This is part two of our series on trailer tires. In this segment, we focus our attention on the GVWR (Gross Vehicle Weight Rating) and the GAWR (Gross Axle Weight Rating) and the importance of identifying and selecting tires with the correct load capacity for your trailer. In part one of this series we covered the differences between ST (special trailer), LT (light truck), and passenger car tires.
Trailer Weight and Tire Load Capacity
A tire that is unable to handle the weight of your loaded trailer can lead to catastrophic tire failure. Pay close attention to GVWR and the GAWR requirements for your trailer.
First, determine the carrying capacity of your trailer. Look for the manufacturer's placard on your trailer and look for the GVWR (gross vehicle weight rating) and/or the GAWR (gross axle weight rating). The GVWR is the maximum LOADED weight for the trailer as specified by the manufacturer. This is the weight of the trailer and all of its contents. This would include the weight of the trailer plus the weight of any horses, equipment, hay, water, spare tire, and any other equipment carried in or on the trailer.
The sum of the weight rating for all of the tires should be equal to or greater than the GVWR. For example, a 2-axle trailer with 2 tires on each axle with a GVWR of 12,000 lbs. would normally be outfitted with 2 axles each having a GAWR of 6,000 lbs. Calculating the load capacity requirement for your tires is as simple as 12,000 GVWR/4= 3,000 (or, 6,000 GAWR/2=3,000). In this example of a tandem axle trailer with two tires on each axle, the trailer tires must each be capable of carrying a load of 3,000 lbs.
Tire codes are molded into the sidewall of the tire and specify the dimensions of the tire, and some of its key limitations, such as load-bearing capacity and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa.
For example, a tire with an ISO Metric code of ST/235/80/R16 Load Capacity rating 3,520 Lbs:
1. ST: Special Trailer – Manufactured and approved for use on a trailer.
225: The width of the tire in millimeters – In this case 235 millimeter
80: The "aspect ratio" of the sidewall height as a percentage of the total width of the tire. In this case, the height of the sidewalls on this tire is equal to 80% of the width of the tire. In this case, 235 x 80% = 188 millimeters which is the height of the sidewall on this tire.
R: This is a radial tire
16: The diameter in inches of the wheel that the tire is designed to fit
Tires are a critical piece of equipment for all kinds of trailers - horse trailers, car haulers, cargo trailers, utility trailers, etc. Using the right tire for the job is critical to keeping you and your horses, cargo, and equipment safe and riding comfortably. Your trailer will pull better and be more stable on the right tires. Feel free to contact us at Trailers of the East Coast with any questions on getting the right tires for your trailer.