Use the same principle they use in agriculture tires:
Car Tire Inner Tube Sizes
E.G. 3.00-4, 3.50-6, 4.00-8, 5.20-10, 6.00-12
The simplest size marker is this one. The first component, 3.00, merely indicates the tire’s width and sidewall height in inches. The rim diameter, expressed as -4, is given in inches. Therefore, a 3.00-4 tire would have a 4″ rim diameter, be 3″ broad, and have a 3″ sidewall. The total height of the tire would be 10″ as a result (4″ plus 3″ plus 3″).
E.G. 6-12, 7-14, 8-16, 9.5-18
Similar to the method described above. However, this approach omits the ‘.00’ bit for the first half of the size. All measurements are once more in inches. It is important to note that tires with extremely similar markings may not be compatible; for example, a 6.00-12 and a 6-12 would have very different sizes.
If you alter the tire size on a four-wheel drive tractor, the gear ratios will be affected, which may have more serious repercussions than
changing the tire size for a two-wheeled rotavator. If in doubt, stick with the precise size specified by the manufacturer or fitted to the vehicle.
E.G. 4.10/3.50-4, 4.10/3.50-6, 5.30/4.50-6
This time, the tire size is divided into three pieces, each measured in inches. The first number, 4.10, represents the tire’s approximate width when mounted on the suggested wheel.
The sidewall height is the second number, 3.50, and the rim diameter is the third number. A 4.10/3.50-4 tire, then, is 4.1″ wide, 3.5″ height on the sidewall, and it fits a 4″ rim. As a result, this tire has a low profile. It is narrower than it is high, etc.
E.G. 11×4.00-4, 13×5.00-6, 18×8.50-8, 25×12.00-9
This approach is the simplest to learn and is frequently used on turf and ATV tires. The overall height of the tire, measured in inches from the bottom to the top, its width, measured in inches, and its rim diameter, measured in inches, make up the first, second, and third parts.
If you want to modify the size of your tires, you can choose the height and breadth based on your requirements, but the rim diameter must remain the same unless you also want new wheels. A 25×12.00-9 ATV tire measures 25 inches high by 12 inches wide by 9 inches broad.
E.G. 10×3, 18×4, 260×85
Although this technique is getting dated, you can still have tires imprinted in this manner. Inches or millimeters can be used for measurements; if you look at the examples above, it should be clear which. The entire tire height is the first component, followed by the width.
This size designation does not include the rim diameter, but it may be calculated easily because the tire sidewall height will match the tire width. A tire that is 18″ tall, 4″ wide, and fits a rim with a 10″ diameter is known as an 18×4 tire (18 total height minus two lots of 4 high sidewalls).
Therefore, a 4.00-10 would be the size of an 18×4 in current terms. A 260×85 tire has a height of 260mm and a width of 85mm. These measurements translate to a 10″ high, 3″ broad tire mounted on a 4″ rim. The size in use today would be a 3.00–4.
E.G. 145R10, 255/60-10, 155R12, 195/50R13
Since this is the typical method for labeling car and van tires, trailer and caravan tires are also frequently marked in this way. The first component is the tire’s width in millimeters, the second, if any, is the sidewall height represented as a percentage of the width, and the third is the rim diameter in inches.
The tire’s sidewall height is assumed to be 80% of the width when there is no percentage indication of the tire size. Sometimes, a tire with an 80% rating in size, such as 155/80-13, will be shown. When the letter ‘R’ appears in size, it denotes a radial structure for the tire.
In other words, a 145R10 is a radial tire that is 145mm wide, with a sidewall height of 116mm (or 80% of 145mm), and fits a 10″ rim. A 195/50R13 tire would measure 195mm broad, 98mm tall at the sidewalls, and fit a 13″ rim.
By converting both measurements to either mm or inches and multiplying the rim diameter by two times the sidewall height, one may get the estimated overall height of the tire.