Measuring trailer wheel size accurately is crucial for selecting the right tires, ensuring proper fitment, and maintaining safe towing practices. The key to correctly gauging your trailer wheel size lies in understanding the two primary dimensions: the wheel diameter (measured in inches) and the wheel width (also measured in inches). These measurements, along with the bolt pattern, are essential for compatibility with your trailer’s axle and intended load.
Understanding the Importance of Accurate Measurements
Accurate wheel size measurement isn’t just about aesthetics; it’s paramount for safety and performance. Installing tires on wheels that are too narrow or too wide can lead to tire failure, uneven wear, and compromised handling. Mismatched wheels can also negatively impact the trailer’s braking system and overall stability, potentially causing accidents. Therefore, taking the time to precisely measure your trailer wheels is a vital investment in your safety and the longevity of your equipment.
Step-by-Step Guide to Measuring Trailer Wheel Size
Here’s a breakdown of how to accurately measure your trailer wheel size:
-
Wheel Diameter: The wheel diameter represents the distance across the wheel from one bead seat to the opposite bead seat. The bead seat is the portion of the wheel rim that the tire bead sits against. To measure this accurately:
- Ideal Scenario: Remove the tire from the wheel. Use a measuring tape or ruler to measure the distance across the wheel, inside-to-inside, where the tire bead would seat. This is the most precise method.
- Tire On Measurement (Less Accurate): If you cannot remove the tire, look for the wheel diameter stamped on the wheel itself. This is usually a two-digit number (e.g., 15 for a 15-inch wheel). If you can’t find it, estimate the diameter by measuring from the outside edge of one side of the tire to the outside edge of the tire on the opposite side. Subtract approximately 2 inches (one inch per side) to account for the tire’s sidewall extending beyond the bead seat. This method is less accurate and should only be used as a last resort.
-
Wheel Width: The wheel width is the distance between the inner edges of the wheel flanges (the outer edges of the wheel rim). Again, the ideal way to measure is with the tire removed.
- Ideal Scenario: Remove the tire. Use a measuring tape or ruler to measure the distance between the inner edges of the wheel flanges.
- Tire On Measurement (Less Accurate): If the tire is mounted, locate the tire size information on the sidewall. For example, a tire size might be “ST205/75R15.” The width of the tire is indicated by the first number (205 in this case, representing the width in millimeters). This number is related to, but not the same as, the wheel width. You will still need to identify the wheel width directly, which is usually stamped on the wheel. Look for a number followed by the letter “J” (e.g., 6J, representing a 6-inch wide wheel).
-
Bolt Pattern: This refers to the number and spacing of the lug nuts on the wheel. This is essential for ensuring the wheel will physically attach to your trailer’s axle.
- Measuring the Bolt Pattern: Count the number of lug nuts. Then, measure the distance between lug nuts. The method for measuring this distance depends on the number of lugs:
- Even Number of Lugs (e.g., 4-Lug, 6-Lug): Measure from the center of one lug hole to the center of the lug hole directly opposite it.
- Odd Number of Lugs (e.g., 5-Lug): This requires a more complex measurement or the use of a bolt pattern gauge. The diameter you need to measure is that of the circle that encompasses all of the lug nuts. Measuring from center to center is not feasible. It is recommended to consult a bolt pattern chart or use a specific bolt pattern measuring tool for accurate results.
- Measuring the Bolt Pattern: Count the number of lug nuts. Then, measure the distance between lug nuts. The method for measuring this distance depends on the number of lugs:
Finding Stamped Information on the Wheel
Most trailer wheels have critical information stamped directly onto them. Look for these markings on the inside or outside of the wheel rim. Common information includes:
- Wheel Diameter: Represented in inches (e.g., 15)
- Wheel Width: Represented in inches, often with a “J” (e.g., 6J)
- Bolt Pattern: Represented as a number of lugs and a diameter (e.g., 5×4.5, meaning 5 lugs on a 4.5-inch diameter circle)
- Load Capacity: The maximum weight the wheel can safely support.
- Offset: The distance between the wheel’s mounting surface and its centerline.
Frequently Asked Questions (FAQs)
Here are some frequently asked questions about measuring trailer wheel size:
FAQ 1: Where can I find the wheel size information on my trailer?
Typically, the wheel size is stamped on the wheel itself, usually on the inside or outside of the rim. Look for markings like “15×6,” which indicates a 15-inch diameter and a 6-inch width. You might also find the bolt pattern information stamped alongside the diameter and width. Check your trailer’s owner’s manual, as well; sometimes this information is provided.
FAQ 2: What tools do I need to measure trailer wheel size?
You’ll need a measuring tape or ruler for measuring the diameter and width. A bolt pattern gauge is highly recommended for accurately determining the bolt pattern, especially for wheels with an odd number of lugs. A tire pressure gauge is also useful for checking tire inflation after any work on the wheels.
FAQ 3: What does ‘offset’ mean when referring to trailer wheels?
Offset refers to the distance between the wheel’s mounting surface (the part that touches the trailer hub) and its centerline. A positive offset means the mounting surface is closer to the outside of the wheel, while a negative offset means it’s closer to the inside. Using the wrong offset can cause tire rubbing or other fitment issues.
FAQ 4: How does tire size relate to wheel size?
The tire size information (e.g., ST205/75R15) includes the wheel diameter as the last number (15 in this example). This tells you the tire is designed to fit a 15-inch wheel. The tire width and aspect ratio are also important factors in determining overall tire dimensions.
FAQ 5: Can I use a wheel with a different bolt pattern on my trailer?
No. The bolt pattern must match the bolt pattern of your trailer’s axle hub. Using a wheel with a different bolt pattern is extremely dangerous and will prevent proper and safe attachment.
FAQ 6: What happens if I use the wrong wheel size on my trailer?
Using the wrong wheel size can lead to several problems, including tire failure, uneven tire wear, poor handling, brake system issues, and even structural damage to the trailer. It’s crucial to use the correct wheel size specified by the trailer manufacturer.
FAQ 7: Can I increase the wheel size on my trailer?
Increasing the wheel size (diameter) on your trailer is possible, but it requires careful consideration. You need to ensure there is sufficient clearance in the wheel well to accommodate the larger diameter tire. You also need to consider the load capacity of the new wheels and tires, and ensure they meet or exceed the trailer’s requirements. Consult a trailer professional before making any changes to wheel size.
FAQ 8: How important is the load rating of a trailer wheel?
The load rating is extremely important. The load rating of each wheel must be sufficient to support its share of the trailer’s gross vehicle weight (GVWR). Never use wheels with a load rating that is lower than the trailer manufacturer’s specifications. Exceeding the load rating can lead to wheel failure and accidents.
FAQ 9: What is the difference between a steel and an aluminum trailer wheel?
Steel wheels are generally more affordable and durable, but they are also heavier and more prone to rust. Aluminum wheels are lighter, more resistant to corrosion, and often offer a more aesthetically pleasing appearance, but they are typically more expensive.
FAQ 10: How often should I inspect my trailer wheels?
You should inspect your trailer wheels before each trip and regularly throughout the towing season. Look for signs of damage, such as cracks, dents, or bends. Also, check for loose lug nuts and proper tire inflation.
FAQ 11: Can I paint my trailer wheels?
Yes, you can paint your trailer wheels, but it’s important to use a paint specifically designed for wheels. This will help protect the wheels from corrosion and ensure a durable finish. Properly prepare the surface by cleaning and priming before painting.
FAQ 12: Where can I buy replacement trailer wheels?
You can purchase replacement trailer wheels from a variety of sources, including trailer supply stores, tire shops, online retailers, and RV dealerships. Be sure to provide the wheel diameter, width, bolt pattern, and load rating to ensure you get the correct replacement.
Conclusion
Measuring trailer wheel size accurately is a fundamental aspect of trailer maintenance and safety. By understanding the key measurements and following the steps outlined in this guide, you can confidently select the correct wheels and tires for your trailer, ensuring safe and reliable towing for years to come. Always prioritize safety and consult with a professional if you have any doubts or questions.