Fork oil, need input.(gsx400e)

[Guest]

am I learning something? Is that because of the angle of each coil in the "more coils per length" being further from "vertical" than each coil in fewer coils per length ?

ie: a vertical force applied to a horizontal rod being easier to bend than applying the same vertical force to a rod at 45 degrees .... Applying vertical force to a vertical rod is the stiffest of all, being a column ...?

More coils per unit length is a longer spring - longer piece of rod = softer. The structure we're considering begins so far out of column that I don't think it's worth that consideration. It's really a coiled up torsion bar. That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds.

I'm in agreement with Rich; cut the close coils. And it's 'rock it science'.

 

[Nessism]

That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds.

The closer wound coils WILL coil bind, that's the whole idea behind winding them tighter. As these coils wire bind the spring rate will increase.

 

[Guest]

Progressive bad, linear good.

+1.

am I learning something? Is that because of the angle of each coil in the "more coils per length" being further from "vertical" than each coil in fewer coils per length ?

Nope. A coil spring is really just a torsion bar spring packaged more conveniently for our uses. The spring rate of a torsion bar is determined by its length (and diameter and material, but we are assuming those stay the same for our discussion), the longer the bar the softer its rate because the helix angle of the twist is less on the longer bar for any given amount of twist on the end. Since a coil spring is just a torsion bar wrapped up it follows the same rules in regards to spring rate. More coils per unit length means a longer torsion bar per unit length and that means a softer spring rate.

That's why I don't consider the close wound end to be 'softer';

You may not consider it to be softer but the math is very clear that it IS softer.


Mark

 

[RichDesmond]

...That's why I don't consider the close wound end to be 'softer'; it's going to deflect at the same rate per wind because it doesn't know how closely it's wound until it binds...

You're redefining spring rate here. Rate is defined as the force required to deflect the spring a given amount. The key here is that it's the whole spring. You're looking at an arbitrarily defined section of the spring. Within that context you are correct, the deflection per wind is the same. But there are more winds per unit length, and so the total deflection is greater for a given force. That's the definition of "softer".

 

[Gorminrider]

by Jove, I think I get it!

...More coils per unit length means a longer torsion bar per unit length and that means a softer spring rate.

"...the deflection per wind is the same. But there are more winds per unit length"

Thanks!

 

[Guest]

You're redefining spring rate here. Rate is defined as the force required to deflect the spring a given amount. The key here is that it's the whole spring. You're looking at an arbitrarily defined section of the spring. Within that context you are correct, the deflection per wind is the same. But there are more winds per unit length, and so the total deflection is greater for a given force. That's the definition of "softer".

I agree; but the rate difference only becomes apparent past the point of coil bind. Up to that point you may as well have wound the same length of wire evenly to the spec length. That's what I was trying to say. It's only when coil bind takes a section of the spring out of the equation - no longer the 'whole spring' - that the 'difference' becomes apparent.

We both know how it works; it's just making that function understandable to those who haven't figured it out yet.

This has been a really informative thread. It's also impressive that you actually make the springs. I had assumed that you had them made in some fab shop to your specs. Bravo.

 

[RichDesmond]

I agree; but the rate difference only becomes apparent past the point of coil bind. Up to that point you may as well have wound the same length of wire evenly to the spec length. That's what I was trying to say. It's only when coil bind takes a section of the spring out of the equation - no longer the 'whole spring' - that the 'difference' becomes apparent...

Hmm, I'm not sure what you're saying. If it's that winding part of the spring with tighter coils, versus winding the same length spring with the wider coils, makes no difference that's not true.
If you wind a spring with "x" coil spacing over the whole length you'll get one rate. If you wind the spring with "x" coil spacing over half it's length, and "1/2x" spacing over the other half it will be softer initially, and then stiffer after the more closely wound section coil binds. The reason being that up until coil bind the total length of wire available to flex is greater, and after coil bind it's less.

 

[Guest]

Hmm, I'm not sure what you're saying. If it's that winding part of the spring with tighter coils, versus winding the same length spring with the wider coils, makes no difference that's not true.
If you wind a spring with "x" coil spacing over the whole length you'll get one rate. If you wind the spring with "x" coil spacing over half it's length, and "1/2x" spacing over the other half it will be softer initially, and then stiffer after the more closely wound section coil binds. The reason being that up until coil bind the total length of wire available to flex is greater, and after coil bind it's less.

Exactly.

I fully understand the principles; well, the basic physics anyway. I think you missed 'with the same length of wire', which would involve increasing the spacing initially and then going narrower.

I guess that until you come up with a spring for the 'soda straw' forks we'll just have to futz with air or cut and spacer. No rush, just a hint.

 

[Guest]

Exactly.

I fully understand the principles;

apparently not

 

[Guest]

apparently not

What is it that you think I don't understand?

I'm saying that - until coil bind sets in - a given length of spring wire, wound to a specific length will have the same rate even if you wind one part wide and another part narrow. I don't think you really got the equal length of wire aspect. Of course if you start winding one part closer you will end up with more length of wire being employed to get to the same overall length of spring, and it's going to be softer - up to coil bind.

The point is that by cutting off a section of the spring it gets stiffer. Cutting the close wound end gets you to coil bind earlier, shortening the spring even more. That's all I was trying to share with those who want to stiffen the front end of a Twin.

I actually do understand the principles. Compared to the physics I work with in my job, this is pretty simple; and yes, part of it involves working with springs.

 

[RichDesmond]

Exactly.

I fully understand the principles; well, the basic physics anyway. I think you missed 'with the same length of wire', which would involve increasing the spacing initially and then going narrower.

I guess that until you come up with a spring for the 'soda straw' forks we'll just have to futz with air or cut and spacer. No rush, just a hint.

I did miss the "same length of wire part". Given that constraint, the initial rate should be the same, and then stiffer after coil bind of the more closely wound section.
Not an experiment I've done though, something else to put on the list for the winter.