A spring’s Spring Rate and a spring’s Load Rate are the two most misunderstood spring terms out there.
But here’s the good news: this is easily correctable.
With a quick overview of the terms, and a small change in language for clarity, you’ll be able to talk springs better than 99% of the population today.
(I made that statistic up. It’s probably more like 99.999%)
A Spring’s Spring Rate
A spring’s Spring Rate is the amount of weight required to deflect a spring one inch. The lower the Spring Rate, the softer the spring. The softer the spring, the smoother the ride.
If you’re still having trouble, think of it as a fat guy on a mattress.
A fat guy on a soft mattress would sink in pretty far, but a fat guy on a hard concrete-like mattress wouldn’t sink in at all.
We could measure the fat-guy-on-mattress rate by seeing just how fat the fat guy has to be in order for him to sink one inch down. So a 400 pound fat guy sinking one inch into a mattress gives us a Mattress Rate of 400 pounds. That’s not a very soft mattress!
If we look at another mattress, we could get one where it would only take 250 pounds of fat guy to sink one inch down.
That’s a noticeably softer mattress at a Mattress Rate of 250 pounds. It was probably made by NASA.
Just replace fat guy with amount of weight and mattress with spring, and you have a near-perfect understanding of Spring Rate.
A Spring’s Load Rate
Load Rate, on the other hand, is completely different. Load Rate is the amount of weight a spring is designed to carry when deflected to a certain height.
Did I confuse you? It’s ok if I did. Load Rate is so troublesome that it’ll be better to just use a different term..
A Spring’s Load Rate Design Rate
That’s much better. Let’s try again.
Design Rate is the amount of weight a spring is designed to carry when deflected to a certain height.
If we go back to our fat guy on mattress example, the Design Rate for a mattress would be how fat the guy the mattress is made for is.
“He wants a mattress? And he wants it soft enough so he sinks down 1.3 inches? We can do that! Just tell me how fat he is so I can set the Design Rate of his mattress.” –Sample dialogue, translated to Fat Guy
Check Your Understanding
Spring Rate is the amount of weight required to deflect a spring one-inch, making it a measure of softness for the spring.
Design Rate is the amount of weight a spring is designed to carry at a certain ride height, making it an engineering consideration.
See the difference? It seems simple now, doesn’t it?