Two tires are exactly the same? Parameter details hide differences

Ultra-low rolling resistance, super load-bearing, super silent, in the circle of trucks, everyone has heard such a shouting voice, right? Under the name of various "super", it seems that every tire has become a "specialty", taking the most common 295/80R22.5 and 12R22.5 tires of our tractor as an example, the two seem to be no different, but in fact they have their own strengths.

First of all, I will leave you a question, when choosing a car, who will you choose for these two types of tires?

▎ It seems to be the same, but in fact, there are high and low

First of all, let's directly talk about the tire specification coefficient that confuses people. In terms of units of measurement, tires mainly have metric and imperial units, the metric unit is the international unit, which was first used as a unit of measurement by France in 1799, using the decimal carry system, adopted at the International Conference on Weights and Measures in 1960, recommended for application in various countries, which is currently the most widely used unit of measurement. In layman's terms, metric units are meters, kilograms, seconds, and so on, which we are very familiar with.

At present, the imperial unit is more used in the United States, Libya and Myanmar and other countries, China's early tire production technology introduced the imperial standard, so the production of bias tires and even later steel wire radial tires also use the imperial specifications. For example, our common units such as inches, pounds, gallons, etc.
 

Then, our common 12R22.5 tires on tractors are in imperial units, refer to the figure above. 12 represents a wheel section width of 12 inches, which is approximately equal to 30.48cm (section width, which can be understood as the data at the widest part of the sidewall on both sides of the tire). While the R stands for radial tires, 22.5 means that the rim (wheel) diameter of the tire is 22.5 inches, which is about 57.15cm.

In addition, another common 295/80R22.5 tire is currently the most widely used metric unit, 295 represents the same section width, which is 295mm, that is, 29.5cm. 80 is the flat ratio of the tire, which represents the cross-sectional height of the tire is 80% of the tire width, 29.5cmX0.8=23.6cm. More generally, the smaller the flat ratio, the lower the tire looks, for example, many low-saddle tractors now use 295/60R22.5 tires. In addition, the R22.5 at the back of the specification is the same as the previous specification of the British tire, and the wheel rim is installed with a diameter of 57.15 cm.

▎Interpretation of the difference: Only the bearing factor is the same

Having said all this, what is the difference between 295/80R22.5 tires and 12R22.5 tires?

Width difference: First of all, the difference between the two tires in terms of width and size is very intuitive, the widest part of the 12R22.5 tire is 30.48 cm, while the widest part of the 295/80R22.5 tire is 29.5 cm, the difference between the two is about 1 cm. So the question is, is there a difference between the tire section width and the tire tread width?

Here I would like to thank the forum card friend Gao Ge and card friend Chen for some data. In order to help everyone understand, the tire section width can be understood as the section width of the tread on both sides of the tire under normal pressure, and the tire tread width refers to the tire ground width. Taking 12R22.5 as an example, the common inflatable section width is 30cm, and the tread width is mostly concentrated in 23cm and 24cm, and the tire width can reach about 25cm in the pursuit of driving force for dump models. The 295/80R22.5, the inflatable section width is about 29.8cm, and the tread width is mostly 24cm.

Let's talk about the advantages first, no matter what kind of tire it is, choosing a tire with a wider tread will bring a larger ground contact area, even if the output horsepower is the same, the load is the same, and the tire pattern is the same on the heavy truck, such as choosing a wider tire, its grip and anti-slip ability will be better, especially in relatively harsh working conditions, it can bring better driving force performance. At the same time, there is a slight difference in driving stability and braking distance.

However, a larger ground contact area does not mean that the tire is better, and such tires also have shortcomings. For example, among the 12R22.5 tires of the same specification, choose 24cm/25cm with a larger tread width, although the grip is better, but it will also produce stronger rolling resistance, which will have a certain impact on fuel consumption.

Tire diameter difference: It is often asked whether the tire size of 12R22.5 is the same as that of 295/80R22.5? In fact, the question here is the diameter of the tire, and the answer is that there is a difference, and the tire diameter of 295/80R22.5 is smaller.

Let's take Bridgestone R150 tires as an example, the difference between the outer diameter of 12R22.5 and 295/80R22.5 is about 4.6 cm, and the size of 295/80R22.5 is relatively smaller. At the same time, we have tested the difference in loading height on the previously loaded tires, the loading height of a certain brand 12R22.5 is about 107cm, and the loading height of 295/80R22.5 tires is about 102cm, that is to say, two identical cars are equipped with tires of different specifications, and the height difference is 2.5cm. (On trucks, there is a certain difference between the free radius and the load radius of the tires depending on the load.) ）

左右对比 明显295/80R轮胎高度更低

In short, the tire diameter of 295/80R22.5 is smaller than that of 12R22.5, and the rolling radius and tire circumference will be different, so if the tire rotates the same number of laps, the 12R22.5 will run longer. Therefore, don't underestimate the difference in radius of 2.5 cm, there will be a difference in fuel consumption between the two under long-term use conditions.

In addition, due to the smaller overall radius of 295/80R22.5 tires, the frame height can be relatively lower, the saddle ground clearance is lower, and there is relatively more room for play in the height selection of the trailer. Of course, in some of the pursuit of a larger amount of tractors, will use smaller flat ratio tires, such as the liberation, Sinotruk, Foton and other car companies for express delivery in the pursuit of the volume of transport in the field, have launched 315/60R22.5 small size tires, in the low saddle, airbag bridge blessing, the volume of transport will directly increase by about 5, 6 square meters.

If you pay attention to the observation, you can find that at present in the long-distance standard load of the trunk logistics transportation, the application proportion of 295/80R22.5 tires is increasing, relatively speaking, in the case of the same tire pattern and the same tire material, 295/80R belongs to the low flat ratio tire, its handling performance is relatively better at the same time, the deformation under heavy load is smaller, and the tire stability is higher, but the corresponding production process and materials of tires have higher requirements. And, there's one piece of information that seems to be overlooked, the weight difference.

Weight difference: According to the previous tire brand technicians, in the same brand, the same material, the same process, 295/80R22.5 size tires will be 4-5 kg lighter than 12R22.5 tires, a 6-axle tractor 22 tires, the weight difference of the whole vehicle is about 88-110 kg, equivalent to the weight of a strong man. For tractors with a capacity of nearly 50 tons, the burden on tires alone is not large, but as the key to reducing the weight of the vehicle system, it is also an indispensable key to realizing the lightweight of the vehicle.

Judging from the above information, 295/80R22.5 size tires look lighter, smaller and more fuel-efficient than 12R22.5 tires, so is there a difference in load factor?
 

In fact, we can pay close attention to the logos on the tires of the tractor, usually no matter what kind of tires there will be two other logos that represent the load carrying performance, the load factor and the PR tire level. For example, the common 152/148M logo, of which 152/148 represents the load index, referring to the GB/T 2977-2016 tire specifications, size and load, you can see that the single-wheel carrying capacity of the two is 3550kg, and the load of the two wheels is 3150kg, which means that there is no difference in the carrying performance of the two (M stands for the maximum speed mark, that is, 130km/h).

After looking at a bunch of parameters, there is a conclusion that in the case of the same brand, the same material, the same process, and the same model, 295/80R22.5 relative to 12R22.5 tires, has certain advantages in terms of fuel consumption, weight and height, so do we choose tires directly on the 295/80R22.5 to choose? In fact, as mentioned above, the choice is made in combination with the transportation conditions, after all, only you know whether the shoes fit or not. By the way, the tires matched by the original car can not be changed at will, because in the calculation of vehicle speed, the rolling radius of the tire is an important parameter, 12R22.5 is larger than the relative rolling radius, if you change to a smaller tire, you need to match the parameters at the service station.

丨Conclusion丨

Judging from the current trend, commercial vehicles are developing towards low carbon, high efficiency and lightweight, in terms of specifications, 295/80R22.5 tires have more development potential for heavy-duty commercial vehicles in terms of lightweight, weight reduction and fuel consumption, which is why this tire model is more recommended at this stage under high-speed standard load conditions.