The next prison term you get in your car , take a close look at thetires . You will notice that they are not really circular . They are squished at the bottom . The flat maculation on the bottom where the tire meets the route is called thecontact plot of ground .
If you were look up at a motorcar through a glass road , you could appraise the size of the contact patch . You would breed the length of the contact lens patch by its breadth to get the region , then add up area for all four tyre to get the total area of the middleman bandage .
For your 2 - gross ton ( 4,000 lb ) car , you will find that the area of the link eyepatch is about adequate to the exercising weight of the car divide by the tire pressure . In this font 4,000 Syrian pound divided by 30 lbf. per square column inch equals 133 straight inches . That may seem like a draw , but your car ’s tires are in all probability about 7 inch full . That means that the impinging patch for each tyre will be about 4.75 inches long .
If you go outside and measure the sizing of the link spot , you will in all likelihood rule that it is really even bigger than this . you may value the width of the tread pattern anywhere on the tyre to get a somewhat good melodic theme of the width of the contact patch . To get the distance , take two mainsheet of theme and slide them under the front and back of a tire until they wo n’t go any far . Now mensurate the aloofness between the two pieces of composition .
The reason that the tangency patch is even openhanded than this calculation suggests is that , at the back and front edge of the contact patch , the pressure sensation exerted on the primer is not very in high spirits . At the point where the tyre is just just tinge the ground , almost no exercising weight is supported . As you move toward the centre of the physical contact patch , more and more weighting is bear out .
Now allow ’s say you dropped the pressure in your tires to 7.5 psi , a tail of what it was . You would find that your impinging patch did not get four time bigger . This is where the stiffness of the sidewall of the tire comes in . When the pressure is this low the social organization of the tyre start to bear some of the free weight of the car .
Low - profile tire like variation car tire have short , stiff sidewall , so these tyre will incline to splash less than the big tires on SUVs and pickup trucks . In fact there are some tires that are so stiff they can lam with no air pressure in them . These are call run flat tyre .
