Trailer Fender Sizes Explained: How to Choose the Right Length, Width, and Height

Trailer fenders come in dozens of dimensions, and choosing the correct size is essential for safety, tire clearance, and legal compliance. This guide breaks down the standard sizing terminology used in the trailer industry and explains how to match fender dimensions to your trailer’s wheels, axle spacing, and mounting requirements.

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1. Understanding the Three Core Fender Dimensions

Every trailer fender is defined by three measurements:

Length

Measured from end to end, length determines whether the fender will properly cover the tire (or tires) on your axle configuration.

• Single-axle fenders: Typically 20–32 inches long

• Tandem-axle fenders: Commonly range from 60–72 inches

• Tri-axle fenders: 90 inches or more

Length is closely tied to wheel diameter and the spacing between axles (for multi-axle trailers).

Width

Width determines the internal clearance between the fender and the tire.

Typical widths include:

• 9 inches (standard for 15–16” wheels)

• 10 inches (standard for 16–17.5” wheels)

• 12 inches (oversized or heavy-duty applications)

Selecting the wrong width may result in tire rubbing or excessive gap between fender and tire.

Height

Height is measured from the ground-contact side of the fender to its topmost point.

Most steel tandem fenders range from 16–18 inches tall, depending on the style (teardrop, radius, or diamond plate).

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2. Key Factors That Determine the Correct Fender Size

To choose the proper fender, confirm the following variables:

Wheel Diameter

Fenders must be tall enough and long enough to cover the tire profile.

Common pairings:

• 15” wheels → 9” wide fenders

• 16” wheels → 9” or 10” wide fenders

• 17.5” wheels → 10” wide fenders (industry standard)

Axle Configuration

• Single-axle: Shorter fenders, simple mounting points

• Tandem-axle: Long fenders (usually 72 inches) with a center “teardrop” or radius section

• Tri-axle: Extended-length fenders requiring higher structural rigidity

Tire-to-Tire Spacing

For tandem trailers, the spacing between your front and rear axle affects the necessary arch profile.

Industry-standard spacing works with most generic tandem fenders, such as 72×10×17 teardrop steel models.

Mounting Method

Your size selection may vary based on whether you use:

• Weld-on mounts

• Bolt-on brackets

• Backing plates

• Integrated steps or supports

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3. Common Trailer Fender Sizes (Industry Standard)

Below are the most widely used fender sizes:

Tandem-Axle Steel Teardrop Fenders

• 72” length

• 10” width

• 17” height

Most common for car haulers, utility trailers, and equipment trailers.

Tandem-Axle Radius Fenders

• 69” length

• 9–10” width

• 15–17” height

Used more often on lighter-duty trailers.

Single-Axle Steel Fenders

• 28–32” length

• 9–10” width

• 12–15” height

Suitable for small utility trailers and lawn equipment trailers.

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4. How Much Clearance Should a Fender Have?

Proper tire-to-fender clearance ensures safety and prevents rubbing.

Standard Clearance Recommendations

• Horizontal (side-to-side): 1” minimum

• Vertical (top of tire to underside of fender): 2–4”

• Front/back tire clearance (tandem only): Should not contact during full suspension travel

Too little clearance causes rubbing; too much clearance reduces debris protection.

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5. Measuring Your Trailer for Replacement Fenders

To size your new fenders correctly, measure the following:

1. Tire diameter (e.g., 28”, 30”, 31.5”)

2. Tire width

3. Axle spacing (for tandem)

4. Existing fender length, width, height

5. Mounting bracket spacing or weld points

6. Desired material (14G steel, 16G steel, aluminum, diamond plate)

Accurate measurements ensure proper fitment and faster installation.

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6. When to Choose a Larger Size

You may need to size up if:

• You upgraded to larger wheels

• Your current fenders rub during bumps

• You carry heavy loads

• You use off-road or extra-wide tires

• Your suspension travel exceeds 2–3 inches

In those cases, moving from a 9-inch width to a 10-inch width often solves clearance issues.

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7. Choosing the Right Size for Long-Term Durability

For most heavy-duty and commercial trailers, the industry moves toward:

• 10-inch width

• 72-inch length

• 17-inch height

• 14-gauge steel

This combination provides durability, weldability, and correct fitment for modern tire sizes—including common 17.5-inch wheel setups on equipment trailers.

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Conclusion

Choosing the right trailer fender size comes down to understanding your wheel diameter, axle configuration, and mounting method. Most tandem trailers use standardized 72×10×17 steel fenders, while single-axle trailers require shorter fenders that match the diameter of a single tire.

Correct sizing ensures safety, prevents tire contact, and improves the overall appearance and durability of your trailer.