Coil spring rate calculator

[Brett.C]

Over the past couple of months I've been working on a coil spring calculator which includes as many calculations needed to set up a live axle or independent suspension.
I started with an exel speadsheet which I found on the web for calculating spring rates for Locosts (homebuilt sportscars based on clubmans).

I quickly discovered that it was full of errors but it was still a good basis to work from. I have (hopefully) fixed these errors, simplified it, and added comments on how to use it.
I have also added calculators for cyclic frequency, to prevent for and aft pitching, and a coil spring calculator so that you can determine what rate a spring may be based on some simple measurements.

I used it recently to recalculate the front springs for my car and it seems to have worked well. I now have a very good compromise between ride and handling and I have even been able to throw away those ugly sway bars.

Problem, I have nowhere to host it as I do not have a web account from where I can host a spreadsheet.
So if someone knows where I can host it or wishes to host it themselves I would be grateful.

Hopefully with your help and input we can host the ultimate resource for taking the pain out of them bumps.

[rx4ord]

Sounds like a great thing Brett. What did you end up as the optimal rate using this system. I would love to know how close you were with the rear springs on the car. Dave

[Brett.C]

The rear springs were pretty close as they were. Over the life I the car I had changed them 3 times to get them about right.

Front wheel rates are now about 135lb and rears 160lb.
A bit on the stiff side but it seems to work well. The shocks are set to their lowest settings at the front and second notch at the rear.
I believe that the springs should do most of the work controlling bump and roll and the shocks should control the rebound.
But everyone has different theories.

[Redned]

Sounds interesting and I can't wait to see/use it. I'm sure it could be hosted right here on OzRodders in the Tech Info section? I'm also sure that the powers that be will chime in soon enough and arrange to do just that but at present they're probably tucking into the left overs from yesterday If that's not the case then I'd be more than happy to place the file on my web space and provide a link to it from here.

Cheers Redned

[rx4ord]

I knew we were twins Brett. Our theories are the same and I am a bit taller that's the only obvious difference. Dave

[PeterR]

Over the past couple of months I've been working on a coil spring calculator which includes as many calculations needed to set up a live axle or independent suspension.
I started with an exel speadsheet which I found on the web for calculating spring rates for Locosts (homebuilt sportscars based on clubmans).

Excel is quite amazing, it was originally intended as a spreadsheet for accountants and it is now used for just about everything that involves a number.

The only pesky part I find with building Excel calculators for other people to use it that it takes me as long to do the fancy formatting to make it user friendly as it does to set up the equations.

I have also added calculators for cyclic frequency, to prevent for and aft pitching.

Interested to hear how you did this, did you use the 10 percent rule?

Does it include roll stiffness, if not I have something that may be of use to you. Years ago I produced an Excel calculator to determine suspension roll stiffness and the effect of adding anti roll bars on front/rear balance, if you feel it would be of any interest to you I can hunt through the archives.

There is also a calculator I did for airsprings in beam and independent axle applications you might find useful. These have the additional wrinkle of being non linear making the calculations quite tedious to do manually. The work was done in a customer's time, so they own the IP and I would have to get the OK from them to pass it on.

[Brett.C]

Thanks Peter.
The calculations I used came from How to Make Your Car Handle by Fred Puhn. The 10% rule works out about right.

Take a look at this and let me know what you think.
http://www.box.net/shared/gcuutlsgbd

We can refine it more and add more to it over time. The idea is to keep things as simple as possible. That way I and others can understand it.

All you need to do is enter the sprung weight on each axle. Any mechanical advantage (if none, ie shock mounted direct to live axle, then enter 1 for wishbone and shock to pivot lengths), and shock mounting angle.
Then from the table you choose a figure in the yellow column dependent on how firm a ride you want. For most rods that will be between 1.2 to 1.6 at the front. Higher at the rear. Looking across to the green column you will find the poundage of spring required. Of course you will have to round this figure to the nearest available size (usually 20lb increments).

You will also see figures telling you the amount of preload and the compression of the spring at normal ride height. From this you can determine the free length of the spring you require.

Anyway, have a play with it, pick it to pieces and give me some feedback, constructive of course

[PeterR]

Anyway, have a play with it, pick it to pieces and give me some feedback, constructive of course

PM sent

[Grechy]

Am I reading this wright?

If all calculations are correct, taking into consideration spring rates,rebound and dampeners, etc.

Dave would have at no time been taller even at birth?

Cheers Paul

[Brett.C]

Ok, Peter has gone over my spreadsheet and fixed up a few errors and he's tidied it up a bit.
Thanks Peter for your input mate.

So if you've already downloaded it I suggest you now download rev2.

I also recommend box.net as an easy to use and FREE place to share files from.

Tasmania is a small island, relatively speaking

[Brett.C]

Ok you 22 who have downloaded it so far, guess what, you'll have to do it again.
But it's worth it I promise you, Peter has excelled (bad pun) himself this time and made it even better, and he promises this will be the last time.

So if one of the mods would like to put this link in the knowledge base where it can be easily found.

And this doesn't just work on fancy double wishbone suspensions, it also works for coils attached to live axles and jag rears.

So instead of swapping out six sets of coils to get that ride right you can now do it once and be done with it.

[YNOTU2]

Good on ya Brett & Peter,
It all looks good from here.

[van460]

just had a go at the spring rate calc

put the info in for both a GH sigma spring and a KB centura spring
and i got 126 for the sigma and 112 for the centura

I though the centura spring would be alot more than that

The spring free hights for both are 345mm for the sigma and 455mm for the centura

The centura has a 30mm smaller captive hight that the sigma

[Kiwipaul]

Hi Guys , I was asked yesterday what is my Jag front end out of I do not no as it was in the car when I got it. The same person was saying that the spring might not be strong enough as I have a big v8 and lot of front steel. What spring are guys with jag front ends running and how do you find what the brales discs are and if they can be machined again?

[ram-rod]

hi Paul I think series 2&3 jag have different brake calipers from series 1. check the width of your discs with a set of verniers and ring your local brake place they will be able to tell you straight away If your discs are under size

sorry guys not wanting to take this off topic.

this calculator will be a very good thing thanks for taking the time fellas