285 65R18 vs 275 70R18 Tire Size: What’s The Difference?

Thinking of switching the tires of your vehicle from one size to another? It shouldn’t be a problem if you change all the tires to the same size. The question is can you change only one or two tires to another size?

285 65R18 vs 275 70R18 Tire Size: What’s the Difference? Can you interchange them? Well, keep reading the article and you will find all the answers.

When you look at tire size, all you see is a bunch of numbers or combinations. These are not random numbers but tire size indexes. They tell you several factors about a tire.

Here in this article, we will discuss the difference between 285 65R18 and 275 70R18 in a way that you can understand the tire size just by looking at the numbers. It will also enable you to decide if they are interchangeable. To begin with, let’s learn the tire sizes right away.

What Size Tire is a 285 65R18?

The tire size of 285 65R18 is 285 millimeters in width, which is 11.22 in inches.The Sidewall Height of the tire is 185.25 millimeters, which is 7.29 inches. This tire is designed to fit an 18-inch wheel rim.

What Size Tire is a 275 70R18?

The tire size of 275 70R18 is 275 millimeters in width, which is 10.83 in inches.The Sidewall Height of the tire is 192.5 millimeters, which is 7.58 inches. This tire is designed to fit an 18-inch wheel rim.

As you can see, there is a difference in size between the two size tires. But can you interchange one or two of them? Find out how 285 65R18 and 275 70R18 differ considering 4 aspects and get your answer.

Find Out How 285 65R18 and 275 70R18 Differ Considering 4 Aspects

The numbers or combinations of a tire size index tell us about 4 factors of a tire – Width, Aspect Ratio, Construction Type, and Rim Diameter.

Let’s say, the tire size index 285 65R18 is fragmented, then we get this 4 information –

  • 285 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 discuss the differences between the two tire sizes considering these 4 aspects.

Width

If you measure from one sidewall to the other sidewall of a tire, you will get the width. It is expressed in millimeters. You can instantly learn the Width of a tire just by looking at the tire size index.

The first three digits of a tire size index indicate the Width of that tire. As you can see, the first three digits of 285 65R18 are 285. It means the width of that tire is 285 millimeters. Likewise, the three-digit number of 275 70R18 is 275. It means the Width of that tire is 275 millimeters. So the difference of the Width is 285 – 275 = 10 millimeters.

Now, if you switch to the tire size which is 10 millimeters more or less in Width, it shouldn’t be a problem. But you cannot switch tire size depending on Width only. You must consider the Sidewall Height as well. The Sidewall Height depends on Width and Aspect Ratio.

Aspect Ratio

The numbers or combinations of a tire size index tell us the Aspect Ratio of that tire. Aspect Ratio is measured in percentage. After the width, the next two digits indicate the aspect ratio of a tire. So, the aspect ratio of 285 65R18 is 65% and the aspect ratio of 275 70R18 is 70%.

We mentioned above that the Sidewall Height of a tire depends on its Width and Aspect Ratio. To be more specific, the aspect ratio of 285 65R18 is 65%. It means the Sidewall Height of this tire is 65% of its Width.

To calculate, the Sidewall Height of 285 65R18 tire size is 285 × 65% = 185.25 millimeters. Likewise, the aspect ratio of the tire size 275 70R18 is 70%. So, the Sidewall Height of this tire is 275 × 70% = 192.5 millimeters.

So, the difference of the Sidewall Height between the tires is 192.5 – 185.25 = 7.25 millimeters. As you can see, there is a big gap between the two tires. Moral of the story is that you cannot interchange between tire sizes 285 65R18 and 275 70R18. Doing so would affect your riding experience and the reading on the speedometer. If you switch from one size to another, make sure to change them all.

Construction Type

The tire size index informs you about the Construction Type of a tire. It is expressed by a letter in the tire size index. Both 285 65R18 and 275 70R18 have the same letter ‘R’. So, both the tires have Radial Construction in terms of construction type.

Such tires have a sophisticated construction with square footprints on the top. The radial type tires are ideal for driving on-roads. They are heat and water resistant. Radial type tires are next-gen tires and can provide great fuel efficiency.  

Another famous construction type is Bias Ply. They are also known as Cross-ply. It is expressed by the letter ‘B’ in a tire size index. This type is great for driving off-roads.

Rim Diameter

To know which tire size fits for your vehicle, you must know the wheel rim size of your vehicle as well as the Rim Diameter of a tire. For instance if your vehicle has an 18-inch wheel rim, you can use the tire which has an 18-inch Rim Diameter.

By looking at a tire size index, you can learn instantly the Rim Diameter of a tire. The last two digits of a tire size index indicate the Rim Diameter. It is measured in inches. As you can see, the Rim Diameter of 285 65R18 is 18 inches. Similarly, the Rim Diameter of 275 70R18 is 18 inches.

It means that if your vehicle has an 18-inch wheel rim, you can use both the tire sizes. But make sure to use the same size tires for all the wheels.

Wrapping Up with a Comparison Table between 285 65R18 and 275 70R18:

Aspects285 65R18275 70R18Difference
Diameter inches32.5933.160.57 (1.8%)
Width inches11.2210.83-0.39 (-3.5%)
Circumference inches102.37104.171.79 (1.8%)
Sidewall Height inches7.297.580.29 (3.9%)
Revs per mile618.91608.25-10.66 (-1.7%)
Aspect Ratio %65705

Clearly, the 285 65R18 tire is wider and smaller in size than the 275 70R18. The 275 70R18 size tire is 0.29 inches bigger than the other one in respect of Sidewall Height.

So, you cannot interchange the tires. In simple words, if you decide to switch from one size to the other, you must change them all. You cannot change only one or two tires to a different size.

Final Words

Now you know how to interpret a tire size by looking at the tire size index. It’s a piece of cake to learn the Width, Aspect Ratio, Construction Type, and Rim Diameter of any tire.

By calculating and comparing these 4 aspects, you can decide which tires are suitable for your vehicle. In the end, it is evident that 285 65R18 and 275 70R18 tires are not interchangeable.

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