Fork Springs

[Larry Fine]

From a Progressive Suspension instruction:

Install your new fork springs into the forks. Mechanically, it makes no difference which way the springs are installed. Some manuals will state; install the spring with the close wound end towards the bottom. This is done because sometimes there will be less spring noise. The springs will perform exactly the same regardless of which direction they are placed.


A post says: Wirth, Ikon, Progressive, Hagon, Wilbers all say tight coils up


And what I believe is an opinion:

Progressively-wound or dual-rate springs give an approximation of rising rate in that the close-wound part is the softest spring and compresses easily on small deflections. However on larger deflections the close-wound part goes coil-bound and the stiffer, loose-wound part does the work. At that time the close-wound part is doing nothing other than acting like a bush or spacer, and is dead weight. You don't want the dead weight to be unsprung (ie the weight of everything between the active part of the spring and the ground) therefore you want it at the top of the spring.

 

[Igofar]

This thread is starting to read like a bad episode of Big Bang theory
I simply pointed out a misprint in the service manual, that was verified by mother Honda (not a parts guy at a dealership) and also pointed out that on the ST1300 model, the OEM springs can only be installed correctly when the smaller end sits on the cartridge correctly, again, as mother Honda pointed out.
Now it seems every keyboard conspiracy commando is attempting to impose their will on everyone.
I don’t matter!
Put the springs in correctly, put the Correct amount of oil in, and go ride.

 

[Larry Fine]

My own take is this:

I think we agree that we should look at it from the bike's perspective, i.e., that the wheel assemblies move around the stationary bike. Also, that a laden ST weighs around 1K lbs, and a wheel assembly (tire, wheel, bearings, axle, brake rotors, etc.) and the moving suspension parts (lower fork sliders, damper rod, brake calipers and brackets, fender, etc.) probably 1/10 of the bike.

Let's say the suspension is being compressed, and the tight coils are now touching. With the tight coils down, they contribute to the moving mass of the front end, while the rest of the spring moves less. With them up, they don't contribute to moving mass, but the entire spring has to move upwards to compress them. I can see the advantages and disadvantages of each orientation.

I think that, while the few pounds of steel may have very little effect on the relatively-stationary mass of a 1K-lb bike, they may contribute more, percentage-wise, to the relatively-moving mass of the front wheel and suspension assemblies. So, while the actual effect may be imperceptible, when both ends are the same diameter, we have to pick an orientation, based on something.

 

[Larry Fine]

This thread is starting to read like a bad episode of Big Bang theory

I take that as a compliment.

Now it seems every keyboard conspiracy commando is attempting to impose their will on everyone.
I don’t matter!

No imposition intended, and certainly you matter.

Put the springs in correctly, put the Correct amount of oil in, and go ride.

Absoloopy!

 

[dwalby]

If you want visualization, cut off this upper part of the spring and pour an equivalent volume of oil in the tube, this is exactly the same situation. But now you can visualize the shorter column of air and understand why it will take less than 100 mm to halve the volume of air.

yeah, I had drawn out something like this after I was almost done typing the last post. Instead of oil, I used a solid rod of the same displacement as the spring in each orientation. I ended up with the same result of air volume and distance in the top part of the fork in both cases. I had already typed out the last post and I wasn't 100% sure either way, so I figured I'd ask one more time.

I'm guilty of overthinking things, thanks for taking the time to sort it out for me.

 

[MidLife]

......I had drawn out something like this........ Instead of oil, I used a solid rod of the same displacement as the spring in each orientation.

That's a good way to model it. May even be easier on our @Igofar!

I'm guilty of overthinking things.....

You were after another sound reason for up or down! Somebody had to do it.

 

[FastST]

What if the spring is upside down and the oil is missing about an inch from the top, and the air is not all the way up, vs when it is the other way around?

 

[Andrew Shadow]

This thread is starting to read like a bad episode of Big Bang theory
I simply pointed out a misprint in the service manual, that was verified by mother Honda (not a parts guy at a dealership) and also pointed out that on the ST1300 model, the OEM springs can only be installed correctly when the smaller end sits on the cartridge correctly, again, as mother Honda pointed out.
Now it seems every keyboard conspiracy commando is attempting to impose their will on everyone.
I don’t matter!
Put the springs in correctly, put the Correct amount of oil in, and go ride.

I may be wrong, up to the OP to clarify. My understanding is that it was an intellectual exercise from the outset. The question was asked out of intellectual curiosity in an attempt to understand if there is any valid technical reason why one orientation is better or worse than the other if there is no physical requirement to install the spring in a particular way. It was not asked with regard to the ST1300 specifically as far as I saw, so its particular requirement for installing the spring a certain way would not seem to be relavent to that question.

 

[FastST]

Install them differently in both forks. Go riding.

 

[ST1100Y]

Put the springs in correctly, put the correct amount of oil in, and go ride.

Yep, that's also my take on this...
I'm not a math genius, algebra is the language of evil spirits to me, but equipped with a good sense of abstract thinking the movements inside them forks are a vivid mental picture...

But to "fan the flames" juST a little

IMHO two, basic ideologies do apply:
Honda focuses on comfort, reliability and durability on normal roads...
cracks, frost beaten patchworks, cobblestone... and clients who rarely follow the suggested 36,000km/22,500miles inspection/overhaul...
(...Why pay for such?! My car's shocks have over 100,000miles and I've never replaced the oil there either... )

MFGs like Wirth, Ikon, Progressive, Hagon, Wilbers, etc... focus on " racetrack dynamics", which happens to be mostly flat like a glass table...
They don't/need to care if 60 to 80% of the spring length bangs and scrapes along the inside of them fork tubes, aging and contaminating the fork-oil with abrasion...
Likely that the "setup" gets rebuild for every individual track anyway...

 

[Larry Fine]

But to "fan the flames" juST a little

Back at ya.

Don't racers usually use linear-rate springs?

 

[ST1100Y]

Don't racers usually use linear-rate springs?

Yeah... lets debate the pros and cons on those...

My Hyperpro actually are linear progressive...
found them two-stage Wilbers springs simply too harsh on the wrists... surely great on a flat racetrack, not so nice when facing recesses or humps on frost beaten alpine roads...

Those surely look interesting... if you have the dough...

AK-20 Axxion Cartridge Kit (AK20H-ST1100) - Traxxion Dynamics

**Due to the very difficult installation and/or modifications required to the forks of this application this is an In-House install only. We require the forks be sent to our facility for this application. Traxxion Dynamics is proud to introduce the next revolution in motorcycle suspension! The...

traxxion.com

 

[MidLife]

Back at ya.

Don't racers usually use linear-rate springs?

Progressives are commonly used by dirt bike racers.

In the old days, progressive was the main way to prevent bottoming out. Drawback: rebound adjustment is not progressive, so can only be a compromise between working well for the soft part of the spring or the stiff section of it.

Then Honda came up with their famous Pro-Link set up, delivering progressive response from a linear spring suspension.

How Pro-Link Works | Cycle World | MARCH 1981

magazine.cycleworld.com

And now the ultimate (it seems), electronic controlled suspension.

 

[SMSW]

Mechanically, it makes no difference which way the springs are installed. Some manuals will state; install the spring with the close wound end towards the bottom. This is done because sometimes there will be less spring noise. The springs will perform exactly the same regardless of which direction they are placed.

Why is there more noise with progressive coils up compared with the progressive coils down?

And the question suggested by Larry's post above, if the rider has hearing loss, will the spring make the same noise?

 

[Larry Fine]

Why is there more noise with progressive coils up compared with the progressive coils down?

Actually, as I mentioned above, with small movements mostly affecting the close coils, with them down, the middle of the spring doesn't have to move; with them up, it has to for the motion to reach them.

And the question suggested by Larry's post above, if the rider has hearing loss, will the spring make the same noise?

Being hard of hearing myself, I have never heard squeaking or scraping sounds from a bike's fork. Even if I did, I would not base the decision on noise concerns.

 

[SMSW]

Actually, as I mentioned above, with small movements mostly affecting the close coils, with them down, the middle of the spring doesn't have to move; with them up, it has to for the motion to reach them.


Being hard of hearing myself, I have never heard squeaking or scraping sounds from a bike's fork. Even if I did, I would not base the decision on noise concerns.

You are taking my questions too seriously.

 

[Larry Fine]

You are taking my questions too seriously.

Doing that is fun for me.

 

[ST Gui]

Install your new fork springs into the forks. Mechanically, it makes no difference which way the springs are installed. Some manuals will state; install the spring with the close wound end towards the bottom. This is done because sometimes there will be less spring noise. The springs will perform exactly the same regardless of which direction they are placed.

Given the thread is an intellectual exercise (my take is the same as Andrew's) and so ignoring the ST1300 part of the discussion — I'm wondering how accurate is the Progress Suspension instruction quoted above.

Or is the difference in performance resulting in the orientation of progressive springs something that can be felt on the street? Could an accompanied rider return a bike after a road test and correctly advise "your fork springs are upside down"?

I didn't notice any difference in handling when I added a caliper and disc to my 750–4. So I'm clearly not the person to offer an opinion on the subject. But I am as curious of the factual difference as well as if it may or may not be perceptible on a city street or a back road.

Unsprung weight is unsprung weight in this non-specific bike exercise as it is in a specific bike exercise which this is not. Is it a bigger consideration of overall fork performance than the air volume resulting from the spring's two orientations? So much so that companies differ on installation? Again we're talking about the thread's context – no mechanical restrictions on orientation.

I suspect that an overwhelming majority of street riders wouldn't know the difference. Even if I'm wrong I'm still curious about the actual factual What and Why.

 

[MidLife]

......the air volume resulting from the spring's two orientations.....

Air volume is same regardless of orientation (for same oil volume).

I suspect that an overwhelming majority of street riders wouldn't know the difference.

I suspect the same. This is just to find a grounded reason for orientation.

I had a progressive spring on the rear shock, but a very gentle progression, evenly distributed from top to bottom, 1 mm per coil.

I had it installed both ways. Absolutely impossible to tell the difference of course.

But the mechanic who worked on the shock (and used to race) said that he would install a progressive shock that is noticeably tighter wound on one side with the tight coils up, to reduce the unsprung weight, the weight that moves up and down with the wheel.

 

[Larry Fine]

But the mechanic who worked on the shock (and used to race) said that he would install a progressive shock that is noticeably tighter wound on one side with the tight coils up, to reduce the unsprung weight, the weight that moves up and down with the wheel.

As I mentioned earlier, with the tight coils up, the entire spring has to move up in order to compress them.