How to Determine the Weight Capacity of a Boat Trailer

Updated 10/22/2018 | Published 10/20/2018

Question:

Hi I’m buying a trailer for a pontoon boat that weighs 3000-3400 lb gross. The trailer has been used to haul a similar boat for years. It has one axle with “F” rated tires . I looked up F rated tire and capacity is just under 4000 lb My question is Does that mean the axle should be capable of hauling almost 4000 lbs or 8000 lb ? 4000 lb x two tires = 8000 lb

asked by: Tom

Expert Reply:

The weight capacity of your boat trailer is always going to be limited by the weakest component which could be the axle, tires, or frame. I would also keep in mind that not all tires with an F load range have the same weight capacity, it will vary by tire size. For example, a 235/85-16 tire with F load range has a 3,960 lb weight capacity whereas a 7.50-16 tire has a 3,197 lb weight capacity.

If you look on the axle tag of your trailer axle it should list the capacity but if not you can always measure the diameter and use the list below to determine axle capacity. The axle capacity will usually be just a bit lower than the gross vehicle weight rating (GVWR) of the trailer which is the most it can weigh. This is usually because the tongue carries between 8-10%.

- 1,000-lb - 2,000-lb Axles: 1-1/2 inch - 1-3/4 inch diameter
- 3,500-lb Axles: 2-3/8 inch diameter
- 6,000-lb - 7,200-lb Axles: 3 inch diameter
- 8,000-lb Axles: 3-1/2 inch diameter
- 9,000-lb Axles: 4 inch diameter
- 10,000-lb or more Axles: 5 inch diameter

Unfortunately, I don't have any info on how to determine the weight capacity of your frame. If there is a 17 digit VIN and you know the make and model of the trailer you could then call the manufacturer and ask them for the GVWR but if this cannot be done then the only other option is to find a trailer expert who specializes in looking at different components of the trailer to determine weight capacity.

expert reply by: Conner L