SPRING Rates - Can u determine it if u have no specs?

rob_macca67

Well-Known Member
Guys... I think I know the answer already to this and its probably a dumb question but here goes...

A mate of mine has a set of brand COIL SPRINGS in his shed that he is going to give to me to see if I can use them. Now, he does not have any info/specs on the springs as they were delivered to him by accident & the manufacturer didn't want them back...
By measuring the heights; Wire thickness; number of turns (may not be important?) - is it possible to work out the spring rate somehow?

I have an idea on how to do it but it requires a lot of effort on my part...

Any ideas?
 

cam04

Well-Known Member
The numbers printed on them are traceable. The trick is to find out who made them. Just typing the serial number into Google can get results, and kings (yellow springs) has an online catalogue you can search. Put a pic up if you have no joy. The ‘rate’ is either single or progressive. Singles look like a boring old cartoon spring and are uniform thickness and coil all the way through. Progressives have different thicknesses and coil spacings along the spring.
 

Outrage

4x4 Earth Contributer
There are formulas for calculating spring rate.

For example: https://suspensionsecrets.co.uk/how-to-calculate-coil-or-leaf-spring-rates/

1668200007448.png


1668200018228.png


Or from another website.
1668200124427.png


What you won't know exactly is the material used. So you would likely have to use a ballpark guess for a typical spring steel, like the 78.5 GPa used in the example. Paint thickness has a small impact on the result too.

From my understanding, heavier vehicles like a land cruiser can use spring rates around 130,000 N/m (or 13.25 kg/mm).

Another way, if it is a single rate spring, is to measure the original height, then add weights, measure the compressed height.

The added weights mass (kg) x 9.813 (gravity acceleration m/s^2) = Force (N).

Divide the 'Force' value by the distance the spring compressed in metres. Gives you the spring rate in N/m.

From the above spring rate though, you can see you might need to add around 130 kg just to get 10 mm of compression for a high rate spring.
 

rob_macca67

Well-Known Member
The numbers printed on them are traceable. The trick is to find out who made them. Just typing the serial number into Google can get results, and kings (yellow springs) has an online catalogue you can search. Put a pic up if you have no joy. The ‘rate’ is either single or progressive. Singles look like a boring old cartoon spring and are uniform thickness and coil all the way through. Progressives have different thicknesses and coil spacings along the spring.
I got a chance to view the coils today. The brand is Dobinsons with the following codes:
# C51-226V (Progressive Rears)
# C51-227V (Progressive Fronts)

I've looked on Dobinson's Website without any luck in finding details. From what I understand they were made for a TD5 Defender.

I measured the heights, etc as follows:

FRONTS: - Progressive Rate
Model: C51-226
Wire Thickness: 14mm
Turns: 10
RHS:470mm
LHS:460mm

REAR:- Progressive Rate
Model: C51-227
Wire Thickness: 19mm (19.5mm with paint)
Turns: 10
RHS:465mm
LHS:455mm

The wire thickness is constant all through the Front and Rear coils.
 

rob_macca67

Well-Known Member
There are formulas for calculating spring rate.

For example: https://suspensionsecrets.co.uk/how-to-calculate-coil-or-leaf-spring-rates/

View attachment 74681

View attachment 74682

Or from another website.
View attachment 74683

What you won't know exactly is the material used. So you would likely have to use a ballpark guess for a typical spring steel, like the 78.5 GPa used in the example. Paint thickness has a small impact on the result too.

From my understanding, heavier vehicles like a land cruiser can use spring rates around 130,000 N/m (or 13.25 kg/mm).

Another way, if it is a single rate spring, is to measure the original height, then add weights, measure the compressed height.

The added weights mass (kg) x 9.813 (gravity acceleration m/s^2) = Force (N).

Divide the 'Force' value by the distance the spring compressed in metres. Gives you the spring rate in N/m.

From the above spring rate though, you can see you might need to add around 130 kg just to get 10 mm of compression for a high rate spring.
I did see this but finding out that the coils are a progressive rate coil - I don't know if this formula will work??


Also, with progressive rate coil, does it matter how they are installed (do they need to go in a certain way with the closer coils at the bottom or top)?
 

John U

Well-Known Member
Make sure the ID, OD, and shock length, and compression before binding are all the same as your current vehicle.

So many variables. I'd suggest if they are not specced for your vehicle, ie youre driving a TD 5 defender, don't bother.
 

cam04

Well-Known Member

I can’t spot them in the catalogue. If you are on a laptop try ctrl F and type it in. Not so good on a phone. Might have to get in touch with them to confirm what they are. Maybe an older number that had been changed which is common enough. It takes 5 minutes to rip a shock apart if it is paired with an incorrect length spring. Best to check.
 

rob_macca67

Well-Known Member

I can’t spot them in the catalogue. If you are on a laptop try ctrl F and type it in. Not so good on a phone. Might have to get in touch with them to confirm what they are. Maybe an older number that had been changed which is common enough. It takes 5 minutes to rip a shock apart if it is paired with an incorrect length spring. Best to check.
Yeah, I tried their catalogue - no good but do plan to ring them on Monday
 
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