How to choose correct Leaf spring rating?
I just upgraded axles from 3500 tandem to 5200. Trailer parts supplier say I should use 2900 lb springs to match the new axles for a total of 11,600 lb capacity. This doesn't sound right to me because...
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Springs are normally rated in lbs/inch. That is, how many pounds of force does it take to deflect the spring 1 inch. If you know the design spring travel, then you can size the spring accordingly.
For instance, if the designed suspension travel is 5 inches and you want the spring to support a 2500 lb load with the spring in the middle of its travel (2.5 inches deflection), then you would want a (2500 lbs/2.5 inches =) 1000 lb/in spring. If you wanted the spring to deflect only 2 inches under a 2500 lb load, then you would want a stiffer (2500 lbs/2 inches =) 1250 lb/in spring. The remaining unused travel gives room for jounce (compression) when the wheel hits a bump.
The calculation method above assumes a linear spring rate. The calculations for a progressive spring rate are a bit more complex - a progressive spring gets stiffer as it compresses.
Unfortunately, the method they use to sell these RV leaf springs (it's a 2500 lb spring - period) doesn't really tell you everything you need to know to understand the deflection and ride characteristics you're going to experience with each particular spring. You need to know the allowable spring travel and the spring rate.
Rusty
For instance, if the designed suspension travel is 5 inches and you want the spring to support a 2500 lb load with the spring in the middle of its travel (2.5 inches deflection), then you would want a (2500 lbs/2.5 inches =) 1000 lb/in spring. If you wanted the spring to deflect only 2 inches under a 2500 lb load, then you would want a stiffer (2500 lbs/2 inches =) 1250 lb/in spring. The remaining unused travel gives room for jounce (compression) when the wheel hits a bump.
The calculation method above assumes a linear spring rate. The calculations for a progressive spring rate are a bit more complex - a progressive spring gets stiffer as it compresses.
Unfortunately, the method they use to sell these RV leaf springs (it's a 2500 lb spring - period) doesn't really tell you everything you need to know to understand the deflection and ride characteristics you're going to experience with each particular spring. You need to know the allowable spring travel and the spring rate.
Rusty
