How to calculate the stiffness of a suspension spring

If you need to know the stiffness of a constant rate car or motorbike suspension spring you can calculate it very accurately with some simple measurements and a bit of easy maths. And here's how. This doesn't really work for progressive/rising rate springs. If you don't know the difference, don't worry, we explain that as well. But for the majority of road car and race springs which are single rate and made of steel this will tell you what you've got. And once you know that, you can work out what you need.

[@dddave999]

Very useful thanks for posting.
Keyed the numbers and formula into excel and got 52.087 Np mm and 296.89 lbs. So I could have a number wrong somewhere but still close to your result.
Crazy how the thickness of the spring wireb changes the stiffness so much!

[@ScottiB2]

Great tee shirt!!

[@paulcornelius300]

Almost fell asleep through this one but thanks for the information your a Lotus Elan hero 👍🏼

[@lunam7249]

Great vid! THANKS!

[@SwearAThon]

Excellent! I needed that..

[@ReshardsAutomotiveWorkshop]

I did not know. Thank you. 👍

[@jordanpene5279]

Awesome video. liked and subscribed!! Thanks

[@rx0788]

Good job

[@king0vdarkness]

Thanks for the video, just double checking, so 9913 is the shear modulus of the steel?

[@usamahnaushad5611]

Thank you so much for this! I am working on my final year project on suspension design and this will be extremely helpful.
I was wondering if I can apply this technique to any other model. My base data is of Honda Civic and I was wondering if I can calculate the spring rate with the same technique.
Thanks!

[@thelotuselanm100restoratio3]

Yes, same formula for any steel suspension spring with closed and ground ends. Cars, motorbikes, bicycle shocks, whatever. Good luck with your finals.

[@mugundhans3809]

Can I apply this technique for the extension springs??

[@triyanpalarora4710]

I have a question
In calculating D, wouldn't we consider D= OD-(2d) ??
Because we would be removing the thickness of spring material from OD on both sides??
or is the calculation done using the pitch diameter of the spring ???

[@ardentartist2050]

no because it is for mean diameter

[@libra53ish]

awesome

[@TheGreatTimSheridan]

I was kind a hoping you were going to stand on the spring and measure it with the caliper.

[@maxwellbapono4443]

good!!thanks! but u are too fast in the speaking aspect