chap83 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 83, the reader should be able to: • • • Prepare for ASE Suspension and Steering (A4) certification test content area “E” (Wheel and Tire Diagnosis and Repair) Discuss tire sizes and ratings Describe tire purchasing considerations and maintenance Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 83, the reader should be able to: • • Explain the construction and sizing of steel and alloy wheels and attaching hardware Demonstrate the correct lug nut tightening procedure and torque Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: aspect ratio back spacing • bead • belt • body ply • bolt circle carcass ply • center section • conicity DOT tire code • E-metric tire • green tire high-flotation tires • hydroplaning • inner liner JWL • LLR • load index • lug nuts • major splice • offset ply steer • rim width • run-flat tires Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: schrader valve • sidewall • speed ratings • spider TPC • TPMS • tread • TREAD Act unsprung weight • UTQGS wear bars Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The friction (traction) between the tire and the road determines the handling characteristics of any vehicle The compounding, construction, and condition of tires are some of the most important aspects of steering, suspension, alignment, and braking of any vehicle A vehicle that handles poorly, pulls, darts, jumps, or steers “funny” may be suffering from defective or worn tires Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 TIRES Tires are mounted on wheels that are bolted to the vehicle to provide the following: Shock absorber action when driving over rough surfaces Friction (traction) between the wheels and the road Tires are available in many different designs and sizes Understanding the construction of a tire is important for the tech to be able to identify tire failure or vehicle handling problems All tires are assembled by hand from many different component parts consisting of various rubber compounds, steel, and various types of fabric material Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PARTS OF A TIRE Tread The part of the tire that contacts the ground is the tread Tread rubber is chemically different from other rubber parts of a tire It is compounded for a combination of traction and tire wear Tread depth is usually 11/32 in deep on new tires (this could vary, depending on manufacturer, from 9/32 to 15/32 in.) Figure 83–1 shows a tread depth gauge NOTE: A tread depth is always expressed in 1/32nds of an inch, even if the fraction can be reduced to 1/16ths or 1/8ths Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 83–1 (a) A typical tire tread depth gauge The center movable plunger is pushed down into the groove of the tire (b) The tread depth is read at the top edge of the sleeve In this example, the tread depth is 6/32 in (a) Wear indicators are also called wear bars When tread depth is down to the legal limit of 2/32″, bald strips appear across the tread (b) See Figure 83–2 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 83–2 Wear indicators (wear bars) are strips of bald tread that show when the tread depth is down to 2/32 in, the legal limit in many states Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Some racing wheels are made from a lighter-weight metal called magnesium These wheels are called mag wheels (an abbreviation for magnesium) True magnesium wheels are not practical for production wheels because their cost and corrosion are excessive compared with steel or aluminum alloy wheels The term mag wheel, however, is still heard when referring to alloy (aluminum) wheels NOTE: If purchasing replacement aftermarket wheels, check that they are certified by the SFI SFI is the Specialty Equipment Manufacturers Association (SEMA) Foundation, Incorporated SEMA and SFI are nongovernment agencies that were formed by the manufacturers themselves to establish standards for safety Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What Does This Mark On a Wheel Mean? The symbol JWL, for the Japan Wheel Light Metal Standard Mark, means the wheel meets the technical standards for passenger-car light-alloy disk wheels The manufacturer is responsible for conducting the inspections set forth in the technical standard, and the JWL mark is displayed on those products that pass the inspection Figure 83–36 A typical JWL symbol for the Japan Wheel Light Metal Standard Mark Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 TIRE VALVES All tires use a Schrader valve to hold air The valve was invented in New York in 1844 by August Schrader for the Goodyear Brothers: Charles, Henry, and Nelson Today, Schrader valves are used not only as valves in tires but on fuel-injection systems, air-conditioning systems, and air shock (ride control) systems Most experts agree the valve stem should be replaced whenever tires are replaced A defective or leaking valve stem is a major cause of air loss Low tire pressure can cause the tire to become overheated Aluminum (alloy) wheels often require special metal valve stems that use a rubber washer and are actually bolted to the wheel See Figure 83–37 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 83–37 (a) A rubber snap-in style tire valve assembly (b) A metal clamp-type tire valve assembly used on most high-pressure (over 60 PSI) tire applications such as is found on many trucks, RVs, and trailers The internal Schrader valve threads into the valve itself and can be replaced individually, but most experts recommend replacing the entire valve assembly every time the tires are replaced to help prevent air loss (a) (b) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 UNSPRUNG WEIGHT The lighter the wheel and tire assembly, the faster it can react to bumps and dips in the road surface and thus the better the ride It is the purpose of the suspension system to isolate the body of the vehicle from the road surface The wheel and tire are unsprung weight because they are not supported by the vehicle’s springs Every time the vehicle hits a bump, the wheel is forced upward Heavy mass of the wheesl and tires would transmit this force through the spring of the vehicle A much lighter wheel and tire assembly reacts faster to bumps and dips in the road surface The end result is a smoother-riding vehicle with greater control Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 NOTE: Putting oversized tires on an off-road-type vehicle is extremely dangerous The increased unsprung weight can cause the entire vehicle to leave the ground after hitting a bump in the road The increased body height necessary to clear the larger tires seriously affects drive shaft angles and wheel alignment angles, making the vehicle very difficult to control An aluminum wheel is generally lighter than the same-size stamped steel wheel This is not always the case, however, so before purchasing aluminum wheels, check their weight! Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 LUG NUTS Lug nuts are used to hold a wheel to the brake disc, brake drum, or wheel bearing assembly Some models of VW, Audi, and Mazda use a lug bolt that is threaded into a hole in the brake drum or bearing assembly Typical lug nuts are tapered so the wheel stud will center the wheel onto the vehicle The taper, usually 60 degrees, forms a wedge that helps ensure that the lug nut will not loosen Steel wheels deform slightly when the lug nut is torqued down against the mounting flange; be certain that the taper is toward the vehicle Many alloy wheels use a shank-nut-type lug nut that has straight sides without a taper Figure 83–38 shows several of the many styles of lug nuts that are available Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 83–38 Various styles of lug nuts Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Size Lug nuts are sized to the thread size of the stud onto which they screw Diameter and number of threads per inch are stated Some vehicles use left-hand threads RH and LH are commonly stated, indicating “right-hand” and “left-hand” threads A typical size is 7/16-20RH, where 7/16 indicates the diameter of the wheel stud and 20 indicates that there are 20 threads per inch A common fractional size is 1/2 x 20 Metric sizes such as M12 x 1.5 use a different sizing method.Other commonly used metric lug sizes include M12 x 1.25 and M14 x 1.5 Obviously, metric wheel studs require metric lug nuts NOTE: Some aftermarket manufacturers offer a stud conversion kit to replace the lug bolt with a conventional stud and lug nut Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Inspection Step-By-Step Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Tire Inspection Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY New tires have between 9/32 in and 15/32 in tread depth Wear bars (indicators) show up as a bald strip across the tread of the tire when the tread depth gets down to 2/32 in All tires are assembled by hand from many different materials and chemical compounds After a green tire is assembled, it is placed into a mold under heat and pressure for about 30 minutes Tread design and the tire shape are determined by the mold design Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) A 205/75R 14 92S tire is 205 mm wide at its widest section and is 75% as high as it is wide The R stands for radial-type construction The tire is designed for a 14-in.-diameter rim The number 92 is the load index of the tire (the higher the number, the more weight the tire can safely support) The S is the speed rating of the tire (S 112 mph maximum sustained) The Uniform Tire Quality Grading System is a rating for tread wear (100, 150, etc.), traction (A, B, C), and temperature resistance (A, B, C) For best overall handling and satisfaction, always select the same size and type of tire that came on the vehicle when new Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) For best overall handling and satisfaction, always select the same size and type of tire that came on the vehicle when new Replacement wheels should have the same offset as the factory wheels to prevent abnormal tire wear and/or handling problems All wheels must be secured with the proper size and style of lug nuts If a wheel stud is broken, it should be replaced immediately to avoid possible wheel damage or loss of vehicle control Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458