Tires and Wheels CHAPTER 3 Tires and Wheels

Tires and Wheels CHAPTER 3 Tires and Wheels

OBJECTIVES After studying Chapter 3, the reader will be able to: 1. Prepare for ASE Suspension and Steering (A 4) certification test content area “E” (Wheel and Tire Diagnosis and Repair). 2. Discuss tire sizes and ratings. 3. Describe tire purchasing considerations and maintenance. 4. Explain the construction and sizing of steel and alloy wheels and attaching hardware. 5. Demonstrate the correct lug nut tightening procedure and torque.

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 LRR • • • • Load index Lug nuts Major splice Offset Ply steer Rim width Run-flat tires Schrader valve Sidewall Speed ratings Spider TPC Tread Unsprung weight UTQGS Wear bars

INTRODUCTION TO TIRES • 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 the steering, suspension, alignment, and braking systems of any vehicle. • 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

PARTS OF A TIRE TREAD • Tread refers to the part of the tire that contacts the ground. • Tread rubber is chemically different from other rubber parts of a tire, and 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. ).

PARTS OF A TIRE TREAD FIGURE 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.

PARTS OF A TIRE TREAD • Wear indicators are also called wear bars. • When tread depth is down to the legal limit of 2/32 in. , bald strips appear across the tread. FIGURE 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.

PARTS OF A TIRE TREAD • Grooves are large, deep recesses molded in the tread and separating the tread blocks. • These grooves are called circumferential grooves or kerfs. • Grooves running sideways across the tread of a tire are called lateral grooves. FIGURE 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.

PARTS OF A TIRE TREAD • Grooves in both directions are necessary for wet traction. • The trapped water can actually cause the tires to ride up on a layer of water and lose contact with the ground, as shown in • This is called hydroplaning. FIGURE 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.

PARTS OF A TIRE SIDEWALL • The sidewall is that part of the tire between the tread and the wheel. • The sidewall contains all the size and construction details of the tire. • WHITE SIDEWALL/LETTERED

PARTS OF A TIRE BEAD • The bead is the foundation of the tire and is located where the tire grips the inside of the wheel rim. • The bead is constructed of many turns of copper- or bronze-coated steel wire. • The main body plies (layers of material) are wrapped around the bead. • Most radial-ply tires and all truck tires wrap the bead with additional material to add strength.

PARTS OF A TIRE BODY PLY • A tire gets its strength from the layers of material wrapped around both beads under the tread and sidewall rubber. • This creates the main framework, or “carcass, ” of the tire; these body plies are often called carcass plies. FIGURE 5 Typical construction of a radial tire. Some tires have only one body ply, and some tires use more than two belt plies.

PARTS OF A TIRE BELT • A tire belt is two or more layers of material applied over the body plies and under the tread area only, to stabilize the tread and increase tread life and handling. • Belt material can consist of the following: • • • a. Steel mesh b. Nylon c. Rayon d. Fiberglass e. Aramid • All radial tires are belted.

PARTS OF A TIRE INNER LINER • The inner liner is the soft rubber lining (usually a butyl rubber compound) on the inside of the tire that protects the body plies and helps provide for self-sealing of small punctures.

PARTS OF A TIRE MAJOR SPLICE • When the tire is assembled by a craftsperson on a tire-building machine, the body plies, belts, and tread rubber are spliced together. • The fabric is overlapped approximately five threads. • The point where the majority of these overlaps occur is called the major splice, which represents the stiffest part of the tire.

PARTS OF A TIRE MAJOR SPLICE FIGURE 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.

TIRE MOLDING • After the tire has been assembled by the tire builder, it is called a green tire. FIGURE 7 Tire construction is performed by assembling the many parts of a tire together on a tirebuilding machine.

TIRE MOLDING FIGURE 8 After the entire has been assembled into a completed “green” tire, it is placed into a tiremolding machine where the tire is molded into shape and the rubber is changed chemically by the heat. This nonreversible chemical reaction is called vulcanization.

METRIC DESIGNATION • European and Japanese tires use metric designations. For example, 185 SR x 14 denotes the following:

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.

METRIC DESIGNATION AMERICAN METRIC TIRE SIZE DESIGNATIONS • After 1980, American tires were also designated using the metric system. For example, P 205/75 R x 14 denotes the following:

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.

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.

How Much Bigger Can I Go? FIGURE 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.

SERVICE DESCRIPTION • Tires built after 1990 use a “service description” method of sidewall information in accordance with ISO 4000 (International Standards Organization) that includes size, load, and speed rating together in one easy-to-read format.

SERVICE DESCRIPTION FIGURE 10 Cross-sectional view of a typical tire showing the terminology.

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: • Speedometer reading • Odometer reading • Fuel economy

HIGH-FLOTATION TIRE SIZES • High-flotation tires for light trucks are designed to give improved offroad performance on sand, mud, and soft soil and still provide acceptable hard-road surface performance. • These tires are usually larger than conventional tires and usually require a wider-than-normal wheel width. • High-flotation tires have a size designation such as 33 x 12. 50 R x 15 LT:

HIGH-FLOTATION TIRE SIZES

LOAD INDEX AND EQUIVALENT LOADS • The load index is an abbreviated method to indicate the load-carrying capabilities of a tire. • The weights listed in the chart represent the weight that each tire can safely support. • Multiply this amount by 4 to get the maximum that the vehicle should weigh fully loaded with cargo and passengers.

LOAD INDEX AND EQUIVALENT LOADS FIGURE 11 Typical sidewall markings for load index and speed rating following the tire size.

SPEED RATINGS • Tires are rated according to the maximum sustained speed. • A vehicle should never be driven faster than the speed rating of the tires.

What Does the Little “e” Mean on the Sidewall? • 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).

What Does the Little “e” Mean on the Sidewall? FIGURE 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.

TIRE PRESSURE AND TRACTION • All tires should be inflated to the specifications given by the vehicle manufacturer. • Most vehicles have recommended tire inflation figures written in the owner’s manual or on a placard or sticker on the door post or glove compartment. FIGURE 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.

TIRE CONICITY AND PLY STEER • Tire conicity can occur during the construction of any radial or belted tire when the parts of the tire are badly positioned, causing the tire to be smaller in diameter on one side. • When this tire is installed on a vehicle, it can cause the vehicle to pull to one side of the road due to the cone shape of the tire.

TIRE CONICITY AND PLY STEER FIGURE 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.

TIRE CONICITY AND PLY STEER • Ply steer is another term that describes a slight pulling force on a vehicle due to tire construction. • Ply steer is due to the angle of the cords in the belt layers. FIGURE 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.

VEHICLE HANDLING AND TIRE SLIP ANGLE • The tire surface contact area or tire patch size is about one-half the area of one page of this book. • All accelerating, braking, and cornering forces of a vehicle are transferred to the pavement at just four spots. • The combined area of these four spots is about equal to the size of this opened book.

VEHICLE HANDLING AND TIRE SLIP ANGLE FIGURE 16 Slip angle is the angle between the direction the tire tread is heading and the direction it is pointed.

RIM WIDTH AND TIRE SIZE • As a general rule, for a given rim width it is best not to change tire width more than 10 mm (either wider or narrower). • For a given tire width, it is best not to vary rim width more than 1/2 in. in either direction.

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.

UNIFORM TIRE QUALITY GRADING SYSTEM • The U. S. Department of Transportation (DOT) and the National Highway Traffic Safety Administration (NHTSA) developed a system of tire grading, the Uniform Tire Quality Grading System (UTQGS), to help customers better judge the relative performance of tires. • The three areas of tire performance are tread wear, traction, and temperature resistance.

UNIFORM TIRE QUALITY GRADING SYSTEM FIGURE 17 Typical “Uniform Tire Quality Grading System” (UTQGS) ratings imprinted on the tire sidewall.

UNIFORM TIRE QUALITY GRADING SYSTEM • TREAD WEAR • TRACTION • TEMPERATURE RESISTANCE

ALL-SEASON TIRE DESIGNATION • Most all-season tires are rated and labeled as M & S, MS, or M S, and therefore must adhere to general design features as specified by the Rubber Manufacturers Association (RMA). • Tires labeled M & S are constructed with an aggressive tread design as well as tread compounds and internal construction that are designed for mud and snow. • The tread rubber used to make all-season tires is also more flexible at low temperatures.

DOT TIRE CODE • All tires sold in the United States must be approved by the U. S. Federal Department of Transportation (DOT). • The DOT tire code requirements include resistance to tire damage that could be caused by curbs, chuckholes, and other common occurrences for a tire used on public roads.

DOT TIRE CODE FIGURE 18 Typical DOT date code. This tire was built the sixth week of 2005.

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.

Tire Date Code Information Saved Me Money! • 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.

SPARE TIRES • Most vehicles today come equipped with space-saver spare tires that are smaller than the wheels and tires that are on the vehicle. • The reason for the small size is to reduce the size and weight of the entire vehicle and to increase fuel economy by having the entire vehicle weigh less by not carrying a heavy spare tire and wheel around.

RUN-FLAT TIRES • Run-flat tires (abbreviated RFT) are designed to operate without any air for a limited distance (usually 50 miles at 55 mph). • This feature allows vehicle manufacturers to build vehicles without the extra room and weight of a spare tire and jack assembly. • A typical run-flat tire (also called extended mobility tire [EMT] or zero pressure [ZP] tire) requires the use of an air pressure sensor/transmitter and a dash-mounted receiver to warn the driver that a tire has lost pressure.

RUN-FLAT TIRES FIGURE 19 Cutaway of a run-flat tire showing the reinforced sidewalls and the required pressure sensor.

RUN-FLAT TIRES FIGURE 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.

RUN-FLAT TIRES PAX RUN-FLAT TIRES • Michelin developed a run-flat tire that has three unique components: • A special wheel that has two bead seats that are of different diameters. The outside bead seat is 10 mm smaller in diameter than the inside bead seat. This means that a conventional tire cannot be installed on a PAX-style wheel. • A urethane support ring that is designed to support the weight of the vehicle in the event of a flat tire. • A special tire that is designed to operate without air.

RUN-FLAT TIRES PAX RUN-FLAT TIRES FIGURE 21 The PAX run-flat tire system is composed of three unique components—a special asymmetrical wheel, a urethane support ring, and special tire.

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.

RUN-FLAT TIRES SERVICING A PAX WHEEL/TIRE ASSEMBLY • If a flat tire occurs or when a PAX tire becomes worn and requires replacement, special care should be taken to properly remove the tire from the wheel. • Because the urethane support ring prevents the tire bead from entering the dropped center section of the wheel, the outside bead should be broken from the wheel, and then the support ring removed before the tire can be removed from the wheel.

GENERAL MOTORS TPC RATING • All General Motors original equipment (OE) tires have a rating that identifies the size as well as the tread design, wear, traction, and heat resistance factors. • All of these factors are combined in a set of numbers and letters that is imprinted in the tire mold. • This is referred to as the Tire Performance Criteria (TPC) rating of the tire. • If a customer wants to have the same tire performance in a replacement tire, then replace the tire with any brand of tire that has the same TPC identification.

GENERAL MOTORS TPC RATING FIGURE 22 The Tire Performance Criteria (TPC) specification number is imprinted on the sidewall of all tires used on General Motors vehicles from the factory.

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 EV 1 electric vehicle.

WHEELS • Today’s wheels are constructed of steel or aluminum alloy. • The center section of the wheel that attaches to the hub is called the center section or spider because early wheels used wooden spokes that resembled a spider’s web. The rubber tire attaches to the rim of the wheel. • The rim has two bead flanges where the bead of the tire is held against the wheel when the tire is inflated.

WHEELS FIGURE 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.

WHEELS FIGURE 24 The wheel rim well provides a space for the tire to fit during mounting; the bead seat provides a tiretowheel sealing surface; the flange holds the beads in place.

WHEELS • WHEEL OFFSET • POSITIVE OFFSET • NEGATIVE OFFSET • BACK SPACING • DETERMINING BOLT CIRCLE • STEEL WHEELS • ALUMINUM WHEELS

WHEELS FIGURE 25 A cross section of a wheel showing part designations.

WHEELS FIGURE 26 Offset is the distance between the centerline of the wheel and the wheel mounting surface.

WHEELS FIGURE 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.

WHEELS FIGURE 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.

WHEELS FIGURE 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.

WHEELS FIGURE 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.

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 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.

What Does This Mark in a Wheel Mean? FIGURE 31 A typical JWL symbol for the Japan Wheel Light Metal standard mark.

TIRE VALVES • All tires use a tire valve, called a Schrader valve, to hold air in the tire. • 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 tire experts agree that the valve stem (which includes the Schrader valve) should be replaced whenever tires are replaced— tires can last four or more years, and in that time the valve stem can become brittle and crack.

TIRE VALVES FIGURE 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.

UNSPRUNG WEIGHT • The wheel and tire are unsprung weight because they are not supported by the vehicle’s springs. • If heavy wheels or tires are used, every time the vehicle hits a bump, the wheel is forced upward. • The heavy mass of the wheel and tire would transmit this force through the spring of the vehicle and eventually to the driver and passengers. • Obviously, 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.

LUG NUTS • Lug nuts are used to hold a wheel to the brake disc, brake drum, or wheel bearing assembly. • Typical lug nuts are tapered so that the wheel stud will center the wheel onto the vehicle. • Many alloy wheels use a shank-nut-type lug nut that has straight sides without a taper. FIGURE 33 Various styles of lug nuts.

LUG NUTS SIZE • Lug nuts are sized to the thread size of the stud onto which they screw. • The diameter and the number of threads per inch are commonly stated. • Since 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 -20 RH, where the 7/16 indicates the diameter of the wheel stud and 20 indicates that there are 20 threads per inch.

LUG NUTS LUG STUDS • Lug studs are usually installed in hubs or drums using a press fit. • Serrations on the shoulder of the stud provide support. • Most studs are replaceable and should be replaced if the treads are damaged.

SUMMARY 1. 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. 2. 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. 3. A 205/75 R x 14 92 S 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 x 112 mph maximum sustained).

SUMMARY 4. 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). 5. For best overall handling and satisfaction, always select the same size and type of tire that came on the vehicle when new. 6. Replacement wheels should have the same offset as the factory wheels to prevent abnormal tire wear and/or handling problems. 7. 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.

REVIEW QUESTIONS 1. 2. 3. 4. List the various parts of a tire and explain how a tire is constructed. What is the aspect ratio? List the factors that should be considered when purchasing tires. Explain the three major areas of the Uniform Tire Quality Grading System. 5. How is the proper tire inflation pressure determined?

CHAPTER QUIZ 1. The part of the tire that is under just the tread of a radial tire is called the ____. a. b. c. d. Bead Body (carcass) ply Belt Inner liner

CHAPTER QUIZ 2. The aspect ratio of a tire means ____. a. b. c. d. Its width to diameter of a wheel ratio The ratio of height to width The ratio of width to height The ratio of rolling resistance

CHAPTER QUIZ 3. A tire is labeled 215/60 R 15 x 92 T; the T indicates ____. a. b. c. d. Its speed rating Its tread wear rating Its load rating Its temperature resistance rating

CHAPTER QUIZ 4. The 92 in the tire designation in question 3 refers to the tire’s ____. a. b. c. d. Speed rating Tread wear rating Load rating Temperature resistance rating

CHAPTER QUIZ 5. Radial tires can cause a vehicle to pull to one side while driving. This is called “radial tire pull” and is often due to ____. a. b. c. d. The angle of the body (carcass) plies Tire conicity Tread design Bead design

CHAPTER QUIZ 6. Tire inflation is very important to the safe and economical operation of any vehicle. Technician A says that the pressure should never exceed the maximum pressure imprinted on the sidewall of the tire. Technician B says to inflate the tires to the pressures recommended on the tire information decal or placard on the driver’s door. Which technician is correct? a. b. c. d. Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 7. When purchasing replacement tires, do not change tire width from the stock size by more than ____. a. b. c. d. 10 mm 15 mm 20 mm 25 mm

CHAPTER QUIZ 8. What do the letters JJ mean in a wheel designation size labeled 14 x 7 JJ? a. b. c. d. The offset of the rim The bolt circle code The back spacing of the rim The shape of the flange area

CHAPTER QUIZ 9. Technician A says that a PAX run-flat tire uses a special wheel. Technician B says that a standard tire can be used to replace a PAX run-flat tire. Which technician is correct? a. b. c. d. Technician A only Technician B only Both Technicians A and B Neither Technician A nor B

CHAPTER QUIZ 10. Wheel back spacing is also called ____. a. b. c. d. Rear spacing Positive offset Negative offset Offset