Electric Vehicles: New requirements for tires’ rolling resistance
Gasoline-powered vehicles ultimately will have to be replaced by an alternative method of power, as the world’s supply of oil is following Hubbert’s Peak Oil model . A tire’s rolling resistance becomes an even more critical factor, simply because any increased resistance means more of a power drain on the batteries, thus limiting the driving range even further.
Rolling resistance essentially is how the tire and surface on which it rolls interact to slow down the speed of rotation. According to the U.S. Department of Energy (DOE) 5-15% of the fuel consumed by a light duty vehicle is traceable to rolling resistance . Words like “drag” or “friction” are also used to describe the retardation. Numerous factors can affect rolling resistance:
– road surface condition – affected by road materials, weather, liquids on surface, etc.
– surface of tire – smooth to rough (tread depth and design as major factors)
– tire width – naturally or caused by tire pressure
– tire composition – types of rubber – smooth, hard, degree of flexibility
– speed of rotation
– tire/wheel radius.
Obviously the smoother the surfaces of the road and tire, the less friction there will between the tire and surface, thus lessening friction and increasing the possibility of the tire sliding across the surface. Rough or soft surfaces increase friction, let alone noise for the former. On one hand, the greater the drag, the more fuel or battery power is required by the vehicle. On the other hand, of course, there is an optimum amount of friction to be able to control the vehicle. Terry Gettys, director of the research and development process of the Michelin Group, stated: “Fundamentally, designing tires for electric vehicles is not different than for engined vehicles .” While, there are certain factors that need to be taken into account, such as thermal regulation, the general thrust is to reduce the rolling resistance as much as possible . Rolling resistance of tires for electric vehicles is about .055 .
As all these factors affect the manageability of a vehicle, it can be expected that there is a plethora of legislation worldwide to address the situation. While automobile manufacturers will install low rolling resistance tires to meet U.S. Corporate Average Fuel Economy (CAFE) standards, there is no requirement concerning what tires a motorist must use to replace them. However, installing tires that have a low rolling resistance, according to the DOE, can save 1.5%-4.5% in fuel consumption . States like California are investigating way that tire manufacturers and distributors need to inform the consumer about ways of selecting tires that offer the best fuel economy. Already, they have a rolling resistance tire regulation, one that went into effect July 2008, and more may be on the way . As of 14 January 2010, heavy trucks and trailers were required to have rolling resistance tires . Europe has followed suit , and in November 2012 a rolling resistance rating system will be mandatory . China, seeing the need to conform to these regulations may opt to follow, as it not only deems safety important but wants to be able to sell tires overseas.
Want to learn more about tires? Interesting whitepapers, articles, and presentations are available here.
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