fork preload

[Banky2112]

look at this guys

you dial in preload, the spring is compressed, in order to do that we made the area the spring can work in smaller, now the total distance it works in is less

we did not change the spring rate in any way, the rate is still the same, it just starts loaded up.

it still has the same rate as it had in the beginning only now it has less area to travel

ok, so we want it to feel stiffer and we put in 1 inch spacers, again we are not making the spring rate any stiffer, we are just loading up the spring more and giving it less room to move. The spring rate is still the same

now, the loaded rate of the spring changes proportional to its change in length. but that does not effect the spring until compressed there for a spring with a stiffer rate would have the same change when compressed.
I have studied the formulas in college but as of now it is not in the head.
anyway, so preloading the spring, it still has the rate of the spring multiplied by the formula for change of length, as such as a stiffer spring would also.

seeing that, you start to realise, replacing the spring and retaining the suspension travel to use all the spring is the answer, to compress the spring to get a stiffer spring limits the travel and will never end up with the end ratio you want from the stiffer spring anyway.

Hookes law, thats it, F=-kx, F is displacement, X is rate and k is resulting force

so spring one is rated at z, and compressed to the end it is r
so spring two is rated at x, and compressed to the end it is q

if compressed and we change F on either spring, we will never get kx to be the same on the other spring anywhere along the travel that is the same

so

the rate does not change as it is already a constant at any point set by the original rate of the spring
in other words, at any point of the travel, you will never get that spring to do what a stiffer spring will do, al you have done is changed the preload and shortened how much area the spring has to perform in.

in order to get a stiffer rate, you have to change the spring

using hooks law, at any time during

so preloading does not change the rate, it changes the rate times Hook's formula. but the starting rate is constant and that is what you need to consider, IF I set the spring rate for a 1000 pound rider, how much suspension travel would I have? and is that enough for the curves I want to hit? Of I changed the spring for a spring that would be designed to have the rate at the amt of compression I wanted, and got on the bike, without having to load up the bike so much, do I not end up with a spring I can use during full suspension travel?

we do not need the springs super stiff, if we did why even use the springs just go rigid. What we need is a spring that can help control the movement of the suspension as we load it up and work the corner. going in we want it to be able to compress at a rate our tire can not wash out as it loads up. that means it compresses, once it stops compressing the tire starts to slip. in other words the spring is part of the traction formula. Now as we transition into leaving the curve we use damping more than spring rate and once leaving we want the spring to expand at a rate that again we keep traction during. We do not want it to POGO.
Pogo is a bad thing. A spring with to much preload will have the tendency to POGO when exiting a curve. A spring of the proper rate will be in the range it is intended to be in at that point.

that is why different bikes have different springs
the need to adjust damping on a touring bike is not there, they will never push a curve like that, but a SS needs the damping to control the spring during hard turns.
As it needs a spring of different rate as a UJM.
PS, I think most springs now days are progressive.

is that clear?

MERICA.......

 

[Bajaedition]

SKOOTER65

thanks for the post, I was trying to remember that formula,
so many people will not understand how the spring rate remains constant even though it gets stiffer, that formula explains that the rate is constant, the displacement and force are what changes

 

[NoNine4me]

Just a slight correction here as I think you have your explanations backwards. Standard wound springs have a constant rate (Also known as the spring rate or spring constant; See Hooke's Law). The force, or "preload", is a function of the amount of compression on the spring: Force = Spring Constant X Amount of Compression.

Progressive springs are just that, progressive. The Spring rate of each section of coil winding is different.

Continue on, great topic for a thread!

Indeed...from an engineer's POV, it sounds backwards but trying to simplify for us, I suggested the idea of more "predictable behaviour" as from the rider's perspective of how the bike is reacting when equipped with progressively wound springs. It's a little more work to analyze the behaviour of a progressively wound spring, especially if we use a slide rule.

 

[NoNine4me]

MERICA.......

look at this guys

...We do not want it to POGO.
Pogo is a bad thing. A spring with to much preload will have the tendency to POGO when exiting a curve. A spring of the proper rate will be in the range it is intended to be in at that point.

that is why different bikes have different springs
the need to adjust damping on a touring bike is not there, they will never push a curve like that, but a SS needs the damping to control the spring during hard turns.
As it needs a spring of different rate as a UJM.
PS, I think most springs now days are progressive.

is that clear?

Yes, POGOing is bad; that's what's happening to me since my weight is too low for the stock spring rate. Even though I have cranked up the fork oil weight to 10wt, when the spring compresses while leaned over, the stiff spring rebounds too quickly and in a series of bumps the bars want to twist out of my hands. That is bad. Even though my sag is set to 35mm, the springs get too stiff in the initial range of travel. I need a spring where the sag can be correct but the spring will allow a range of travel to be compliant with the road surface and let the fork move smoothly as it should, in the middle of its range of motion. Going to the right rate of spring will help with this.

Also tire choice makes a big difference. That is why I'm doing one thing at a time; the current Pirelli Angels I'm running, which last a long time and stick pretty well, have a stiffer carcass and aren't especially compliant. I'm going to go with a set of Dunlop Q3's, see how much difference the tire alone makes, and then move on to springs and Gold Valves.

I expect the tires to make a big difference.

 

[Bajaedition]

tires, their shape and their compound will all affect pogoing
as well as damping

If you cannot get the static sag to be 10 mm while the rider sag is 30 to 40 mm then you swap springs. either softer or stiffer.

here is a good dicussion
Sport Rider Technicalities-Spring Rate and Preload