I get asked this question all the time, so here is how to work out the spring rate using a standard Stagea rear spring;

First remove the spring, then measure the ID of the coil, in this case 88mm;



If you don't have a set of verniers then you can use a ruler, yep 88mm;


Always measure the other end, some coils are conical, in this case 79mm;


Then measure the OD of the wire, in this case 12 mm;


If you don't have a set of verniers then you can use a spanner, simply select the right size spanner, yep 12mm.


Last job, count the numbers of coils, this one has 9 and a bit coils, let's call it 9.125 coils;


Then post up the numbers in this thread for Sydneykid to work out the spring rate like this;

Coil ID = 88/79 mm
Wire OD = 12 mm
# of Coils = 9.125 turns
Spring rate = 181 lbs/inch (3.327 kg/mm)


I will pop onto this thread every few days (sorry not every day) and calculate any spring rates that are posted.

Happy spring rate checking

D: cheers

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Some people want to know the spring rates without removing the coils from the car. It a little more tricky and the results are not as accurate, but here is how it is done. Yes, I know this one is on the floor, but use your imagination that it is still mounted in the car.

First measure the lower OD of the coil, this is hard to do without verniers as the shock shaft gets in the way of a ruler. You can buy cheap plastic verniers from SupaCheap, AutoOne, AutoBarn, AutoPro etc for a $few that will do this job accurately enough. In this case 112mm;


Then measure the upper OD of the coil, in this case 103 mm;


As usual measure the wire OD, in this case 12mm (yes, you can use the spanner trick here as well);


Then count the coils, in this case 9.125;


Then post up the numbers in this thread for Sydneykid to work out the spring rate like this;

Coil OD = 112/103 mm
Wire OD = 12 mm
# of Coils = 9.125 turns
Spring rate = 181 lbs/inch (3.327 kg/mm)


I will pop onto this thread every few days (sorry not every day) and calculate any spring rates that are posted.

Happy spring rate checking

Interesting. If you're using a formula, could you post it up as I'm curious, or is it a look-up table?

Cheers.

Intellectual property

Coil ID = 90/88 mm
Wire OD = 13 mm
# of Coils = 7.2 turns

thanks

281 lbs/inch - 5 kg/mm

Yes:cheers:

Curious.. well I have some rear springs sitting here.. well known brand.. they will fit r32 gts-t shocks I think, but not sure whether they are reasonable option.

ID: 76/76mm
Wire O/D: 11mm
Coils: 10.5mm
Spring Rate = ???

All are via steel ruler, so maybe a little inaccure

Want to give guessing the brand a try?

Coils: 10.5mm??
If that is 10.5 turns
Spring rate is 142 lbs/inch - 2.5 kg/mm

yes, sorry 10.5 turns..

approximately 142lbs/inch .. almost seem a little too soft compared to your suggested "optimal" 200lbs/inch rate for gts-t so might not use them.. although they seem quite firm compared to my stock springs (probably long dead at 15 years old )

They are Kings.. KDRL-10's.. I was thinking the spring rate must be the only difference between the S13 because fit wise similar I've been told between s13 rears and R32 (?). Proper R32 GTS-T springs are listed as KDRL-101's.

Anyone else?

Pretty sure i measured ok..

Upper OD : 96mm
Lower OD : 98mm
Wire OD : 13mm
# of coils : 7.65 (cusco's are a little weird)

...how would this spring rate be on an r33 gts-t.

They are cusco adjustable coilovers

Thanks SK

How close is 335 pounds/inch.

Quick question though. How accurate is this method considering the different properties of steel used and forms of heat treatment etc? 5%, 10%?

You might wanna check that coil OD, 96/98mm top and bottom is not normal.
But if it is right, they are 465 lbs/inch (8.3kg/mm).

The more common is 75 mm ID (ie; 101 mm OD), that gives 400 lbs /inch (7.2 kg/mm).




Too harsh for me, hope it isn't a rear spring.




Well, I could have guessed they would be some Japanese brand.

Hi Roy, I am not a metalurgist, so pardon me if this is excessively simplistic. The Japanese, German and Australian standards for automotive spring steel are basically same for the 2 types, hot wind and cold wind. The hardening and tempering requirements are obviously different, but the end result is very closely aligned. The program I work with utilises the base data from the BHP coil winding standard, so it is very accurate. If the coil spring manufacture has adhered to either of the 3 standards, then the end result is very predicatable. Garbage in, garbage out obviously applies.

The simulation program is used by OE spring manufactures for HSV, Holden and Mitsubishi, Ford have their own in house program as far as I know. But I have checked hundreds of Ford springs and the simulation is still accurate. Obviously it does far more than work out the spring rate, but I am only using that part for this thread.




PS; 335 lbs per inch:confused: AAAhh, you have to subtract the wire OD twice from the coil OD to get the coil ID. Yes?