load. They do, however have a lower coefficient of friction, therefore less traction. Evaluation of tiresurfacingbase contact stresses and. With respect to tire shape, the area of interest is the crown region and the dimensions of tread width and tread radius, figure 15.

A tire repair should be installed by a tire service technician who has been trained to do a complete, proper repair. Going to use simple math, round numbers no calculator. From point a to point b, somewhere near the midline of the contact patch, the tread stays stuck to the road at this slip angle anyway and lateral deflection in the carcass and. For example, doubling the tire load or pressure does not usually result in doubling of the contact patch area.

Jan 25, 2014 the tire contact patch all vehicles are supported by a cushion of air contained in four flexible rubber tires. Analysis of tire contact parameters using visual processing. It is important that the tire technician remove the tire from the rim so that the inside can be thoroughly inspected. In fact, having the wrong tires can definitely cause an. The influence of the vertical load and of air pressure from the tire against contact patch area in the figure 6 is the variation of the total contact patch area, according to vertical load and air pressure from the tire.

Tire tech information calculating approximate tire dimensions. By assuming a contact patch between the tire and the ground we develop a partial differential equation for the distribution of the friction force along the patch. To find the amount of weight the tire supports, multiply the surface area by the air pressure reading psi for that tire. Place a sheet of paper under the tire and slowly lower the tire until all of the bikes weight of off of the jack.

While the shape changes, the size area of the contact patch remains relatively unchanged. With this, each element of the tyre is able to generate a slightly lower force, but this balance is outweighed by the presence of a larger number of elements contact area. A narrow, soft tire would not be strong enough, nor would it last very long. This tire has been punctured through the shoulder area long enough ago for part of the nail head to have worn away. The tire contact patch, or tire footprint, is the area of the tire that directly connects the vehicle with the driving surface. From 390 lb to 773lb almost double the tire load the contact patch size only increases by 25%, even assuming laterally constrained sidewalls. So contact patch is dependent on force and pressure and has no regard for dimensions. It is commonly used in the discussion of pneumatic i.

Unit loading over the tires contact patch areas can easily vary over a 2. It turns out that real tire construction can significantly affect this. The static contact patch of some friction measuring devices david woodward, phillip millar. This helps convert the drivers input into cornering stability, responsive handling and tractionespecially in dry conditions. Higher load on the tire results in a larger contact patch. Increasing the size of the contact patch introduces more surface area and thus vastly improves the chance of the maximum coefficient of friction actually being achieved.

Pdf calculating the contact area of trailer tyres in the field. The second of the two tire factors affecting contact pressure is tire design. The aim of the research in this paper is to investigate the effects of tyre contact pressure distribution on surface deformation. Hard to believe, but shaq puts more rubber down than most cars do. The shape of a tires contact patch or footprint greatly influences its performance and is dependent on its profile or aspect ratio. Now consider row a2 tread deformation, and focus on what happens within the contact patch, say, of a lorry tyre that bears on the road surface with a vertical wheel load \p\, say. The force of friction is proportional to the normal force fmu x n, where f is along the surface and n is perpendicular to. It is of fundamental importance in the field of vehicle dynamics, as it allows to understand the relationship between the deformation of the tire and the longitudinal forces i. When you install wider tires without changing anything else, the size of the tires contact patch i. A bigger contact patch does not give a tire more resistance to sliding. Tyre load, area of contact, and pressure post mon feb 02, 2009 2. Contact patch the risks due to under and over inflation. Many times, a simple object such as a nail in the tread can result in severe damage to the sidewall that cannot.