What is fitment?

Introduction

Curious about "Fitment"? If you are, take a moment to read through this. Trust us, it’s worth it.

Wheel Offset and Backspacing

You’ve finally saved enough to buy the perfect wheels for your car. What’s next? Naturally, you hit Google to learn about your car’s bolt pattern and spacing. Before rushing off to eBay, hold up! There’s more to consider—like offset, backspacing, clearance, and overall diameter.

Understanding Wheel Offset

Wheel offset is the distance (in millimeters) from the hub mounting surface to the centerline of the wheel.

• Positive Offset (+25 mm): The wheel's hub is closer to the curbside, pushing the wheel into the caliper/brake. Too much can cause the wheel to tuck or rub against the suspension.

• Negative Offset (-25 mm): The hub is closer to the car's center, pushing the wheel outward, which can create a flush or aggressive look depending on the wheel's design.

Measuring Backspacing

To measure backspacing, check the back of your wheel. For example, an 18” wheel with an 8” width and a +55 offset would have specific backspacing based on these measurements.

Basic Calculations

If math isn’t your thing, here’s a quick guide:

Example: 205/60-15 Tire

• Tire width = 205 mm
• Aspect Ratio = 60% of the tire width
• Sidewall height = 0.6 * 205 = 123 mm
• Rim diameter = 15 inches

To calculate tire diameter:

$$\text{Diameter} = \left(\frac{2 \times 205 \times 0.6}{25.4}\right) + 15 = 24.69 \text{ inches}$$

Convert from mm to inches:

$$\text{Tire width in inches} = \frac{\text{Tire width in mm}}{25.4}$$

Formula to find tire height in inches:

$$\left(\frac{2 \times \text{Tire width mm} \times \text{Tire ratio}}{25.4}\right) + \text{Rim diameter (in inches)} = \text{Tire height (in inches)}$$

Offset and Fitment

Adjusting the offset affects fitment:

• Positive Offset: Moves the wheel inward, increasing the gap between the tire and fender.
• Negative Offset: Pushes the wheel outward, potentially extending past the fender.

Important Notes on Fitment

If you change the wheel width, it will impact how the offset positions the wheel:

• A 7.5" wheel with a +25 offset will sit tucked, while a 10" wide wheel with the same offset may sit flush or protrude.

Backspacing

Backspacing is similar to offset but measured differently. It’s the distance from the back edge of the wheel to the mounting surface.

Need Help?

Still confused? That’s where GGCRACING comes in! Browse our gallery of rides, complete with suspension and wheel details, to find the perfect fitment for your setup. For assistance or to snag great deals, email us at customerservice@ggcracing.com