Are 33-inch tires the same as 285? There is no doubt that trying to figure out which size tire will fit your truck, jeep, or off-road rig can be a bit of a guessing game.
Being able to read and understand different sizes and measurements is extremely important. That’s why in today’s post we are going to cover the basic differences between 33-inch and 285 tires.
Keep on reading to learn more!
Understand Metric and Imperial Tire Sizes
Are 33-inch tires and 285 tires the same? That’s exactly what we want to find out. But first, you need to know the parts of the tire and understand what metric and imperial mean in terms of tire sizes to be able to pinpoint the differences.
Parts of the Tire
The entire assembly is made up of two parts, the rim (metal bit) and the tire around the outside. The combination of the two gives you the wheel. The part on the side along the circumference of the tire is called the sidewall. Over the top, you’ve got the tread area or tread face.
Now that you know the basics, let’s try to understand what metric size means. The metric size we are concerned with is 285/70/17.
The 285 in this metric size refers to the width of the tread in millimeters, which stretches from one sidewall to the other.
The second measurement (70) is the aspect ratio. And that’s where it can get confusing for some people. This is the sidewall measurement, which means 70 percent of the tread width. There isn’t a direct measurement for the sidewall, just the percentage.
The final measurement (17) refers to the diameter of the rim in inches.
Calculating Overall Diameter
Now you know what each number in the metric system means. To calculate the overall diameter, you need the tread width (285 mm), sidewall height (70 percent of 285 mm), and the rim diameter (17) in inches. Here are the steps you need to follow:
Step 1: Calculate the height of the sidewall
This is easy to do. Just multiply 285 mm by 70 percent to get 199.5 mm. Every tire has two sidewalls: one at the top, and the other one at the bottom. So, you have to multiply 199.5 by 2 to get 399 mm.
Step 2: Convert the rim diameter to metric
You can convert the rim diameter to metric by multiplying 17 by 25.4 to get 431.8 mm.
Step 3: Add everything and convert to inches
Then, go ahead and add everything up, which is 399 mm plus 431.8 mm to get 830.8 mm. But, we don’t talk about tire overall diameter in millimeters, instead, we use inches. So, you have to convert the 830.8 mm into inches. All you’ve got to do is divide 830.8 mm by 25.4 to get 32.7 inches.
All we have done in the previous section is convert metric tire size to imperial measurements. But what are imperial measurements?
A good example of imperial tire measurements is 33 x 12.5 R17. In this example, R refers to radial construction. The first two digits (33) refer to the overall diameter of the tire in inches. The 12.5 refers to the width of the tread in inches. The R17, on the other hand, stands for the diameter of the rim in inches.
What Are 285 Tires?
The simplest definition would be, tires with a tread width of 285 millimeters. The measurements of 285 tires are usually expressed in metrics. The metric system is represented in different units of measurement, including millimeters, inches, and percentages.
There are two popular 285 tire sizes, 285/75/16 (285/75 R16) and 285/70/17 (285/70 R17). The first number is the width of the tire in mm, the second number is the percentage of the width of the tire (aspect ratio ) that corresponds to the height of the sidewall, and the third number is the rim diameter in inches.
The R refers to radial construction, which is the standard for most tires you will come across on the market. But tires could also have a bias belt or diagonal construction.
The 285/70/17 and 285/75/16 are normally the acceptable metric tire sizes for 33-inch tires. But the actual diameter of 285 tires varies from one manufacturer to another.
The 285 tires, therefore, vary in true diameter. This means some 285 tires are either smaller or larger than 33-inch tires.
What Are 33-Inch Tires?
These are tires that have an overall diameter of 33 inches. These tires are defined by imperial measurements.
Some popular examples of 33-inch tires are 33 x 12.5 R17, 33 x 12.5 R20, and 33 x 12.5 R15. Unlike the 285 metric tire size, the 33-inch imperial size has only one unit of measurement, which is inches. The 33 refers to the overall tire diameter in inches, the 12.5 is the tread width in inches, while the 17, 20, or 15 is the rim diameter in inches.
Are 33-Inch Tires the Same as 285?
Having understood what the metric and imperial tire sizes are, now we can tell if there are any differences between these two.
Metric Vs Imperial
The 285 tires come with a metric system (that is presented in millimeters, inches, and percentage), whereas the 33-inch tires come with an imperial system (that is presented in inches).
The overall diameter of 285 tires usually differs from one manufacturer to another. But the overall diameter of 33-inch tires is the same from one manufacturer to another, which is 33 inches. The metric tire size system includes the sidewall measurement (the aspect ratio), but the imperial system doesn’t include one.
For this comparison, we will use both the metric (285/70-17) and imperial (33/12.5-17) sizes.
When you place these tires side by side, you will notice that the 33-inch tire is slightly larger than the 285 tire. This is so because the overall diameter of the 33-inch tire is slightly larger by approximately 1 percent or 0.32 inches. In millimeters, the difference in overall diameter is around 8.04 mm.
The rim diameters of both tires, however, are the same, which in this case is 17 inches.
Another slight difference that you will observe is in the circumference. The 285 tire has a circumference of about 102.76 inches, whereas the 33-inch tire has a circumference of approximately 103.75 inches. The difference in circumference, therefore, is about 0.99 inches or 1 percent.
The difference is quite significant when you consider the overlay comparison. When you place the 33-inch and 285 tires in overlay, you will observe the difference in the width of the tread.
In our example, the 285 tire has a tread area width of 285 mm, whereas the 33-inch tire has a tread face width of approximately 318 mm. The difference is 33 mm or about 11.6 percent.
Revolutions Per Mile
This refers to how many times a tire (either 33-inch or 285) revolves to cover one mile. Revolutions per mile for each tire size mostly depend on the manufacturer of the tire. The RPM is either obtained from calculations or laboratory tests.
The revolutions per mile for the 285 tire is approximately 616.6, whereas the revolutions per mile for the 33-inch tire is roughly 610.69. Based on these figures, the 285 tire takes more revolutions to cover one mile compared to the 33-inch. In this example, the difference is around 5.91.
Will 33-Inch Tires Fit on Stock With No Lift
It depends mostly on the vehicle. But for a Jeep Wrangler, it is possible to fit 33-inch tires on a standard height. You can install 285/70/17 tires on a JK with no lift and wheels with an offset of -6.
You should, however, expect the Jeep to have an aggressive stance. The tires may poke out a little further from the guard, though. But you shouldn’t expect difficulties driving the Jeep. Contrary to what people say online, you will be surprised by how easy it is to turn your steering wheel to the left and right. You will have no problems driving downtown when doing some light off-roading.
But if you want to disconnect the sway bars and do some hardcore stuff with your Jeep, then you will need a lift kit.
Why You Need to Lift Your Vehicle for 33-Inch Tires
The easiest way to amp your Jeep is to lift it before installing 33-inch tires. Lifting will allow you to do hardcore stuff with your vehicle because it will boost stability when driving on rough terrains. The drive will be much smoother and comfortable.
You have to choose the appropriate lift height for the best performance. Lift height usually ranges from 1.5 to 6 inches, depending on the tire size. When installing 33-inch, you will need a lift height of 2.5 to 3 inches.
If you normally take your truck or Jeep off-road less often, then a lift of 2.5-inch could be enough. But you may need a higher lift for serious off-road driving. For a Silverado, check out our guide.
The Bottom Line
Are 33-inch tires the same as 285? There are a few differences between these two tire sizes. The 285 tire size is expressed in metric, while the 33-inch is presented in imperial. The overall diameter of most 285 tires is smaller than that of 33-inch tires. The 33-inch tires, on the other hand, tend to have a wider tread width compared to the 285 tires.