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TIRES AND WHEELS

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  1. 109 TIRES AND WHEELS

  2. Figure 109-1 (a) A typical tire tread depth gauge. The center movable plunger is pushed down into the groove of the tire.

  3. Figure 109-1 (b) The tread depth is read at the top edge of the sleeve. In this example, the tread depth is 6/32 in.

  4. Figure 109-2 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.

  5. Figure 109-3 The tire tread runs around the circumference of the tire, and its pattern helps maintain traction. The ribs provide grip, while the grooves direct any water on the road away from the surface. The sipes help the tire grip the road.

  6. Figure 109-4 Hydroplaning can occur at speeds as low as 30 mph (48 km/h). If the water is deep enough and the tire tread cannot evacuate water through its grooves fast enough, the tire can be lifted off the road surface by a layer of water. Hydroplaning occurs at lower speeds as the tire becomes worn.

  7. Figure 109-5 Typical construction of a radial tire. Some tires have only one body ply, and some tires use more than two belt plies.

  8. Figure 109-6 The major splice of a tire can often be seen and felt on the inside of the tire. The person who assembles (builds) the tire usually places a sticker near the major splice as a means of identification for quality control.

  9. Figure 109-7 Tire construction is performed by assembling the many parts of a tire together on a tire-building machine.

  10. Figure 109-8 After the entire tire has been assembled into a completed “green” tire, it is placed into a tire-molding machine where the tire is molded into shape and the rubber is changed chemically by the heat. This nonreversible chemical reaction is called vulcanization.

  11. FREQUENTLY ASKED QUESTION: Why Do I Get Shocked by Static Electricity When I Drive a Certain Vehicle? Static electricity builds up in insulators due to friction of the tires with the road. Newer tires use silica and contain less carbon black in the rubber, which makes the tires electrically conductive. Because the tires cannot conduct the static electricity to the ground, static electricity builds up inside the vehicle and is discharged through the body of the driver and/ or passenger whenever the metal door handle is touched. NOTE: Toll booth operators report being shocked by many drivers as money is being passed between the driver and the toll booth operator. Newer tire sidewall designs that use silica usually incorporate carbon sections that are used to discharge the static electricity to ground. To help reduce the static charge buildup, spray the upholstery with an antistatic spray available at discount and grocery stores.

  12. FREQUENTLY ASKED QUESTION: How Much Does Tire Pressure Change with a Change in Temperature? As the temperature of a tire increases, the pressure inside the tire also increases. The general amount of pressure gain (when temperatures increase) or loss (when temperatures decrease) is as follows: 10°F increase causes 1 PSI increase 10°F decrease causes 1 PSI decrease For example, if a tire is correctly inflated to 35 PSI when cold and then driven on a highway, the tire pressure may increase 5 PSI or more.CAUTION: DO NOT LET AIR OUT OF A HOT TIRE! If air is released from a hot tire to bring the pressure down to specifications, the tire will be underinflated when the tire has cooled. The tire pressure specification is for a cold tire. Always check the tire pressures on a vehicle that has been driven fewer than 2 miles (3.2 km). Air pressure in the tires also affects fuel economy. If all four tires are underinflated (low on air pressure), fuel economy is reduced about 0.1 mile per gallon (mpg) for each 1 PSI low. For example, if all four tires were inflated to 25 PSI instead of 35 PSI, not only is tire life affected but fuel economy is reduced by about 1 mile per gallon (10 X 0.1 = 1 mpg).

  13. Figure 109-9 Notice that the overall outside diameter of the tire remains almost the same and at the same time the aspect ratio is decreased and the rim diameter is increased.

  14. FREQUENTLY ASKED QUESTION: How Much Bigger Can I Go? Many owners think they can improve their vehicle by upgrading the tire size over the size that comes from the factory to make their vehicle look sportier and ride and handle better. When changing tire size, there are many factors to consider: 1. The tire should be the same outside diameter as the original to maintain the proper suspension, steering, and ride height specifications. 2. Tire size affects vehicle speed sensor values, ABS brake wheel sensor values that can change automatic transmission operation, and ABS operation. 3. The tire should not be so wide as to contact the inner wheel well or suspension components. 4. Generally, a tire that is 10 mm wider is acceptable. For example, an original equipment tire size 205/75 X 15 (outside diameter = 27.1 in.) can be changed to 215/75 X 15 (outside diameter = 27.6 in.). This much change is less than 1/2 in. in width and increases the outside diameter by 1/2 in.NOTE: Outside diameter is calculated by adding the wheel diameter to the cross-sectional height of the tire, multiplied by 2. - SEE FIGURE 109–9 . 5. Whenever changing tires, make sure that the load capacity is the same or greater than that of the original tires. 6. If wider tires are desired, a lower aspect ratio is required to maintain the same, or close to the same, overall outside diameter of the tire.Old NewP205/75 × 15 P215/70 × 15205 × 0.75= 154 mm 215 × 0.70 = 151 mmNotice that the overall sidewall height is generally maintained. If even larger tires are needed, then 225/60 15s may be OK–let’s check the math: 225 X 0.60 = 135 mm Notice that this is much too short a sidewall height when compared with the original tire (see no. 6). 7. Use the “plus 1” or “plus 2” concept. When specifying wider tires, the sidewall height must be reduced to maintain the same, or close to the same, original equipment specifications. The “plus 1” concept involves replacing the wheels with wheels 1 in. larger in diameter to compensate for the lower aspect of wider tires.Original Plus 1205/75 X 15 225/60 X 16The overall difference in outside diameter is only 0.5 in., even though the tire width has increased from 205 mm to 225 mm and the wheel diameter has increased by 1 in. If money is no object and all-out performance is the goal, a “plus 2” concept can also be used (use a P245/50 X 17 tire and change to 17-in.-diameter wheels). Here the overall diameter is within 1/20” of the original tire/wheel combination, yet the tire width is 1.6 inches (40 mm) wider than the original tire. Refer to the section entitled “Wheels” later in this chapter for proper wheel back spacing and offset when purchasing replacement wheels.

  15. FREQUENTLY ASKED QUESTION: What Effect Does Tire Size Have on Overall Gear Ratio? Customers often ask what effect changing tire size has on fuel economy and speedometer readings. If larger (or smaller) tires are installed on a vehicle, many other factors also will change. These include the following: 1. Speedometer reading. If larger-diameter tires are used, the speedometer will read slower than you are actually traveling. This can result in speeding tickets! 2. Odometer reading. Even though larger tires are said to give better fuel economy, just the opposite can be calculated! Since a larger-diameter tire travels farther than a smaller-diameter tire, the larger tire will cause the odometer to read a shorter distance than the vehicle actually travels. For example, if the odometer reads 100 miles traveled on tires that are 10% oversized in circumference, the actual distance traveled is 110 miles.3. Fuel economy. If fuel economy is calculated on miles traveled, the result will be lower fuel economy than for the same vehicle with the original tires.Calculation: mph = RPM × diameter × 3.14 gear ratioRPM = mph × gear × ratio diameter × 3.14gear ratio = RPM × diameter × 3.14 mph

  16. Figure 109-10 Cross-sectional view of a typical tire showing the terminology.

  17. FREQUENTLY ASKED QUESTION: If I Have an Older Vehicle, What Size Tires Should I Use? Newer radial tires can be used on older-model vehicles if the size of the tires is selected that best matches the original tires. See the following cross-reference chart.Cross-Reference Chart(This Chart Does Not Imply Complete Interchangeability.)Pre-1964 1965 to 1972 80 Series Metric Alpha Numeric P-Metric 75 Series P-Metric 70 Series 78 Series Radial Radial590-13 600-13 165-13 A78-13 P165/75R13 P175/70R13640-13 650-13 175-13 B78-13 P175/75R13 P185/70R13725-13 700-13 185-13 D78-13 P185/75R13 P205/70R13590-14 645-14 155-14 B78-14 P175/75R14 P185/70R14650-14 695-14 175-14 C78-14 P185/75R14 P195/70R14700-14 735-14 185-14 E78-14 P195/75R14 P205/70R14750-14 775-14 195-14 F78-14 P205/75R14 P215/70R14800-14 825-14 205-14 G78-14 P215/75R14 P225/70R14850-14 855-14 215-14 H78-14 P225/75R14 P235/70R14590-15 600-15 165-15 A78-15 P165/75R15 P175/70R15650-15 685-15 175-15 C78-15 P175/75R15 P185/70R15640-15 735-15 185-15 E78-15 P195/75R15 P205/70R15670-15 775-15 195-15 F78-15 P205/75R15 P215/70R15710-15 815-15 205-15 G78-15 P215/75R15 P225/70R15760-15 855-15 215-15 H78-15 P225/75R15 P235/70R15800-15 885-15 230-15 J78-15 P225/75R15 P235/70R15820-15 900-15 235-15 L78-15 P235/75R15 P255/70R15

  18. FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the Sidewall? Most countries have government agencies that regulate standards for motor vehicles sold and/or driven within their jurisdiction. In the United States, the U.S. Department of Transportation and National Highway Traffic Safety Administration are responsible for developing many of the nationwide standards for vehicles. Tires that are certified by their manufacturers to meet U.S. standards are branded with “DOT” (Department of Transportation) preceding the Tire Identification Code on their sidewall. In Europe, because so much personal and commercial travel extends beyond the borders of any one country, the Economic Commission for Europe (E.C.E.) helps develop uniform motor vehicle standards for its member countries to regulate and standardize passenger and commercial vehicle components.Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet specific limits. These standards were phased-in starting in 2004. The tires must pass noise emission testing, and the standards will continue to expand in scope until 2009, when the standards will be applied to all tires sold in Europe. The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets all regulations, including the load index and speed symbol that appear in its service description. The letter “e” and number code combination (positioned in a circle or rectangle) identify the country originally granting approval, followed by two digits indicating the Regulation Series under which the tire was approved. Tires that have also been tested and meet the “pass-by” noise limits can have a second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .The following list indicates selected E.C.E. codes and the countries they represent:Code Country Code CountryE1 Germany E14 SwitzerlandE2 France E15 NorwayE3 Italy E16 FinlandE4 Netherlands E17 DenmarkE5 Sweden E18 RomaniaE6 Belgium E19 PolandE7 Hungary E20 PortugalE8 Czech Republic E21 Russian FederationE9 Spain E22 GreeceE10 Yugoslavia E23 IrelandE11 United Kingdom E24 CroatiaE12 Austria E25 SloveniaE13 Luxembourg E26 Slovakia

  19. FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the Sidewall? Most countries have government agencies that regulate standards for motor vehicles sold and/or driven within their jurisdiction. In the United States, the U.S. Department of Transportation and National Highway Traffic Safety Administration are responsible for developing many of the nationwide standards for vehicles. Tires that are certified by their manufacturers to meet U.S. standards are branded with “DOT” (Department of Transportation) preceding the Tire Identification Code on their sidewall. In Europe, because so much personal and commercial travel extends beyond the borders of any one country, the Economic Commission for Europe (E.C.E.) helps develop uniform motor vehicle standards for its member countries to regulate and standardize passenger and commercial vehicle components.Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet specific limits. These standards were phased-in starting in 2004. The tires must pass noise emission testing, and the standards will continue to expand in scope until 2009, when the standards will be applied to all tires sold in Europe. The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets all regulations, including the load index and speed symbol that appear in its service description. The letter “e” and number code combination (positioned in a circle or rectangle) identify the country originally granting approval, followed by two digits indicating the Regulation Series under which the tire was approved. Tires that have also been tested and meet the “pass-by” noise limits can have a second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .The following list indicates selected E.C.E. codes and the countries they represent:Code Country Code CountryE1 Germany E14 SwitzerlandE2 France E15 NorwayE3 Italy E16 FinlandE4 Netherlands E17 DenmarkE5 Sweden E18 RomaniaE6 Belgium E19 PolandE7 Hungary E20 PortugalE8 Czech Republic E21 Russian FederationE9 Spain E22 GreeceE10 Yugoslavia E23 IrelandE11 United Kingdom E24 CroatiaE12 Austria E25 SloveniaE13 Luxembourg E26 Slovakia

  20. FREQUENTLY ASKED QUESTION: What Does the Little “e” Mean on the Sidewall? Most countries have government agencies that regulate standards for motor vehicles sold and/or driven within their jurisdiction. In the United States, the U.S. Department of Transportation and National Highway Traffic Safety Administration are responsible for developing many of the nationwide standards for vehicles. Tires that are certified by their manufacturers to meet U.S. standards are branded with “DOT” (Department of Transportation) preceding the Tire Identification Code on their sidewall. In Europe, because so much personal and commercial travel extends beyond the borders of any one country, the Economic Commission for Europe (E.C.E.) helps develop uniform motor vehicle standards for its member countries to regulate and standardize passenger and commercial vehicle components.Besides physical specifications, the E.C.E. standards now require tire “pass-by” noise to meet specific limits. These standards were phased-in starting in 2004. The tires must pass noise emission testing, and the standards will continue to expand in scope until 2009, when the standards will be applied to all tires sold in Europe. The E.C.E. symbol on a tire’s sidewall identifies that the manufacturer certifies that the tire meets all regulations, including the load index and speed symbol that appear in its service description. The letter “e” and number code combination (positioned in a circle or rectangle) identify the country originally granting approval, followed by two digits indicating the Regulation Series under which the tire was approved. Tires that have also been tested and meet the “pass-by” noise limits can have a second E.C.E. branding followed by an “-s” (for sound ). = SEE FIGURE 109–12 .The following list indicates selected E.C.E. codes and the countries they represent:Code Country Code CountryE1 Germany E14 SwitzerlandE2 France E15 NorwayE3 Italy E16 FinlandE4 Netherlands E17 DenmarkE5 Sweden E18 RomaniaE6 Belgium E19 PolandE7 Hungary E20 PortugalE8 Czech Republic E21 Russian FederationE9 Spain E22 GreeceE10 Yugoslavia E23 IrelandE11 United Kingdom E24 CroatiaE12 Austria E25 SloveniaE13 Luxembourg E26 Slovakia

  21. CHART 109–1 Speed ratings are based on continuous operation at the speed rating speed.*The exact speed rating for a particular Z-rated tire is determined by the tire manufacturer and may vary according to size. For example, not all Brand X Z-rated tires are rated at 170 mph, even though one size may be capable of these speeds.

  22. Figure 109-11 Typical sidewall markings for load index and speed rating following the tire size.

  23. Figure 109-12 The E.C.E. symbol on a sidewall of a tire. Notice the small -s at the end, indicating that the tire meets the “pass-by” noise limits.

  24. Figure 109-13 A typical door placard used on a General Motors vehicle indicating the recommended tire inflation. Note that the information also includes the tire size and speed rating of the tire as well as the recommended wheel size.

  25. Figure 109-14 Conicity is a fault in the tire that can cause the vehicle to pull to one side due to the cone effect (shape) of the tire.

  26. Figure 109-15 Notice the angle of the belt material in this worn tire. The angle of the belt fabric can cause a “ply steer” or slight pulling force toward one side of the vehicle.

  27. FREQUENTLY ASKED QUESTION: Is There a Rule-of-Thumb for Rim Size? According to the Tire and Rim Association, Inc., the answer is no. Each tire size has a designated rim width on which it is designed to be mounted so as to provide the best performance and wear. The width of the specified rim also varies with rim diameter. A 235/45 X 17 tire may require a 7.5-in. rim but a 235/45 X 19 tire may require an 8.0-in. rim. A rule-of-thumb that has been used is to multiply the width of the rim by 33.55 to determine the approximate tire size for the rim. For example, consider the following. Rim width 5.0 in. X 33.55 = 167.85 (165 mm) tireRim width 5.5 in. X 33.55 = 184.50 (185 mm) tireRim width 6.0 in. X 33.55 = 201.30 (195 mm) tireRim width 6.5 in. X 33.55 = 218.00 (215 mm) tireRim width 7.0 in. X 33.55 = 234.90 (235 mm) tireRim width 7.5 in. X 33.55 = 252.00 (245 mm) tireRim width 8.0 in. X 33.55 = 268.00 (265 mm) tireRim width 8.5 in. x 33.55 = 285.00 (285 mm) tireRim width 9.0 in. X 33.55 = 302.00 (305 mm) tireRim width 10.0 in. X 33.55 = 335.60 (335 mm) tireAlways check with the tire manufacturer as to the specified tire rim width that should be used.

  28. Figure 109-16 Slip angle is the angle between the direction the tire tread is heading and the direction it is pointed.

  29. Figure 109-17 Typical “Uniform Tire Quality Grading System” (UTQGS) ratings imprinted on the tire sidewall.

  30. REAL WORLD FIX: Tire Date Code Information Saved Me Money! This author was looking at a three-year-old vehicle when I noticed that the right rear tire had a build date code newer than the vehicle. I asked the owner, “How badly was this vehicle hit?” The owner stumbled and stuttered a little, then said, “How did you know that an accident occurred?” I told the owner that the right rear tire, while the exact same tire as the others, had a date code indicating that it was only one year old, whereas the original tires were the same age as the vehicle. The last three numbers of the DOT code on the sidewall indicate the week of manufacture (the first two numbers of the three-digit date code) followed by the last number of the year. The owner immediately admitted that the vehicle slid on ice and hit a curb, damaging the right rear tire and wheel. Both the tire and wheel were replaced and the alignment checked. The owner then dropped the price of the vehicle $500! Knowing the date code helps assure that fresh tires are purchased and can also help the technician determine if the tires have been replaced. For example, if new tires are found on a vehicle with 20,000 miles, then the technician should check to see if the vehicle may have been involved in an accident or may have more miles than indicated on the odometer.

  31. Figure 109-18 Typical DOT date code. This tire was built the sixth week of 2005.

  32. Figure 109-19 Cutaway of a run-flat tire showing the reinforced sidewalls and the required pressure sensor.

  33. Figure 109-20 A conventional tire on the left and a run-flat tire on the right, showing what happens when there is no air in the tire.

  34. TECH TIP: PAX Replacement Tip In most cases, the fastest and easiest approach to follow if a PAX tire requires replacement is to purchase a replacement tire/wheel assembly. While more expensive than replacing just the tire, this approach is often used to help the vehicle owner get back on the road faster without any concerns as to whether the replacement tire was properly installed.

  35. Figure 109-21 The PAX run-flat tire system is composed of three unique components—a special asymmetrical wheel, a urethane support ring, and special tire.

  36. Figure 109-22 The Tire Performance Criteria (TPC) specification number is imprinted on the sidewall of all tires used on General Motors vehicles from the factory.

  37. FREQUENTLY ASKED QUESTION: What Is a Low-Rolling-Resistance Tire? Low-rolling-resistance (LRR) tires reduce rolling resistance, which is the power-robbing friction between the tire and crown. The E-metric tire, designated for use on electric or hybrid vehicles, operates at higher inflation pressures, reduced load percentages, and lower rolling resistance. These tires were first used on the GM EV1 electric vehicle. To soften the ride of tires pumped with additional air, a new tire profile was developed. Narrower rim width and rounder sidewalls make the tire more shock absorbent. To make the tires roll more freely, low-rolling-resistant tread compounds are molded into smaller tread elements that flex easily and with less friction when they touch the road. LRR tires are available from most major tire manufacturers, including Michelin the Energy MXV4 Plus and Goodyear VIVA 2. According to tire engineers, the basic tradeoff of low rolling resistance is poor wet traction performance. To improve wet road performance and traction requires the use of more silica in the tread, which increases the cost of the tire. Neither a technician nor a vehicle owner can determine the relative rolling resistance unless the tires are compared using a coast-down test from highway speed to zero or a laboratory testing machine.

  38. Figure 109-23 The size of the wheel is usually cast or stamped into the wheel. This wheel is 7 inches wide. The letter “J” refers to the contour of the bead seat area of the wheel.

  39. Figure 109-24 The wheel rim well provides a space for the tire to fit during mounting; the bead seat provides a tire-to-wheel sealing surface; the flange holds the beads in place.

  40. Figure 109-25 A cross section of a wheel showing part designations.

  41. Figure 109-26 Offset is the distance between the centerline of the wheel and the wheel mounting surface.

  42. Figure 109-27 Back spacing (rear spacing) is the distance from the mounting pad to the edge of the rim. Most custom wheels use this measurement method to indicate the location of the mounting pad in relation to the rim.

  43. Figure 109-28 Bolt circle is the diameter of a circle that can be drawn through the center of each lug hole or stud. The bolt circle is sometimes referred to as PCD for pitch circle diameter.

  44. Figure 109-29 Measuring the bolt circle on a five lug wheel is difficult, but a quick and easy way includes measuring as shown to determine the approximate bolt circle of a five-lug wheel.

  45. Figure 109-30 Measure center-to-center distance and compare the distance to the figures in the chart in the text to determine the diameter for a five-lug bolt circle.

  46. FREQUENTLY ASKED QUESTION: What Does This Mark in a Wheel Mean? The symbol JWL, for the Japan Wheel Light Metal Standard Mark, means that the wheel meets the technical standards for passenger-car light-alloy wheels. See the mark in - FIGURE 109–31 . 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.

  47. Figure 109-31 A typical JWL symbol for the Japan Wheel Light Metal standard mark.

  48. Figure 109-32 (a) A rubber snap-in style tire valve assembly. (b) A metal clamp-type tire valve assembly used on most highpressure (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.

  49. Figure 109-33 Various styles of lug nuts.

  50. TIRE INSPECTION 1 Check the tire information placard, usually located on the driver’s door or door jamb, for the specified tire size and inflation pressure.