Following traditional marking method, tire size is represented by main technical parameters of tire.
1, Bias Tire
Two group of figures connected by minus are commonly used to mark tires. The first set of number indicates section width, and the second one shows rim diameter. As this traditional marking method originated from the United States, the two groups of figures adopt English Unit, such as 9.00-20, 11.00R22.5, 13.6-38, 23.5-25, all those represented by inches, while some countries adopt metric system or metric-inch mixed tag method. For example 260－508 are all millimeter; 185R15, the front number is millimeter, while the later one is inch. Such representative method of size is applied widely. Automotive tire, agricultural machinery tire and off-the-road tire use this marking method.
Moreover, there are many other marking methods: using “X” to connect the two group figures, that is D X S, and the unit is inch, such as animal vehicle tire 32×6、28×6; ultrahigh pressure carrier tire 18×4.4、39×13、56×16. Some countries also use “×” and “－” to connect three groups of tires. The first group is outer diameter of tire, the second is the width of cross-section and the third one id rim diameter, that is D×Sf－d. For example, using metric system to show aircraft tire 545×175－254; using imperial symbol to represent is 24×7.7－10; using metric-inch mixed tag method is 360×135－6, 380×150－4.
2, Radial Tire
Radial tire often uses the letter “R” as its code. R is the prefix of Radial, “－” is replaced by R to connect the two group figures. Such as 9.00R20、11R22.5, showed by inch; 185R15, the former figure is metric system, and the later is inch. Groupe Michelin use “X” as its code, such as 10.00-20X, 175－14X; the Soviet Union used “P” as its code, for example 155－13P,5.90-15P; Italy uses “Cinturato” as its code.
As the variety and size of tire is increasing, the cross-section contour changes a lot. So the traditional marking method can’t get use to new demand. The marking method stipulated by the world is to use the width of tire section (mm), tire flat rate (%), structure code of tire (such as R represents radial tire) and symbol of rim diameter. For example 175/70SR14, the first group figure shows that the width of tire section is 175 mm, the second group figure represents tire flat rate is 70%, 70 tire series, the third group figure 14 expresses rim diameter in inch. SR means fast radial tire, and S means mark of speed stage.
3, Tubeless Truck Tire
After tubeless truck tire switching to use deep slot rim, its rim diameter changed. For example, 8－22.5 ( equal to 7.50-20 inner tube base tire), 10－22.5 (equal to 9.00-20 inner tube base tire) in inch. Some tubeless truck tire is directly marked “无内胎” or “TUBELESS”.
While the size of specification number just shows the code of the tire, not the real size. And the margin of two adjacent norms doesn’t exceed 10~ 15 %.
4, tractor Tire
a. Narrow Rim Tractor Tires
Although this kind of tire is gradually eliminated, it still occupied of a certain number. Any tire, whose ratio of the rim width and tire cross-section width in the range of 65%, is narrow rim tractor tires. The specification method is similar to oblique cross tire, using the form of S-d. The only one difference is using decimal point in code of section width, such as 11.45-24, 13.00-28, 9.00-36.
b. Wide Rim Tractor Tire
The wide rim tractor tire’s ratio of the rim width and tire cross-section width is in the range of 80%. The difference between wide rim tractor tires and narrow rim tractor tires is that wide rim tractor tires adopt integer to show the cross-section. Such as 10－28、11－38、12－38.
c. Ultra-wide Rim Tractor Tires
The ultra-wide rim tractor tires’ ratio of the rim width and tire cross-section width is in the range of 85%~90%. And the difference between ultra wide rim tractor tire and wide rim tractor tires is that ultra wide rim tractor tires adopt only one decimal place whose number is not “0” , such as 11.2-28(replaced 10－28),12.4-38(replaced 11－38), 13.6-24(replaced 12－24). Now the series of agriculture tire has developed to the level of ultra wide rim tractor tires.
d. Low Profile Agricultural Machinery Tires
Tractor tires and agricultural machinery tires develop towards low profile tire. “L” means low profile. The quantitative value of section width is integer, and it can have one decimal place. Such as 9.5L-15, 11L-15,14L- 16.1; Logging tire 30.5L-32. “SL” has also been used, but it is only used for agricultural tire, such as 7.50-10SL, 10.00-15SL.
According to the size, truck tire and automobile tire can be divided into mini, light, middle, and heavy size tire. The signs of different style tire are not the same.
(一) International standard tire specification of ISO
According to international rule, the distance and introduction is,
255 / 70 R 22.5 140 /137 J
255－nominal tire cross section width, mm
70－tire flat rate,%
R－sign of tire structure, the structure of radial tire
22.5－nominal rim diameter (tubeless tire), in
140－single tire load index, 24.5 KN
137－twins load index, 22.5 KN
J－sign of speed, 100km/h.
(二) Sign of British Standard
a. Mini Truck Tire
It often refers to mini truck tire, whose nominal cross section width is 4.50~5.00in, and nominal rim diameter is 10～12in. The tire is installed on open or deep notch rim. For example:
5.00 - 12 ULT
5.00－nominal tire cross section width, in
- － hyphen
12－nominal rim diameter, in
ULT－sign of reading material kinds of car (mini truck tire)
b. Tires of Light Truck, tractor and multi-purpose passenger cars
This kind of tire is often installed on deep notch or half-deep notch tire for road driving. Its rim diameter is below 16in, and tire nominal cross section width is below 9.00in. For example:
8.25 - 16 LT
8.25－nominal tire cross section width, in
16－nominal rim diameter, in
LT－sign of reading material kinds of car
c.Tires of truck and autobus
It often refers to tires of middle and heavy truck and bus, whose nominal rim diameter is 18～24in, nominal tire cross section width is 7.5~14 in. This tires are installed on I、II、III rim for road driving. For example, 9.00-20 diagonal tire, 11.00R20.
9.00 - 20
9.00－nominal tire cross section width, in
20－nominal rim diameter
11.00 R 20
11.00－nominal tire cross section width, in
R－sign of radial tire
20－nominal rim diameter, in
d. Tubeless Tire
(1) As light truck’s demand, tubeless tire is installed on deep notch rim. Its nominal rim diameter is larger than the same level rim, installed with inner tire, 1.5 in, and its nominal tire cross section width, except 6.50 in, is larger than the same level tire which is equipped with inner tire, 1 in. Meanwhile, it’s no need to add zero behind the size of section width. There is a list of the sign of tubeless tire of light truck and corresponding one with inner tire.
(2) Tubeless Tire of Truck
Its nominal rim diameter is larger than the same level rim, installed with inner tire, 2.5 in, and its nominal tire cross section width, except 7.50 in and 8.25 in, is larger than the same level tire which is equipped with inner tire, 1 in. Its section width is integer, and it’s no need to add zero behind the size of section width. There is a list of the sign of tubeless tire of truck and autobus and corresponding one with inner tire:
e. The Signs of other type Truck Tires
Ml is the tire of mining and forestry truck
HT is the tire of heavy truck
MH is tire of family travel car
ST is the tire of highway trailer
The Symbol of the Tires of Sedan
The symbol of the tires of sedan includes size, structural feature, load, characteristic of speed, and other usage characteristics.
(1) Size and Structural feature
The name of the specification of tires generally indicates the following:
a. nominal cross section width/ nominal rate of fla
b. the code of tire structure. The code of tire structure is expressed with the following letters. D means oblique structure, and R means radial structure.
c. The following list is the code of nominal rim diameter and the code of the tire, installed on rim.
The code of rim nominal rim diameter, mm The code of rim, mm The code of rim nominal rim diameter, mm
10 254 13 330 15 381
12 305 14 356 16 406
(2) The Characteristics of Usage Condition
The characteristics of usage condition include load index and signs of speed.
a. Signs of Speed, Under the specified usage condition, the signs of speed show tires’ speed level, when tire bears the load. According to international standard, the sign of sedan tire speed is L~ H level, and the corresponding speed level is 120～210km/h.
b. Other using Characteristics, The using characteristics of the tire side are load and pressure. Tubeless tire is often marked with the word “tubeless”. Sometimes, other marks have been put into use, such as the form of pattern and sense of direction.
(3) The examples of the signs of Tire Specifications
a. Normal section oblique car tire. The aspect ratio is 0.96. The cross section is close to circle. The signs are: 5.20, 5.60, 5.90, 6.40, 6.70, 7.10, 7.60, and 8.20,etc.
b. Low profile rubber car tire (the aspect ratio is about 0.88) ,and the bottom of sign is .00 or .50. For example, 5.00, 5.50, 6.00, 6.50, 7.00, 7.50, 8.00, 6.00-15, 7.50-14, etc.
c. Low cross section oblique car tire (the aspect ratio is about 0.82). The sign of it is 5.95, 6.15, 6.45, 6.95, 7.35, 7.75, 8.25, 8.55, 6.95-14, 7.35-15, etc.
d. The metric system of the tire. Using metric system indicates rim, British system shows rim diameter, “R” represents radial structure and one letter expresses speed level, such as 155SR13 and 215HR15. The rim of the metric system of the tire starts from 125 to 235, treating 10mm as one level.
Except “R”, many other signs have been used. For example, Michelin uses “X”; Prelli uses “Cinturato”; the Soviet Union uses “P” to mark radial structure, like 155－13P.
e. “70”series of car tire is one of widely used tire. Its specification method is similar to the metric system of tire, but only 70 nominal flat rate is added before signs of structure and speed. This rim starts from 145 to 215, treating 10mm as one level. With a certain rim, the load capacity of tire increases with the augment of rim diameter.
The specification methods of “60”series and “50”series are similar to “70” series. We only need to change “70”to“60”or to“50”.
f. In United States, if having the same codes of letter, regardless their rim diameter, the tires of letters-digital system have the same load capacity. For example, under a certain inter pressure, the load capacity of ER70SR14和ER70SR15 tire is the same. The first letter of specification indicates tire’s load capacity. In the letters-digital system, when the inner pressure is 0.17Mpa and 0.22Mpa, letter means the maximal workload.