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Wheel Fitment 101 - Subimods.com

Wheel Fitment 101

Are you searching for your first set of aftermarket wheels? You’ve probably noticed that there is an extremely wide variety of sizing available. Because every chassis has a different sweet spot for fitment, it’s best to understand what all of these numbers mean so you can make an informed decision and get that stance you truly desire! 

Let's start with the basics. I hated math class too, so I’ll keep the numbers round for the sake of keeping it easy to follow! 

Wheel Offset: This is the calculated distance from the center of the wheel to the mounting surface. 

In layman's terms, that means this is how far in or out the wheel will stick, and it's measured from the middle of the wheel. A higher offset mounts closer to the face, and will be more sunk in. A lower offset mounts farther into the wheel, and pushes the wheel outward towards the fenders. 

  • An 18x10 +0 wheel mounts exactly 5” in, dead center to the wheel.
  • An 18x10+25 wheel mounts exactly 4” in, sunk in an inch further than the 0 offset wheel
  • An 18x10-25 wheel mounts exactly 6” in, pushed out an extra inch past the 0 offset wheel

Make sense? Here’s where things get a little more complex. In the real world, you usually won't find such round examples. It's also important to know, as the offset and width of the wheel starts changing, the design of the wheel's face may change as well. 

Wheel Width in relation to offset: 

As you step into a wider wheel, you will find that if you have a vehicle with larger brakes or narrow fenders, choosing the right offset is key, and will depend entirely on how wide the wheel is. 

For example, the most common size wheel to see run on STI models is 18x9.5+38, however certain wheels in this spec will not fit, as the spoke design may hit the caliper. In this instance, a different offset is needed to run the wheel without a spacer, the offset is too high. 

So say you are set on this wheel, and wish to look into a lower offset to clear that big brake kit of yours. You’re a rebel, and cookie cutter fitment isn't for you. I respect that. Now, you must take into account how much more room you’ll have before you start scrubbing the fenders at a lower offset. 

We’ve got a few options! (today, we are going to assume you are not breaking out the cut off wheel for the sake of a wide body kit or flares)

Ride Height: 

Your vehicle's height will determine where you want to land on sizing. If you are at stock height, you may want to look towards something more narrow with a higher offset to it. As you lower the vehicle, you will want something wider or lower offset for a flush fitment, but at a higher ride height that same wheel would poke well outside of the fenders. 

Alignment:

When you lower your vehicle, you will gain a bit of negative camber as you go. The factory adjustment points on Subaru’s typically allow for about a degree in either direction, so the lower the offset / wider the wheel you choose, the more the need for some suspension modifications come in. Running anything more aggressive than that 18x9.5+38 (give or take a few points on the offset) you’ll likely need to begin dialing in a little camber to clear the fenders. The more you go, the more you’ll need. 

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