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# Spring Rates

### Tech Articles

Discussion and questions related to the course Practical Corner Weighting

Hello,

Just wondering how you decide what spring rates you should start? Is there a certain criteria you use based on the vehicle?

Thanks,

Chris

There are a few theories out there based on sprung to unsprung ratio and suspension frequency.

Found an example here but there are a load on websites and in books -

https://www.drtuned.com/tech-ramblings/2017/10/2/spring-rates-suspension-frequencies

If you can't a more informed source from someone running a similar car, this is a good place to start.

Note that theoretical method relies on a decent amount of suspension travel...tried it on my old race car and it didn't end well!

Hi Chris,

My approach to this is to start with suspension frequencies, which is what Denis is referring to. Thanks for posting that link Denis, I scanned through it and it looks like a good basic explanation.

Essentially there are some approximate guidelines on the target frequency you should be aiming for depending on the type of competition you're involved in. One end of that spectrum would be a high downforce prototype (high target freq) and the other a Baja truck (low target freq). No matter the level you're competing at, you start with a theoretical calculation to build the car around but then you always go and test different combinations.

It's a question that has come up a few times and I'm pretty keen to produce a suspension tuning course in the new year which will cover component selection. I could also do a gold members webinar on this if there was some interest.

Cheers,

Tim

I don't want to approach this with "the easy way out" by asking what other people are doing. That is a great starting point, but to fully learn you need to know the theory.

Chris

Probably just as well Chris...most of what most people say on the internet is wrong anyway!

NM, posted in wrong thread - oops!

If only because springs affect just about every possible variable in suspension, doing it the right way might be a tad difficult. As you figure out more, you find more complex concepts or topics to get lost in. I tend to agree with the rest of the guys, natural frequency of your suspension is an excellent starting point. If you're working on something less... generic, say a porsche, you may end up out of phase using it as a starting point(The front frequency is higher than rear, resulting in pitching up and down over a bump) when trying to balance the over/understeer of the vehicle.

If you're after a different perspective, or just trying to learn more, roll stiffness distribution is also an interesting place to start.

Tims webinar sounds interesting, that's a pretty big topic to cover, I'm curious to see how you do it.

Just to make things more confusing, remember the tyres (tires for the US chaps) are themselves springs with their own frequencies and damping affect. For most this isn't a problem, but with lightly loaded rear axles on front wheel drive cars it can be a big problem.

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