![]() Now it doesn’t matter how far we push the weight down before releasing it, this combination of spring and weight “likes” bouncing at 3Hz. When released, the weight bounces up and down at (say) three times per second – so at a frequency of 3 Hertz (Hz). We then put a heavy weight on top of it and push down firmly on the weight. Let’s say we take a coil spring out of a car and mount it vertically on a surface. So what is all this about – and then when we’ve got that sorted, how do we measure natural frequencies? Natural frequencies ![]() Measuring the natural frequency of the suspension takes away this confusion. It’s why in all good suspension textbooks, spring rates are never referred to – just natural frequencies.Ī stiff spring doesn’t necessarily mean stiff suspension – it depends on the motion ratio and the weight acting through the spring. It’s called the suspension’s ‘natural frequency’ and it allows direct comparison of suspension stiffness of different cars. It’s a technique that takes into account motion ratio, spring rate, and mass acting through the wheels. Well there is an approach that allows you to compare the suspension rates between different cars. You think: gosh, I thought comparing spring rates would be easy! And don't forget I don’t care much about ride quality so my car’s springs are probably stiffer than you’ll want.” The owner of the other car then adds: “And of course my car's weight distribution is different to yours, what with this heavier engine and its slightly different location in the wheelbase. So you think: hmm, that means that the rate at the wheels is going to be (1) different to the rate at the spring, and (2) at any given suspension deflection, is likely to have a different wheel rate to your car. ![]() The motion ratio is how much the spring compresses for a given movement of the wheel. You say to the owner: "What rate springs are you running?" He tells you what they are in pounds/inch and then adds: "But my car’s motion ratio is different to yours – and the motion ratio on my car actually varies through the wheel travel." ![]() You’re trying to sort out your suspension, and you are admiring a similar car where its handling and ride are excellent. Let's say you want to compare the spring rates you are running in your car with someone else. ![]()
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