Magical fork spring orientation

[cangy1000]

Can anyone remember which way up they they go off top of your head...or where i can find out?

[2stroke4stroke]

Under Newton's Third Law it makes no difference to the action of the spring but it is normal to put the tighter coils to the top to reduce unsprung weight (slightly).

[cangy1000]

Cheers for that 2stroke4stroke. I remember they do tell you to put the tight coils either top or bottom, didn't realise that was the only reason  

 

[pschrauber]

1 hour ago, 2stroke4stroke said:

Under Newton's Third Law it makes no difference to the action of the spring but it is normal to put the tighter coils to the top to reduce unsprung weight (slightly).

Just fork springs, to shock springs I wan't the thighter coil part of the spring being mounted as much up as possible so that debris can't build up between rear shock spring and rear shock body.

[section swept]

5 hours ago, 2stroke4stroke said:

Under Newton's Third Law it makes no difference to the action of the spring but it is normal to put the tighter coils to the top to reduce unsprung weight (slightly).

As all of the spring is carried in the fork tube pressing down on the bottom of the fork slider all of the spring is unsprung weight. The fork slidertube is unsprung weight to. It’s fun working out what is and isn’t sprung and unsprung weight! I never did trust Newton’s Law preferring instead to follow the writings of Bart Simpson, his diagrams on which part of a progressive spring compresses first are a joy to the eye. The calculations as to which part of the progressive spring rebounds first are a positive cure for insomnia. Girder fork discussion anyone.....anyone???

Edited September 30, 2018 by section swept

[faussy]

11 hours ago, section swept said:

As all of the spring is carried in the fork tube pressing down on the bottom of the fork slider all of the spring is unsprung weight. 

Not quite. At the end of the day you could argue the whole bike is pressing down on the bottom of the fork slider.

The very bottom of the spring is the only piece of the spring that is unsprung, everything else (including the upper windings of the spring) is connected to the bottom of the fork slider via an element of spring, hence its sprung weight

Edited October 1, 2018 by faussy

[collyolly]

If you are going to worry about the difference in unsprung weight between each end of a variable Spring rate Spring then I suggest you give up trials, as the first thing you add to your bike around here in the winter is a couple of Kilos of mud !

Yes I am aware that everything helps, in that case never eat a chip again.

[faussy]

21 hours ago, 2stroke4stroke said:

Under Newton's Third Law it makes no difference to the action of the spring but it is normal to put the tighter coils to the top to reduce unsprung weight (slightly).

It also raises the centre of gravity (slightly) 

[section swept]

21 hours ago, collyolly said:

If you are going to worry about the difference in unsprung weight between each end of a variable Spring rate Spring then I suggest you give up trials, as the first thing you add to your bike around here in the winter is a couple of Kilos of mud !

Yes I am aware that everything helps, in that case never eat a chip again.

Stay away from the Christmas pudding?

[section swept]

22 hours ago, faussy said:

Not quite. At the end of the day you could argue the whole bike is pressing down on the bottom of the fork slider.

The very bottom of the spring is the only piece of the spring that is unsprung, everything else (including the upper windings of the spring) is connected to the bottom of the fork slider via an element of spring, hence its sprung weight

Yes but through the spring, and unless it is attached at the top it is a free component. It drops down into the fork stanchion tube and sits on the bottom of the fork slider, with the weight of the machine and rider pressing down through the springs at the front end. At the rear we have a dichotomy as the damper carries the spring and the damper(s) are attached both top and bottom, there the top half is sprung and the bottom half is unsprung, a reason why some units are fitted upside down and not just for looks or clearance issues. Years of working on race cars doing corner weights and calculations to achieve the impossible ie make the driver better has helped me set up bikes that respond in almost the same mode. USD front forks is another way of reducing unsprung weight giving the damper less to do when controlling wheel movement on compression and rebound. If you put your bike onto a stand with the wheels free of the ground, anything that drops down or moves down is going to be unsprung weight. Anything that is attached to the frame is sprung weight. The drive chain it could be argued is both as it hangs down on the underside and is pulled across the top but it is carried by the rear wheel sprocket so the portion that is closest to the gearbox sprocket could be said to be sprung weight. The side stand if attached to the swing arm is unsprung weight but if attached to the frame tubes it is sprung weight, that’s why many bikes have the stand on the swinging arm. There in lies another reasonable case for stating that some of the swing arm is sprung weight and some is unsprung as it is carried by the wheel but also carried by the pivot point. There is also the issue of the rider dabbing, this can unsettle the suspension and the second the riders weight is transferred to the ground the suspension can unload slightly and upset the riders balance. Those who bunny hop and bounce about like they are on a pogo stick have developed a better sense of balance and machine control, sime do it violently some do it as a performance control and smoothness trying to plan with the reaction of the suspension. End of sermon, enjoy your bike ( ? theres no unsprung weight on an old bicycle save for a tiny amount of absorption through the tyre walls) stay away from suet puddings to reduce sprung weight⚖️?️‍♂️?????

[faussy]

The spring isnt a free component, it is bound at the top and bottom. It is attached or in contact with the top of the yoke so to speak. Unless your suspension has an inch gap between the top of the spring and the fork cap, but every front suspension that i have is in a state of preload so the spring is always in contact with the cap. If you use your example of a bike on a stand with the wheels off the ground, the top of the spring does not moves down

Its well known that in a conventional shock suspension setup the line between unsprung and sprung lies roughly halfway along the spring

Edited October 2, 2018 by faussy

[section swept]

Yep so the weight of the spring is pushing down on the bottom of the fork, I rest my case.

[section swept]

On 02/10/2018 at 9:49 AM, faussy said:

The spring isnt a free component, it is bound at the top and bottom. It is attached or in contact with the top of the yoke so to speak. Unless your suspension has an inch gap between the top of the spring and the fork cap, but every front suspension that i have is in a state of preload so the spring is always in contact with the cap. If you use your example of a bike on a stand with the wheels off the ground, the top of the spring does not moves down

Its well known that in a conventional shock suspension setup the line between unsprung and sprung lies roughly halfway along the spring

With reference to the last paragraph, the damper is attached both at the top and bottom, any angle between the pivot points will influence this ‘line’. As the damper is hanging from the top mounting that’s sprung weight, the lower end of the damper is attached to the swinging arm or in the case of a mono shock the linkage,  which again is unsprung weight. The spring in compression adds its weight to the unsprung movement because it is pushing down on its seat and up against the top seat ( your first paragraph) so it is totally weight on the unsprung movement, unless it (the spring) was clamped in some way to be hanging off of the top mounting. Remove the spring retainer collets which are also unsprung weight and the bike collapses, the springs are still sitting on the damper lower spring seat which is unsprung weight. That’s why some people fit the damper and spring units upside down increasing sprung weight but reducing unsprung weight, the damper body is now carried with the frame but the spring is still a part of the unsprung weight as it is still pushing up and down upon the spring seat and retaining collett. It’s all baffling stuff but believe me I’ve had the jigs and suspension set ups to fully prove to engineering students the science and process involved. The spring is trapped between whatever holds it in position, collets or adjustable pre load rings, it’s oscilations when in action or as a static contained force are what acts against the frame weight and the undulations that the wheels follow, or the weight the spring must bear with or without rider load.

Edited October 5, 2018 by section swept