Elite restoration begins!

[Lotus-e-Clan]

What's your definition of 'progressive'?

Linear rate springs require equal amounts of additional force to be applied for any given deflection at any point in their compression (until they become coil bound anyway.) This is demonstrated in the table of spring deflections shown in my earlier post.

Progressive rate springs require increasing amounts of additional force to be applied for any given deflection as compression increases. If the spring in my table were progressive, then the additional force required to deflect the spring by a further 1" would progressively increase as the spring is compressed.

ATB Richard

When you test a progressive spring in a rig and compress it as you describe - you are only testing its COMPOUND RATE in terms of force required to shorten its ENTIRE length in equal steps.

It is not possible to test 'progressive behaviour 'along its length' in a rig like that. It doesn't matter if the progressive design has within its length;- variable coil No, variable wire diameter, or variable coil diameter, the entire spring will compress in equal steps as you found!

Translating progressive spring behaviour to the car....

• During large low resonance inputs, when the car transfers its weight into a corner, the entire spring (progressive or uniform) will shorten according to the compound rate ...it doesn't matter if it is a progressive spring or a uniform spring , the car will lean-in uniformly - not progressively in variable steps.
  
  During small high resonance inputs however, when you ride over rough ground, a progressive spring responds first at the weaker area of the spring;- ie within large diameter coils, region of greater coil number, or region of thinner wire. This will give a softer 'resonance' and better refinement.

That's my understanding of the purpose of 'progressive springs' anyway!

I think we have different ideas about progression and your idea doesn't make any sense to me at the moment.

[richardw]

What's your definition of 'progressive'?

Linear rate springs require equal amounts of additional force to be applied for any given deflection at any point in their compression (until they become coil bound anyway.) This is demonstrated in the table of spring deflections shown in my earlier post.

Progressive rate springs require increasing amounts of additional force to be applied for any given deflection as compression increases. If the spring in my table were progressive, then the additional force required to deflect the spring by a further 1" would progressively increase as the spring is compressed.

ATB Richard

When you test a progressive spring in a rig and compress it as you describe - you are only testing its COMPOUND RATE in terms of force required to shorten its ENTIRE length in equal steps.

It is not possible to test 'progressive behaviour 'along its length' in a rig like that. It doesn't matter if the progressive design has within its length;- variable coil No, variable wire diameter, or variable coil diameter, the entire spring will compress in equal steps as you found!

Translating progressive spring behaviour to the car....

• During large low resonance inputs, when the car transfers its weight into a corner, the entire spring (progressive or uniform) will shorten according to the compound rate ...it doesn't matter if it is a progressive spring or a uniform spring , the car will lean-in uniformly - not progressively in variable steps.
  
  During small high resonance inputs however, when you ride over rough ground, a progressive spring responds first at the weaker area of the spring;- ie within large diameter coils, region of greater coil number, or region of thinner wire. This will give a softer 'resonance' and better refinement.

That's my understanding of the purpose of 'progressive springs' anyway!

I think we have different ideas about progression and your idea doesn't make any sense to me at the moment.

Here's the definition I use on wikipedia: https://en.wikipedia.org/wiki/Coil_spring "Spring rate is the measurement of how much a coil spring can hold until it compresses 1 inch. The spring rate is normally specified by the manufacture. If a Spring has a rate of 100 then the spring would compress 1 inch with 100lbs of load."

[Pete Boole]

Maybe the Elite springs are not conical enough to exhibit the progressive nature? Happy to have thread hijacked Richard!

Pete

[fueltheburn]

Agree with Peter
You can't test a progressive spring on a bench under compression the way you have as once you stick the 2 different K numbers together they still depress proportianately and give a linear output as a single unit.
If one part of the spring depresses 3/4" for every 100kg and the other part depresses 1/4" for every 100kg - they as a complete unit will always depress 1" for every 100kg.

The individual "K" numbers both adhere to hookes law and must therefore act linear when weight is applied.

Frequency response is likely the main point of having them progressive.

[fueltheburn]

I would guess the best way to test a progressive spring is under hydraulic actuated simulation with varying speeds and force to test it's frequency response.

The ultimate version for suspension frequency response would be hydraulic moog valves and monitored by a control unit given info by load and g sensors..... oh wait a minute

[Lotus-e-Clan]

Agree with Peter
You can't test a progressive spring on a bench under compression the way you have as once you stick the 2 different K numbers together they still depress proportianately and give a linear output as a single unit.
If one part of the spring depresses 3/4" for every 100kg and the other part depresses 1/4" for every 100kg - they as a complete unit will always depress 1" for every 100kg.

The individual "K" numbers both adhere to hookes law and must therefore act linear when weight is applied.

Frequency response is likely the main point of having them progressive.

I agree with Keiran!

Richard, I think you maybe miss the point about the purpose of progressive springs - it gives the spring an additional 'characteristic' beyond its primary purpose to resist weight transfer?

[richardw]

This is an education for us all!

I believe the missing component in the arguments above is that the progressive nature of a single spring is based on the progressive closure of the gaps between the coils in a part of the spring. This can either occur as a result of progressively narrowing the pitch of the spring (i.e. the gap between the coils) so that in part of the spring they close up before the whole spring is fully compressed, and/or by tapering the spring wire progressively to achieve the same result. In both cases, once the coils touch, they are 'removed from action' and cause the remaining effective wire length to be shortened, thus increasing the spring rate.

ATB Richard

[Pete Boole]

Anyway!! Back to the painting! Shaun was right - even though I have an excellent respirator I still feel "chesty" tonight, after doing some priming , so I'm going to get the paint spraying done for me (even though I would love to do it myself) - not worth ruining my lungs!

Pete

[DavidOliver]

An attempt to give my opinon on the 9 pages of comments on spring rates and progressive springs.

Spring rate calculations.
The outside diameter has a very large influence on spring rate, as an example the difference between 2inch and 4inch diameters is 16 times which is 4/2 to the fourth power, 2x2x2x2.
In the Peter K calculation the difference in spring rate is in fact 11.35 times, not 16, as the calculation actually uses the MEAN coil diameters of 40mm and 90mm.
In practical terms our cars do not have 2inch diam. springs and the difference for conical sections of a spring might be 4inch to 3.5 inch which gives a spring rate difference of 1.7 times.

The calculations refer to Force at compressed length which needs a figure to be put into the formula and for the 4inch calculation the compressed length given would be 765/65, that is 11.76 inches which is almost as much as the length of the uncompressed spring and coil binding would have occurred beforehand.
The Lotusbits test shows a maximum compression of 6inches with linear Spring rate, so no coil binding had occurred to that point. I assume the test start point was for a spring with static corner weight applied or perhaps the test is to cover both spring loading (road bumps) and spring unloading (bodyroll).
If the wheel has say a 5inch vertical movement the spring will compress some 3inches (suspension geometry of 1.6) and the load on top of static corner weight would be 3x65 = 195lb.
RichardW refers to the analogy of a coiled torsion bar with a length equal to Number of coils times coil diameter. This length is not the uncompressed length referred to in the Spring rate calculation.
I believe the analogy is correct except it does not include the coiling effect which we have seen has a major effect on spring rate.

In my opinion the coil diameter wil not change under load, and the hosepipe analogy for unwinding is not related to car springs as you have a pressurised liquid trying to straighten a flexible containment.

What do car springs do? (A simplistic description)
Reduce the transmission of wheel movement over irregular road surface to the chassis for comfort.
Allow the wheel to ride over the road irregularity to reduce shock loading.
Reduce the bounce of wheel over irregularities to return the wheel to the road surface to return traction for steering/braking/accelerating. This combined with the shock absorber to take out rebound.

So why progressive, and how much progressive?
A spring with single size wire diameter and coil diameter can produce resonance in the spring for a single wheel impact. This is greatly reduced with variable diameters, much easier to manufacture variable coil diameter than variable wire diameter. The variations can be quite small to be effective.


After all this I wonder what the Automotive Engineers opinons are.
I am sure we have got it wrong somewhere. I would like to know.

Dave the cog.

[DavidOliver]

Back to Restoration.
An initial photograph on this blog shows the Engine and gearbox removed.
While you are getting the body painted may I suggest you open up the gearbox and check the soundness of the Maestro components particularly the gear clusters. I had tooth failure on my Elite, and while you are at restoration it is such an easy job, I do not know how available spares are or even box alternatives.
This might save you time when you approach restoration being finalised.
And then what will you undertake?


Dave the cog.

[Pete Boole]

Back to Restoration.
An initial photograph on this blog shows the Engine and gearbox removed.
While you are getting the body painted may I suggest you open up the gearbox and check the soundness of the Maestro components particularly the gear clusters. I had tooth failure on my Elite, and while you are at restoration it is such an easy job, I do not know how available spares are or even box alternatives.
This might save you time when you approach restoration being finalised.
And then what will you undertake?


Dave the cog.

I'm ahead of you there Dave! I'm going to be using the Series 2 Getrag 'box - much stronger, and will easily handle the extra torque from the 2.5l engine I'm building.

Pete

[Pete Boole]

And then what will you undertake?


Dave the cog.

I've also got a TREVOR in bits!!

Pete

[Pete Boole]

Booked in with Mike in the new year for paint

Pete

[Pete Boole]

Just when you thought it was safe to put the resin away: Bodged repair to front bumper to sort out. I was going to do all these bits as and when, but they've all got to be ready for the paint shop in a month's time.





There are also lots of gel cracks to repair as well. Coming on though!!

Pete

[Lotus-e-Clan]

Always take longer than you want it to when you want to do it right (lots of 'wants' in there ).

I thought I wasn't rushing the FG gel crack repairs I did to my first Clan back in the 80's. My big mistake was not leaving the fine tissue /resin repair long enough before flatting back (weeks needed if temps are low). Then the paint went-on too soon -- looked great for a couple of weeks - then the sinkage appeared.

You must have done loads of FG work on the red racey V8 so doubtless you won't make the same mistakes!

Looking forward to seeing it progress .. . I love Elites - especially in white !