Spring Rate units

[RacingHardTV]

Hello everyone,

when I was looking for a few setups online, I found out that some have Ibf/in instead of Hz for their spring rate. I googled for converting it and used my own knowledge from my engineering studies to have a go on this problem, but lead to conclusion that Ibf*in equals Hz....

Can someone who has ibf/in as their unit please say what their softest and hardest setting can be for a given car (e.g. the Beetle Gr3 or so) and then we can check if simple percentage calculations can offer a quick tool to convert those 2 units

Example:
(If 2.40 hz equals 700 Ibf/in the game then 3.30 hz equals (3.30*700)/2.40 = 962.5 Ibf/in)

Thanks in advance for anyone who is willing to help. If this problem has been solved anywhere else before, give a link please. 👍

 

[Famine]

Hello everyone,

when I was looking for a few setups online, I found out that some have Ibf/in instead of Hz for their spring rate. I googled for converting it and used my own knowledge from my engineering studies to have a go on this problem, but lead to conclusion that Ibf*in equals Hz....

Can someone who has ibf/in as their unit please say what their softest and hardest setting can be for a given car (e.g. the Beetle Gr3 or so) and then we can check if simple percentage calculations can offer a quick tool to convert those 2 units

Example:
(If 2.40 hz equals 700 Ibf/in the game then 3.30 hz equals (3.30*700)/2.40 = 962.5 Ibf/in)

Thanks in advance for anyone who is willing to help. If this problem has been solved anywhere else before, give a link please. 👍

It's not an "i". It's an "l"... lb is short for pounds (from the French libre, and the earlier Latin libra).

It's also not lbf*in (poundinch), rather lbf/in (pounds per inch). Pounds per inch (or pounds equivalent force per inch, as pounds are mass, not weight; lbf is the equivalent force of one pound at standard gravitational conditions, or about 4.45 Newtons) are the amount of force in pounds required to compress the spring by an inch.


You can't directly convert between Hertz (natural frequency) and lbf/in - or kgf/mm, or N/m - without knowing the mass of the vehicle. The formula for converting a spring rate to Hz is:

• F = 1/(2π) * sqrt (Spring Rate/Mass)

Where the spring rate (K) is in Newtons per metre, and the mass is in kilograms.

If you want to do it the other way round and get a spring rate from the natural frequency, it's:

• Spring rate = Mass * (F*2π)^2

I have a Mazda Atenza Gr.4 that weighs 1,380kg (assuming 50:50 weight distribution). Stock settings have it with a natural frequency of 2.8 Hz front and rear, so plugging those numbers in we get:

Spring rate = 1380kg * (2.8*2*π)^2
Spring rate = 1380kg * (17.6)^2
Spring rate = 1380kg * 309.5
Spring rate = 427,125N/m

As 1kgf is about 9.81N and 1m is 1,000mm, that roughly converts to 43.5 kgf/mm. To convert to Imperial, 1kg is about 2.205lb and 1 inch is about 25.4mm - so that's just about 500lbf/in.

So on that car, 2.8Hz is 500lbf/in. If the car was 50kg heavier or lighter, it wouldn't be.

 

[RacingHardTV]

Perfect.

Thank you very much for your detailed answer. (Can't thank you enough for this)

I think that I wanted the solution too quickly and failed it on my own.

Thanks, thanks, thanks.

Edit: You mentioned the weight distribution.
That is pretty disappointing that we dont know the actual distribution of the cars and therefore there is most likely a room for error in the assumption. But it is better than notthing. Thanks

 

[dr_slump]

So on that car, 2.8Hz is 500lbf/in. If the car was 50kg heavier or lighter, it wouldn't be.

The question is if in GTS spring rates get adjusted with changes in weight or if it's just based on stock weight.

Most likely the latter, because otherwise it wouldn't make sense to have lbf/in.

 

[ynot]

I just want to be able to soften or harden the springs. I am assuming lowering the number makes them softer and raising the number makes them harder. Am I correct? Never heard of Natural Frequency being used in car setups.

 

[GT_Astroboy]

I just want to be able to soften or harden the springs. I am assuming lowering the number makes them softer and raising the number makes them harder. Am I correct? Never heard of Natural Frequency being used in car setups.

That is correct, the lower the frequency, the softer the spring and vice-versa.