Top Mistakes People Make When Replacing Trailer Fenders (And How to Avoid Them)

Replacing trailer fenders seems straightforward, but it’s one of the most commonly botched maintenance jobs on utility trailers, equipment trailers, car haulers, and boat trailers. Incorrect installation can lead to tire rubbing, weld failure, cracked fenders, and unsafe towing conditions.

This guide details the most frequent mistakes people make when replacing trailer fenders—and how to avoid them with proper fitment and installation techniques.

⸻

1. Choosing the Wrong Fender Size

This is the number one mistake across all trailer types.

Common sizing errors include:

• Fenders too narrow for the tire

• Fenders too short to cover both tires on tandem trailers

• Incorrect height for wheel diameter

• Wrong profile (radius vs. teardrop)

How to avoid it

Always check:

• Tire diameter

• Tire section width

• Axle spacing

• Required fender height

• Required fender length

Standard tandem trailers almost always use 72×9×17 or 72×10×17 fenders.

⸻

2. Installing the Fender Too Close to the Tire

Setting the fender too low or too close to the tire causes rubbing during:

• Suspension compression

• Tire flex

• Heat expansion

• Rough terrain towing

Minimum clearance requirements:

• 2–4 inches vertical

• 1 inch horizontal on each side

⸻

3. Mounting the Fender Too High

A fender mounted too high fails to protect against:

• Road debris

• Water spray

• Loose gravel

• Mud

It can also violate state fender coverage laws.

How to avoid it

Center the highest point of the fender over the tire’s vertical centerline.

⸻

4. Not Aligning the Fender with Both Tires (Tandem Trailers)

Tandem-axle fenders must align precisely with both tires.

Common misalignments:

• Teardrop center not centered between the wheels

• One tire rubbing while the other has excess clearance

• Fender installed tilted forward or backward

Solution

Measure distance from tire to fender front and rear before welding or bolting.

⸻

5. Welding to Dirty or Painted Surfaces

Welding on top of:

• Rust

• Paint

• Old welds

• Dirt or grease

…leads to weak welds that crack over time.

Correct method

• Grind down to clean bare metal

• Remove rust completely

• Ensure proper fitment before applying heat

⸻

6. Not Using Backing Plates on Steel Tandem Fenders

Long-span fenders without reinforcement often:

• Flex

• Crack

• Vibrate

• Fail at weld points

Solution

Install backing plates or use fenders with built-in reinforcement, especially on 14-gauge steel.

⸻

7. Using Aluminum Fenders on Heavy Equipment Trailers

Aluminum is not recommended for:

• Car haulers

• Equipment trailers

• Trailers carrying tractors, machinery, or vehicles

Why?

• Aluminum cracks under vibration

• Harder to weld

• Less forgiving under sudden loads

Use steel (14G or 13G) for any heavy-duty application.

⸻

8. Using the Wrong Bolt Hardware (Bolt-On Installations)

Cheap hardware leads to:

• Corrosion

• Loose bolts

• Fender rattling

• Structural failure

Correct hardware

• Stainless steel

• Zinc-coated or galvanized bolts

• Nylon lock nuts or locking washers

⸻

9. Over-tightening Aluminum Fenders

Aluminum can crack if over-tightened.

How to avoid it

Tighten bolts firmly but evenly, and avoid excessive torque.

⸻

10. Ignoring Axle Spacing When Buying Tandem Fenders

Not all tandem trailers use the same spacing.

Industry standard:

33–36 inches center-to-center between axles

If spacing differs, the teardrop center may hit a tire.

Solution

Measure axle spacing before ordering fenders.

⸻

11. Failing to Check Suspension Travel

Many fender failures come from not accounting for:

• Leaf spring compression

• Axle articulation

• Load-induced sag

How to avoid it

Test vertical travel by:

• Jacking the trailer

• Compressing the suspension

• Ensuring fender clearance throughout movement

⸻

12. Painting Steel Fenders Without Priming

Paint alone does not prevent rust.

Correct method

• Apply rust-inhibiting primer

• Allow full cure

• Finish with paint or powder coating

⸻

13. Ignoring Tire Profile When Upgrading Tires

Upgrading from 15” → 16” → 17.5” tires changes:

• Diameter

• Width

• Fender height requirements

Rule of thumb:

Larger wheel = taller and wider fender needed.

⸻

14. Installing Only One New Fender

Replacing only one side creates:

• Unmatched materials

• Uneven appearance

• Unequal wear resistance

Recommendation

Replace both for symmetry and longevity.

⸻

Conclusion

Replacing trailer fenders seems simple, but avoiding common mistakes ensures safe towing, prevents tire rubbing, and extends the lifespan of the fenders. The key is choosing the correct size, using proper materials, maintaining clearance, and installing the fenders on clean, stable surfaces with adequate reinforcement.