It is very essential to know the size of a tire before you purchase it. When you look at tire size, you can see a bunch of numbers. What do these numbers signify? These are called tire size indexes. They tell you 4 important factors about the size of a tire.
Can you interpret the tire size index? 265 65R18 vs 275 65R18 Tire Size: What’s the Difference? Here we are; this article will help you to interpret tire size index. You will be able to understand the size of a tire properly just by looking at the numbers. It will enable you to understand if 265 65R18 and 275 65R18 tires are interchangeable. First of all, let’s learn the tire sizes right away.
If you know the exact size of a tire, you can decide if the tire is compatible with the vehicle or not. The tire size of 265 65R18 is 265 millimeters in Width, which is 10.43 in inches.The Sidewall Height of the tire is 172.25 millimeters, which is 6.78 inches. This tire is designed to fit an 18-inch wheel rim.
The tire size of 275 65R18 is 275 millimeters in Width, which is 10.83 in inches.The Sidewall Height of the tire is 178.75 millimeters, which is 7.04 inches. This tire is designed to fit an 18-inch wheel rim.
As things stand, there is a difference in the size of the two tires. But how can you know the tire size just by looking at the tire size index? Let’s find out right below.
The numbers on a tire size index are not random numbers. You can learn 4 aspects about a tire from the tire size index – Width, Aspect Ratio, Construction Type, Rim Diameter. You can instantly learn these aspects of a tire just by looking at the numbers. It will help you to decide the right tire size for your vehicle for purchasing or switching.
Let’s say, the tire size index 265 65R18 is fragmented, then we get this 4 information –
- 265 stands for – Tire Width in Millimeters
- 65 stands for – The Aspect Ratio of Height/Width
- R stands for – Construction Type
- 18 stands for – Rim Diameter in Inches
Here we will compare the tire sizes 265 65R18 and 275 65R18 regarding these 4 aspects. It will help you to decide if the two size tires are interchangeable or not.
To begin with, the tire size index informs you the Width of a tire. It is measured in millimeters. To get the Width, you need to measure from one sidewall to the other sidewall of a tire. Width determines if the tire is wider or thinner.
The first three digits of a tire size index indicate the Width. As you can see, the first three digits of one of the tires are 265, and the other’s are 275. It means that the Width of the tire 265 65R18 is 265 millimeters. Likewise, the Width of the tire 275 65R18 is 275 millimeters. So the difference is 275 – 265 = 10 millimeters.
Hence, the 275 65R18 tire size is wider than 265 65R18. Now, the question is can you interchange the tires? Can you switch only one or two tires to another size? Well, to get the answer, you need to compare the Aspect Ratio or Sidewall Height of the two tires.
The next thing you can learn from the tire size index is the Aspect Ratio. After the Width, the next two digits indicate the aspect ratio of a tire. So, the aspect ratio of 265 65R18 is 65 and the aspect ratio of 275 65R18 is also 65. The aspect ratio is measured in percentage.
The most important thing about aspect ratio is that it tells the Sidewall Height of a tire. As the Aspect Ratio of 265 65R18 is 65%, the Sidewall Height of this tire will be 65% of its Width. Similarly, the Aspect Ratio of 275 65R18 is 65%. So, the Sidewall Height of this tire will be 65% of its Width.
To calculate, the Sidewall Height of 265 65R18 is 265 × 65% = 172.25 millimeters, which is 6.78 in inches. As for 275 65R18, the Sidewall Height is 275 × 65% = 178.75 millimeters, which is 7.04 in inches.
Evidently, there is a big gap between the Sidewall Height of the two tires. In simple words, the 275 65R18 tire is taller in size than the 265 65R18. So, the moral of the story is that you cannot interchange the two tires. If you want to switch from one size to another, you have to change all the tires. Otherwise, it will affect your vehicle performance.
You can learn the Construction Type of a tire instantly just by looking at the tire size index. The letter in the tire size index informs you about its construction type.
As you can see, both the tires have the letter ‘R’ in their tire size indexes. It means that both the tires have Radial Construction. Such tires have a sophisticated construction with square footprints on the top. The radial type tires are ideal for driving on-roads. They provide great gas efficiency. These tires are highly water and damage resistant.
Another well-known construction type is Cross-ply. It is also known as Bias-ply. This type of Construction Type is expressed by the letter ‘B’ in the tire size index. They are better for driving off-roads.
Rim Diameter is another essential aspect to learn about a tire. Fortunately, you can learn the Rim Diameter of a tire instantly just by looking at the tire size index. The last two digits of a tire size index indicate its Rim Diameter. It is measured in inches.
The Rim Diameter of 265 65R18 is 18 inches. Similarly, the Rim Diameter of 275 65R18 is also 18 inches. The suitability of a tire with your vehicle depends on the Rim Diameter. If the wheel rim of your vehicle is 18 inches, you need a tire which has an 18-inch Rim Diameter. So, both the tires are suitable for the vehicle which is 18-inch in wheel rim. As the tires are not equal in size, you can use only one tire size at the same time.
Wrapping Up with a Comparison Table between 275 65R18 and 265 65R18:
|Aspects||275 65R18||265 65R18||Difference|
|Diameter inches||32.07||31.56||-0.51 (-1.6%)|
|Width inches||10.83||10.43||-0.39 (-3.6%)|
|Circumference inches||100.77||99.16||-1.61 (-1.6%)|
|Sidewall Height inches||7.04||6.78||-0.26 (-3.6%)|
|Revs per mile||628.78||638.98||10.20 (1.6%)|
|Aspect Ratio %||65||65||–|
Evidently, both the tire sizes are usable for an 18-inch wheel rim. But there’s a huge difference between the two tire sizes. The difference of the Sidewall Height is 7.04 – 6.78 = 0.26 inches. So, one tire is taller than the other one. So, if you decide to switch from one size to another, make sure to switch them all. Otherwise, it can affect your riding experience.
The numbers are essential for understanding the size of a tire. As you have read the whole article, we assume now you know a lot about tire size. Now you can calculate tire width, sidewall height, construction type, and rim diameter of a tire just by looking at the tire size index. In the same way, you can calculate and compare these 4 aspects and decide which tires are suitable or interchangeable for your vehicle.