Why Does a Shorter Leaf Spring have a Higher Capacity than an Identical Longer Spring

Updated 05/29/2015 | Published 05/27/2015

Question:

I just purchased 2 SP-218275 springs to replace 2 original springs that came on my 2004 Cougar 290 5th whl. The tag on the Al-Ko axels say that they are 4400 lb . axels. The PR4 info says they are for a 4800 lb axel. My problem with this is that the other 3 leaves are inches shorter than the leaves in the 4400 lb springs.. This has me worried. My question to you is why would a spring that is rated for 400 lb more have the same thickness leaves but be inches shorter.but yet be rated for 400 lb. more? I would think to get a higher rating they would need to have thicker or longer leaves.

asked by: Paul J

Expert Reply:

A lot goes into giving something its weight capacity. The springs have been designed and tested for 4,800 pound trailer axles, 2,400 pounds per spring. It is actually more difficult to flex a shorter piece of steel than a longer one so it makes sense that a shorter spring would have a higher capacity. As long as you can properly install the springs and they are appropriately rated for the trailer then it wouldn't be a problem.

expert reply by: Michael H