How to Measure Your Trailer for Replacement Fenders (Step-by-Step Guide)

Accurate measurements are essential when replacing trailer fenders. Choosing the wrong size can lead to tire rubbing, improper coverage, mounting issues, or difficulty welding or bolting the fender into place. This guide provides a clear, step-by-step process to measure your trailer correctly and select the right fender size.

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1. Tools You’ll Need

To get precise measurements, gather:

• A tape measure (at least 8 feet for tandem fenders)

• A straight edge or level

• Pen and paper or notes app

• Optional: calipers for measuring wheel width

These tools ensure accuracy, especially for tandem-axle applications where multiple dimensions must align.

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2. Identify Your Trailer Type

Before measuring, confirm whether your trailer is:

• Single-axle

• Tandem-axle

• Tri-axle

Each configuration requires different fender lengths and profiles. Most replacement measurements are for tandem-axle trailers, which commonly use 72-inch teardrop fenders.

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3. Measure the Wheel Diameter

Measure the diameter of the tire from ground to top.

Common diameters:

• 14”–15” wheels: Often use 9” wide fenders

• 16” wheels: 9” or 10” width fenders

• 17.5” wheels: Typically require 10” wide fenders

Wheel diameter affects fender height and width requirements.

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4. Measure the Tire Width

Measure the width of the tire tread.

Most trailer tires fall in the:

• 7–9 inch range for 15–16” wheels

• 8–10 inch range for 17.5” wheels

Your fender must provide at least 1 inch of clearance on each side of the tire.

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5. Measure the Fender Length

For single-axle trailers, measure the distance from the front edge of the tire to the rear edge.

For tandem-axle trailers, measure:

1. The distance from the front of the front tire to the back of the rear tire

2. Add 2–3 inches for proper coverage

Most tandem trailers fit standard lengths such as:

• 69”

• 72” (industry standard)

• 76”+ for specialty applications

If your measurement is close to 72 inches, a 72×10×17 teardrop fender is the typical correct match.

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6. Measure the Fender Height

Height is the distance from the bottom mounting edge to the top center of the fender.

Measure from:

• Ground → top of the tire

• Tire top → desired fender clearance (2–4 inches)

Then combine those measurements to approximate required fender height.

Common tandem fender heights:

• 16–18 inches

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7. Measure Axle Spacing (Tandem Only)

One of the most important dimensions for tandem trailers is axle spacing.

Measure from:

• The center of the front axle → center of the rear axle

Typical spacing ranges:

• 33–36 inches for most utility and equipment trailers

This ensures the center arch or teardrop aligns correctly between the wheels.

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8. Check Tire-to-Tire Clearance

Measure the distance between the rear edge of the front tire and the front edge of the rear tire.

Adequate clearance allows for:

• Suspension travel

• Prevention of rubbing

• Proper fit of the fender’s center arch

For most trailers, a 72-inch fender accommodates standard tire spacing.

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9. Identify Your Mounting Method

Your measurements may vary depending on:

• Weld-on mounts

• Bolt-on brackets

• Backing plates

• Integrated step supports

Welded installations require more precision because the fender must sit level and centered for structural integrity.

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10. Assess Clearance Requirements

Standard fender clearance recommendations:

• Vertical clearance: 2–4 inches above the tire

• Horizontal clearance: 1 inch on each side

• End clearance (tandem): Enough room for suspension movement

If your trailer has heavy loads or off-road use, aim for the upper end of the clearance ranges.

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11. Compare Your Measurements to Standard Fender Sizes

Match your numbers to industry-standard options such as:

• 32×10 single-axle fenders

• 69×9 tandem radius fenders

• 72×10×17 teardrop steel fenders (most common)

If your measurements fall slightly outside a standard size, choose the next size up to avoid rubbing or insufficient coverage.

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12. Document and Verify

Before ordering, write down your measurements in this format:

• Tire diameter: ____

• Tire width: ____

• Axle spacing: ____

• Tire-to-tire clearance: ____

• Fender length needed: ____

• Fender height needed: ____

• Mounting style: ____

Double-check each number to prevent ordering the wrong fender.

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Conclusion

Measuring your trailer correctly ensures your replacement fenders fit securely, provide adequate clearance, and comply with industry standards. Most tandem trailers with 16” or 17.5” wheels will align with standardized sizes such as 72×10×17 steel fenders, but verifying exact dimensions is essential.

Accurate measurements reduce installation time, improve safety, and ensure long-term durability of your trailer’s fender system.