Parts Needed To Convert Boat Trailer From Single to Tandem Axle Trailer

Published 09/01/2015

Products Featured in This Question

4-Leaf Double-Eye Spring for 3,500-lb Trailer Axles - 25-1/4" Long

(2331)

$57.38

Tandem-Axle Trailer Hanger Kit for Double Eye Springs - 3-1/4" Tall Front/Center/Rear

(712)

$93.87

U-Bolt Kit for Mounting 3,500-lb, Round Trailer Axles - 5-1/2" Long U-Bolts

(2200)

$78.24

Question:

Returning satisfied customer... I have a 24foot pontoon boat trailer equipped with 20.5 x8-10 tires on a single axle. I want to convert this to a dual axle setup with 14inch tires your ST215/75R14 on spoke rims. I would like to use 1 idler axle and 1 axle with electric brakes. Im estimating the boat weight at 3600# - Pontoon Forum give or take but want to be on the safe side. The trailer spring mounts spacing center to center is 67inch and face of hub to face of hub is 82. I need some help in ing the correct components. I will need the shackle / spring kit and Im anticipating eye end springs. Thanks

asked by: Don B

Expert Reply:

I can offer you suggestions for double-eye leave springs, a U-bolt kit, and a hanger kit, but we do not offer axles that match your spring center measurement and your hub face measurement, so the axles must be custom ordered. You will want to order the axles locally from an authorized trailer axle dealer. We do suggest ordering 3,500 pound axles. It is very common for tandem axle boat trailers to have 3,500 pound axles on them, and this will allow you to use electric brakes rated for 3,500 pounds.

Our most popular double-eye leaf spring for 3,500 pound axles is # e54SR. This 4-leaf spring is 25-1/8 inches long and has a spring width of 1-3/4 inches. The part number includes one spring.

For a 3,500 pound round 2-3/8 inch diameter axle, a U-bolt kit like # APUBR-1 will work well. This U-bolt kit includes 5-1/2 inch long U-bolts, U-bolt plates, and hex nuts. This kit is for one 3,500 pound axle.

A tandem axle trailer hanger kit that I think will work well for you is # APT5. This hanger kit is designed to work with # e54SR springs. Since you want to put larger wheels on your trailer, the 3-1/4 inch hangers that come with this kit will help provide a little additional room, over kits with shorter hangers, for your tire clearance.

When changing your trailer from a single axle to a tandem axle, you will want to make sure that your tongue weight stays around 10 percent of your trailer's weight. We recommend mocking up your trailer and weighing it to make sure your axle placement is correct to provide the correct tongue weight. You can use the existing placement of your axle as the location to place the hangers for your equalizers to start your mock up.

Once you have the trailer mocked up, you will want to weigh the trailer under the wheels, find the actual tongue weight, measure the distance from the tongue to the center between the axles, and determine the total weight of the trailer. Using the formula from the worksheet I have attached for you, you will be able to determine what adjustments need to be made in the location of your axles.