Decoding the Numbers: Are 33-inch tires the same as 285?

The off-roading niche has seen a renaissance in the past two decades, with automakers pushing with new SUVs and trucks designed for exploring the wilderness, overlanding, and just having off-road fun. Even EV manufacturers joined the off-road craze, launching some excellent off-road trucks and SUVs.

As a result of that, tiremakers also started launching numerous off-road models, from mild all-terrain tires to extreme off-road monsters. These off-road tires also come in various dimensions, and each one brings different advantages.

You can have all/terrain/off-road tires with higher sidewalls for added flotation capabilities or with smaller sidewalls for a more responsive ride on hardpacked surfaces. There is also the tread width, which can significantly affect the off-road performance of your truck or SUV.

Unfortunately, tiremakers use two different sizing codes – metric and imperial. To make things even worse, the metric size actually includes imperial measurements for the wheel size because that's how we've measured wheels since always.

As a result of this, people tend to get confused, which is why you will see many drivers on forums use 33-inch and 285 mm tires interchangeably. The first time I saw that, even I was confused because 285 mm is 11.22 inches, while 33 inches equals 838 mm. So, what's the deal with that? Is there really a correlation between the two? Are these people crazy or something?

Well, put on your seatbelts because we are delving deep into off-road tire sizes. In this article, I'll answer the lingering question of whether 33-inch and 285-mm tires are the same, but I will also teach you how to calculate tire dimensions so you never get confused in the future. Let's strip down the layers of complexity, and help you understand how to choose the right tires for your off-roading needs.

Understanding Tire Sizes

Since the off-road tire world includes many different sizes, it's crucial to have a better understanding of the tire sizes before making a decision. Here is everything you need to know about off-road tire sizes – expert style!

1. The Metric System and Tire Sizes

The metric system is widely adopted in the tire industry and used for passenger car tires. For reference, I will use the LT285/75R16 tire size because that's the one people confuse with 33-inch tires.

In that code, the LT designation indicates that this is a light truck tire made for higher loads. Then, 285 represents the tire's width in millimeters, and 75 represents the aspect ratio, i.e., the height of the tire's sidewall as a percentage of the width. In this case, the sidewall height would be 213.75 mm. The 'R' stands for Radial, indicating the tire's construction, and 16 is the wheel diameter in inches.

As you can see, this system is very antiquated and uses two different measuring systems, metric and imperial. People got used to it, and it will probably stick as long as we drive cars. However, not all tires are coded with the metric/imperial.

2. The Imperial System and Tire Sizes

33-inch tires, along with 35-inch, 27-inch, and 39-inch tires, are considered flotation sizes. The reason they are called that is that they have large sidewalls, making them good candidates for driving at lower pressures for increased flotation, which helps with traction and drivability on the sand and over large rocks.

However, these tires have different enumerations. For example, I will take a 33X12.5R18LT tire. Here, the first number, 33, indicates the diameter of the whole tire when fully inflated and not under load. The letter "X" is only used for separation, while 12.5 indicates the tread width from sidewall to sidewall. Finally, "R" stands for Radial, while 18 is the diameter of the wheel in inches. Finally, the LT designation indicates that this is a light truck tire made for higher loads.

So, to sum it up, "33X12.5R18LT" represents a tire with a 33-inch overall diameter and 12.5-inch width, made with radial construction, meant to fit an 18-inch wheel, and designed for light trucks.

3. Load and Speed Ratings

The load and speed ratings are also important when you choose a set of tires for your SUV or truck. They sit right next to the tire size. For example, an LT285/75R16 tire most often comes with a 123R load/speed rating.

The load rating is directly correlated to how much weight the tire can carry. This is crucial, as going over the tire's load capacity can cause bulges, tread separation, and potential blowouts. The load rating is marked with a number. In this case, a 123 load rating means the tire has a load capacity of 3417 lbs (1,550 kg).

Meanwhile, the speed rating is marked with a letter next to the load rating. Here are all the speed ratings used on passenger car tires:

• S: 180 km/h (112 mph)
• T: 190 km/h (118 mph)
• U: 200 km/h (124 mph)
• H: 210 km/h (130 mph)
• V: 240 km/h (149 mph)
• W: 270 km/h (168 mph)
• Y: 300 km/h (186 mph)

4. Calculating the Overall Tire Diameter on P-metric and LT-metric Tires

Since metric and imperial measures don't mix well together, here is how you can calculate the overall diameter on P-metric and LT-metric tires so you can make a connection to flotation sizes.

Again, I will use the LT285/75R16 size here, as that is the one people most often confuse with 33-inch tires. Here, the overall diameter isn't directly given, so we will need to do a bit of math to come up with it:

Calculate the height of the sidewall (in millimeters): Width (mm) * Aspect Ratio (%) / 100. For the example tire, this would be 285 mm * 0.75 = 213.75 mm.

Convert the sidewall height from millimeters to inches (since the wheel diameter is in inches): Sidewall height (mm) / 25.4. For the example tire, this would be 213.75 / 25.4 = 8.41 inches.

Since the overall diameter of the tire includes the top and bottom sidewalls and the wheel's diameter, you add these together: (2 * Sidewall height in inches) + Wheel diameter (inches). For the example tire, this would be (2 * 8.41) + 16 = 32.82 inches.

Hey, isn't that close to 33 inches? Indeed, it is, and it's the main reason why people confuse 285 and 33-inch tires. In fact, comparing the two is so wrong because there are many 285 tires with low-profile sidewalls that would have much smaller overall diameters.

For example, a popular tire size for high-performance cars is 285/35R18. Here, the overall diameter of the tire is 21.92 inches, which is a huge difference.

Comparing 33-Inch Tires and 285-mm Tires

So are 33-inch tires the same as 285? Well, by now, you probably learned that comparing 285 to 33-inch tires is like comparing apples to oranges. Or, like comparing the wheelbase of one car to the length of another. But let's get into more detail.

1. Physical Differences and Similarities

When it comes to the exact LT285/75R16 size that is popular among drivers of SUVs, it has an overall diameter of around 33 inches. However, you can also find 33-inch tires that fit 18-inch wheels and even 20-inch wheels. Meanwhile, you can also find tires with 285 mm wide treads with much lower sidewalls.

Still, calculating the overall diameter of the tire is crucial to make sure that it fits the wheel wells on your truck/SUV. In that sense, 33-inch tires are easier to gauge, as you don't need to make any calculations. However, you will also need to consider the tread width, as wider tires might not fit your particular vehicle.

2. Performance Differences and Similarities

Again, comparing 33-inch and 285 is not fair, as both can come with higher or lower sidewalls and narrower or wider treads.

With that said, 33-inch tires usually have higher sidewalls for higher ground clearance and better flotation capabilities. These tires also conform better over the surface when aired down, which makes them essential for rock crawling.

Meanwhile, 285-section tires are considered very wide, which leads to higher longitudinal traction and lateral grip. However, not all 285-section tires come with higher sidewalls. For that, you will need to look at the number next to the slash, which is the ratio (in %) to the tire width. Hence, the higher the number, the higher the sidewall.

Appropriate Uses for 33-Inch and 285mm Tires

It is highly recommended that you choose tires that fit your vehicle. However, if you are ready to make some modifications to improve the off-road capabilities, you can fit larger and wider tires without having issues with fender rubbing.

1. Off-Roading and Sport Performance

33-inch tires are widely used among off-road enthusiasts due to their large sidewalls and wide footprint. However, the particular size that's often misjudged as a 33-inch tire, LT285/75R16, also has a sizeable sidewall and a fairly large footprint. So, that one will also be great for off-roading.

2. Comfort and Fuel Efficiency

33-inch tires are large and heavy, which can greatly increase the fuel consumption of your vehicle. Meanwhile, 285-section tires are usually narrower than 33-inch tires, which lowers the rolling resistance and keeps your MPGs high.

Furthermore, narrower 285-section tires will be quieter and generally more comfortable than 33-inch tires that are 12.5 inches wide (317.5 mm).

Other Considerations when Choosing between 33-Inch and 285mm Tires

While size plays the biggest role when choosing new tires, it isn't the only consideration you need to make before splurging the cash. Your driving needs are also a big factor, but also your vehicle's compatibility with the new tire size and regulations in your area.

1. Vehicle Compatibility

Choosing tires that are too high or too wide may rub against the fenders or wheel wells of your vehicle. This can cause excessive wear on the tires and your vehicle body and lead to serious issues like tread separation and blowouts.

If you want to fit larger tires on your SUV or truck, there are multiple lifting kits to choose from nowadays. Each model is extensively covered, but SUVs like the Jeep Wrangler and Toyota 4Runner are especially suitable for aftermarket upgrades.

2. Local Regulations and Standards

Different regions may have different legal requirements for tire sizes, treads, and types. Some jurisdictions may have regulations governing how much larger or smaller replacement tires can be compared to the original equipment tires.

Others may have specific rules regarding off-road or studded tires. You will probably be fine with smaller upgrades but check with the authorities in your area if you really want to go overboard and put 37-inch or 39-inch tires on your SUV or truck.

3. Price and Availability

Larger and wider tires are equivalent to more money spent. For starters, they are much more expensive to buy, and because of the higher rolling resistance and weight, they will also increase the fuel consumption of your vehicle.

FAQs: 33-Inch Tires Vs 285mm Tires

1. How do I convert tire sizes from inches to millimeters?

To convert tire width from inches to millimeters, you can simply multiply the width in inches by 25.4 (since 1 inch equals 25.4 millimeters). For example, a tire that is 33 inches in diameter equals 838.2 mm in diameter.

2. Can I replace my vehicle's 33-inch tires with 285 mm tires?

It really depends on the other two numbers on the sizing designation of the 285 mm tire. Namely, you can probably fit an LT285/75R16, which has a diameter of 32.82 inches, or an LT285/70R17 tire with a diameter of 32.7 inches. Your vehicle will be closer to the ground, but not by much.

However, you will also need to pay attention to the width. 33-inch tires are usually 12.5 inches wide, while a 285-section tire would be 11.22 inches wide (285 mm / 25.4). In this case, the 285-section tires will fit inside the wheel well without any issue, but you will also get a narrower tire with a lower overall grip.

3. How do different tire sizes affect vehicle performance?

Different tire sizes can significantly affect vehicle performance in various ways. Larger and wider tires can offer improved grip and stability, particularly in off-road conditions or during spirited driving.

However, larger tires are heavier, which can have a negative impact on fuel economy and performance. Putting really heavy tires will also increase the stopping distances due to the higher rotational mass.

4. What are the benefits of using 33-inch tires?

33-inch tires offer many benefits for off-road-capable vehicles like trucks and SUVs. For starters, they will increase the ground clearance, attack, and departure angles, which greatly increases the capability of the vehicle over uneven terrains.

Furthermore, these tires have a larger footprint that increases traction on slippery surfaces while also enabling flotation over sand. Not to mention, due to the sizeable sidewalls, 33-inch tires can be driven at lower pressures, which can be helpful when driving over larger rocks because the tire conforms to the rock.

Still, it's important to note that you can put much larger off-road tires nowadays, with 35-inch, 37-inch, 39-inch, and mammoth 40-inch or 41-inch sizes available.

5. Are there specific types of vehicles that require either 33-inch or 285-mm tires?

Some rugged versions of trucks and SUVs come with 33-inch tires from the factory. A good example is the Jeep Wrangler Rubicon, which is a hardcore off-road version of probably the best off-roading vehicle on the market. The brand-new 2024 Toyota Tacoma also comes with 33-inch tires in its overland-ready Trailhunter trim.

Meanwhile, various trucks and SUVs, like, for example, the Hummer H3 and second-gen Toyota Tundra, come with LT285/75R16 and LT285/70R17 tires, respectively. However, numerous other vehicles, including performance SUVs and sports cars, also come with 285-section tires, though with shorter sidewalls.

6. How do tire sizes impact off-road capabilities?

Tire size can have a big impact on the off-road capabilities of a vehicle. Wider tires increase traction over most surfaces, including dirt, gravel, sand, intermediate terrains, and rocks. Meanwhile, having a larger sidewall means the tire can be run at lower pressures to provide flotation or conform better to the surface.

However, some off-roaders, particularly those that drive through mud or snow, might prefer narrower tires. The reason is that these tires put more pressure on the surface, which aids with the digging action necessary to increase traction in mud and snow. However, for most off-road enthusiasts, a wider tire would be a better bet.

7. Will changing my tire size affect my vehicle's fuel efficiency?

Absolutely! Wider tires have a higher rolling resistance, which means the engine will need to work harder to retain the same speed. As a result, the fuel consumption will increase, and your vehicle will also be slower.

Also, the tire's weight plays a huge part when it comes to fuel consumption. Not only do heavier tires add to the overall weight of the vehicle, but they also add rotational mass, which further decreases fuel economy.

Finally, larger tires will change the gearing of your vehicle, which will also have a negative effect on fuel consumption.

8. How do 33-inch and 285-mm tires compare in terms of price and availability?

33-inch tires are generally more expensive than most 285-section tires, sometimes up to 30%. This is due to the larger amount of material used in their construction, as well as the specialized designs often used for these sizes.

Although large tires are not as easy to come by, they have become much more accessible in recent years. Today, most popular all-terrain and off-road tires come in 33-inch, 35-inch, and 37-inch sizes, so the range of options is pretty wide. That said, most highway all-season tires aren't available in these off-road-focused sizes.

9. Will changing from 33-inch to 285-mm tires affect the comfort of my ride?

Yes, changing from 33-inch to 285-mm tires could affect the comfort of your ride. This is because the size and width of your tires can influence several factors that contribute to ride comfort, including road noise and ride quality.

Generally, tires with larger sidewalls will be more comfortable over bumps. However, that is not always the case because some tires with very large sidewalls have additional reinforcements to make them usable at lower pressures, which can make the ride harsher.

Meanwhile, wider tires are quieter than narrower tires, but only if you compare the same model. Again, there is a variation in design among different tires, and some are quieter than others. Moreover, aggressive off-road tires tend to be loud, even when compared to wider highway tires.

Conclusion

As we delved deep into tire sizing, we uncovered that 33-inch and 285-section tires are not the same. In fact, comparing them is wrong because they represent completely different values. A tire is not just a chunk of rubber; it's a precisely engineered marvel that balances comfort, performance, fuel efficiency, and safety, so using such comparisons certainly doesn't help.

I know that people do this to simplify things, but today at least, it's easy to find the right size, as you can find many tire size calculators online. So, use them to your advantage because they will help you align the tire size with your driving lifestyle. You can even use the equations from this article – they can be done in under a minute!

Remember, choosing the right tire size will ensure optimal performance, but more importantly, that you are more satisfied with the ride! It is an important decision to make, and a costly one, so spending a few more minutes to find the right fit is a no-brainer!