Reading Your Sidewall There is a lot to learn from the sidewall of your tire. Although at first glance you may think you stumbled across tire hieroglyphics, you've actually found molded into the tires side its own user manual.
Example Tire Size: P205/55R16 91W P identifies your tire as a Passenger Tire. The P stands for PMetric. If your tire size starts with LT rather than a P than it identifies the tire as a light truck tire. 205 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which it is fitted.
(There are 25.4 millimeters per 1 inch.)
55 is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. For example, this aspect ratio of 55 means that the tire's section height is 55% of the tire's section width.
R indicates the construction used within the tire's casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.
16 The last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.
Load Index and Speed Rating
91 The load index and speed rating, or service description, are the numbers that follow the tire size.
The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 - 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On each U.S. passenger car tire, the load limit is listed in pounds. European tires have the load limit listed in kilograms and sometimes pounds.
W Speed ratings are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a maximum speed of 112 mph. Even though a tire can perform at this speed, continental tire does not advocate exceeding legal speed limits. DOT Serial Number The "DOT" symbol certifies the tire manufacturer's compliance with the U.S. Department of Transportation tire safety standards. Tires made in the United States have the DOT serial number located on the inside sidewall near the rim.
Below is a description of the serial number. Starting with the year 2000, four numbers are used for the Date of Manufacture, the first two numbers identify the week and the last two numbers identify the year of manufacture.
Prior to year 2000, three numbers are used for the Date of manufacture, first two numbers identify the week and the last number identifies the year of manufacture. To identify tires manufactured in the 90s, a decade symbol (a triangle on its side) is located at the end of the DOT serial number.
How to Build a Radial Tire Tires are not just round and black -- they are sophisticated products that can take years of research and development to produce. If you have ever wondered how tires are made, the following is a roadmap for the construction of a radial tire:
Start with Rubber and Additives Tire construction starts when raw chemical additives such as sulfur, carbon black and solvents are combined with natural and synthetic rubber. The process takes place in a large machine called a banbury.
In addition to mixing and grinding, the banbury heats the rubber to make it workable in preparation for further applications. The raw product emerges in the form of long, flat bands of rubber, which are then worked in rolling mills.
Six Main Components
The Green Tire The six components (tread, ply, belts, sidewalls, liner and beads) come together on the tire-building machine. These six components are assembled into what is known as an uncured, or green, tire in two stages.
The carcass of the tire, including beads, plies, sidewalls and liner, is constructed on one side of the machine. The tread and the underlying belts are assembled next to the carcass on the other side of the machine. The two sub-assemblies are then joined together and the result is a green tire.
Vulcanization The next phase is vulcanization, the molecular transformation of the soft, gummy green tire into the tough, and long-wearing, modern passenger tire. The green tire is placed in a curing mold and is subjected to intense pressure and high heat internally and externally for a specified period of time. Simultaneously, the tread pattern is imprinted onto the rubber. When it comes from the mold, the tire is ready for final finish and inspection.
Final Finish and Inspection For showroom quality, any excess rubber is trimmed off the cured tire. Every tire is thoroughly inspected. The tire then undergoes various uniformity checks to assess ride and comfort quality. Once the tires have passed all the checks and inspections, they are sent to the distribution warehouse for shipment. History of the Passenger Tire Dateline 3500 B.C.--Today, man invented the greatest invention ever seen, THE WHEEL!
Thousands of years later, the wheel has come a long way. For one thing, it is no longer made of wood and it is guaranteed that the ride is much smoother. What hasn't changed is the fact that it is still one of man's greatest inventions. Could you imagine where we would be today without it?
The early wheel was very simple: a solid curved piece of wood. Later, leather was added to soften the ride. As time progressed it became solid rubber, which led to today's tire--the pneumatic, or air inflated, radial tire.
The first wheels made of metal or wood were very durable but did not provide a very comfortable ride. The nearest thing to the first tire was a metal hoop. There were many individuals that made contributions in creating the tire as we think of it today.
Vulcanization and Charles Goodyear Rubber was not always as useful as it is today. Early rubber did not hold shape; it would be sticky in hot weather and become inflexible in the cold.
In 1839 Charles Goodyear was credited with the discovery of the vulcanization process. Vulcanization is the process of heating rubber with sulfur. This transforms sticky raw rubber to firm pliable material, which makes rubber a perfect material for tires.
The story of Charles Goodyear is a sad one. Although he dedicated his entire life to making rubber a better form, he would never profit from all his work. Charles Goodyear died bankrupt.
Forty years later, a rubber company would honor his hard work by using his name for their new tire company.
Solid Rubber Tires Soon after the discovery of vulcanization, tires were made out of solid rubber. These tires were strong, absorbed shocks and resisted cuts and abrasions. Although they were a vast improvement, these tires were very heavy and did not provide a smooth ride.
Today there are still types of tires made of solid rubber.
Pneumatic Tires The pneumatic tire uses rubber and enclosed air to reduce vibration and improve traction. Robert W. Thomson, a Scottish engineer, first patented the air-filled tire. Unfortunately the idea was too early for its time and was not a commercial success.
In 1888 John Boyd Dunlop of Belfast, Ireland, became the second inventor of the pneumatic tire. Dunlop claimed to have no knowledge of Thomson's earlier invention.
The second time around, the pneumatic tire caught the public's attention. The timing was perfect because bicycles were becoming extremely popular and the lighter tire provided a much better ride.
Bias Ply Tires For the next fifty years, vehicle tires were made up of an inner tube that contained compressed air and an outer casing. This casing protected the inner tube and provided the tire with traction.
Layers called plies reinforced the casing. The plies were made of rubberized fabric cords that were embedded in the rubber. These tires were known as bias ply tires. They were named bias ply because the cords in a single ply run diagonally from the beads on one inner rim to the beads on the other. However, the orientation of the cords is reversed from ply to ply so that the cords crisscross each other.
Today you can still find bias-ply tires as authentic equipment for antique and collector cars, as well as for certain type of off-the-road tractor tires.
Radial Tires The first introduced steel-belted radial tires appeared in Europe in 1948. Radial tires are so named because the ply cords radiate at a 90 degree angle from the wheel rim, and the casing is strengthened by a belt of steel fabric that runs around the circumference of the tire.
Radial tire ply cords are made of nylon, rayon or polyester. The advantages of radial tires include longer tread life, better steering and less rolling resistance, which increases gas mileage. On the other hand, radials have a harder riding quality and are about twice as expensive to make.
Driving Tips for Wet Roads Driving in the rain can be dangerous; in fact thousands of car accidents each year are caused by wet driving conditions.
Routinely Check Your Tires It is a good idea to always check your tires before you hit the road. To ensure your tires are working at their best, make sure you do the following routine maintenance:
Recover From a Skid Skids can even happen to the most cautious drivers. If your car does skid, remember not to slam on the brakes, and do not pump the brakes if you have an anti-lock braking system (ABS). Instead apply pressure to the brakes in a firm manner and steer the car in the direction of the skid.
Keep a Safe Distance It takes about three times longer to break on wet roads than on dry roads. Since more distance is required to brake, it is important not to tailgate. Keep more than two car lengths between you and the vehicle in front of you.
Recover from Hydroplaning When it rains, water creates a barrier between the road and your tires. The liquid film that forms can cause you to lose traction and glide or hydroplane across the water's surface. If this happens, do not brake. It is better to take your foot off the gas, hold the steering wheel in place, and lightly apply the brakes. If you have a manual transmission, push in the clutch and let the car slow down on its own. Maintenance Your tires are the only part of your vehicle that actually touches the road when you drive. It only takes a couple of minutes of maintenance each month to keep your tires working at their best.
Check Your Air Pressure Once a Month Incorrect air pressure is the leading cause of tire damage. To avoid tire damage you need to check your tire's air pressure once a month.
The correct tire pressure can be found in the following places:
Don't get stranded and avoid costly towing expenses. Check your air pressure on your spare regularly. Note: If you have different rims than came on your vehicle originally, make sure that the bolts on your spare tire are the correct fitting.
Failure to keep your tires properly inflated can increase wear and will have a negative effect on your vehicles handling.
When checking and adjusting tire pressure, the following should be kept in mind:
Tread Depth To prevent hydroplaning and skidding, your tires must have proper tread depth. The minimum tread depth is 1/16th of an inch.
Ask anyone: the easiest way to check your tread depth is the penny test. Take a penny and place it in the tread of your tire. If part of Lincoln's head is covered by the tread, your tires have enough tread. If you can see Lincoln's entire head, you should buy a new tire.
You should also check your tire tread for uneven wear. Irregular wear shortens the life of your tires. If you think you have uneven wear, you should take you vehicle to Tireman.
Rotation The best way to prevent uneven wear is to have your tires rotated every 5,000 - 7,000 miles or as specified in your vehicle's owner manual.
Potential Tire Troubles
You should replace your tires with the same type of tires that came on your vehicle original equipment. This includes tire size, type and speed rating. Safe Winter Driving Thanks to their special compound, winter tires offer the elasticity required to ensure maximum grip throughout the cold season, regardless of the road conditions. Summer tires can become hard when the temperature falls below 45 degrees, thereby losing the flexibility needed to build up sufficient grip for braking, starting off and cornering. Because of their greater suppleness in the cold, winter tires are able to interlock with asphalt, snow and ice, even at lower temperatures.
Here a few tips to keep you from slipping and sliding on the way to work in the morning:
How to | Tire Tips
Question: What does UTQGL mean?
Answer: UTQGL stands for Uniform Tire Quality Grade Labeling, a system that classifies tires as to treadwear, traction and heat resistance. Each tire manufacturer performs its own tests in these categories, in accordance with government prescribed test procedures. Based on these tests, each manufacturer then assigns grades, which are branded on the tire sidewall, Example: Treadwear 400 Traction AA Temperature A
Question: How is the tread wear grade determined?
Answer: Treadwear tests are performed on a government-prescribed 400-mile section of public highways near San Angelo, Texas. Test vehicles travel the same course at the same time, so all tires experience the same conditions. During the test, tread groove depths are measured every 800 miles. The same procedure is followed with a set of reference control tires. After 7200 miles of testing, the tread depths of test tires and reference control tires are compared and the test tires are graded on the basis of relative wear.
Question: If my treadwear grade is 400, how long will the tire last?
Answer: The best way to understand a treadwear grade is to compare the grade of one tire with another. For instance, a tire with a treadwear grade of 400 might be expected to last twice as long as a tire with a treadwear grade of 200. However, there is no way of accurately predicting how long your tires will last. This is determined not only by tire quality, but also by road surface quality, personal driving habits, tire inflation pressures, wheel alignment and frequency of tire rotation. The treadwear grade is only a reference point to indicate how one tire performs in relative terms to another on the government-controlled treadwear course. It was never intended to project the exact mileage a particular tire might deliver.
Question: The traction grade on my tire is A. what does that tell me?
Answer: Put simply, it grades the tire's ability to stop a car in a straight line on a wet test surface. For example, a tire with an AA grade will stop more quickly in a straight line on wet pavement than a tire with a C grade. Note that these traction tests are performed on government-maintained concrete and asphalt skid pads that have a specified degree of wetting to simulate most road surfaces. These test do not measure braking under dry pavement conditions, or cornering traction under any conditions. Traction grades range from AA, A, B to C with AA being the best.
Question: Is the temperature grade on my tire important?
Answer: Yes, it represents a properly maintained tire's ability to dissipate heat under controlled indoor test wheel conditions. A tire is graded "C" if it meets the minimum performance required by the Department of Transportation (DOT). Grades of "B" and "A" represent higher levels of performance than the minimum required by the DOT. All tires must meet the minimum speed requirement of 85 mph set by Federal Motor Vehicle Safety Standard 109.
Question: Is tire rotation helpful?
Answer: Yes, because tire rotation can provide more even tire wear, maximize tire life, and provide better handling for the life of your tires, if the correct tire rotation guidelines are followed. For example: if you drive a front-wheel-drive car, your front tires absorb most of the forces associated with load, acceleration, driving, steering and braking, all of which contribute to tire wear. The difference in wear rate between the front and rear tires on a front-wheel-drive car can be as much as three to one. To obtain relatively equal mileage on front and rear tires, you should rotate your tires every 3,000 to 5,000 miles. If you notice any signs of premature, irregular or uneven wear patterns, rotate the tires more often. Ask your tire dealer to recommend a tire rotation pattern that is right for your vehicle.
Question: May I use my "temporary spare only" tire in my tire rotation pattern?
Answer: No, temporary means just that. For proper and safe rotation, only use tires of a like construction and size. Temporary spares are of a different size and construction than the other tires on your vehicle and require much higher inflation pressures. However, if you have a regular full-size spare in your trunk, you may include that in you rotation pattern. Check with you tire dealer for proper procedures.
Question: Is tire-sizing nomenclature complicated, or is it just me?
Answer: It is assuredly not just you! Four sizing systems are in use for passenger tires: P-Metric, European Metric, Millimetric and Alpha Numeric. The most widely used in the U.S. is the P-Metric system. If the size branded on your sidewall is arranged as follows P215/65R15 95S (the specific numbers may vary), then you have a p-Metric size tire. The P stands for passenger car tire; the 215 is the tire's "section width" - its width at the widest point - in millimeters; the 65 is the tire's "aspect ratio" - the percentage of its sidewall height relative to its section width - and the R is for radial construction. The 15 is the rim diameter, in inches, and the 95S is the service description (95 being the load index - which corresponds to a table of maximum load capacity in pounds - and S being the speed rating). And this just describes one sizing system; we have three more to go!
Question: Then, what's the European or Millimetric size?
Answer: Essentially, this system is a conversion of the original (and now obsolete) numeric sizing system from inches to millimeters. If the tire size on your sidewall is arranged like 185/70R14 88S, (again, your specific numbers may vary), then you have a European Metric size. The 185 is the tire's section width, in millimeters, while the 70 indicates aspect ratio. Next, the 14 is the rim diameter, in inches, and the 88S is the service description (load index and speed rating). R simply indicates that it is a radial construction.
Your tire is a millimetric size if the size is arranged like 240/55R390. In this example the 240 is the section width in millimeters, the 55 is the aspect ratio, the R means the tire is of radial construction and the 390 is the rim diameter, in millimeters.
Question: What should I know about light truck tire sizing?
Answer: There are three light truck sizing systems in use today. The LT-Metric light truck sizing system mirrors the P-Metric system for passenger tires. For instance, a size such as L235/75R15/C on your sidewall breaks out this way: the LT stands for light truck; the 235, your tire's section width in millimeters; the 75, aspect ratio; the R, radial construction and 15, the rim diameter in inches. Last, the C represented the tire's load range.
Keep in mind that nearly 50% of all new vehicles built in the U.S. are not "cars" in the traditional meaning, but includes minivans, pickups and SUVs. Nonetheless, many are being fitted with P-Metric passenger car tires, which tend to emphasize ride comfort and fuel economy. However, many light truck vehicles require higher load carrying capacity than offered by P-Metric tires primarily for commercial purposes, and thus come fitted with light-truck-sized tires.
Question: The tire size on my pickup reads 31x10.50R15LT/C. What does this mean?
Answer: It means you have a light truck "flotation" tire, designed to deliver better traction on sand and soft soil found in watery off-road situations. The 31 indicates the tire's overall diameter in inches while the 10.50 shows the tire's section width in inches. The R means the tire is a radial, the LT stands for light truck tire and the C indicates the tire's load range.
Question: When is the light truck numeric sizing used?
Answer: This older sizing system is still used on older commercial vehicles. The tire size branded on the sidewall looks like this: 9.50R16.5SLT/D. In this example, the 9.50 represents the tire's section width in inches; the R, radial construction; the 16.5, the rim diameter in inches; the LT, Light Truck and the D, the tire's load range.
Question: What do I need to know about aspect ratio?
Answer: Simply put, the lower the aspect ratio, the shorter the sidewall, and in most cases, the quicker the steering response. In engineering terms, a tire's aspect ratio is the dimensional relationship of the tire's section height to section width, expressed as a percentage. For example: a tire with an aspect ratio of 75 has a sidewall which is 75% as tall as the tire is wide, at its widest point. A 50 aspect ratio (also called a 50-series tire) is half as tall as it is wide.
Question: How do I know when I need new tires?
Answer: Ask a Tireman tire expert to replace your tires if the tread depth is 2/32nds of an inch or less as indicatedby the tire "wear bars" molded into the tread grooves. Also known as treadwear indicators, tire wear bars are raised areas in the tread grooves, which become even with the tread surface when the tire is worn to 2/32nds. You can't miss them. Most states require replacement of tires worn to this tread depth because of the increased possibility of tire failure, sudden traction loss in the rain and virtually no traction in snow.
In southern states where torrential downpours test a tire's ability to get rid of water through its tread grooves, you would do well to replace tires before they reach 2/32nds. In snow belt areas, replacement before you get to the wear bars is also wise. In deep snow, the tire must be able to compress and clean out packed snow from its tread grooves.
Question: How should I choose tires right for me?
Answer: Start by checking the vehicle tire placard or your Vehicle Owner's Manual. Both list the original equipment and optional tire types and sizes suitable for your vehicle. However, let's say your SUV originally came with P-Metric all-season tires and you live in a heavy-snow-belt area. Think about replacing your all-season tires with a more aggressive LT-Metric type tire. Or, if you live in the farm belt where mud is an issue, think about a mud-terrain type tire. Because there are so many tire types to consider, it may be wise to discuss your tire needs with a Tireman Expert.
Question: Who should install my new tires?
Answer: Tireman has professionally trained tire installers at all locations. Additionally, our investment in the latest equipment available ensures we're prepared to handle lower profile tire and wheel combinations found on many of today's vehicles.
Question: How do I know what inflation pressure to use?
Answer: First, check the vehicle placard in your vehicle. The automobile manufacturer has already determined the best inflation pressure for use in your tires under standard operating conditions. The air pressure should never be below the minimum listed on the vehicle placard or above the maximum recommended inflation pressure branded on the tire sidewall. Our advice is to use the pressure listed on the placard.
Question: How often should I check inflation pressure in my tires?
Answer: You should check the inflation pressure in your tires, including the spare, at least once a month and always before extended driving. Check the pressure when your tires are cold - that is, when your vehicle has been parked for at least three hours. If necessary, add air to inflate your tires to the pressure(s) specified on the vehicle placard. Since this reading will be most accurate with cold tires, drive to the nearest source of air whenever possible.
Never 'bleed" or reduce inflation pressure when your tires are hot. When tires heat up from driving, it is normal for inflation pressures to increase above recommended cold inflation pressure levels. But if you let air out of a hot tire, it will be under-inflated when it cools down.
Also use a high-quality air pressure gauge to check your tires, don't trust your eyes. You can't tell by looking if a tire is properly inflated.
A rule of thumb, for highway use, all passenger and light truck tires should be inflated at or more than 20 psi. For any 16.5-inch rim diameter light truck tire, the minimum highway inflation pressure is 30 psi.
Question: What might happen if I run my tires under-inflated or over-inflated?
Answer: Under-inflation can cause extreme sidewall flexing. The result may be dangerous heat buildup that can lead to premature tire failure. Over-inflation can cause your tires to be more susceptible to impact damage. either under-inflation or over-inflation may adversely affect vehicle handling and treadwear.
Question: What are tire speed ratings all about?
Answer: Officially, the speed rating of a tire indicates the highest speed at which the tire can carry a specified load under specified conditions. Letters from A to Z symbolize a tire's certified speed rating, ranging from 3 mph to above 186 mph. The speed ratings most commonly in use are:
Q 100 mph V 149 mph
R 106 mph W 168 mph
S 112 mph Y 186 mph
T 118 mph Z Zr speed capability above 149 mph.
ZR_When ZR appears in the tire size designation along with a service description - such as P275/40ZR17 93W - the maximum speed rating (indicated by the "W" in "93W") indicates the tire's speed rating - in this case, 168 mph.
In this latest effort to standardize tire designations, all ratings except unlimited Z-speed rated tires incorporate the speed symbol and load index in the tire's service description. Example: P225/60R15 95H. The 95H is the tire's service description indicating a maximum load carrying capacity of 1521 lbs. and a maximum speed rating of 130 mph. While all tires are speed rated to indicate speed capabilities in excess of national speed limits, Michelin North America, Inc., does not endorse the operation of any vehicle in an unsafe or unlawful manner.
Question: Why are speed-rated tires so expensive?
Answer: Because speed-rated tires must meet ultra-high performance demands, they generally have been engineered to provide dramatically better handling. A V-speed-rated tire, for instance, has been built with state-of-the-art tread designs, tire profiles, carcass materials and construction, using exotic tread polymers and compounds. While Q, S, or non-speed-rated tires meet or exceed all DOT requirements, they generally do not feature the advanced and costly construction built into ultra-high performance speed-rated tires.
Question: What if I replace and H-rated tire with an S-rated tire?
Answer: You should replace original equipment speed-rated tires with tires of the same or higher speed rating if the speed rating of the vehicle is to be maintained. If you replace H-rated tires (capable of speeds up to 130 mph) with S-rated tires (capable of speeds up to 112 mph), you need to know that the handling of the vehicle will be different, and that now, its maximum speed capability is limited to that of the lowest speed-rated tire on the vehicle. In this example, you would have lowered the speed capability of your vehicle from 130 mph to 112 mph.
Question: I am buying two new tires. Where do they go, front or rear?
Answer: Always on the rear. In a cornering maneuver on wet pavement, if your front tires lose grip first, your vehicle will tend to lose control by going straight, even in a turn. This is understeer, which can be controlled by slowing down and steering in the direction of the turn. This will allow your car to come back into line.
But if the rear tires lose grip first, your vehicle could spin, which is oversteer and more difficult to control. This requires you to make quick, precise steering corrections in the opposite direction of the turn, not a natural reaction. It is easier to control understeer than oversteer.
For the record, the best choice to make when replacing tires is to buy four new tires, all the same brand, type and size.
Question: If I buy just one tire, what should I buy, and where should it go?
Answer: The only sound reason to buy just one tire is to replace one tire damaged by an accident or road hazard, in an otherwise good set of four. You should always buy the same size, type, brand and tread design as the tire you're replacing. An all-season tire should be replaced with an all-season tire. A Mud&Snow tire should be replaced with a Mud&Snow tire an H-speed-rated tire should be replaced with an H-speed-rated tire. In this way you will enjoy a safer, more satisfying driving experience.
Question: What's the difference between an all-season tire and an all-terrain type tire?
Answer: An all-season tire is designed with a long lasting, aggressive tread pattern designed to get rid of water and snow, balancing the wet and snow traction capability with dry pavement performance. It generally features lots of biting edges that enhance snow and wet traction, It can even be branded as an M&S tire (Mud and snow.)
An all-terrain type tire is a light truck tire that has been designed with an even more aggressive tread pattern. This type of tire may be driven on- or off-road in virtually any type of weather and road ondition. In rain and on mud, an all-terrain tire's open, self-cleaning tread provides excellent traction, and its rugged edges grip on rocky and uneven terrain.
Question: Should I be concerned about tire load carrying capacity?
Answer: If you replace original equipment tires with the same size and type replacement tires, your newest tires will be able to handle the weight of your vehicle and its maximum allowable load. However, if you switch from an LT-Metric to a P-Metric or if you are changing sizes, you should consult your tire dealer. He or she will review your tire selection against industry tire load and inflation tables to make certain you aren't installing tires incapable of supporting your vehicle and its load. A replacement tire must always meet or exceed the load carrying capacity of the original equipment tire.
Question: Can changing tire sizes confuse my vehicle's on-board computers?
Answer: It can if you substantially change the overall diameter of your tires. Maintaining the original, specified diameters as closely as possible ensures that your on-board computers will function properly and thereby effectively manage such systems as your anti-lock braking system, traction control, fuel management system, electronically controlled automatic transmission and electronic handling stability system. Changing tire diameters sends erroneous readings to the computers. These systems won'tfail, but they will be impacted to varying degrees. If you have any questions about this potentially troublesome issue, contact your tire dealer.
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