Like other car compartments, tires come in numerous sizes and shapes. What makes things a bit more complicated is that they are measured by different manufacturer criteria, easily confusing first-timers if they do not pay attention.
In the past months, we have received many questions regarding this issue. Are 33-inch and 285 tires interchangeable? This article will clear up all your bafflement.
In this article:
33-inch and 285 Tires: Are They The Same?
Yes, though there are some basic differences (which we will discuss later). They are largely similar in most parts. “285” points to the tread width in millimeters, while “33” denotes the tire’s diameter in inches.
In short, “285” indicates the metric sizes for 33” tires. Since both numbers do not comply with a similar measurement system, they can be confusing.
1. Converting Millimeters to Inches
To further explain how 285 and 33” are equal, let’s calculate the tire’s overall diameter. We will take a 285/70/17 tire for this example.
- 285 (millimeters): tread width
- 70: Sidewall height (70% of 285 millimeters)
- 17 (inches): rim diameter
Trace along the following steps:
Step 1. Measure the exact sidewall height
The calculation is a piece of cake, even for primary students. Multiply 285 by 70 and receive 199.5 (mm).
And since each tire boasts two sidewalls (top and bottom ones), you must multiply 199.5 mm by 2. Our final result is 399 mm.
Step 2. Convert its rim diameters to metric
Now convert the tire’s rim diameter (in inches) to metric (in millimeters). Multiply 17 inches by 25.4, and you will get 431.8 millimeters.
Step 3. Add up the results from steps 1 and 2.
Now add up what you already have from the previous two steps: 399 + 431.8 = 830.8 (mm).
Finally, let’s return to our primary purpose: converting the measurements into inches. Take 830.8 mm and divide it by 25.4. You will get 32.7 inches, approximately close to 33′.
2. What Is The Difference in Measurements and Performance?
Despite their similarities, note that no two measurement systems are identical. Hence, it’s understandable that certain variations set these two tires apart. What are they?
Overall Tire Size
As you can see, 285 tires are from metric systems (presented in percentage/inches/millimeters). There are other influencing factors, too (sidewalls, rims, stock ratios, etc.), which is why 285 tires manufactured by different brands might not share the same overall diameter.
On the other hand, 33” tires belong to imperial systems (inches), not involving aspect ratios and sidewall measurements. As a result, 33” wheels from different tire manufacturers have exactly the same overall diameter.
So do not be surprised if 33” tires are slightly bigger than 285 (you will see that more clearly when putting them against each other). That’s because the 33 tires’ overall diameter slightly exceeds 285 by 1% (their diameter difference: 0.32 inches/8.04 mm).
Their circumferences are dissimilar, too. The circumference of 285 tires reaches 102.76 inches, while 33-inch ones have circumferences of 103,75 inches (the difference in circumference is 1% – 0.99 inches)
|Tire Size (mm)||Tire Size (Inches)||Overall Di||Overall Di||Tread Wit||Tread Wit||Rim Diam||Rim Diam||Sidewall Height (m||Sidewall Height (Inches)|
Revolution Per Mile
Revolution Per Mile (RPM) refers to the times a tire revolves to travel one mile. The numbers vary across each brand, but generally, the RPM for 285 tires is about 616.6, while 33” tires have an RPM of roughly 610.69 (the actual difference: 5.91)
How Can We Use 33” Instead of 285 Tires?
Yes. But the two tires are similar but not 100% identical, so slight adjustments as below are necessary:
- Suspension Lift Kit: Since 33” tires are slightly larger, we suggest lifting the car’s body to prevent its tires from rubbing the wells. Not to mention, most off-road drivers love giving their wheel-drive vehicles a more rugged look.
- Wheel offsets: The term refers to how deep the entire wheel fits into the wells. You can consider backspacing the tires, but do not overdo it. Otherwise, the wheels might poke partially out of the fenders, leading to high accident risks.
- Fender trimming: If you only want to apply slight changes, working on the fenders is your best bet. A little trimming will be enough but remember not to interfere with the steel portions. Otherwise, your tires may become rusty.
How To Lift The Cars to Fit 33” Tires?
We just mentioned that you should lift the tow vehicles a little. But how much, though? We have no one-size-fits-all answer, but here are some suggestions for common car/axle truck models:
- Jeep Wrangler: 3-4”
- IFS Truck: 4-5”. Be careful of the axles, though. Their position under the chassis paves the way for excellent cornering/stability but limits the wheels’ downward travel. Hence, they might put your CV joints under excessive stress if the cars are lifted too much.
- Ford Ranger: About 3”. But remember to remove the crash bars first.
Can We Use 33” and 285 Tires Together?
No. Their sizes are not 100% identical, and mismatched mud tires are considered the death of most automobiles in hazardous road conditions. Your car’s tread, grips, and tractions are heavily affected, leading to power loss and collisions!
Either just 33” or just 285; do not use them together. We mean you can replace a whole set of 285 with all four 33” tires but not mix them up.
This article has addressed these inquiries for you. If you want to use 33” instead of 285, remember the extra tips above to ensure a safe and smooth trip. And feel free to write to us for more advice on your beloved vehicle!