4000 SW Macadam Ave. Portland, OR Phone Fax Orders

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1 4000 SW Macadam Ave. Portland, OR Phone Fax Orders -TIRES- General Information What are they and what do they do? -Tires literally keep your vehicle in touch with the road. Furthermore, tires are the only component on your Porsche that actually stop your vehicle (brakes merely help slow you down). So, needless to say, good tire condition is critical to your safety and to the safety of other vehicles around you. Tires are produced with wear bars that help educate you when your tread depth has reached minimum thickness. Driving on tires that are below the wear bars can cause hydroplaning, a flat tire, and possible tire blow-outs. Be on the lookout for irregular treadwear patterns as well. These can indicate other issues such as misalignment due to faulty tie rod ends or other worn suspension components. -One of the most overlooked aspects of tires is air pressure. Low tire pressure can cause the vehicle to pull to one side or another as well as increase tire wear. As well, the Department of Energy estimates that the average vehicle owner can improve fuel economy by 3.3% by keeping tires properly inflated. So, keep your tires in good condition and they will keep you and your vehicle on the road. -Symptoms of common issues include vehicle pulling, uneven wear, noise and vibration, poor handling or loss of control. Construction materials -The branding on the sidewall of a tire is required to list the materials and number of layers of each material used to reinforce the rubber. A typical tire's basic construction materials are usually presented as follows: TREAD 2 POLYESTER + 2 STEEL + 1 NYLON SIDEWALL 2 POLYESTER -The branding in this example identifies that molded into the rubber under the centerline of the tread lies two radial body plies of polyester cord, two belts of angled steel cord and one circumferential cap ply of nylon cord. It also identifies that in each sidewall at the widest points between the tire's inner and outer sidewalls (tire section width) lies two radial body plies of polyester cord (a continuation of the same two body plies that were listed under the centerline of the tread). -Many high-speed tires use circumferential reinforcements above the steel belts. These are either in the form of belt edge strips (approximately 1-inch wide bands covering only the inner and outer edges of the steel belts), full cap plies (covering the entire width of the steel belts) or

2 a combination of both. However, because belt edge strips are not present under the centerline of the tread, they are never reflected in the basic construction material's branding for the tread area. -Many ultra high performance tires also use fabric or steel cord reinforced sidewalls to increase steering response and cornering stability. However, because sidewall-reinforcing material is not present at the widest points of the tire's sidewalls, they are never reflected in the basic construction materials branding for the sidewall area. Sidewall Markings In addition to the tire's brand and line names (tire model), there is a lot of information provided by the manufacturer on the sidewalls of the tires they produce. While not all information is branded on every tire, the illustration includes the typical information found on many tires. Calculating Approximate Tire Dimensions Most modern passenger car and light truck tires feature size designations that indicate the tire's dimensions in a combination of metric, mathematical and English systems. While this unusual combination of millimeters, percentages and inches is a byproduct of the evolution of global tire specifications, it also provides the ability to calculate/estimate basic tire dimensions.

3 -Example size: 225/45R17 The first three numbers in a typical size (225/45R17) are the tire's indicated section width in millimeters, measured from sidewall to sidewall. -The second pair of numbers (225/45R17) is the tire's aspect ratio or profile. This is a ratio of sidewall height to section width. The section height's measurement can be calculated by multiplying the section width by the aspect ratio. The answer will be the height of one sidewall. For example: 225mm x 0.45 = 101.3mm -The last number (225/45R17) is the diameter of the wheel in inches. -To calculate the overall diameter of a tire, the sidewall height must be multiplied by 2 (remembering that the tire diameter is made up of 2 sidewalls, the one above the wheel and the one below the wheel touching the ground) and add the diameter of the wheel mm mm mm = 634.4mm -WARNING: These calculations (and those provided by all online tire dimension calculators) only reflect nominal tire dimensions, which are often subtly or substantially different than the tire's actual physical size and/or the dimensions provided by the tire manufactures. Drivers working with close fitment tolerances or trying to maintain the original tire diameter of staggered size fitments (similarities or differences) should use the tire manufacturer's specifications for the exact tire(s) they are considering. -Actual Tire Section Width is Dependent on Wheel Width All tire sizes are assigned specific rim widths upon which they are measured (measuring rim), as well as can often be mounted on slightly narrower or wider wheels (rim width range). Therefore, it is important to note that actual tire section width will depend on the wheel width the tire is mounted on. The rule of thumb is that tire section width changes by 0.2" for every 0.5" change in rim width, being reduced if mounted on narrower then measuring wheel and increased when mounted on wider wheels. P-Metric and Euro-Metric tire sizing -What's the difference between the tire sizes of P225/60R16 and 225/60R16? P-metric sized tires were introduced in the United States in the late 70s and are installed on vehicles primarily used to carry passengers including cars, station wagons, sport utility vehicles

4 and even light duty pickup trucks. Their load capacity is based on an engineering formula which takes into account their physical size (the volume of space for air inside the tire) and the amount of air pressure (how tightly the air molecules are compressed). Metric or Euro-metric sized tires are the ones without the "P" at the beginning, (such as 185R14 or the 225/60R16 listed above). Using metric dimensions to reflect a tire's width actually began in Europe in the late 60s. Euro-metric and P-metric tires in the same size (i.e. P225/60R16 & 225/60R16) are equivalent in their dimensions with just slight differences in their load capacity calculations and inflation pressure tables. So if Euro-metric and P-metric tires have the same numeric size, the same tire performance category and the same speed rating, the two are considered equivalent and interchangeable if used in axle pairs or sets of four. How to Read Service Descriptions, Load Index, & Speed Rating -Using a P195/60R15 87S tire size as our example, the 87S at the end of the size represents the tire's service description. A service description identifies the tire's load index and speed rating. Service Descriptions are required on all speed rated (except for Z-speed rated) tires manufactured since The first two digits (87S) represent the tire's load index and are followed by a single letter (87S) identifying the tire's speed rating. -Load Index The load index (87) is the tire size's assigned numerical value used to compare relative load carrying capabilities. In the case of our example the 87 identifies the tires ability to carry approximately 1,201 pounds. The higher the tire's load index number, the greater its load carrying capacity. 88 = 1,235 pounds 87 = 1,201 pounds -A tire with a higher load index than that of the Original Equipment tire indicates an increase in load capacity. Typically, the load indexes of the tires used on passenger cars and light trucks range from 70 to Speed Rating In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met. It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair. The most common tire speed rating symbols, maximum speeds and typical applications are shown below: L 75 mph 120 km/h Off-Road & Light Truck Tires M 81 mph 130 km/h Temporary Spare Tires N 87 mph 140km/h

5 P 93 mph 150 km/h Q 99 mph 160 km/h Studless & Studdable Winter Tires R 106 mph 170 km/h H.D. Light Truck Tires S 112 mph 180 km/h Family Sedans & Vans T 118 mph 190 km/h Family Sedans & Vans U 124 mph 200 km/h H 130 mph 210 km/h Sport Sedans & Coupes V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars -When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities. W 168 mph 270 km/h Exotic Sports Cars Y 186 mph 300 km/h Exotic Sports Cars -While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed. 225/50ZR16 in excess of 149 mph, 240 km/h 205/45ZR17 88W 168 mph, 270 km/h 285/35ZR19 99Y 186 mph, 300 km/h -Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below: 285/35ZR19 99Y 186 mph, 300 km/h 285/35ZR19 (99Y) in excess of 186 mph, 300 km/h Porsche N-Specification Tire Approvals -Sports car tires are very complex products meeting numerous, largely contradictory demands. Finding the proper structure that balances these demands for any given application is the great challenge in tire design. Because of the integral role that tires play in vehicle performance, Porsche has integrated tire development throughout their process of vehicle development. To be an Original Equipment tire provider on a Porsche vehicle or be approved by Porsche for the replacement market requires the joint product development efforts of the tire engineers working alongside the Porsche vehicle engineers. -The focus in recent radial tire development for Porsche vehicles has primarily included optimum handling on dry surfaces and the safest possible behavior on wet surfaces, even at high speeds. Tires developed by various manufacturers, in concert with Porsche, offer a specific set of wet grip properties which few, if any, other automobile manufacturers demand in equal measure from the tires they use on their vehicles. -Tires may be specified for a particular vehicle or range of vehicles and must successfully pass the tire company's laboratory tests to assure that they would be capable of adequately

6 supporting the Porsche vehicle while allowing it to reach its top speed on the German Autobahn. Additional laboratory, test track and race track tests are conducted to confirm that the prototype tires meet Porsche's noise, hydroplaning and handling requirements. Prototype tires will also be evaluated to assess their high-speed durability, uniformity and serviceability. Upon test completion, the tires will be released for production. -Production tires that have passed all of the tests and received the engineering department's release can be branded with an N-specification. The N-specification brandings include: N-0 (Nzero), N-1, N-2, N-3 or N-4. These markings on a tire's sidewall clearly identify them as approved by Porsche for their vehicles. The N-0 marking is assigned to the first approved version of a tire design. As that design is refined externally or internally, the later significant evolutions will result in a new generation of the tire to be branded with N-1, N-2, N-3, etc., in succession. When a completely new tire design is approved, it receives the N-0 branding and the succession begins again. -It is recommended that only matching tires be used on Porsche vehicles. Since many Porsche vehicles are fitted with differently sized tires on their front and rear axles, this means matching the tire make, tire type and N-specification. If a vehicle was originally delivered with N- specification tires that have been discontinued and are no longer available, it is recommended to change all four tires to a higher numeric N-specification design appropriate for that vehicle. Mixed tire types are not permissible. -Tires should be replaced no less than in pairs on one axle at a time. Only tires of the same tire make and type must be used. However, in case of tire damage such as cuts, punctures, cracks or sidewall bulges that cause a single tire to be replaced for safety reasons, the remaining matching tire on that axle must not exceed 30 percent wear. If the remaining tire has more than 30 percent wear from new, it should also be replaced. Handling inconsistencies may result if this is not done. -Initially, new tires do not offer their full traction. Drivers should therefore drive at moderate speeds during the first miles ( km). If new tires are installed on only one axle, a noticeable change in handling occurs due to the different tread depth of the other tires. This happens especially if only rear tires are replaced. However, this condition disappears as new tires are broken in. Drivers should adjust their driving style accordingly. -NOTE: The last two paragraphs are excerpts from recent Porsche vehicle owner's manuals. Uniform Tire Quality Grade (UTQG) Standards -The U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration's (NHTSA) Uniform Tire Quality Grade Standards (UTQG) were originated to provide consumers with useful information to help them purchase tires based on their relative treadwear, traction and temperature capabilities. -Treadwear Grades UTQG Treadwear Grades are based on actual road use in which the test tire is run in a vehicle convoy along with standardized Course Monitoring Tires. The vehicle repeatedly runs a prescribed 400-mile test loop in West Texas for a total of 7,200 miles. The test tire's and the Monitoring Tire's wear are measured during and at the conclusion of the test. The tire manufacturers then assign a Treadwear Grade based on the observed wear rates. The Course Monitoring Tire is assigned a grade and the test tire receives a grade indicating its relative treadwear. A grade of 100 would indicate that the tire tread would last as long as the test tire, 200 would indicate the tread would last twice as long, 300 would indicate three times as long, etc.

7 -Traction Grades UTQG Traction Grades are based on the tire's straight line wet coefficient of traction as the tire skids across the specified test surfaces. The UTQG traction test does not evaluate dry braking, dry cornering, wet cornering, or high speed hydroplaning resistance. The Traction Grade is determined by installing properly inflated test tires on the instrumented axle of a "skid trailer." Traction Grades Asphalt g-force Concrete g-force AA Above A Above B Above C Less Than Temperature (Resistance) Grades The UTQG Temperature Grade indicates the extent to which heat is generated/ or dissipated by a tire. Temperature Grades Speeds in mph A Over 115 B Between 100 to 115 C Between 85 to 100 Looking for new tires When should I replace my tires? -The Law According to most states' laws, tires are legally worn out when they have worn down to 2/32" of remaining tread depth. To help warn drivers that their tires have reached that point, tires sold in North America are required to have molded indicators called "wear bars" across their tread pattern from their outside shoulder to inside shoulder. Wear bars are designed to visually connect the elements of the tire's tread pattern and warn drivers when their tires no longer meet minimum tread depth requirements. -Common Sense However, as a tire wears it is important to realize that while its dry traction and handling will improve its ability to perform in rain and snow will diminish. At 2/32" of remaining tread depth, resistance to hydroplaning in the rain at highway speeds has been significantly reduced and traction in heavy snow has been virtually eliminated. If rain and wet roads are a concern, you should consider replacing your tires when they reach approximately 4/32" of remaining tread depth. Since water can't be compressed, you need enough tread depth to allow it to escape through the tire's grooves. If the water can't escape fast enough your vehicle's tires will be forced to hydroplane (actually float) on top of the water, loosing traction. -If snow covered roads are a concern, you should consider replacing your tires when they reach approximately 6/32" of remaining tread depth to maintain good mobility. The reason that you need more tread depth in snow is because your tires need to compress the snow in their grooves and release it as they roll. Because tread depth is an important element for snow

8 traction, winter tires start with deeper tread depths than standard all-season or summer tires. Some winter tires even have a series of wear bars molded in their tread pattern indicating approximately 6/32" remaining tread depth. Measuring Tire Tread Depth with a Coin -U.S. coins can be substituted for a tire tread depth gauge as tires wear to the critical final few 32nds of an inch of their remaining tread depth. Place a penny into several tread grooves across the tire. If part of Lincoln's head is always covered by the tread, you have more than 2/32" of tread depth remaining. 2/32" remaining tread depth shown Place a quarter into several tread grooves across the tire. If part of Washington's head is always covered by the tread, you have more than 4/32" of tread depth remaining. 4/32" remaining tread depth shown Place a penny into several tread grooves across the tire. If the top of the Lincoln Memorial is always covered by the tread, you have more than 6/32" of tread depth remaining. 6/32" remaining tread depth -Once you have determined the approximate remaining tread depth in the first location, you can complete your measurement of each tire by placing the coin into additional locations at least 15 inches apart around the tire's central circumferential groove, as well as in its inner and outer grooves. This will help detect uneven wear caused by mechanical or service conditions. Measuring Tire Tread Depth with a Tire Gauge -While U.S. coins can be used to estimate remaining tread depth as a tire approaches the end of its useful life, the established method of measuring remaining tread depth in the U.S. is with a gauge that reads in 32nds of an inch (other countries measure tread depth in millimeters). Typical tire tread depth gauges measure up to 32/32nds (or 25-26mm) since almost all passenger car and light truck tires begin with less than one inch of tread depth. -To use a tread depth gauge, follow the steps below.

9 STEP 1; Confirm which measuring scale you are using. Some tread depth gauges measure in 32nds of an inch (left), while others measure in both 32nds of an inch and millimeters (right). STEP 2; Push the tread depth gauge against a hard, flat surface to confirm it "zeros out" when fully compressed. STEP 3; Push the measuring scale into the gauge as far as it will go. STEP 4; Place the probe into the center of a circumferential tire groove and push down on the gauge's base.

10 STEP 5; Do not place the probe on the molded tread wear indicators or on any raised surfaces of the tread design. STEP 6; Carefully remove gauge by holding its barrel (without touching the probe) and confirm the tread depth reading. STEP 7; Place the probe into additional locations around the central circumferential tire groove at lease 15 inches apart and repeat. STEP 8; Place the probe into the inner and outer circumferential grooves and repeat. STEP 9; Average all readings. STEP 10; Identify the percentage of tire wear by confirming the tire's original/new tread depth in its specs compared to the remaining tread depth just measured. NOTE; Incorrect air pressure, vehicle alignment, loose or worn parts, driving conditions, load, etc, can cause rapid or uneven tire wear. An accurate tread depth gauge can detect developing wear patterns earlier than simply looking at the tread. This often allows the cause to be identified and corrected before excessive or irregular tread wear ruins the tire. Determining the Age of a Tire -When it comes to determining the age of a tire, it is easy to identify when a tire was manufactured by reading its Tire Identification Number (often referred to as the tire s serial number). Tire Identification Numbers are really batch codes that identify the week and year the tire was produced. The U.S. Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) requires that Tire Identification Numbers be a combination of the letters DOT, followed by ten, eleven or twelve letters and/or numbers that identify the manufacturing location, tire size and manufacturer's code, along with the week and year the tire was manufactured. -Tires Manufactured Since 2000 Since 2000, the week and year the tire was produced has been provided by the last four digits of the Tire Identification Number with the 2 digits being used to identify the week immediately followed by the 2 digits used to identify the year. Example of a tire manufactured since 2000 with the current Tire Identification Number format:

11 In the example above: DOT U2LL LMLR Manufactured during the 51 st week of the year 07 Manufactured during Tires Manufactured Before 2000 The Tire Identification Number for tires produced prior to 2000 was based on the assumption that tires would not be in service for ten years. While they were required to provide the same information as today s tires, the week and year the tire was produced was contained in the last three digits. The 2 digits used to identify the week a tire was manufactured immediately followed by a single digit used to identify the year. Example of a tire manufactured before 2000 with the earlier Tire Identification Number format: In the example above: DOT EJ8J DFM Manufactured during the 40 th week of the year 8 Manufactured during the 8 th year of the decade -While the previous Tire Identification Number format identified that a tire was built in the 8th year of a decade, there was no universal identifier that confirmed which decade (tires produced in the 1990s may have a small triangle following the Tire Identification Number to identify the decade). -Nothing Lasts Forever...and Tires Are No Exception Tires are manufactured by bonding rubber to fabric plies and steel cords. And despite the antiaging ingredients mixed into the rubber compounds, there is a realization that tires are perishable, as well as a growing awareness that some tires will actually age out before their treads will wear out. -For the most part today's tires deliver more miles and years of service than ever before. In the 1970s, typical bias ply tires lasted less than 20,000miles and were only expected to be in service for about two years. While passenger car and light truck tire technology and American driving conditions in the past resulted in tire treads wearing out before the rest of the tire aged, it may

12 not always be true of today's even longer lasting tires that are approaching 80,000 miles of treadwear. -How many years will tires last before aging out? Our experience has been that when properly stored and cared for, most street tires have a useful life in service of between six to ten years. Selecting the correct tires -Selecting the right tires for your vehicle is an important decision. Your safety, as well as driving enjoyment over the next years and thousands of miles will be determined by this decision. The information provided here and the advice/recommendations from us and the experts at the Tire Rack will ensure you select tires that match your vehicle...and the way you drive it! What is the right size for my vehicle? -For cars and vans, staying within a 3% diameter change is desirable. Pick-ups and sport utility vehicles (SUVs) are usually engineered to handle up to a 15% oversize tire. Most tire dimensions can be calculated. While at first a 3% diameter increase or reduction in tire diameter may sound very limiting, in most cases it allows approximately a 3/4" diameter change. -Additionally to help with the selection of substitute sizes, a system called "Plus Sizing" was developed. We use Plus Sizing to take into account the diameters of the available tires and the wheels, and then helps select the appropriate tire width that ensures adequate load capacity. Maintaining the tire's overall diameter helps maintain accurate speed data going into the computer. Do I need summer tires, winter tires, all-season tires? -Ask yourself these questions to determine which performance category you should choose from: -What is the worst driving condition I will encounter? -What are the typical driving conditions I will encounter? -Balancing the requirements of your driving conditions. -If your worst driving conditions and your typical conditions are similar, one set of tires will be all you need. If you live at the edge of the snowbelt and infrequently get snow you may want to select an all-season tire. If your worst driving condition occurs frequently (you drive through snow all winter) and is dissimilar to your typical driving condition (you commute to work on the expressway during the week and spend your weekends at the beach), you may want to consider selecting two sets of tires for your vehicle. Each set will be designed to master the specific conditions without compromising your driving satisfaction at the extremes. While purchasing two sets of tires may appear expensive, the set you're not using won't wear while you are using the other set, and combined they'll provide longer total wear than either set could individually! Mixing tires -Since tires affect the personality and performance of your vehicle, all four tires should be as identical as possible or handling problems may arise. If your tires don't match, it is possible that one end of your vehicle won't respond as quickly or completely as the other, making it more difficult to control. -As a general rule, tires should not be mixed on any vehicle unless specified as acceptable by the tire or vehicle manufacturer. Drivers should avoid mixing tires with different tread patterns, internal constructions or sizes, and use identical tires on all of their vehicle's wheel positions in order to maintain the best control and stability. Additionally, drivers should never mix winter tires with all-season/summer tires, or mix run-flat tires with non-run-flat tires.

13 -Because tires play such an important role in every vehicle's comfort qualities and handling capabilities, it is always best to drive on tires that are identical in every detail, including tire brand, model, size and remaining tread depth. Anything else involves some type of compromise. How do I compare price vs. value? -Why is it that the price of fuel for our vehicle seems relatively inexpensive while the cost of its tires seems high? If we keep track of our total costs, we will find that typical total fuel costs for just 10,000-20,000 miles of driving actually exceed our tire costs. And believe us, we've found that the quality and performance of our tires has a lot more to do with our driving satisfaction than our fuel does. -When you are selecting new tires and find one that is perfect, although more expensive than another tire that appears to be a close second; consider evaluating your situation by comparing "how much per mile" each tire will cost. If you plan to drive your vehicle another 30,000 miles and are considering the "perfect" tires at $100 each, and the other at $90 each; you may be surprised to find out that the cost of the "perfect" set costs just 1.3 cents per mile...while the close set costs 1.2 cents per mile. Will saving the $40 today make up for not having selected the "perfect" tire that you will be driving on for the next two years? Breaking In Your Tires -Since tires are comprised of many layers of rubber, steel and fabric, your new tires require a break-in period to ensure that they deliver their normal ride quality and maximum performance. As tires are cured, a release lubricant is applied to prevent them from sticking in their mold. Some of the lubricant stays on the surface of your tires, reducing traction until it is worn away. Five hundred miles of easy acceleration, cornering and braking will allow the mold release lubricant to wear off, allowing the other tire components to begin working together. It is also important to note that your old tires probably had very little tread depth remaining when you felt it was time to replace them. As any autocrosser or racer who has tread rubber shaved off of his tires will tell you, low tread depth tires respond more quickly. Don't be surprised if your new tires are a little slower to respond. -NOTE: Be careful whenever you explore the capabilities of your new tires. Remember that every tire requires a break-in period of 500 miles for optimum performance. Tire Maintenance Tire Pressures -Under-inflated tires not only cost you at the pump but also cost you in regards to tire wear and can potentially cause an accident due to a tire blow-out. For every 1psi that all four tires are under-inflated, MPG is reduced by an average of 0.4%. U.S. Department of Energy data; Fuel economy benefit: up to 3% Equivalent gasoline savings: up to $0.09/gallon -We recommend checking your tire pressures(including your spare) at least every other week. If you are unsure on which tire pressures to run on your vehicle, simply check the sticker on your driver s door jamb(b-pillar) or in your owner s manual. Keep in mind that these pressures are for full load(people and gear), so modify your pressures accordingly if you don t carry a full load. The tire pressures should be set when the tires are cold.

14 Checking Tire Inflation Pressure -Regardless of its size, every tire's load capacity, durability, traction and handling is dependent on using the right inflation pressure for the application. Since both too little and too much inflation pressure sacrifices some of the tires' performance, maintaining the "right" inflation pressure is very important. -The pounds per square inch (psi) pressure number branded on the tire's sidewall identifies the maximum cold inflation pressure that specific tire is rated to hold. However, the tire's maximum pressure is not necessarily the correct pressure for every vehicle upon which the tire can be used (almost all vehicle manufacturers' recommended tire inflation pressures are less than the tires' maximum pressure). Therefore when checking and adjusting tire inflation pressures, the "right" inflation pressures are those provided by the vehicle manufacturer, not the "maximum" inflation pressure branded on the tire's sidewall. The vehicle manufacturer's pressure recommendation can be found on the vehicle's tire information placard label, as well as in the vehicle owner's manual. -If a vehicle does not have a B-pillar, then the placard is to be placed on the rear edge of the driver's door. And if the vehicle does not have a B-pillar and the driver's door edge is too narrow, the placard is to be affixed on an inward facing surface next to the driver's seating position. For vehicles produced between 1968 and 2003, the original tires size(s) and inflation pressures (including the spare) are listed on a vehicle placard. Earlier placards can typically be found on: The driver-side door or doorjamb, Fuel filler door, Glove box or center console door, The engine compartment. Air Pressure - Correct, Underinflated and Overinflated -Advantages of Correct Tire Inflation Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling. -Disadvantages of Underinflation An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle s tires are underinflated by only 6 psi, it could lead to tire failure. Additionally, the tire s tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. -Disadvantages of Overinflation An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. Higher inflated tires cannot isolate road irregularities well, causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures. Air Pressure, Temperature Fluctuations

15 -Your tires support the weight of your vehicle, right? No they don't! It's the air pressure inside them that actually supports the weight. Maintaining sufficient air pressure is required if your tires are to provide all of the handling, traction and durability of which they are capable. However, you can't set tire pressure...and then forget about it! Tire pressure has to be checked periodically to assure that the influences of time, changes in ambient temperatures or a small tread puncture have not caused it to change. -The tire pressure recommended in your vehicle's owner's manual or tire information placard is the vehicle's recommended cold tire inflation pressure. This means that it should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it. Since air is a gas, it expands when heated and contracts when cooled. In most parts of North America, this makes fall and early winter months the most critical times to check inflation pressures...days are getting shorter...ambient temperatures are getting colder...and your tires' inflation pressure is going down! -The rule of thumb is for every 10 Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower). Air Pressure, Time Fluctuations -While tires appear solid, the molecular structure of the rubber used to manufacturer them actually looks like strands of cooked spaghetti stuck together. These molecular strands are stretched and returned to their relaxed state every time the tire rolls (about 800 times every mile). -Since typical tire pressures range from 30 to 35 psi for cars (with light truck tire pressures often higher), there is a constant force trying to push the air through the tire. This allows some of the air to escape (called permeation or diffusion) right through the microscopic spaces between the rubber molecules. And somewhat like a rubber balloon, the air will eventually escape if it is not replenished. -All things being equal, a tire's inflation pressure will go down by about 1 psi every month. This means that if air isn't added for two to three months, the tire's inflation pressures will probably be 2 to 3 psi low. -In order to help maintain more constant tire pressures we should check them more frequently. Once a month and before trips is the minimum, once a week is preferred. This will allow us to refill lost pressure that escapes over time, as well as discover any pressure losses due to slow leaks caused by minor punctures before significant pressure is lost and the tire's internal structure is damaged. Air Pressure: When and How to Set -Check and Adjust First Thing In The Morning. This must be done before rising ambient temperatures, the sun's radiant heat or even driving short distances temporarily warms the tires. -Indoor-to-outdoor Temperature Variation. Significant differences between the conditions tire pressures are set (the warmth of an attached garage, heated garage or service shop) and in which the vehicle will be driven (winter's subfreezing temperatures) requires inflating tires 1 psi

16 higher than recommended on the placard for every 10 F difference in temperature between interior and exterior temperatures. -Afternoon Ambient Temperature Increase.* Set 2 psi above vehicle manufacturer's cold inflation recommendations when installing new tires or if the vehicle has been parked in the shade for a few hours. -Tire Heat Generated While Being Driven (or at speeds of less than 45 mph).* - Set 4 psi above vehicle manufacturer's cold inflation recommendations. -Heat Generated While Being Driven Extensively (or at sustained speeds greater than 45 mph).* Set 6 psi above vehicle manufacturer's cold inflation recommendations. *NOTE: Tires on a parked vehicle exposed to direct sunlight will appear overinflated due to the heat absorbed from the radiant energy of the sun. Pressures cannot be accurately set on these tires until all have stabilized in the shade. Air Pressure vs. Dry Performance -Underinflation has a significant impact on tire wear, rolling resistance and durability, as well as a noticeable influence on how quickly and precisely the tires respond to the driver's input. The tires installed on one of TireRack s BMW 330Ci test cars were inflated to the vehicle manufacturer's recommended inflation pressures of 29 psi front and 33 psi rear, while the other car had its tires inflated 30% lower (20 psi in the front and 23 psi in the rear). -The underinflated tires delivered acceptable steady-state cornering force once they stabilized on our test track's skid pad, but the car was uncooperative anytime it was asked to change directions. It proved to be over 2 seconds slower around their test course (2 seconds represents about a 7% loss of handling performance). Air Pressure vs. Wet Performance -An underinflated tire will tend to wear the shoulder areas of the tread faster than the center. This is because there is insufficient air pressure to allow the center of the tread to carry its fair share of the weight. Underinflation has a significant impact on tire wear, rolling resistance and durability, as well as a noticeable influence on how effectively the tires can resist hydroplaning to maintain wet traction. -One of the ways tire manufacturers evaluate their products' hydroplaning and wet traction effectiveness is by driving them over a glass plate covered with a specific depth of water. The water is dyed for better visibility and to allow high-speed cameras in underground rooms to photograph the tires from below. Michelin has provided several photographs of its HydroEdge premium All-Season tire to help illustrate this tech feature. This photograph shows a tire properly inflated to 35 psi sitting still in the water on the glass plate. This provides an accurate idea of the tire's footprint size and shape. The black area is where the tire's rubber compound is pressed on the glass, and the green areas identify water in the tire's circumferential and high-angle lateral grooves, and on the remainder of the glass plate.

17 A properly inflated tire will have enough pressure in the center of its tread to resist collapsing. This picture is of a tire properly inflated to 35 psi, driving across the glass at 60 miles per hour. You will notice that the footprint still shows good contact with the plate, but is slightly smaller than the static tire's footprint. A tire that is slightly underinflated will apply less pressure to the center of the tread and it will become slightly concave. This picture is of a tire inflated to only 30 psi, again driving across the glass at 60 miles per hour. With the same amount of standing water on the plate, the center of the tire's tread is lifted as the tread design unsuccessfully attempts to evacuate water as the tire rolls across the plate. You will notice that the actual footprint shows poor contact with the plate and is significantly smaller than the footprint in the photograph of the properly inflated tire. A tire that is significantly underinflated will allow the center of the tread to collapse and become very concave, trapping water rather than flowing it through the tread design. This final picture is of a tire inflated to only 25 psi, driving across the glass plate at 60 miles per hour. With the same amount of standing water, the water lifts the center of the tire's tread as its footprint rolls across the plate. You will notice that the actual footprint shows little contact with the plate and has been virtually reduced to the shoulder areas. -While driving at the edge of a tire's ability in wet conditions is challenging, the car with the properly inflated tires provide handling that was predictable. Driving the car with the underinflated rear tires proved to be much more difficult to drive and forced the driver to slow down to retain control, producing lap times that were several seconds slower than the properly inflated car. Hydroplaning: The Role Tires Play -Hydroplaning happens when one or more tires is lifted from the road by a wedge of water that gets trapped in front of and under a tire as the vehicle drives through water. Hydroplaning most frequently occurs during heavy rainstorms when water creates puddles on the highway or expressway. -As a rule, tread design affects hydroplaning resistance at high speeds and in deep water. Tread compound affects wet traction at lower speeds or in shallow water. -Directional tread designs (sometimes called Unidirectional tread designs) are frequently used on tires intended to better resist hydroplaning. Their multiple tread grooves are aligned in a repeating "V" shape to increase the tire s ability to channel water from between the tire s footprint and the road. Somewhat like the vanes of a water pump continually pushing water in one direction through the engine, the grooves of a directional tire are designed to push water in

18 one direction through the tire (forward on an angle to the sides). Directional tread designs are especially helpful in increasing hydroplaning resistance when relatively wide Plus Two, Plus Three or Plus Four tire and wheel applications result in fitting a much wider tire to a vehicle than its Original Equipment size. Air Pressure/Load Adjustment for High Speed Driving -Beginning with the vehicle manufacturer's recommended tire pressure for normal highway conditions, tire inflation pressures are initially increased and then the tire's rated load capacities (branded on the sidewalls) are reduced as speeds climb. -In the example shown below, the vehicle manufacturer's recommended 35 psi for a 225/45R17 91W Standard Load tire installed on a vehicle initially rises in 1.5 psi increments for every 10 km/h (6.2 mph) increase in speed until the inflation pressures max out with an increase of 7.5 psi when the vehicle's top speed has increased 50 km/h (31mph). Then as the vehicle's top speed continues to climb, the rated load capacity of the tire is reduced in 5% increments for every additional 10 km/h until the vehicle's top speed has increased an additional 30 km/h (18.6 mph). For W-Speed Rated Tires Vehicle Top Speed mph km/h psi Required Tire Pressure Increase bar Tire Load Capacity % of Branded Maximum % of value branded on sidewall W-Speed Rated Tire 35 psi O.E. Example % % % % % % % % % NOTE: Never exceed the maximum cold inflation pressure branded on the tire's sidewall. Clearing the Air About Nitrogen Tire Inflation -Tires are typically inflated with air that s a combination of roughly 78% nitrogen (N 2 ), 21% oxygen (O 2 ) and 1% miscellaneous gases. And since all gasses expand when heated and contract when cooled, tire inflation pressures rise and fall with changes in temperature by about one psi (pound per square inch) for every 10 Fahrenheit change in temperature. -Fortunately compressed air is often available at gas stations, tire stores and auto repair shops. Unfortunately the compressed air often provided contains varying degrees of moisture depending on relative humidity and the compressor system s ability to dry the air by removing moisture. So what can we do to help maintain more constant tire pressures? We could change what we inflate our tires with. Nitrogen molecules have a more difficult time escaping through the microscopic spaces that exist between a tire's rubber molecules. psi lbs.

19 -Pure nitrogen has been used to inflate critical tire applications for years, primarily because it doesn't support moisture. These include racing tires (IndyCar, Formula 1, NASCAR), aircraft tires (commercial and military) and heavy-duty equipment tires (earthmovers and mining equipment). The challenge facing nitrogen inflation hasn't been its application, it's been its method of supply and cost. -What are the effects of using pure nitrogen to inflate tires? Nitrogen is a gas and is still affected by changes in ambient temperature (about one psi for every 10 Fahrenheit). Nitrogen filled tires will require pressure be added during the fall/winter months as ambient temperatures and tire pressures drop. Nitrogen is good but can't change the laws of physics. -Nitrogen reduces the loss of tire pressure due to permeation through rubber over time by about 1/3. This helps maintain the vehicle's required tire pressures a little longer, but doesn t eliminate the need for monthly tire pressure checks. This is good for people who don t maintain their vehicles well. -Nitrogen is non-corrosive and will reduce oxidation and rust due to the absence of oxygen and moisture. This will help minimize wheel corrosion to promote better bead sealing. Tires that are used routinely will be replaced long before any life benefit would be received by using Nitrogen. This is most beneficial for drivers who drive their vehicles infrequently (car collectors, track drivers, snow tire users, motor home owners, etc). -Nitrogen assures more consistent pressure increases due to increases in operating temperatures in a racing environment because of the absence of moisture. This is especially good for participants in track days, high-performance drivers education schools and road racing. Drivers should use standard air if pressure adjustments are required when a local source of nitrogen can t be found during a trip. While this reduces the benefit of higher nitrogen content, it is far better than running the tires underinflated in search of a source. This is the main reason we don't feel that nitrogen is worth the money; most commercial air lines will have some moisture in them, reducing nitrogen's advantages. -So what should drivers do? Overall, inflating tires with nitrogen won't hurt them and may provide some minimal benefits. Is it worth it? If you go someplace that provides free nitrogen with new tires, why not? Rather than pay extra for nitrogen, most drivers would be better off buying an accurate tire pressure gauge and checking and adjusting their tire pressures regularly. Tire Pressure Monitoring Systems (Direct vs. Indirect) -The United States Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) has developed a Federal Motor Vehicle Safety Standard that requires the installation of tire pressure monitoring systems (TPMS) that warn the driver when a tire is significantly underinflated. The standard applies to passenger cars, trucks, multipurpose passenger vehicles and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle. -Maintaining the correct tire pressure for a vehicle is an important factor in how much load its tires can safely carry. The correct pressure will carry the weight without a problem. Too little tire pressure will eventually cause catastrophic tire failure. -Tires aren't invincible. If a tire is allowed to run low on air pressure, the rubber is forced to stretch beyond the elastic limits of the fabric and steel reinforcing cords. When this happens, the bond between the various materials can weaken. If this is allowed to continue, it will

20 eventually break the bonds between the various materials and cause the tire to fail. And even if the tire doesn't fail immediately, once a tire is weakened it won't heal after being reinflated to the proper pressure. So if a tire has been allowed to run nearly flat for a period of time, the tire should be replaced, not simply repaired or reinflated. -Studies have shown that running tires with too little air pressure is not uncommon. It's been estimated that about one out of every four vehicles on the road is running on underinflated tires. This also means that one out of every four drivers is needlessly sacrificing their vehicle's fuel economy and handling, and reducing their tires' durability and tread life. This has made tire pressure maintenance an important safety issue throughout the automotive industry and caused the U.S. government to pass legislation mandating tire pressure monitoring systems. The main purpose of these systems is to warn the driver if their tires are losing air pressure, leaving the tires underinflated and dangerous. -The National Highway Traffic Safety Administration (NHTSA) provides vehicle manufacturers options with which they can comply with the law. One option is to install a direct tire pressure monitoring system that uses pressure sensors located in each wheel to directly measure the pressure in each tire and warns drivers when the air pressure in any of their tires drops at least 25% below the recommended cold tire inflation pressure identified on the vehicle placard. Another option is to install an indirect tire pressure monitoring system that would warn the driver when a single tire has lost at least 25% of its inflation pressure compared to other tires on the vehicle. While direct systems could offer more precise warning thresholds, indirect systems cannot offer the same information or accuracy. What s the difference? Direct vs. Indirect -Direct Monitoring Systems Direct systems are typically more accurate and reliable and most are able to indicate which tire is underinflated. -Direct tire pressure monitoring systems measure, identify and warn the driver of low pressure. Because direct systems have a sensor in each wheel, they generate accurate warnings and can alert the driver instantly if the pressure in any one tire falls below a predetermined level due to rapid air loss caused by a puncture. In addition, direct tire pressure monitoring systems can detect gradual air loss over time. Some direct systems use dashboard displays that provide the ability to check current tire pressures from the driver's seat. -Direct systems attach a pressure sensor/transmitter to the vehicle's wheel inside the tire's air chamber. Most Original Equipment and some aftermarket systems attach their air pressure sensor/transmitter to special tire valves. The transmitter's signal is broadcast to the in-car receiver and the information is displayed to the driver. -Indirect Monitoring Systems In the interest of providing a lower cost Original Equipment system, indirect tire pressure monitoring systems were developed by vehicle manufacturers wishing to comply with the law while minimizing development time and cost. -Indirect systems use the vehicle's antilock braking system's wheel speed sensors to compare the rotational speed of one tire to that in another position on the vehicle. If one tire is low on pressure, its circumference changes enough to roll at a slightly different number of revolutions per mile than the other three tires and alert the vehicle s onboard computer. Indirect systems (except for the TPMS on several Audi models and Volkswagen models) are unable to generate accurate readings in cases where all four tires are losing pressure at the same rate,