Mustang Wheel Backspacing vs Offset Explained

March 22, 2021

Backspace vs Offset

It's time to put a new set of wheels on your beloved Mustang. You've been eyeing that set of Velgen VF5 wheels. Maybe this is the finishing touch on a months-long restoration project, or you are just beginning planned modifications, or those boring factory rims just won't do anymore. The most important thing about this upgrade is determining what wheels will fit on your ride. Beyond wheel size, there are several specifications to ensure correct wheel and tire fitment, including bolt pattern, offset, and backspacing.

A bolt pattern is easy to figure out (we've got a chart below), but let's first look at offset and backspacing. Wheel backspacing vs offset involves two different methods of measuring a wheel's location when secured to the wheel hub. In other words, this involves how far in or out the wheels from the hub.



Mustang Offset vs Backspacing

Mustang EcoBoost Autocross Car Mustang EcoBoost Handling Build

Offset is the measurement between the wheel center and the mounting area. Backspace is the measurement between the mounting surface and the inside edge. We'll review why each of these measurements is important.

This is an oversimplification, but think of offset as a measurement of the front part of your wheel while backspacing measures the wheel's back area. Both measurements identify where the wheel's mounting surface is positioned inside the rim.



Mustang Wheel Offset

What Is Mustang Offset?

As we mentioned, wheel offset measures the distance between the wheel's center and the mounting face in millimeters. Offset can be zero, positive, or negative.

  • Zero Offset: This measurement means there is no distance between the wheel hub surface and the centerline of the wheel.
  • Positive Offset: A positive offset is when the wheel's mounting surface is past or outside the centerline. Here, the imaginary plane that passes through the wheel's vertical center is behind the plane of the mounting surface. A positive offset allows your wheels to mount close to the car's interior and offer more clearance between the fender and outside edge of the tire. Simultaneously, too much positive offset can affect your car's steering as the suspension or interior of the wheel may obstruct proper turning.
  • Negative Offset: In this situation, the mounting face is toward the inside of the wheel's centerline (closer to the brakes). Here, the imaginary plane of the wheel's centerline in front of the mounting surface. Using a negative offset pushes your wheels further toward the outside of your Mustang. This will give your car a wider stance and offer greater clearance from the suspension. Keep in mind that protruding wheels and tires may run afoul of motor vehicle laws and make day-to-day driving more of a challenge (hello, curb rash).

The correct offset is essential for proper fitment as well as appearance. Also, an improper offset can affect your car's safe operation and increase wear on the wheel bearings and other components.



Mustang Wheel Backspacing

What is Mustang Backspacing?

Backspacing is the measurement of determining the depth of a wheel's mounting surface. Unlike offset, which is measured in millimeters, backspace is measured in inches. The proper backspace will provide enough clear area for the brakes and suspension to operate without interference from the tire and wheel.

Less backspace means the wheel will protrude less closely into the wheel and adjacent systems. In other words, there's less risk of tire and wheel rubbing against the brakes or suspension.

More backspace means the wheel will protrude more closely into the wheel well and nearby components. Here, there's a greater chance of rubbing against nearby components.

Calculate backspacing by measuring the distance between the wheel's mounting face (on the backside of the wheel) and its outer lip. This will vary depending on the design and size of the wheel, just like offset. First, lay the wheel down with the wheel's backside facing up. Remember to use a soft surface, so the front of the wheel isn't damaged during the process. Next, place a flat item--like a wooden plank or piece of cardboard--across both sides of the rim. With a tape measure or ruler, determine the distance from the wheel's mounting face to the starting point of the plank or cardboard.

Mustang Wheel Backspacing Measurement

Here's the formula for calculating backspace:

One-half of wheel width + offset (in inches) + 1/2”

For example, an 8” wheel with zero offset would have a 4.5” backspace: 8/2 + 0 + 1/2 = 4.5

How To Correctly Measure Wheel Width: Don't measure from the outermost edge of the rim. Instead, measure from the bead lip or seat (where the tire sits on the inside of the rim). This dimension goes from the bead lip on one side to the opposite bead lip.



Mustang Wheel Offset Chart


Year/Model Factory Wheel Size Offset Bolt Pattern Stud Size Center Bore
2015-2021 Mustang (EcoBoost & GT) 17-20" 35-50mm (H) 5"x114.3mm 1/2"x14mm 70.3
2010-2014 Mustang (including GT) 17-19" 35-50mm (H) 5"x114.3mm 1/2"x20mm 70.3
2005-2009 Mustang (including GT) 16-18" 35-50mm (H) 5"x114.3mm 1/2"x20mm 70.3
1994-2004 Mustang (including GT & Cobra) 15-18" 35-50mm (H) 5"x114.3mm 1/2"x20mm 70.3
1985-1993 Mustang GT 15-16" 15-25mm (M) 4"x108mm 1/2"x20mm 63.4
1979-1993 Mustang 14-16" 15-25mm (M) 4"x108mm 1/2"x20mm 63.4



GT350R Wheel Offset

Help With Mustang Wheel Offset and Backspacing

Figuring out your Mustang's wheel offset and backspacing can be confusing and frustrating, especially as owner's manuals on recent models don't include this information. A first step is to reach out to the experts at Steeda to lend a hand! Keep in mind that these offset and backspacing specs are for a stock Mustang. All this information changes if you make any modifications to the brakes, suspension, or wheel wells.

Before investing in a new set of wheels, work with us to ensure these new rims will work on your Mustang. We would be happy to help with identifying exactly which Mustang wheels will work on your car.

Source: Tread Connection, Truck Trend, YouTube, Mustang Specs





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