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

Hi Rob,
Yes you can, number of coils are important.

This Web site has the maths, and other data you need

How To Calculate Spring Rates – How To Adjust And Tune – Suspension Secrets

Tony

Originally Posted by TonyC

Hi Rob,
Yes you can, number of coils are important.

This Web site has the maths, and other data you need

How To Calculate Spring Rates – How To Adjust And Tune – Suspension Secrets

Tony

Had a look on that site and not sure how to bring it back to a common spring rate as in "lbs/in"
Their example they used is also not real clear as the "G" figure they quoted to use (79.3GPa) is not what they actually used in the calculation. They used 78.5GPa. Not sure where the "8" comes into the Calc as well

I’ve always used 78GPa for spring steel. 78.5 is just fine and won’t make a significant difference to the answer.

8 is just a constant.

To convert N/m to lb/in you need to convert Newtons to lbs force (x.225) and metres to inches (x39.37). Just multiply N/m by 0.0057 to get lb/in.

I use mm and MPa for the measurements as its more engineeringy. MPa = GPa x 1000, so 78GPa = 78000MPa.

Then you have an answer in N/mm. You can then multiply N/mm by 5.71 to get lb/in.

Confused? Excellent, then my work here is done.

Cheers,
Jon

Originally Posted by jon3950

I’ve always used 78GPa for spring steel. 78.5 is just fine and won’t make a significant difference to the answer.

8 is just a constant.

To convert N/m to lb/in you need to convert Newtons to lbs force (x.225) and metres to inches (x39.37). Just multiply N/m by 0.0057 to get lb/in.

I use mm and MPa for the measurements as its more engineeringy. MPa = GPa x 1000, so 78GPa = 78000MPa.

Then you have an answer in N/mm. You can then multiply N/mm by 5.71 to get lb/in.

Confused? Excellent, then my work here is done.

Cheers,
Jon

Thanks for that Jon, much appreciated... Will this formula work when the coils are a Progressive Rate Coil?

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)?

Spring Details are below:

Brand: Dobinson Coils


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

Yes, it works for progressive springs. However in a progressive spring the number of working coils reduces as the spring compresses.

A coil spring is just a torsion bar that has been rolled into a coil. The longer a torsion bar is, the less force is required to twist one end relative to the other, so the softer the spring is.

As a coil spring compresses the wire twists, like a torsion bar does. The longer the wire, or the more coils there are, the softer the spring.

A progressive spring is wound so that some of the coils are closer than the rest. At its free length it works the same a linear spring. As it compresses, these closer coils bind up and can no longer twist. Therefore the number of working coils reduces and the spring rate increases.

To measure the different rates of a progressive spring you need to compress it and work the number of working coils at a given height. Or you can measure the gaps and work out how much it will close up.

Originally Posted by Robmacca

Had a look on that site and not sure how to bring it back to a common spring rate as in "lbs/in"
Their example they used is also not real clear as the "G" figure they quoted to use (79.3GPa) is not what they actually used in the calculation. They used 78.5GPa. Not sure where the "8" comes into the Calc as well

Hi Rob,
Sounds like Jon has answered your question, and knows way more on the subject than I do.

Given you know what the spring are, why don't you ask Dobsons.

Tony

Originally Posted by TonyC

Hi Rob,
Sounds like Jon has answered your question, and knows way more on the subject than I do.

Given you know what the spring are, why don't you ask Dobsons.

Tony

Yes, I plan to ring them on Monday + I'll ask if it matters which way the coil in...

Originally Posted by jon3950

Yes, it works for progressive springs. However in a progressive spring the number of working coils reduces as the spring compresses.

A coil spring is just a torsion bar that has been rolled into a coil. The longer a torsion bar is, the less force is required to twist one end relative to the other, so the softer the spring is.

As a coil spring compresses the wire twists, like a torsion bar does. The longer the wire, or the more coils there are, the softer the spring.

A progressive spring is wound so that some of the coils are closer than the rest. At its free length it works the same a linear spring. As it compresses, these closer coils bind up and can no longer twist. Therefore the number of working coils reduces and the spring rate increases.

To measure the different rates of a progressive spring you need to compress it and work the number of working coils at a given height. Or you can measure the gaps and work out how much it will close up.

Thanks again Jon...

One more thing - does it matter how the coil is installed (is there a right way up?)