Can You InterChange Between 275/70R18 and 275/65R18 Tire?

Almost any car owner has some idea about the tire brand. Unfortunately, very few of them know what a tire size index is. You can learn everything about tire size by looking at the tire size index. 

Talking about the tire size index, we are not going to talk about that in this article. Instead, we will be showing an in-depth comparison between 275/70R18 and 275/65R18, where both represent tire size index. The advantage is, you can learn everything about this index by going through this comparison. 

So, it will be like killing two birds with one stone when you learn the difference between 275/70R18 and 275/65R18, which we are going to discuss in this article. 

275/70R18 vs 275/65R18 Tire Difference: 4 Major Facts to Compare

The 275/70R18 tire is the new generation of the 275/65R18, with an increased aspect ratio. But that doesn’t mean there won’t be much difference. Stick to the article to find out more.

Before going to the main comparison, we should mention that we are going to break down the difference into 4 parts. Why? Because the tire size index usually consists of 4 parts. So, breaking down the tire 275/70R18, we will get the following – 

  • 275 stands for – Tire width in meters
  • 70 stands for – The aspect ratio of height/width
  • R stands for – Construction type
  • 18 stands for – Rim diameter in inches

We suggest reading the article on 285/70R17 vs 285/75R17 to know more about the tire size index.


Both tires 275/70R18 and 275/65R18 have the same first digit, which is 275. It suggests the width of both tires is the same, which is 275. Hence, the width is usually measured in millimeters, it is clear that both tires are 275 millimeters wide.

In order to find the width of a tire, you have to measure it from one sidewall to the other. Generally, the width that is written in the tire size index is measured directly by the manufacturers and it is 100% accurate.     

Aspect Ratio

In the tire size index, the aspect ratio is represented by the second digit. Therefore, tire 275/70R18 has an aspect ratio of 70 whereas, tire 275/65R18 has 65.

So, the difference in the aspect ratio of these tires is 5. It may seem minor, but this can have a significant impact on the compatibility of the tire.

The aspect ratio is expressed in percent and it is the ratio of the height and width of the tire. So, when we say a tire has an aspect ratio of 70, it suggests the height is 70% of the width of the tire. So, the equation goes like this –

Aspect Ratio of Tire = Height/Width x 100%

Construction Type

There is a letter in every tire size index, indicating the construction type. It is the letter after the second digit that represents the aspect ratio. Although we may see ‘R’ most of the time, there can be other letters as well. 

Here both tires 275/70R18 and 275/65R18 have the letter ‘R’. It indicates their “Radial Construction” so that anyone can understand that these are radial type tires.

These tires have sophisticated constructions with square footprints on the outside. Here is the overview of the usual construction types of tires –

  • R – Indicates the tire is a radial type
  • B – Indicates the tire is a bias ply or cross ply type  

Rim Diameter

The very last digit of the tire size index represents the rim diameter. It is the inner circular blank of the tire where the wheel adjusts.

To find the rim diameter, you need to start measuring from one open bead to the other in the same direction. Basically, ‘inch’ is the common unit of rim diameter.

When we compare 275/70R18 with 275/65R18, we find no difference in the rim diameter. Because both tires have the same last digit, which is 18. It means any one of these tires will easily fit a rim having 18 inches of diameter.    

A Deep Comparison Between Tire Size 275/70R18 and 275/65R18 

Time to draw the comparison chart of 275 70R18 vs 275 65R18. This comprehensive chart will give a quick overview in a short time.  

Parameter275 70R18275 65R18 Difference
Section width10.8 inch10.8 inch0 inch (0%)
Overall diameter33.2 inch32.1 inch-1.1 inch (-3.3%)
Circumference104.2 inch100.8 inch-3.4 inch (-3.3%)
Revs per km608.3628.8+20.5 (+3.4%)
Sidewall height7.6 inch7 inch-0.5 inch (-7.1%)
Aspect Ratio7065-5 (-3.5%)

To summorize 275/70R18 vs 275/65R18, we find changes in ground clearance to 0.5 inches and changes in the diameter to 3.3%, which is greater than 3%.

As a result, if one pair of 275/70R18 tires and the other pair of 275/65R18 tires are kept, there is a possibility of greater danger.

The following 2 pictures will show a comparison of 275/70R18 and 275/65R18 from front and side. 

Overall Verdict

At the end of this discussion, you may know everything about the difference between 275/70R18 and 275/65R18. Also, you may understand what tire size is. Perhaps, this will take you one step closer to choosing the perfect tire for your car. 

Whether you want to switch your existing 275/65R18 tires with 275/70R18 is up to you to decide. To avoid danger, try to change all 4 tires with the new ones, don’t keep two tires of one size and the other two tires of another size.

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