How do I know what bearings I need for my trailer?

When it comes to trailer bearings, knowing which ones you need can seem confusing. However, with a bit of information about bearing sizes, types, and measurements, you can easily figure out the right bearings for your trailer. In this article, we’ll walk through the step-by-step process for identifying and selecting replacement trailer bearings.

Step 1: Determine Your Trailer’s Hub Size

The first thing you need to know when selecting bearings is the hub size of your trailer. Trailer hubs come in a standard set of sizes, measured by the hub’s bolt pattern. Common hub sizes for trailers include:

• 3.5 inches
• 4 inches
• 5 inches
• 5.5 inches
• 6 inches

To determine the hub size, you’ll need to count the number of bolts and measure the distance between two opposing bolt holes. Use a tape measure to find the center-to-center measurement in inches. For example, if you count 5 bolts and the distance between two is 4 inches, you have a 5 x 4 or 5 inch hub.

Step 2: Identify Your Trailer’s Inner and Outer Bearing Numbers

Once you know the hub size, you can use it to look up the bearing part numbers needed. Trailer bearings come in matched inner and outer sets. The inner bearing supports the spindle and the outer bearing allows the hub to spin around it.

Here are some of the common trailer bearing numbers based on hub size:

Hub Size	Inner Bearing	Outer Bearing
3.5 inches	L44649	L44610
4 inches	L44643	L44610
5 inches	L44649	L44649
5.5 inches	LM67048	LM67010
6 inches	LM67010	LM67048

You’ll need both the inner and outer bearing numbers for your hub size when ordering replacements.

Step 3: Determine the Bearings’ Dimensions

Bearings are also specified by their dimensions – the outside diameter and width. Knowing these dimensions will ensure the bearings fit properly within your hub and allow it to spin freely.

Bearing dimension numbers can usually be found printed directly on the bearing. If not, you can measure them yourself with a caliper. Dimensions follow a standard numbering format:

• The first 2 digits are the width in millimeters.
• The last 3 digits are the outer diameter in millimeters.

So for example, a 6205 bearing would have:

• Width: 62 mm
• Outer diameter: 205 mm

Replacement bearings need to match the original dimensions to fit correctly.

Step 4: Choose Sealed or Unsealed Bearings

The final decision is whether you need sealed or unsealed bearings. Sealed bearings have an integrated rubber seal built in to keep lubricant in and contaminants like water and dirt out. Unsealed bearings have no seal, allowing you to pack them with grease yourself.

For boat trailers and other wet applications, sealed bearings are usually preferred. Unsealed bearings are common on older utility trailers where frequent repacking is acceptable. Make sure to get the same type of bearing that is currently installed.

Step 5: Purchase Matched Bearing Sets

With the bearing numbers, dimensions, and type identified, you can now buy your replacement bearings. It’s important to purchase them in matched sets for the inner and outer bearings.

Sets are readily available at most auto parts stores or online retailers. Having both the inner and outer bearings ensures compatibility, proper spacing, and smooth spinning when installed.

Some key retailers for trailer bearings include:

• AutoZone
• O’Reilly Auto Parts
• NAPA Auto Parts
• Amazon
• etrailer

Buying from a reputable source ensures you get high quality bearings built to spec. Avoid cheap counterfeits that can fail quickly and cause damage.

Conclusion

Identifying and replacing worn trailer bearings is made easy by following these steps:

1. Determine hub size
2. Look up bearing part numbers
3. Match dimensions
4. Choose sealed or unsealed
5. Buy quality matched sets

With the right bearings installed, your trailer hub will roll smoothly for thousands of miles. Regular inspection and repacking or replacement as needed will keep your bearings in tip-top shape on the road.

FAQs

How can I tell if my trailer bearings need to be replaced?

Signs that your trailer bearings need replacement include:

• Excessive noise, vibration, or wobbling coming from the wheel hub
• Leaking grease around the seal
• Overheating hubs after driving
• Rusted or damaged bearings
• Dragging or locked up brakes

How often should trailer bearings be repacked or replaced?

For light duty use, trailer bearings should be inspected annually and packed with fresh grease. For heavier duty use, inspect and repack bearings every 6 months or 6,000 – 12,000 miles. Complete bearing replacement is recommended every 30,000 – 50,000 miles.

Can I replace trailer bearings myself?

Yes, with some mechanical ability, basic tools, and the right replacement bearings, most people can replace trailer bearings themselves. Just be sure to follow all safety precautions. If you are unsure, have a professional mechanic do the repair.

What tools do I need to repack trailer bearings?

The basic tools needed to repack trailer bearings include:

• Pipe or bearing packer tool
• Grease gun
• Rubber mallet
• Wheel bearing grease
• Rags and brake cleaner

What type of grease should I use when packing bearings?

Use a high quality wheel bearing grease meeting the NLGI GC-LB certification. Common brands include Valvoline Multi-Purpose, Lucas X-Tra Heavy Duty, and Timken Premium. Avoid general purpose greases.

Bearing Measurement and Sizing Table

Use this handy reference table to identify bearing sizes by their dimensions:

Bearing Number	Outside Diameter	Width
25580	255 mm	80 mm
30205	302 mm	05 mm
6205	205 mm	62 mm
6306	306 mm	62 mm
6310	310 mm	62 mm
15625	625 mm	15 mm

Common Wheel Hub Sizes

Reference this table for typical trailer hub bolt patterns:

Bolt Pattern	Hub Size
4 x 100 mm	4 inches
4 x 115 mm	4.5 inches
5 x 127 mm	5 inches
5 x 150 mm	6 inches
6 x 139.7 mm	5.5 inches
6 x 150 mm	6 inches