Progressive Fork Springs
- Thread starter olympus
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According to some physics geeks talking about valve springs, the answer for us would be tight coils at the top.
"In a progressively wound spring, the more closely wound coils make contact after a small amount of movement and become ineffective. That's what raises the spring constant. The spring constant increases for a progressively wound spring when these coils make contact and no longer flex. If they aren't contributing to the spring load, it doesn't make sense to have them moving up and down. That just adds weight to the valve assembly. So the point of putting them against the cylinder valve head is to minimize the weight that is moving (the sprung weight is being minimized). When you do that, the resonant frequency of the assembly is increased - there is less mass being supported for any given spring load."
Reference https://www.physicsforums.com/threa...gine-why-the-closer-coil-must-be-down.553482/
"In a progressively wound spring, the more closely wound coils make contact after a small amount of movement and become ineffective. That's what raises the spring constant. The spring constant increases for a progressively wound spring when these coils make contact and no longer flex. If they aren't contributing to the spring load, it doesn't make sense to have them moving up and down. That just adds weight to the valve assembly. So the point of putting them against the cylinder valve head is to minimize the weight that is moving (the sprung weight is being minimized). When you do that, the resonant frequency of the assembly is increased - there is less mass being supported for any given spring load."
Reference https://www.physicsforums.com/threa...gine-why-the-closer-coil-must-be-down.553482/
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We don't have enough fork travel for a progressive spring to add any real benefit.
Wheels can leave the ground when the bike is launched - that's the main reason why we care about "sag," rebound damping, and "progressive" springs.
If your close wound "progressive" part of your spring is consumed by "sag" the instant that you sit on the bike, what good is it? Under that condition, the only time it helps is when you and the bike are launched over a ramp/rise, or when unweighted, on the rebound off of a bump. In that moment, when the wheels are leaving the ground, the light spring reduces any part of that launch that might be added to by the spring if the spring was too stiff at full unweighted extension. That is, when your rebound damping is inadequate because the weight of the bike/rider are eliminated - because of the launch.
All of that is kind of academic unless you have more than just 3 or 4 inches of travel. Out bikes use maybe an inch or inch and a half of travel in sag, leaving not much for a progressive spring to add real benefit unless it is stiff enough to allow you to run a stiffer main spring.
Wheels can leave the ground when the bike is launched - that's the main reason why we care about "sag," rebound damping, and "progressive" springs.
If your close wound "progressive" part of your spring is consumed by "sag" the instant that you sit on the bike, what good is it? Under that condition, the only time it helps is when you and the bike are launched over a ramp/rise, or when unweighted, on the rebound off of a bump. In that moment, when the wheels are leaving the ground, the light spring reduces any part of that launch that might be added to by the spring if the spring was too stiff at full unweighted extension. That is, when your rebound damping is inadequate because the weight of the bike/rider are eliminated - because of the launch.
All of that is kind of academic unless you have more than just 3 or 4 inches of travel. Out bikes use maybe an inch or inch and a half of travel in sag, leaving not much for a progressive spring to add real benefit unless it is stiff enough to allow you to run a stiffer main spring.
Fast Eddie
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You can not compare valve spring action to fork spring action. Every time a valve opens it opens all the way. Most of the time a fork is used it is not operated all the way.
Thus, every time a valve spring is compressed, those close windings go coil bound... every time. As mentioned previously... IF the fork springs are correctly specified for the job, those close windings will NOT go coil bound most of the time in normal use.
Thus, the opposite to what is suggested for the valve springs applies to fork springs.
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Most "progressive " fork springs are not progressive at all .
They only become progressive when the closer wound coils become coil bound , something that within their normal operating range will never happen .
This has been discussed before .
If unsprung weight is an issue then the heavier part of the spring ( closer wound coils ) should go up .
But there is another thing to consider :
mark the middle point of a progressive wound spring .
Then compress it , say , 15 cm .
You will notice that the mark is no more in the middle , but moved towards the closer wound coils .
This means that when the spring is installed close coils up , the middle point will travel ( rub ) over a greater distance inside the stancion , = more friction .
So my vote goes to closer wound coils down .
They only become progressive when the closer wound coils become coil bound , something that within their normal operating range will never happen .
This has been discussed before .
If unsprung weight is an issue then the heavier part of the spring ( closer wound coils ) should go up .
But there is another thing to consider :
mark the middle point of a progressive wound spring .
Then compress it , say , 15 cm .
You will notice that the mark is no more in the middle , but moved towards the closer wound coils .
This means that when the spring is installed close coils up , the middle point will travel ( rub ) over a greater distance inside the stancion , = more friction .
So my vote goes to closer wound coils down .
Fast Eddie
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Seems to me that the obvious solution here is to instal one side with close coils up and t’other with close coils down.
That way you’re guaranteed to be 50% right...
That way you’re guaranteed to be 50% right...
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I spoke with RGM on the matter, in turn they have contacted the company who manufactures the springs.. they recommend closed winding to the top...
Fast Eddie
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Dave Degens says bottom.
Who’s done more testing on the track??
Either way, I refer you back to my 50% solution...!
Actually... I refer you back to my ‘it makes no noticeable difference’ solution!
But, FWIW, I stand by my unsprung weight argument, meaningless as it may be.
Who’s done more testing on the track??
Either way, I refer you back to my 50% solution...!
Actually... I refer you back to my ‘it makes no noticeable difference’ solution!
But, FWIW, I stand by my unsprung weight argument, meaningless as it may be.
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I have just found the Progressive Suspension USA installation instructions and to quote; "Some manuals will state; install the close wound end toward the bottom. This is done because sometimes there maybe less spring noise." The springs will perform exactly the same regardless of which direction they are placed"
Dave
Dave
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I installed Progressive springs on my Mk2 in the early 90s, after I got a bit frustrated trying to dial in the suspension with oil only.
I was quite satisfied with them for a long while (tighter wind up) compared to the stock springs. Until I installed the Lansdowne dampers.
I regularly get > 3.5" of travel on my forks with spirited riding, as I rode with a zip tie on the stanchion for a while.
I was interested I what the progressives looked like as they underwent compression, so I did a small test today.
This first image is at full length of 19.25".
This next image is 18.25", which would be about the amount.of sag.
This next image is 17.5"
At 15" the progressive coils became fully bound.
I neglected to mark the center point of the spring, but counting coils it appears to be at the 26th coil, or 7" on the 15" compressed length, about 77% of it's original uncompressed value.
I was quite satisfied with them for a long while (tighter wind up) compared to the stock springs. Until I installed the Lansdowne dampers.
I regularly get > 3.5" of travel on my forks with spirited riding, as I rode with a zip tie on the stanchion for a while.
I was interested I what the progressives looked like as they underwent compression, so I did a small test today.
This first image is at full length of 19.25".
This next image is 18.25", which would be about the amount.of sag.
This next image is 17.5"
At 15" the progressive coils became fully bound.
I neglected to mark the center point of the spring, but counting coils it appears to be at the 26th coil, or 7" on the 15" compressed length, about 77% of it's original uncompressed value.
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Fast Eddie
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Good pics.
And it got me wondrin’...
It doesn’t seem right to call them progressive springs, aren’t they really just ‘2 stage’ springs?
It looks to me like the softer spring gets used first whilst the firmer spring remains ‘solid’ and the firmer spring only comes in when the softer one is coil bound.
And it got me wondrin’...
It doesn’t seem right to call them progressive springs, aren’t they really just ‘2 stage’ springs?
It looks to me like the softer spring gets used first whilst the firmer spring remains ‘solid’ and the firmer spring only comes in when the softer one is coil bound.
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Not sure I fully agree.
The spring is the same material throughout. There is no softer or firmer section. They both compress at the same rate is my guess, and it is the binding of the more tightly wound percentage of the overall length that makes them, as you rightly point out, dual rate.
Not necessarily progressive....
And there was plenty of "looser" coil yet to compress at 15".
The spring is the same material throughout. There is no softer or firmer section. They both compress at the same rate is my guess, and it is the binding of the more tightly wound percentage of the overall length that makes them, as you rightly point out, dual rate.
Not necessarily progressive....
And there was plenty of "looser" coil yet to compress at 15".
Fast Eddie
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The closer coils are softer in action, even with the same material, as I understand it...
So the softer and firmer springs can’t compress at the same rate... can they?
But there’s no real ‘progression’ ... just two separate spring rates built into the same spring?
So the softer and firmer springs can’t compress at the same rate... can they?
But there’s no real ‘progression’ ... just two separate spring rates built into the same spring?
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If I look at the pics, the frequency of the closer coils are ~1/4" and the looser ones are ~3/8".
At the point of binding the closer coils, the frequency is 3/16 and 5/16.
Same.
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The material is the same throughout, as the coils bind they reduce the effective length of the spring and increase its spring rate. Same effect as when you cut coils off a spring, it gets stiffer. A spring is a long rod, the longer the rod the easier it is to bend, shorter stiffer.
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Hence, progressive.
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Nigel's comments got me thinking about my IKON shocks, which are truly progressive in their coil frequency.
And they are close coils down.
Clearly, the windings of at least my "progressive" fork springs are dual-rate.
And they are close coils down.
Clearly, the windings of at least my "progressive" fork springs are dual-rate.
Fast Eddie
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I didn’t realise that. Happy to stand corrected !
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So if I understand correctly.,since the entire spring is made of the same material the rate is the same and the coils compress at the same rate. The closer wound coils will become coil bound, effectively shortening the spring making it "stiffer". Sounds like dual rate to me. Now if I just knew if I should but the closer wound coils at the top or bottom. Oh wait I think there is a thread about that somewhere.
I think what I will do is just get a single rate spring of the appropriate stiffness for me and not worry about it.
I think what I will do is just get a single rate spring of the appropriate stiffness for me and not worry about it.
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