Does Adding a Second Axle to Trailer Increase Weight Carrying Capacity

Question:

I read the QandA on the installation of a second leaf spring axle to a boat trailer. I would like to add a second axle to my trailer which has a single torsion axle. I would also like to add disk brakes. Do you have kits to add a second torsion axle like those for the spring axle?

asked by: Ben

Helpful Expert Reply:

We do not offer torsion axles due to shipping size and weight restrictions. We do offer leaf spring beam axles up to a 3500-lb rating and we offer Timbren axle-less suspensions as well. If you want to add a second axle to an existing single-axle trailer you potentially can do so but there are a few things to keep in mind.

Adding the second axle does NOT necessarily increase the trailer's weight-carrying capacity. This might be the case but only if the axles were the trailer's lowest-rated component part, or its "weakest link", if you will.

A trailer's weight capacity depends on all of the components that go into it: coupler, frame, suspension, axles, hubs, wheels and tires. You could add a second axle to a trailer that doubles its axle capacity but this does not ensure the other parts of the trailer, such as its frame or coupler, have that same doubled capacity. Proper trailer design does require engineering knowledge and unless you can confirm with the trailer maker that the frame has the capacity to support the increased load, then adding the second axle will not increase trailer capacity. It WOULD take some of the weight load off the original axle but not necessarily do anything more.

When brakes are installed only on one axle of a tandem axle trailer the brakes should be installed on the front axle if both are torsion axles, or on the rear axle if both are leaf spring axles. If you mix a torsion axle and a leaf spring axle and only one will have brakes then the rear axle gets the brakes.

I have linked for you two articles on adding disc brakes to a trailer. One covers hydraulic discs and the other electric-over-hydraulic installations. These will help you get a sense of the degree of effort and cost.

Some of the 3500-lb leaf spring axles we offer come with hub/drums and electric brakes as a complete kit. Wiring in electric brakes is a lot easier than running the hydraulic lines for disc brakes so you might consider this option. I linked our page for beam axles and for axle-less suspensions as well as an article on trailer suspension.

expert reply by: Adam R