Effect of Road Tires

Resistances to ground were measured for a small van with four tread 4 polyester, 2 nylon ply tires (sidewall 6 polyester plies) showing the effect of ground surface [107]. The resistance at a source potential of 50 V was mea- 

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The situation is complicated, however, because some of the drag on a skidding tire is due to the elastic hysteresis effect discussed in Section XII-2E. That is, asperities in the road surface produce a traveling depression in the tire with energy loss due to imperfect elasticity of the tire material. In fact, tires made of high-elastic hysteresis material will tend to show superior skid resistance and coefficient of friction. 

Fifteen tire brand-vehicle combinations were collected from Phoenix, AZ Los Angeles, CA Detroit, MI and Hartford, CT. Six different vehicle types and three different tire manufacturers were studied as detailed in Table 34.1. Vehicle-brand combinations are denoted by the vehicle type followed by the letter denoting the specific manufacturer, e.g., SUV/Minivan-A. The geographic locations were chosen based on ambient temperature and ozone level. Both on-road and full-size spare tires were collected ranging in age from two weeks to six years old. In total, over 1500 tires were analyzed in this study. A small number of tires from Miami, FI and Denver, CO were collected to evaluate the effects for road roughness on aging. No significant effect was observed and these tires were not included in the analysis. 

Effect of Liquids on Friction (a) Why do cars tend to slip on a wet road Why is the risk higher with a worn-out tire (b) Why do certain people lifting something heavy without gloves spit on their palms (c) Describe in a short essay how it would be to live in a frictionless world. 

The pressure-temperature relationship. Charles s law is expressed as the effect of a temperature change on gas volume. However, volume and pressure are interdependent, so the effect of temperature on volume is closely related to its effect on pressure (sometimes referred to as Amontons s law). Measure the pressure in your car s tires before and after a long drive, and you will find that it has increased. Frictional heating between the tire and the road increases the air temperature inside the tire, but since the tire volume doesn t change appreciably, the air exerts more pressure. Thus, at constant volume, the pressure exerted by a fixed amount of gas is directly proportional to the absolute temperature ... 

After a tire model has been inflated, it is loaded with a vertical force to simulate the weight of the vehicle. Figure 8.7. In this stage, another contact condition takes effect -contact of the tire tread with the road. The inflation P is still normal to the surface and the contact with the rim continues to be engaged. 

In such a system, the coefficient of friction depends on the fluid dynamics, in particular on the viscosity r of the lubricant. For this reason, hydrodynamic lubrication is also called fluid lubrication. A well-known example of hydrodynamic lubrication is the effect of aquaplaning. When a car is driven at high speed on a wet road, the water forced between the surfaces of the tires cannot escape and separates the car from the road traction is lost. The build-up of the lubrication film either can be solely due to the relative movement of the bearing surfaces or can be achieved by active pumping of the lubricant (for a textbook, see Ref [954])... 

Natural mbber was also used extensively in its oil-extended form in winter tires in the 1970s (57). Use of oil-extended natural mbber treads, found to have excellent traction on ice and snow, superseded studded synthetic mbber treads when studs were banned in certain countries and states owing to the damage they cause to partially cleared roads. This concept has been extended into aH-season tires, which account for over 75% of original equipment and replacement tires in the United States. It has been shown (58) that part replacement of styrene—butadiene mbber (SBR) in the formulation of aH-season tire tread compounds with oil-extended natural mbber increases ice and snow traction, reduces rolling resistance, and has no effect on normal wet grip. Also, there is only a minor trade-off in wear performance, because below a tire surface temperature of approximately 32°C, the wear of natural mbber is superior to SBR, whereas above this temperature the reverse is tme (59). Thus, wear of an aH-season tire ultimately depends on the surface temperature of the tread over its annual cycle of temperatures. 

Over rough surfaces, an opposite effect, not easily measured in the laboratoiy, becomes apparent to the rider. A tire inflated to veiy high pressures (for example, 120 pounds) bounces off the peaks of the road surface, making the bike harder to control, and negating any theoretical decrease in rolling resistance. For... 

I m sure you ve seen movies and TV shows where road blocks are put up and the villain or hero crashes right through and gets away. This is for effect, as decently equipped police departments have portable road blocks studded with over siied spikes. For P.D.s who can t affort these or need to stop traffic immediately without calling in, you can t beat my tire shredding road blocks. They can also be used by civilians to teach trespassers the error of their ways. 

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