Determining your trailer hub size is crucial for ensuring proper wheel fitment, safe towing, and avoiding costly repairs. It involves measuring the bolt pattern and inner and outer bearing sizes to identify the correct replacement hub for your trailer.
Understanding the Importance of Correct Trailer Hub Size
Choosing the correct trailer hub is paramount for several reasons. A mismatched hub can lead to wheel instability, bearing failure, and even complete wheel detachment while driving. This not only puts you and other drivers at risk but can also cause significant damage to your trailer and cargo. Using the wrong hub can also negatively affect braking performance and increase tire wear. Investing the time to accurately determine your trailer hub size is an investment in safety, longevity, and peace of mind.
Methods for Determining Trailer Hub Size
There are three primary methods for determining your trailer hub size:
Identifying the Bolt Pattern
The bolt pattern refers to the number and spacing of the studs that secure the wheel to the hub. This is typically represented as two numbers, such as 5 on 4.5, where the first number indicates the number of studs and the second number indicates the diameter of the circle they are arranged on (the bolt circle diameter).
- Measuring the Bolt Pattern: For hubs with an even number of studs (e.g., 4, 6, or 8), measure the distance between the centers of two studs directly opposite each other. For hubs with an odd number of studs (e.g., 5), measure from the center of one stud to the outer edge of the stud directly across from it. There are also bolt pattern measurement tools available for purchase.
- Checking the Wheel: Often, the bolt pattern is stamped or labeled on the back of the wheel itself. This is a quick and easy way to confirm the hub’s bolt pattern.
- Consulting the Trailer Manual: If available, the trailer owner’s manual will provide the correct bolt pattern specifications for your trailer.
Measuring Inner and Outer Bearing Sizes
The inner and outer bearings are critical components within the hub that allow the wheel to rotate smoothly. Their size directly relates to the hub’s capacity and the spindle it fits on. Identifying the bearing sizes is essential for ensuring proper fitment and functionality.
- Removing and Inspecting the Bearings: Carefully remove the hub assembly and extract the inner and outer bearings. Look for stamped or etched markings on the bearing itself. These markings will usually consist of a part number (e.g., L44643, L68149).
- Using a Caliper: If the markings are worn or illegible, use a caliper to measure the inner diameter (ID), outer diameter (OD), and width of both the inner and outer bearings. Compare these measurements to bearing specification charts readily available online.
- Checking Bearing Races: The bearing races are the hardened surfaces that the bearings roll against within the hub. If you are only replacing the hub and not the bearings, matching the old races to the new hub is critical. Verify the new hub will accept your current races.
Utilizing the Trailer VIN
The Vehicle Identification Number (VIN) is a unique identifier for your trailer. It contains valuable information about the trailer’s specifications, including potentially the hub size.
- Locating the VIN: The VIN is typically found on a sticker or plate attached to the trailer frame, often near the tongue.
- Contacting the Manufacturer: Contact the trailer manufacturer with the VIN. They should be able to provide you with the hub specifications for your particular trailer model.
- Using Online VIN Decoders: Several online VIN decoders can provide some trailer specifications, although they may not always include the hub size. It’s best to use this method as a preliminary check and confirm the information with the manufacturer or a qualified mechanic.
Frequently Asked Questions (FAQs)
FAQ 1: What tools do I need to measure trailer hub size?
You’ll need a tape measure, a caliper (preferably digital), a socket wrench set, bearing grease, and potentially a bolt pattern gauge. Safety glasses and gloves are also highly recommended.
FAQ 2: Can I determine hub size without disassembling the hub?
Unfortunately, you cannot accurately determine the inner and outer bearing sizes without disassembling the hub. However, you may be able to determine the bolt pattern by visually inspecting the wheel and hub.
FAQ 3: What is the difference between a 5 on 4.5 and a 5 on 4.75 bolt pattern?
The difference lies in the diameter of the bolt circle. A 5 on 4.5 bolt pattern has a bolt circle diameter of 4.5 inches, while a 5 on 4.75 bolt pattern has a diameter of 4.75 inches. These two are NOT interchangeable.
FAQ 4: How do I measure the bolt pattern on a 5-lug hub?
Measure from the center of one stud to the outer edge of the stud directly across from it. Specialized bolt pattern measurement tools are also available.
FAQ 5: What happens if I use the wrong size hub?
Using the wrong size hub can lead to wheel instability, bearing failure, brake failure, and even complete wheel detachment, causing serious accidents and damage.
FAQ 6: Where can I find bearing specification charts?
Bearing specification charts are readily available online from bearing manufacturers like Timken and SKF, as well as from various trailer parts retailers.
FAQ 7: Should I replace the entire hub or just the bearings?
Consider replacing the entire hub if it is damaged, corroded, or shows signs of wear. If only the bearings are worn, you can typically replace just the bearings and races, provided the hub is in good condition.
FAQ 8: What type of grease should I use for trailer hubs?
Use a high-quality, water-resistant marine grease specifically designed for trailer wheel bearings. This type of grease provides superior protection against corrosion and water intrusion.
FAQ 9: How often should I repack my trailer wheel bearings?
It is generally recommended to repack trailer wheel bearings every 12 months or 12,000 miles, whichever comes first. More frequent maintenance may be required for trailers used in harsh conditions or for long-distance towing.
FAQ 10: What is a “hub pilot” versus a “lug-centric” wheel?
A hub-centric wheel is centered on the hub by the center bore diameter, providing precise wheel alignment. A lug-centric wheel is centered by the lug nuts, which can sometimes lead to vibration if not properly tightened. Knowing this distinction is vital for proper wheel selection after hub replacement.
FAQ 11: What if the markings on my bearings are completely gone?
If the markings are completely gone, carefully measure the inner diameter (ID), outer diameter (OD), and width of both bearings with a caliper. Then, consult bearing specification charts or contact a bearing supplier to identify the bearing based on these measurements.
FAQ 12: Can I upgrade to a larger hub size for increased capacity?
Upgrading to a larger hub size typically requires replacing the entire axle and potentially the wheels. This is a significant undertaking and should only be done after careful consideration and consultation with a qualified trailer mechanic to ensure compatibility and safety.