Are 33-Inch Tires the same as 285’s (Metric Vs MM)

When comparing a 33” tire to a 285 wide tire, you are essentially talking about two completely different measurements. The 33” refers to the width of the tire (285) multiplied by the height percentage of the sidewall (75), in millimeters, x2 because there are two sidewalls, divided by 25.4 (inches) plus the wheel size in inches (16”). Phew!!! That’s a mouthful and a lot to digest at once so let’s break it down into a simple formula.

YES, 285 wide tires are the same as 33” tires although 285 is the tread width in millimeters and 33″ is the tire diameter. 285/75/16 is usually the accepted metric equivalent size for 33’s.

Let’s see what that looks like in a formula form

285 = the width of the tread in mm

75 = the height percentage of the sidewall in mm (285 width x .75 = 213.75mm)

Divide mm by 25.4 to get inches

So….. 213.75 x 2 sidewalls = 427.5mm (divided by 25.4 = 16.831″)

16.831″ + 16″ wheel = 32.831″ approximate tire diameter.

Let’s now look into this in a bit more detail

Are 33-Inch Tires the same as 285’s (Metric Vs MM)

As mentioned, 285 and 33 are referring to two completely different measurements. . Metric tire sizes can be a bit more complicated when it comes to understanding what size they really are.

Let’s see what that means

Metric vs Millimeters

Because each tire manufacturer uses their own molds, and there’s no set industry pattern, the 285/75/16 is usually the accepted metric size for 33’s, even though the physical diameter of the tire can vary from manufacturer to manufacturer. Two different 285’s can actually vary in true diameter. Meaning some are smaller than 33″ and some are larger, depending on the brand. This means a 33 inch tires can be wider by 11 1/2 or 12 1/2 inches in width.

One way to find out the exact diameter of a tire is by going to the tire manufacturer’s website and checking the manufacturing specs on that specific tire and then comparing “apples with apples”.

Fitting 33 inch tires on your truck

How much lift needed for 33inch

Bigger tires is the single most effective method of gaining improved ground clearance. This is especially important for overcoming obstacles in an off-road situation. There are however a few limitations, especially when it comes to IFS (Independent Front Suspension) 4WD vehicles.

Let’s now look at a few factors to consider when fitting 33” tires on your truck.

Lift Kit

Before you even consider fitting 33” tires on your IFS truck, you’ll need to have a minimum 2” lift kit installed. Depending on your truck, sometimes this isn’t enough, since you’ll still need to make additional modifications to prevent scrubbing at full lock. This is especially true if you want to retain full functionality and articulation which is important for off-road. If you decide to go 3” or higher, beware there are serious implications to any IFS suspension, but more on that later.

Who should fit 33” tires? There are mixed opinions when it comes to large tire upgrades, and depending who you ask, you’ll get differing opinions. I give it a resounding YES! In fact I am currently running 33” tires on my truck and they work beautifully! The added clearance, aggressive look, and improved traction and stability in my opinion is well worth it. It comes at a price though.

Click here for more info on fitting 33” to your truck

Wheel Offset

Wheel offset or backspacing is a factor that gets little consideration, and it can create complications if you’re not sure exactly how much brake caliper clearance is required. It’s been widely agreed that 16×8 are recommended option. The problem here is, you don’t want to go too negative offset on the wheels else you risk to much wheel “poke”.

What is the difference/meaning of backspacing vs Offset?

Backspacing is the distance measured from the hub mounting surface to the inside edge of the wheel. When you decrease backspacing, you gain more inside wheel clearance. There is a fine line between keeping the tires in the guards and preventing scrub on arches, UCA, Brake calipers, etc.

Offset is measured in mm and generally refers to how your wheels sit inside the wheel wells. You get positive and negative offset wheels. When it’s positive the imaginary line is more towards the front and negative means the mounting surface is more towards the rear of the rim creating a deep dish effect.

Fender & Arch trimming to fit 33’s

In many instances there are a few plastic sections on the inner fender guards that needs to be trimmed away since they will scrub at full articulation. So get familiar with your Stanley knife and cutter and do some trimming of those wheel arch/guards where they are making contact. Look out for the inner guard pinch weld and inside of the fender flare. They usually need some trimming, depending on the tire and vehicle.

Fender trimming goes hand in hand with backspacing/Wheel offset as well as how wide the tire is. A wider tires will require more wheel arch clearance and room to move when flexing off-road and when turning at full lock.

When you squeeze oversized tires into a wheel arch without lifting the truck, you’ll need to trim away a lot of the inside fender and arch plastic to allow the tire to tuck behind the arch when turning and flexing off-road.

Will the 285/75/16 throw out your speedo?

When you upgrade from a stock tire to one with a taller aspect ratio (Side wall), increasing the wheel circumference, your speedo can be thrown out. In the case of 33” tires the diameter will be larger and have an increase in the aspect ratio. This might throw-out your speedometers reading slightly. The increase in tire circumference means the actual speed will be higher the faster you travel.  

The below table will give you an indication of how the speedometer reading is affected from a 265/70/16 to a 33”.

Speedometer reading20mph30mph40mph50mph60mph70mph80mph90mph
Actual Speed21.432.242.953.664.37585.896.5

Below are the actual differences between the stock 16” tire and the upgraded 285/75/16

MeasurementStock Tire (265/70/17)Upgrade (285/75/16)Differences
Diameter30.6”32.8” (833mm)+7.2%
Width10.4”11.2” (285mm)+7.7%
Sidewall7.3”8.4” (213mm)+15.1%
Circumference96.1”103.1” (2619mm)+7.2%
Revs/Mile659615 (382mm)-44

How much lift to fit 33” Tires on a Ford Ranger

f you want to fit a larger 33” tire without a suspension lift, there is some modification needed. The Ranger T6 crash bars protrude from the wheel well and the bigger 285/70/17 tire makes contact. These will need to be removed/modified first so as not to damage the new tires. They are quite a PITA to remove so be prepared. Once removed, and a 20+ offset aftermarket wheel is fitted you should be able to get the 33” tires to fit comfortably.

Click here for the full breakdown of fitting bigger wheels to a Ford Ranger

How much lift to fit 33” on a Jeep Wrangler

33-inch tires can be fitted to a stock Jeep Wrangler JK, but with minimum clearance on the front bumper and not enough clearance for full articulation off-road.

Before running out and fitting bigger tires to your JK, make sure you understand all the implications and that there are other factors that comes into play such as backspacing, clearance, fuel economy, handling and more.

To take full advantage of the Jeeps legendary articulation, you would do well to fit a 3-4” lift before fitting 33” tires.

Click here for the full breakdown of fitting 33” tires to a Jeep Wrangler

Big lifts on an IFS Truck

When lifting any IFS truck, the front suspension configuration determines the complexity of the upgrade. In the case of a SFA or LIVE axle, the axle is not physically attached to the chassis. This allows you to fit big tires and higher lifts easier. The CV angles are not compromised since they are always in line with the diff and axle.  This allows you to fit 3”, 4” and even higher with less hassles. Fitting 33” tires to a Solid/Live axle truck requires less additional modifications and in most cases little to no Body or arch modifications.

An IFS front axle on the other hand is a more complex process and you are limited. Unfortunately most 4WD’s in production these days are IFS suspensions. Manufactures are more concerned about on road performance and safety so they produce IFS trucks which appeals to a larger market.

The main problem with IFS suspension upgrades are the CV axles. The diff of an IFS truck is mounted directly against the underside of the chassis. This makes for excellent stability and cornering, however, it limits the downward travel of the wheels and places the CV joints under more stress when the vehicle is lifted too high.

It’s not recommended to go higher than a 3-inch lift kit on an IFS vehicle, and if you do decide to go higher, you’ll need additional modifications such as diff drop kits, adjustable UCA (Upper Control Arms), LCA, and Stabilizer arms.

Conclusion

We have mentioned quite a few variables to consider before dropping a load on expensive oversized tires. You should first determine what the primary application for the upgrade is. Is it purely for aesthetics or will you need maximum practicality, off road ability, while maintaining maximum articulation.

Jade C.

4-Wheel drives and off-road driving techniques has been my passion for over 20 years. Here we strive to provide the most accurate, up-to-date, information about the functionality, common faults and latest technology built into most 4 Wheel Drives.

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