Tires of American and European production differ in marking. Often a situation arises when it is necessary to convert inches to centimeters. In this article, we will describe how to decipher tire sizes in centimeters.
Metric tire marking
The main dimensions of tires are prescribed by marking, these include:
- Tire profile width - the distance, expressed in millimeters or inches, between the outer sides of the sidewalls of an inflated tire, excluding elevations, trim or belts. The specified value should not exceed the product rim width by more than 30%.
- Tire series. Specifies the ratio of the width and height of the product profile. Allows you to distinguish rubber in this way:
- low profile - series less than 70%;
- high profile - in the range of 70-82%;
- full profile - more than 85%.
- Tire construction. There are radial and diagonal tires. In the first case, the fibers of the cord layer are placed perpendicular to the circumference of the wheel. In the second variant, the cord threads are overlapped. Radial tire design is more common, these tires provide better wheel traction. pavement they are more reliable in operation.
- wheel radius.
How to understand what tire markings mean? The designations on the side of automobile rubber are applied by tire manufacturers. Factory marking is in metric or inch system. For example, the size of tires marked with the metric system 265/75 R15 corresponds to the designation of the inch system 31 × 10.5 R15. The interpretation of these designations in centimeters means:
- The designation 265/75 R15 indicates the dimensions of the tire:
- 265 - a figure that determines the width of the tire (one centimeter is equal to ten millimeters, 265 mm = 26.5 cm);
- 75 is the percentage (75%) that determines the relationship between the height of the tire profile and the width of the rubber (265 * 0.75 \u003d 198.8 mm or 19.9 cm), the number found indicates the height of the tire profile;
- R - denotes the radial type of tires;
- 15 - wheel diameter, the size is indicated in inches, you can convert the indicated parameter into centimeters by multiplying the digital value of interest by 2.54, since 1 inch is 2.54 cm, as a result we get 15 * 2.54 \u003d 38.1.
- The designation 31 × 10.5 R15 stands for:
- 31 - wheel height (31 inches or 31 * 2.54 = 78.7 cm);
- 10.5 - tire width (10.5 inches or 10.5 * 2.54 \u003d 26.7 cm);
- R - indicates the radial type of tires;
- 15 - determines the diameter of the wheel (15 inches or 15 * 2.54 = 38.1 cm).
- subtract its radius from the total height of the tire (78.7-38.1 \u003d 40.6 cm);
- divide the resulting value by 2 (40.6 / 2 \u003d 20.3 cm).
Differences in the marking of tires
Tire marking with inch system When deciphering tire sizes, pay attention to the letter in front of the tire dimensions:
- "P" - indicates the "P-metric" system used for minivans, light pickups (with a carrying capacity of up to 0.5 tons). This system is very convenient, it is often used by tire manufacturers.
- "T" - "spare" tires are marked with the indicated letter: rubber can be used until the main tire is repaired or replaced.
- "LT" stands for "Light Truck-metric" system, designed for trucks and vehicles capable of transporting large loads. Vehicles with a load capacity of up to 1 ton fall into this category.
- "ST" - indicates "Special Trailer Service", products are designed for trailers, they can also be used to transport boats or cars.
Letter values can be at the end of the tire marking, in which case they mean:
- "LT" - the tire refers to products with early marking:
- "Numeric" - numerical, tires are designed for vehicles transporting heavy loads, trailers
- "Wide Base" - tires with a wide base, manufacturers make such products with a rim diameter of 16.5 inches;
- "Flotation" - flotation, large-sized tires that allow the car to move on a sandy surface or mud.
- "C" is a commercial tire used for vans and distribution vehicles capable of transporting large loads.
If at the beginning of the marking there is no letter designation and a three-digit number, for example, 45R15, then this is a tire with a metric size of the Euro-metric system applicable on tires of European manufacturers. The indicated dimension corresponds to the decoding according to the P-metric system, but differs in smaller loads.
- 235 - product width (235 mm = 23.5 cm);
- 710 - a figure indicating the outer diameter of the tire (710 mm \u003d 71.0 cm);
- 460 - tire rim diameter (460 mm = 46 cm);
- A - the designation of asymmetric rubber sides, for example, 460A means that the outer side has a diameter of 45 cm, and the inner one is 47 cm.
Such non-standard markings are designed for vehicles with wheels of a specific size that differ in side profiles from standard metric or inch products. Faced with non-standard markings, it is better to find out their decoding from the tire manufacturer.
Comparison of calculated data
Dimensions requested by the tire calculator to perform calculations Independent decoding of tire sizes requires a certain accuracy of calculations. You can check whether the conversion of values \u200b\u200bfrom centimeters to inches and vice versa is done correctly using tire calculators. With their help, you can also find out how many tire sizes are suitable for a particular car model.
Tire calculators are easy to find on the Internet, they usually have American and European systems of sizes at the same time. Therefore, by entering the tire sizes recommended by the car manufacturer in the metric system, it is possible to get a list of American and European tires. It is very convenient, if necessary, to select the brand of rubber of interest, as well as view the possibility of changing tire sizes recommended by the manufacturer. When using tire calculators, it is necessary to take into account the error arising from rounding, so it is better to translate the dimensions of interest manually, then compare them with the options calculated by the Internet resource.
Conclusion
American labeling rubber, if you do not take into account the inches that are unusual for us, it is very convenient to use. But in most situations, you have to deal with the metric notation. Converting inch dimensions to centimeters is not difficult if you understand the decoding of the designations applied by manufacturers to the side surface of tires. In this case, it is necessary to take into account the error of calculations, which may arise due to inattention or rounding of the obtained values. To correctly calculate the dimensions, it is better to use the manual method, then compare the obtained parameters with the data of tire calculators. We do not recommend using only one method, since there is also a certain rounding error in the embedded electronic computing programs.
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To simplify the determination of tire size, a special tire calculator, allowing the user to do without the need to decipher the digital values on the side surfaces of the rubber. With the help of such a calculator, the difference in tire sizes, profile height and other parameters are determined. In addition, such a calculator allows you to receive other related information, for example, on deviations in the operation of the speedometer, changes in the value ground clearance and so on.
Purpose of the visual tire calculator
A visual calculator allows each car owner to easily determine the size of tires and the width of the required disks. With its help, it is possible to determine the diameter of the wheels, the error of speedometers, the increase in the road track and changes in the clearance under the bottom of the car. Using the tire calculator, it is extremely easy to determine optimal size suitable for a specific car model. The built-in size conversion system allows you to instantly transform values from inch to meter and vice versa.
It is advisable to take advantage of the calculator's potential in cases where the car owner switches to using tires and wheels that are different from the original size. It allows you to visually determine the main dimensions, and then model them for the selected car. In turn, the selection of tires with its help is impossible, since initially it does not provide for division by manufacturer.
Selection and comparison of tires according to the calculator 2.0
In the case of installing new disks and tires of a different size based on the data received from the calculator, it is advisable to additionally carry out a number of measurements. Determine the appropriate distance inside between the wheel and suspension, and from the tread to the shock cup. In addition, you will need to measure the distance between the tread, fender and tie rods.
In turn, when choosing new tires, it is necessary to proceed from the expediency of a slight deviation in geometric dimensions new tires from previously used ones. A significant size will cause instability in the movement of the car.
Each car is initially created for certain parameters and dimensions. This fully applies to the allowable size of the discs and rubber used. Accordingly, the selected rubber models must be within the established limits. The use of a tire calculator allows you to simplify the selection process as much as possible, depending on a particular vehicle.
The Russians have to regularly deal with the replacement of rubber, primarily seasonal. The easiest solution in this situation is to use rubber of the same size. While maintaining the dimensions of the rubber, the wheel will also retain its original dimensions.
In cases where tires of a different size are selected, the selection of appropriate discs is required to obtain a wheel with the required dimensions. However, due to the change standard sizes tires have the ability to control the driving characteristics of the car, giving additional softness or rigidity. The higher the profile used, the softer the car feels on the road. As the profile decreases, stiffness increases, and narrow tires give more grip on snowy surfaces, so they look more advantageous on winter roads.
At the same time, when choosing the dimensions of tires and wheels, it is required to adhere to the allowable sizes. For example, too wide tires will touch the wheel arches in motion, rubbing them, and wearing out intensively on their own. It is also worth considering the fact that changing the size of the wheels affects the operation of the speedometer, in particular, the magnitude of the error.
From the outside, it may seem that the variety of available configurations greatly complicates the calculations, but the tire calculator greatly simplifies the selection process using 3D modeling. Correct selection tires, it's not only necessary security, but also optimization road opportunities car. At the same time, the presence of a metric and inch size system allows you to work without problems with both American and European standard sizes.
The first and second columns contain standard sizes of tires and disks. In the remaining columns, the dimensions desired for installation. The calculator will help determine tolerances and selection alternatives.
The tire calculator allows you to compare the dimensions of tires of different sizes. For example, choose wider tires, but keep the outer diameter of the wheel the same or find out how much the car's ground clearance will change if you put tires of a different profile.
To select an alternative size in one half of the calculator, you need to specify the standard or existing tire size, in the next half - the desired or alternative.
The calculator displays the recommended rim width for a particular tire size, as well as the outer diameter and wheel width. Most important parameter is the outside diameter of the wheel. You should pay the most attention to its change.
The second important parameter is the actual height of the tire profile. It is usually expressed as a percentage of the width: for example, 205/55 R16, where 55 is 55% of the tire's width. That is, 205*55/100=112.75 mm is the actual profile height of this tire.
Tires of different widths, standardly installed on a car, have different profile heights in percent, but the same in millimeters. For example, tires with dimensions 275/40 R20 and 315/35 R20 have a profile height of 110 and 110.25 mm, respectively.
Some features of the selection of tires:
- The wider the tires, the better handling, but less hydroplaning resistance and more rutting, and reduced comfort - low profile tires are stiffer.
- Lower profile - heavier wheel. This is due to the fact that the disk is heavier than rubber, the mass of the wheel increases and this worsens the performance of the suspension. In addition, the mass of metal is distributed closer to the outer edge of the wheel and increases the moment of inertia (for cars with a powerful engine, this is not essential).
- With an increase in the profile, the car becomes more rolly, it reacts worse to control, but it goes through bumps more easily, the tires are less sensitive to the sharp edges of the pits, and comfort becomes better.
- A significant change in the outer diameter of the wheel leads to a distortion of the readings of the car's instruments, in particular, mileage and speed.
Our tire calculator - professional calculations in no time!
Instruction
Look at the nameplate in the doorway on the driver's side for the recommended tire size. Write it down on paper or memorize it. Find wheels with this size in the car shop and use a tape measure to measure the outer diameter of the tire. Write this value down on paper. Drive the car into the pit and turn the front wheels completely: first in one direction and then in the other direction. Measure the distance from the tire to the nearest structural element with a ruler or tape measure and write these values down on paper.
When choosing the tires you like, consider the diameter of future rims, and, depending on the size of the future tire, select the width of the rims. The required disc width is equal to the tread width. It may be easier to find a disc with a slightly larger diameter and the desired width. For example, take 14-inch rims instead of 13 and fit tires on them. This option will be even more advantageous in terms of durability, but at the same time more expensive.
Try to buy tires dimensions which will be approximately the same as recommended. For example, the manufacturer recommends tires with dimensions 175/70R13 86S. 175 is the overall width of the tire in millimeters, /70 is the height of the tire profile as a percentage of the width, R-13 is the mounting diameter corresponding to the diameter of the discs, 86 is the load factor, S is the speed index. It is worth noting that the overall tire width may differ from the tread width, so if you want a wider tread, then pay attention to this feature. Do not take tires with low load and speed ratios.
If you want to put R16 wheels on your car instead of R13, find the right tire width. Since 175mm wide R16 tires don't exist, it's more realistic to find 215mm or wider tires. Look at your notes and calculate how many centimeters you have left. Increasing the tire width by 1cm more than recommended reduces the measured distance between the wheel and the body by 5mm. Please note that it is not advisable to increase the diameter of the wheel by more than 3 cm, as this will lead to increased consumption fuel and to a deterioration in the traction characteristics of the machine. Select suitable tires and measure their diameter with a tape measure. Compare with recommended wheel diameter. If the excess of the recommended dimensions of the future wheel is within your calculated norm, you can safely buy the selected tires. The speed and load coefficient in this case will significantly exceed the recommended one, which will have a beneficial effect on the durability of rubber.