Do you know these little things about car tires

International standard tire code, expressed in millimeters as the percentage of section height and flat ratio. Add: tire type code, rim diameter (inch), load index (allowable bearing mass code) and allowable vehicle speed code. For example, 175 in 175 / 70r 14 77h means that the tire width is 175mm, 70 means that the flat ratio of the tire section is 70%, that is, the section height is 70% of the width, the rim diameter is 14 inches, the load index is 77, and the allowable speed is class.
General tire specifications can be described as: [tire width mm] / [percentage of tire thickness and tire width] R [hub diameter (inch)] [load factor] [speed identification] or [tire width mm] / [percentage of tire thickness and tire width] [speed identification] R [hub diameter (inch)] [load factor] For example, tire: 195 / 65 R14 88H or 195 / 65h R15 88 can be interpreted as: tire width - 195mm, the percentage of tire thickness to tire width is - 65%, that is, tire thickness = 126.75126.75/195 * 100 = 65 (%). Hub diameter - 15 inch load factor - 88 speed factor - H. generally speaking, understanding [tire width] / [percentage of tire thickness to tire width] R [hub diameter (inch)] is helpful to replace tires suitable for your vehicle. Understanding the [load factor] [speed system mark] of tires is helpful to driving safety. Tire speed identification table speed identification maximum speed common model n 140 km / h spare tire spare tire 150 km / HQ 60 km / h snow tire, light truck tire winter, LT tire 170 km / h light truck tire LT tires 180 km / HT 190 km / Hu 200 km / HH 210 km / h sports car sports car 240 km / h sports car carsz 240 km / h sports car (or greater than 240 km / h) W 270 km / h special sports car exotic sports car 300 km / h special sports car exotic sports car note: 1. The more common tire speed marks are, s, t, H2. If the tire has no speed mark, unless otherwise specified, it is generally considered that the maximum safe speed is 120km / h. The following are some common marks on tires. This figure is a typical North American tire mark for reference only.
Tire size / tire size, load rating index / load factor, speed rating index / speed identification. Radial tires are generally used for the wheels of cars. The specifications of radial tire include width, aspect ratio, inner diameter and speed limit symbols. Taking crown 3.0 car as an example, its tire specification is 195 / 65r15, indicating that the width between the two sides of the tire is 195mm, 65 indicates the aspect ratio, "R" represents the word radial, indicating radial tire. 15 is the inside diameter of the tire, in inches. Some tires are also marked with speed limit symbols, which are represented by letters P, R, s, t, h, V and Z respectively.
In particular, it should be pointed out that the aspect ratio, which means the percentage of tire wall height in tire width, is between 50 and 70 for passenger cars. The smaller the value, the more flat the tire shape. With the increase of vehicle speed, in order to reduce the center of gravity and axis of the car, the diameter of the tire is shrinking. In order to ensure sufficient bearing capacity and improve driving stability and grip, the width of the tire and rim has to be increased. Therefore, the cross-section shape of the tire has developed from the original approximate circle to the flattened ellipse. In recent years, cars have realized radial tire tubeless, commonly known as "atomic tire". This kind of tire is not easy to accumulate heat during high-speed driving. When the tire is pierced by nails or sharp objects, the air leakage is slow, and it can continue to drive for a distance. In addition, atomic tire has the advantages of simplifying production process, reducing weight and saving raw materials. Therefore, assembling atomic tires has gradually become a trend in the field of cars. Tire specification classification at present, there are many ways to express tire specifications. Generally, there are four kinds of tire specifications on the market: British system, German system, metric system and American system. We will briefly explain the next four kinds. The specification of the British system is adopted by the former vassal countries of Britain, and the unit is inches. For example, 4.00 h 18 4pr means 4 inches wide, applicable to speeds below 20km / h, tire rim diameter of 18 inches and 4 ply strength. In the metric system, the description of tire characteristics is relatively complete at present. It is similar to the German system, but the sign of "-" low-pressure tire is cancelled, and the word "R" is used instead to represent the radial tire. For example, the rear wheel of FZR400 is 140 / 60r18 64H, and the R of R18 means that the tire is radial tire. The German specifications are similar to the "metric system". In addition to the tire width expressed in mm, the flat ratio of the tire is also increased, the inner diameter of the tire is still in inches, and there are load index and speed marks behind the inner diameter. For example: 140 (tire width 140mm) \ 70 (flat ratio 70%) - (low tire pressure) 18 (inner diameter 18 inches) 66 (load index 66) H (speed mark below 210km / h), while the prefix of American regulations indicates the applicable vehicle type of the tire, the second letter indicates the width of the tire, the third word indicates the flat rate, the fourth letter indicates the speed mark, and finally the diameter suitable for the steel ring. Among them, the value of J in the load index table ranges from 21 to 74. The larger the value, the stronger the load capacity. Generally, for 400cc to 750cc heavy vehicles, the J value is about 63 to 67 and the front wheel is about 57 to 58; In addition, the speed mark of tubeless wheel indicates the maximum speed that the tire can withstand. It is expressed in English letters. The later the letter, the higher the allowable speed limit. S: table is applicable to less than 180 km / h; Height meter: applicable to below 210 km / h; V: the meter is applicable to more than 210 km / h; S. H and V can be seen by ordinary vehicles and are also called high-speed tires. Generally, if the tire is lower than the above speed mark, it is not marked with speed mark. Therefore, as long as we see the speed mark after the s letter, it can be regarded as high-speed tires. For vehicles with low flat ratio, the tread becomes very wide under the same diameter because the tire wall is short. In this way, the grounding area can be increased, the pressure that the tire can bear is also large, and the tire is very sensitive to the road surface. Although the tire with high flat ratio has sufficient buffer thickness, the feeling of the road surface is poor, and the lateral resistance during turning is weak, so it can not have very stable performance. When the locomotive turns at high speed, the body must have a large roll, so the lateral stress is small. Moreover, in order to consider the small convex and concave road surface of the tire, it can still calmly absorb the vibration. Therefore, 80% of the low flat radiation tire can give full play to its performance.
The ratio of the maximum width measured from the tire section to the height from the rim to the tread is the flat ratio, which is expressed in percentage, that is, the height accounts for the percentage of the width. Most of them are 100 to 80 used on locomotives. However, at present, high-performance imitation racing cars also use tires with high flat ratio of 70 ~ 60, and commercial tires also begin to appear vehicles with wide surface and low flat ratio. Due to the large lateral shear force when turning, ultra-low flat tires with a flat ratio of 45% will even appear in four-wheel sports cars, but the general sports cars are still between 50 ~ 55 in order to maintain comfort.
As the name suggests, the specification of front tire is the specification and size of automobile front tire; The front and rear tire specifications of most cars are the same. In a few sports cars, rear wheel drive and other high-performance special-purpose vehicles, the front and rear tire specifications will be different. If the displacement is taken as the measurement standard, generally, the larger the displacement is, the larger the tire specification will be. Of course, the tire specification will directly affect the comfort, beauty and passing performance of the whole vehicle. International standard tire code, expressed in mm as the percentage of section height and flat ratio, followed by: tire type code, rim diameter (inch), load index (allowable bearing mass code), allowable vehicle speed code. For example, 175 in 175 / 70r 14 77h means that the tire width is 175mm, 70 means that the flat ratio of tire section is 70%, that is, the section height is 70% of the width, the rim diameter is 14 inches, the load index is 77, and the allowable vehicle speed is class H. The displacement of small car is between 0.8-1.5, and the corresponding front tire specification is 155 / 65r13 73t -- 175 / 70 r 14 77h. The size of the front tire is small, so the friction between the front tire and the ground is reduced during driving, so it is more economical in terms of fuel. This is also the main reason why most consumers choose small displacement cars, but the resulting negative impact is that its limited tread diameter will greatly reduce its Trafficability and comfort, When driving a small displacement car over a ridge, you often have no bottom. Small tires make the steering gear lighter. In most small displacement cars, power steering is not equipped. The displacement of large cars is between 1.6-6.0, and the tire specification is in the range of 185 / 60 R 14-245 / 50 r 18. Large size tires will make the whole body look domineering. Good adhesion to the ground ensures its acceleration performance and body stability at high speed. Some special off-road vehicles and modified racing cars have different front and rear tire specifications. Generally, the front is small and the rear is large. If it is a four-wheel drive model, it will also involve the problem of inter axle differential. Because the sizes of the front and rear wheels are different, the driving of the car will be affected When the car is walking on the ground, it will take longer for the rear wheel to turn around than the front wheel, which will affect the normal movement of the front and rear axles.
Rear tire specification rear tire specification, as the name suggests, is the specification and size of automobile rear tire; Most cars have the same front and rear tire specifications. In a few sports cars, rear wheel drive and other high-performance special-purpose vehicles, the front and rear tire specifications will be different. For example, in the annual refitted car competition in California, some car friends will refit their front and rear tires with different specifications, so that the front and rear tires will have a diameter difference of 1-2 meters, highlighting their differences. The drivers' clothes are also quite distinctive, giving people a very "alternative" feeling. It will be more convenient for two-wheel drive vehicles to carry out this modification, because the problem of inter axle differential will not be involved in the modification process. Even if the specifications of front and rear tires are different, it will not affect the normal driving of the vehicle. If you want to refit a four-wheel drive vehicle with inconsistent front and rear tire specifications, it will be a lot of trouble compared with a two-wheel drive vehicle. A four-wheel drive vehicle will involve the problem of inter axle differential. Because the sizes of the front and rear wheels are different, there will be a speed difference between them. If the inter axle differential is not installed, the two wheels will "compete" with each other, Therefore, the vehicle will not operate normally, resulting in serious damage to tires and transmission shafts!