How To Read Tire Sizes In Inches
When youre out shopping for new tires, youll notice that the size is listed in inches. But what do all those numbers and letters mean? Heres a quick guide to reading tire sizes so you can find the right ones for your car.
The first number is the width of the tire in millimeters. The second number is the height of the sidewall, or aspect ratio. This is a percentage of the width, so if its 50%, that means the sidewall is half as tall as the tire is wide.
The third number is the diameter of the wheel in inches. Now that you know how to read tire sizes, you can be sure to get exactly what you need for your car!
Where To Find Your Tyre Size
The best place to find your tyre size is on the sidewall of the tyres currently fitted to your car. Some vehicles such as BMWs & Mercedes have different sized tyres on the front and rear so if you check on the tyre you need replacing you can be sure youre replacing your tyre with one exactly the same size. Reading the markings on your tyres may look confusing, however once you know what to look for finding your tyre size is actually fairly easy.
Tyre size information can also be found:
In your vehicle handbook
How To Calculate Tire Size
Let’s learn how to find tire sizes. We’ve got the tire code and the data required for us to calculate various tire measurements, such as the tire diameter and sidewall height.
To calculate the sidewall height, we multiply the profile ratio by the tire width . The formula is, therefore:
- sidewall height = profile ratio × width / 100
So, for the tire code shown in the figure above, P215/65R15, you would calculate the sidewall height as:
- sidewall height = 65 × 215 / 100 = 139.75 mm
Converting to inches , that’s 5.5 inches. We know the diameter of the wheel is 15 inches, so the diameter of the tire is given by:
- tire diameter = wheel diameter +
So, for our example, that’s:
- tire diameter = 15 + = 26 inches
To calculate the circumference, we use the classic circle equation:
- circumference = × diameter
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Changing Tire Size On Same Rim
Its not uncommon to want to change the size of your tires. Maybe youre looking for a different look, or maybe youre trying to increase your performance. Whatever the reason, there are a few things you need to know before changing tire size on same rim.
First, you need to make sure that the new tires will fit on your current rims. You can do this by measuring the width and diameter of both the old and new tires. As long as the new tires are within 2 inches of the old ones in width and diameter, they should fit on your rims.
Second, youll need to adjust your speedometer and odometer readings. This is because changing tire size will affect how far your car goes per revolution of the wheels. To adjust for this, simply multiply your current reading by the percentage difference in circumference between the old and new tires.
For example, if your speedometer reads 60 mph and you switch from 35-inch tires to 33-inch tires , simply multiply 60 by 0.05 to get a new speedometer reading of 63 mph. Finally, keep in mind that changing tire size may also affect your gas mileage. Larger tires require more energy to turn, which means youll use more gas overall.
So if fuel efficiency is a concern for you, be sure to take this into account when choosing new tires!
Usdot Tire Identification Number
You may notice another set of letters and numbers on your tire’s sidewall beginning with “DOT.” This is not an indication of tire size, but rather that the tire complies with Federal Motor Vehicle Safety Standards. The “DOT” stands for Department of Transportation and is followed by the tire identification number.
The first two letters or numbers after DOT refer to the manufacturing plant where the tire was produced and the last four numbers indicate the week and year the tire was made. The numbers 4318, for instance, indicate that the tire was manufactured during the 43rd week of 2018.
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Uniform Tire Quality Grading
Another group of stamping on certain types of tires is the Uniform Tire Quality Grading or UTQG. This grading and stamping is required for passenger car tires in the all season and summer categories. Dedicated winter tires, Light Truck and Motorcycle tires are excluded from this requirement.
Quality grading is designed to make the tire purchase decision easier for you. Ideally, the system is intended to provide simple, comparative data so you can make an intelligent buying decision. However, the ratings are based upon test results achieved under special conditions. This means its possible to misinterpret the comparative data as it relates to your individual driving habits, conditions, etc. You should still rely on your service or tire professional for assistance.
Quality grading designates the comparative performance levels of a tire based on government-specified tests but commissioned by the individual tire manufacturers. All tire manufacturers are required to grade regular and all-season passenger tires in three categories:
Traction Grades AA, A, B and C The traction grades from highest to lowest are AA , A, B and C. They represent how well tires stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. C-rated tires will have the lowest traction performance.
WARNING: THE TRACTION GRADE ASSIGNED IS BASED ON A WET BRAKING TRACTION TEST AND DOES NOT INCLUDE CORNERING TRACTION.
Width Height And Size
Perhaps the most commonly discussed piece of data about a tire is a number in the format “XXX/XXRXX,” which describes a tire’s size and shape in a somewhat arcane way. Using 235/55R18 as an example, 235 is the tread width in millimeters. The higher that first number, the wider the tire. The 55 is the height of the tire expressed as a percentage of the width we just saw. The lower this number, the shorter and more aggressively the tire sits on the wheel. The R means the tire is of radial construction and the 18 is the diameter of wheel the tire fits, expressed in inches. This string is a real hodgepodge of numbers but it carries the essence of a tire’s applicability.
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Where To Find A Car Tire Size
No matter what vehicle you drive, finding the manufacturer-recommended tire size should be easy. The best place to start looking is the owner’s manual.
Don’t worry if you can’t locate the manual you may also find a tire fit guide in these locations:
- The driver’s side door jamb
- Inside your glove box door
- Within your gas tank hatch
You can also find tire size data on the sidewall of your current tires . However, no matter where you find your tire size, you will have to decipher a sequence of numbers and letters. Don’t worry if it looks confusing at first â every letter and number has a straightforward meaning. Let’s break down how to read car tire size.
Choosing The Correct Tire Size
Make your tire size selection in strict accordance with vehicle documents and tire manufacturer recommendations. If the combined wheel and tire diameter arent correctly matched, there may be drastic differences in ride height and speedometer readings.
For example, fitting 17-inch-diameter wheels to a car that is designed to have 14-inch-diameter wheels will change the ride height. That means the car body will be higher off the ground. There will also be a slight increase in top speed, and the speedometer will no longer be accurate. Last but not least, the car will accelerate slower.
Switching to different tire sizes can only be done in compliance with all legal requirements and regulations plus the recommendations of the vehicle, wheel, and tire manufacturers. At the very least, the wheel must have complete freedom of circular motion and the tires adequate load capacity must be observed.
The internal construction of tires fitted on any vehicle must either be radial or bias-ply. Fitting mixed tire constructions for cars, caravans, and other light trucks is unsafe and illegal. The only permissible exception is the use of a spare tire for an emergency.
Concerning the choice of wheels or rims, the same guidelines apply. Motorists must use the standard wheels or rims approved by the vehicle manufacturer as recommended.
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Is A 50 Or 60 Tire Wider
There is no definitive answer to this question as tire width can vary depending on the manufacturer and model. However, in general, a 50 or 60 tire will be wider than a standard tire size. This is because wider tires provide more grip and stability on the road, which is beneficial for both performance and safety.
If you are unsure about what size tire to choose for your vehicle, it is best to consult with a professional who can help you select the right option.
How To Read Tire Size
- Maintaining Your Vehicle
Installing the right tires on your vehicle is essential to the overall performance and safety of your vehicle. Your tire choice should reflect the conditions in which you drive and your preferences for vehicle response and handling. To make the most informed decision, though, you must understand how to read tire size when it’s time to buy tires.
Thankfully, determining the correct tire size for your vehicle is relatively simple. All the information you need is immediately available either in your owner’s manual or somewhere on the vehicle itself. Already know how to read tire size numbers? Skip the explanation and find the right Bridgestone tire for your vehicle online or by visiting a Bridgestone tire dealer near you.
While actual, physical measurements like width and diameter are factors in finding the right tire size, there are additional details to consider. Knowing how to read car tire sizes also means understanding terms like load index and speed rating that affect your vehicle’s overall capabilities.
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Department Of Transportation Safety Code
This assures that your tire complies with all Department of Transportation safety standards. After the DOT insignia is your tires identification number, which begins with the tires manufacturer and plant code where the tire was manufactured . The ninth and tenth characters tell the week the tire was manufactured. The final number signifies the year the tire was manufactured.
How To Determine Tire Size
This article was co-authored by Howard Fleischmann and by wikiHow staff writer, Sophia Latorre. Howard Fleischmann is an Automotive Tire and Repair Specialist and the CEO of Community Tire Pros & Auto Repair, with ten locations throughout Phoenix, Glendale, Yuma, and Casa Grande, Arizona. Howard specializes in full-service auto repair and tire replacement and care for domestic/imported vehicles and large trucks. Howards dedication to Community Tire Pros & Auto Repair has earned their team multiple awards and features including the 2021 Phoenix Magazine AZ State 48 Best of the Best!, the 2020 Best of Phoenix in Auto Repair, the 2013 Master SBD award, the 2013 National Top Shop award by Tire Review, the 2012 Diversity Champions Phx Business Journal, the 2009 BBB Ethics award, the 2008 Phx Chamber of Commerce Impact Award – Small Business of the Year, and the 2008 ASU Spirit of Enterprise award. Howard is often referred to as The Car Guy for local TV stations and is a regular on TVs Channel 3 Sunday, Good Morning Arizona monthly. This article has been viewed 55,853 times.
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How To Find Your Tyre Size
If youre in need of new tyres then the first thing youll need to know is what tyre size your vehicle needs.
You can start searching for your tyre size by inputting your registration number, however for many vehicles there may be more than one size option and so to narrow your search youll need to look for the information on the vehicle itself.
Heres our handy guide to understanding & reading your tyres.
Where Can I Find My Tire Size
The tire size for your vehicle and wheels can be found in two places:
Tire Size Example: 255/55 R18 XL
- The first three numbers of a tire size measures the width in millimeters from sidewall to sidewall.
- If the tire size is 255/60 R16, the width of the tire is 255 millimeters.
- The two digit number after the slash mark is the aspect ratio which measures the tire’s cross-section to it’s width.
- If the tire size is 255/60 R16, the 60 means that the height is 60% of the tire’s width. The bigger the aspect ratio, the bigger the tire’s sidewall will be.
- In between the Aspect Ratio and Rim Diameter, is the construction of the tire.
- If the tire size is 255/60 R16, the “R” stands for Radial, which means the layers of the tire run in straight lines across the tire.
- If there is a “B” instead of an “R” listed on your tires, the “B” stands for Bias construction which means the layers run diagonally across the tire.
- Located after Construction is the wheel size, which tells us the size of the wheel/rim that the tire is intended to fit and is measured from one end of the wheel to the other.
- If the tire size is 255/60 R16, the 16 means that the wheel is 16″ in diameter.
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Reading Tire Size Documentation
What do all these letters and numbers mean? Heres all the information on the tire sidewall quickly decoded:
- 1) The width of the tires in millimeters
- 2) Percentage height of the sidewall in relation to the width
- 3) Radial construction
- 4) Rim diameter in inches
- 5) Load index
- 6) Speed index
- 7) Self-Supporting Run-flat tire
- 8) Mercedes Original Equipment key
- 9) Suitable for mud and snow conditions
- 10) Compliant with Department of Transportation motor vehicle safety standards
- 11) Week of manufacture
- 12) Year of manufacture
The documentation supplied with your vehicle outlines the recommended tire sizes for your car. Compatibility is determined according to its outer dimensions diameter/rolling circumference and width and labeled as a standardized tire size indicator on the sidewall.
Also, the size must comply with the vehicles requirements regarding speed rating and load range. Together, the load index and speed index make up the full service description for a passenger car tire. It must correspond to the information provided in the vehicle documents.
How To Find My Tire Size
Before starting the process of buying new tires its important to know your tire size. There are a lot of variables when it comes to tire sizing such as their width, aspect ratio, and radius. An automobiles make and model can be the same but that doesnt always mean that the tires are too. Tires can differ based on trim level. An example of this is the 2015 Honda Civic Sedan. The original equipment tires for the LX model is 195/65R15 whereas the EX-L models are size 215/45R17. Therefore its always good to double check your manufacturers recommended tire size before making that all important decision on what tire to get.
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Let Us Help You Read Your Tire Size To Find The Right Tire For Your Vehicle
If you’re looking for a quick and easy way to find tires that fit, use the Goodyear Tire Finder instead.
Can I Put Larger Tires On My Car
While it’s certainly possible to upgrade your tires’ size, it’s usually best to stick to your manufacturer-recommended tire size for optimal performance. Increasing the size of your tires may give your car more ground clearance, but it may also affect handling, drivetrain performance and fuel economy. Keep in mind the changes to key figures mentioned above, such as load index and speed rating, and how they may affect your vehicle’s capabilities if you decide to increase tire size.
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How Do Tire Sizes Work
You’ve probably seen this strange set of numbers and letters on your car’s tires and wondered what exactly they mean. It’s called a tire code, and it specifies the size and type of tire. Let’s go through each part of the code and make you a tire code expert.
The first letter is optional, so you might not always see it. It gives information about the intended use or the class of vehicle the tire fits. Possible values are:
- P: Passenger car
- ST: Special Trailer
- T: Temporary
Up next is a 3-digit number that indicates the width of the tire in millimeters, measured at the widest point of the sidewall . Expect the width of the tire actually in contact with the road to be smaller than this value.
Next is a forward-slash for character separation, then there’s a 2- or 3-digit number representing the profile of the tire. This number is the ratio of sidewall height to the tire’s width as a percentage . So, for example, if the value was 50%, the sidewall height would be half of the width. If it is not present, you can assume a profile ratio of 82%. If the number is more than 200, then it represents the tire’s diameter in millimeters.
Following the profile ratio, you may see an optional letter indicating the type of tire construction. Radial is now the most common and the standard design for car tires today, with over a 98% market share. Here is a summary of radial and some other constructions you may see:
So that’s the tire code and tire size explained.