Roadholder external springs

Ludwig obviously knows what he's talking about here *IF* only discussing dual rate springs but has accidentally created confusion as his notes do not apply to the off the shelf progressive type springs available in our forks and shocks. note the 3 graphs above. To confuse more Peel forks are dual rates overlapping, [valve spring + long spring] yet both also progressive wound multi rate springs, the longer being a custom spring from the famous Geof that would not tell me the value of the 4 rates he figured out. I got his last set and he's no intention to make more. I guess I should delay Peel and mower and truck and home projects some more charting these springs in case others might care to mimic. I'd nail all thread vertical to shed wall with a scale under and crank down an inch at a time and read the scale. This gets into the fork dampening inertia vitals when tire barely holding side loads so slight hesitation d/t extra moving mass to keep tire in contact => Splat. Another thing going on not mentioned is the sound like waves of compression bouncing back/forth along length of un bound coils.

[video]https://www.youtube.com/watch?v=ubRlaCCQfDk[/video]

More static sag from those close coils :?:

john robert bould said:

Sorry Ludwig, but you stated the spring rate will only increase when the close coils are coil bound? mayby i have lost something in the translation?
You are correct in stating the springs shown are true progressive . When load is applied the soft coils will start to compress the wide coils in a ratio of how much each coil is rated/ wound.. just done this in the workshop! I placed a 12lb spring on top of a 40lb spring , the 40 lb started to compress straight away ..but very slow ....Then with more compression of the two the 40 lb reacted to the 12lb after 25 mm the stronger was now just over 3.3 mm shorter.

ludwig said:

For the same wire thickness , a closer wound spring will be softer , because more wire per inch of spring length .
If you load a dual wound spring , ( like in John's example 15lb/in and 30lb/in ) , the spring will act like a 15lb/in spring , TILL the closer wound coils get coil bound .
From then on , it will act like a 30lb/in spring .
The cross over point depends on the ratio between closer and wider windings .
Both sections will ALLWAYS compress at the same time ( but at a different rate ), because they are both subjected to the same load .

I would think that is pretty obvious ?

The springs shown on the Hagon shock are dual rate , but the closer wound section will NEVER become coilbound before the end of travel of the dampers , so in practice they are linear springs .

About wich side up : the closer wound end of the spring is heavier , so there is an advantage to have that side up , for lower unsprung weight .

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Click to expand...

Ludwig is exactly right. One point you may be missing though is that a 12lb spring on a 40lb spring will not be the same as a 12lb-40lb dual rate spring. The two springs will be less than 12lb until the light spring is coil bound then it will be 40lb after, the dual rate will be 12lb to coil bound then 40lb after. Also remember we are talking spring rate not absolute force here.

Just for the record I have never recommended anyone run engine oil (or anything else for that matter) in their roaholders, maybe you have gone back and fixed that by now though.

Cheesy said:

Ludwig is exactly right. One point you may be missing though is that a 12lb spring on a 40lb spring will not be the same as a 12lb-40lb dual rate spring.

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Exactly. The combined spring rate is 9.230769231 to be precise. And off course both springs will start compressing immediately as soon as they are subjected to a load.


Tim

john robert bould said:

Sorry Ludwig, but you stated the spring rate will only increase when the close coils are coil bound? mayby i have lost something in the translation?

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How should the spring rate increase then? This kind of "progressive" spring with a constant wire and helix mean diameter but different pitch angle is a serial connection of springs and thus has a combined spring rate which is constant again. Unless you take one spring out of the equation - it goes coil bound - there is no effect which can change the spring rate.


Tim

I would like to add a word of caution here about using this type of fork springs ( and then I’ll shut up ..) .



If you like a plush ride ,it might be tempting to install such springs with a clear cutoff between soft and hard ( Hobot’s middle diagram) , but there is a catch :
Rebound damping is closely related to spring strength .
A stronger spring requires more damping .
If the rebound damping is set for the stronger section of the spring ( think std roadholder dampers ) , then riding over a succession of small bumps like a cobblestone road may cause a pumping down effect :
the fork will compress easily because of the soft spring section , but the rebound damping may not allow the fork to extend fast enough before the next bump.
If the damping is set for the softer section , rebound may be too brutal when hitting a big bump . Both situations are potentially dangerous .
So , unless you have progressive rebound damping , I would stick to linear fork springs .

Ludwig.
Love reading your posts, and hope you keep adding to topics... Mayby its a German thing? I have just worked 25 years with Hans Lingl a German Company here in the UK.. I had a young German student working with me for a year..we had good fun. when he learned how to swear ,he was funny with the pronouncation [think i spelt that wrong] ...so no shutting up!

ludwig said:

I would like to add a word of caution here about using this type of fork springs ( and then I’ll shut up ..) .

If you like a plush ride ,it might be tempting to install such springs with a clear cutoff between soft and hard ( Hobot’s middle diagram) , but there is a catch :
Rebound damping is closely related to spring strength .
A stronger spring requires more damping .
If the rebound damping is set for the stronger section of the spring ( think std roadholder dampers ) , then riding over a succession of small bumps like a cobblestone road may cause a pumping down effect :
the fork will compress easily because of the soft spring section , but the rebound damping may not allow the fork to extend fast enough before the next bump.
If the damping is set for the softer section , rebound may be too brutal when hitting a big bump . Both situations are potentially dangerous .
So , unless you have progressive rebound damping , I would stick to linear fork springs .

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Ludwig Thanx for the head expanding on dual spring conflicting with some dampening rates and/or valve speed, which requires exotic materials in the elites. Some shocks use rods through holes with different tappers at various sections so may help control a real dual spring or finer tune one leg of a fork. Peel has suspension spring height tuckers so an unknown to explore. I'm still in damper fog but found this article that other damper dummies may catch up some.
http://assets.ngin.com/attachments/docu ... pening.pdf

....you know I've a theory about all these so called progressive springs as just marketing spin. I've not got over in my head that all springs are progressive as isn't the fact that an equally wound coil spring becomes harder to compress the more you compress it makes it "progressive" I've had this conversation with quite a few "experts" and no one has convinced me yet......but what do I know. Oh and that IKON item....once those coils become coil bound it's no longer a spring but a solid tube with no "springiness" at all isn't it?

Dommie Nator said:

....you know I've a theory about all these so called progressive springs as just marketing spin. I've not got over in my head that all springs are progressive as isn't the fact that an equally wound coil spring becomes harder to compress the more you compress it makes it "progressive" I've had this conversation with quite a few "experts" and no one has convinced me yet......but what do I know. Oh and that IKON item....once those coils become coil bound it's no longer a spring but a solid tube with no "springiness" at all isn't it?

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Well it depends a bit on your definition of progressive really, non-linear may be a better term. A standard spring will have a linear relationship between force and displacement (again the linear or progressive term is referring to the spring constant not the absolute force) so yes the force does increase as the spring is compressed. A progressive spring has an increase in spring constant as it is compressed so the fore to displacement is non linear. Also the spring rate will only increase as it becomes coil bound, so even if a spring is progressively wound it will still be a linear rate spring if it doesnt become coil bound.

....thanks....another one for my list.

Dommie Nator said:

....thanks....another one for my list.

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Wot you worrying about the science of springs for Cab?

If yer wanna make that cafe racer of yours faster... put a proper motor innit... Innit?

Lol..noo I'm not worried at all.....I just don't understand the science.....and the more it's explained the less I know. :| And as for making my Café racer faster. ....well the cafes around my way aren't that far apart. :wink:

Dommie Nator said:

I've not got over in my head that all springs are progressive as isn't the fact that an equally wound coil spring becomes harder to compress the more you compress it makes it "progressive"

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Compress a spring twice as much by twice the force: Linear.

Compress a spring twice as much by less than twice the force: Degressive.

Compress a spring twice as much by more than twice the force: Progressive.

It refers to spring rate and not spring travel or force. The spring rate is the factor that couples force and travel and it can be linear, progressive, degressive or actually a combination of these - on the Commando there is such a spring: The diaphragm spring of the clutch.



Tim