Calculation of Tire Size in Tractors

Suppose that we will change, reduce or enlarge the tire size of our tractor. Can we wear a tire we like, like?
Double pull, ie 4×4 tractors must match the proportions of the front tire and the rear tire. For this, it is necessary to know the exact meaning of the numbers on the tire.

There are three numbers on the tires to indicate dimensions. Like 320 70 24. The problem is solved if you know exactly what these figures mean, and most people know it is incomplete or incorrect.

1-) The first number, 320, is the expression of the tire’s base width in mm. So the base width of our sample tire is 32 cm. Everyone knows that.
2-) The last number, ie 24, represents the wheel diameter and the number is always given in inches. Everyone knows that.
3-) The number that is important and the number unknown by the geographer is the middle number. The width of the tire’s cheek. This is important here.
This figure is neither millimeter nor cm nor inches. This number is not a unit of length, but a “percentage” language.
What’s the percentage?
Answer: Percentage of tire side to tire base!
It is very simple to calculate the width of the cheek. All we have to do is find the tires of the tires we want to change. If this difference in cheek height is less than 3 cm, we can replace these two tires tirelessly or replace each other.

Here’s an example:
280 85 24 (base 280 mm, up to 85% of cheek base)
280 x 0.85 = 238 mm i.e. 23.8 cm. (this is the width of the cheek)
Other tire:
320 70 24 (base 320 mm, up to 70% of cheek base)
320 x 0.70 = 224 mm i.e. 22.4 cm. This is our second cheek width.
Let’s look at the difference:
23.8 – 22.4 = 1.4 this is a side difference. 1.4 x 2 = 2.8 cm for both cheeks at the top and bottom.
Since the difference is less than 3 cm, we can use these two tires easily instead of each other.
This is the ideal figure for the difference that the gearboxes can tolerate, 3 cm difference. Otherwise, there may be contractions in the tractor.
Simply think of the original factory tires that come on the tractor. Even they wear out in time to finish their teeth and when the teeth of 5 cm are exhausted, a full 10 cm diameter difference can occur between the rear tire and the front tire. It’s interesting that my gear can still work without trouble.
In a nutshell:
By the order of 320, 70, 24 digits:
Base width (in mm), percentage of the side to base (in%), rim diameter (in inches)
Note 1: 1 inch: 2.54 cm 25.4 mm
Note 2: It is not necessary to add the last digit to calculate as long as the wheel is not changed.
Note 3: If you also make changes to the rim size, the last number with the rim diameter is added to the calculation. His account is a bit different.
Now let’s do this for you. We do it with “newspaper test”:

Newspaper test:
1-) Pull the tractor on a flat, hard floor.
2-) Open a newspaper paper about 1 meter ahead of the front wheel.
3-) Without connecting the fronts (4×2), just pass the front wheels through the journal.
4-) Put this newspaper in the side
5-) Do the same thing with another newspaper only this time ‘connecting the fronts’ (4×4 form).
Then compare these two newspapers. According to the results:
A-) If there is no difference between them: front-rear tire compatibility super
B-) In the second trial (4×4 form), if the newspaper is wrinkled more than the first newspaper: there is a discrepancy between front and rear tires. The worse the newspaper is, the more incongruity it is. It means that there is an increase in fuel, a fall in dodge, plus a risk of malfunction. It is used by taking into consideration these risks of lacquer.
C-) In the second trial (in the form of 4X4), if the newspaper is torn in the torn yard: incompatibility is in dangerous level. The probability of failure is high. Unless there is a very urgent situation in the soil layer, the asphalt layer should never be touched. So size change is necessary.
Another problem that arises when changing the wheel sizes is that the dimensioning in agricultural and work machinery is given in the old style inch format. While the new metric system has begun to be used, many companies still continue to offer sizes in inches. Then:
What are the dimensions of the wheel dimensions defined in inches? Also how are they translated into the system of the merits?
The reading of the dimension phrases given in inches is slightly different. Here again 3 numbers are given, but since it is a large unit inches, there are fractions and decimals at the points where necessary. That is, the number four of 12.4 expresses only fractions in decimal. It is not a separate unit.
Also, the middle number, which is always the fault, appears again and this time the cheek neck is not expressed in centimeters but in inches.
As an example, let’s take 12.4 / 11 24 times the size of the front wheels used in most tractors.
12.4: width of the base in inches. We have a base width of 12.4 x 2.54 = 315 mm (31.5 cm). (Most producers round this to 320)
11: elevation in inches (no more slices). 11 x 2.54 = 279.4 mm (27.94 cm) we have a cheek height (most manufacturers roll it to 280)
24: this is the diameter of the wheel that has never changed at all.
We can call the size of 12.4 / 11 24 as 315 280 24 or as 320 280 24. Because of the millimeter rolls between them, the 1-2 mm width and sidewall differences should not have any qualifications on heavy duty machines such as tractors. When a tractor with a 7 cm tooth size squats the rear tire, it loses 140 mm in diameter just in front of it, and still retains the front-to-rear transmission ratios. 1-2 or even 5 mm difference is nothing besides this.

Another important point is that some old tires only have 2 numbers. In these cases, the tire sidewall height is the same as the base width and there is no need to specify. This is also the case when the middle digit is ’00’.
For example, a tire of size 6.50 / 00 16 actually refers to a size of 6.50 / 6.50 16, where ’00’ is actually 100% of the ratio of the bottom to the bottom.


All the figures are given in full inches, and the tires are mostly English and British based, making this a bit of a hassle because they are easy to leave traditions.
With the above method, we can compare and compare the desired tire size in inches.
Note: Tires specified by expressions such as 6×13 refer only to the base width and the total diameter of the tire. He does not care about the cheek width. It is used only on some heavy duty and special industrial machinery.
Additional information: The tire base widths always actually end in 5. 195, 245, 315. The reason is just an old habit. The new has begun to change.


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