Trailer Axle Diameter and Weight Capacity for Boat Trailer
Updated 01/23/2018 | Published 01/22/2018
Question:
I currently have a torsion axle aluminum boat trailer with a 3” single axle, 5 stud hub, and 14” wheels/tires. The boat and engine total combined weight is around 2500lbs. I found on your site that a 3” axle is capable of around 6000-7200lbs which should be more than sufficient. There is however a slight bow with the top of the tires leaning inward. My question is, should the hub have 6 studs vs 5? Are the tires/wheels the appropriate size? Could these factors result in the tops of the tires bowing in?
asked by: Bobby F
Expert Reply:
Both sprung axles and torsion trailer axles typically have some positive camber, meaning that there is a bend in the axle. When NOT under load the center of the axle is higher than the spindle ends; once the axle's rated weight is applied the axle beam flattens out.
This initial bend allows the trailer tires to be flat on the road surface when there is weight on them. This provides for even tire wear and better traction.
An axle's diameter can provide some indication of its weight capacity but there should be an identification sticker or plate on the axle itself that tells you its weight rating. A 3-inch axle could be rated as low as 3500-lbs or as high as 7200-lbs. Your trailer's main information sticker should indicate either or both axle weight rating and the trailer's gross weight rating (the most it and the boat/motor all together can weigh). Naturally it is never good to exceed either.
When a trailer axle bends under load so that the tops of the tires lean inward this tends to indicate an overloaded condition. If tires wear more on the inside edges of the tread than on the outside edges this again usually indicates that the axle/trailer is overloaded.
The way to know you are towing within the trailer's capacity is to verify your boat and motor weight and compare this to the trailer's rating.
