How to Find Axle capacity of a Trailer to Choose the Right Replacement Slipper Springs

Question:

I have a 1997 magic tilt boat trailer with slipper springs that are rusty. I have measured the springs from center of the bolt eye to the end of the spring and it measures 31-inches. They a 4 leaf 1-3/4 springs with 9/16-inch bolts. How can I tell the rating of my old slipper springs?

asked by: Lee L

Expert Reply:

The leaf springs on a trailer will need to meet or slightly exceed the axle capacity. So if you know the axle capacity then each spring should be rated for at least 1/2 of that capacity on a single axle trailer. The axle capacity may be listed somewhere on the trailer frame near the front of the trailer.

Another option is to pull off a hub and retrieve the inner and outer bearing numbers stamped into the sides of the bearings. With that information I can determine the likely hubs that are on it and from there the likely axle capacity.

Based on your measurements spring # SP-040275 is a possible fit. This spring is rated for 1,850 pounds for use on a 3,700 pound trailer axle.

expert reply by: Michael H