Boat trailer axles vary according to their maximum weight capacity, and info on an axle’s weight rating may or may not be provided by reputable trailer parts dealers. If you want to know the weight rating of an axle, you can use the diameter of the tube as gauge. The wider the diameter, the more weight the axle can support.

The typical 1200-lb axle, for instance, would have a diameter of between 1.5 and 1.75 inches. This commonly comes as a straight type. Meanwhile, a 3500-lb axle is around 2.375 inches in diameter and comes as a straight, drop, or V saddle axle. A drop axle gives the trailer more stability because it provides a lower center of gravity.

The 6000-lb axle has a diameter of around 3 inches, and, like the 3500 axle, is also available in straight, drop, or V saddle variety. The V saddle design brings the center of gravity even lower, providing greater stability for heavier loads. There are heavier axle variants in the market, but they’re mostly used in logistics.

In addition, contrary to popular belief, the shape of the axle doesn’t do much in increasing the axle’s maximum carrying capacity. A 1.5-inch square axle and a 1.75-inch round axle will have the same weight rating. It is the diameter of the axle, more than its shape, which determines its weight capacity.


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