I’d like to develop a FAQ page for suspension. Please help me create this page by asking the question and answering it if possible. Only relevent questions please…
Here’s my first question to start off…
Q: What’s the differance between linear rate and pregressive rate springs?
A:???
The spring rate is the rate at which a spring will compress a specified distance with an applied force acting against it. Typically this is expressed in lbs-in. A spring with a 350 lbs/in. rate will depress 1 in. for every 350 lbs. applied to the spring. A linear rate designates the spring has uniform measure in regard to the springs dimensions from top to bottom. A linear spring’s rate can be measured:
spring rate = 11,250,000 x ( d to the 4th power) / 8 x N x ( D to the 3rd power)
d = outside wire diameter in inches
N = number of active, or complete, coils
D = mean, or center, wire diameter
The other two numbers are constants for steel springs.
A variable rate spring is a coil spring that is not uniform in measure in regard to the spring’s dimensions from top to bottom. The diameter of the wire may vary, or the overall diameter of the spring may taper, or a combination of both to alter the spring’s rate of compression at some point. A progressive rate will require progressively more weight to compress the spring one inch the further it travels. If our before mentioned 350lb-in. spring was progressive, it might have a 375lb-in rate the next inch, and a 400lb-in rate the following inch. Variable, or progressive, rate springs cannot be measured easily.
In both spring types, the rate of compression is different than the load. The spring load is the amount of weight necessary to compress the spring a given measure. Our linear spring will compress 3 inches with a load of 1050 lbs acting on it, at a rate of 350lb-in. Our progresive rate spring will compress 3 inches with a load of 1125 lbs acting on it, at a varible rate of 350lb-in to 400 lb-in. Load is important only in designing springs to ensure proper support of the vehicle’s weight, and will not affect handling performance. The rate of a spring is important in regards to handling, as it is the measure of force necessary to compress the spring. A progressive rate has the advantage of a softer rate to absorb small irregularities in the road surface, and then as it compresses, a higher rate to absorb larger irregularities. The problem with progressive springs is that in practice, a car’s springs only operate in a limited range of their total travel, and therefore the amount of progression in spring rate must be kept small. A linear rate spring with the assistance of good jounce bumpers or stops like Koni’s uerathane design have often proven the better route.