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Progressive springs - which way up

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Progressive springs - which way up

Postby phil23fair » Sat Oct 10, 2020 9:17 am

Does it matter which way up progressive fork springs are fitted provided they are both the same way up?
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Re: Progressive springs - which way up

Postby gizmo » Sat Oct 10, 2020 11:23 am

I've always put the tighter coil to the top but I can't honestly say if it's right or wrong.
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Re: Progressive springs - which way up

Postby HxPaul » Sat Oct 10, 2020 12:47 pm

It doesn't matter,as long as there both the same way up.
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Re: Progressive springs - which way up

Postby phil23fair » Sat Oct 10, 2020 1:25 pm

Thanks for the replies
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Re: Progressive springs - which way up

Postby Warkton Tornado No.1 » Sat Oct 10, 2020 4:27 pm

I've always fitted them with the most 'coilbound' toward the top as the theory (bearing in mind we're considering a two wheeler with a frame largely made of scaffold tubing.....) is that it reduces unsprung weight to have the least 'coilbound' part bearing onto the links.

As there appears to be no other 'rules' I go along with that.

However, what it does do, is reduce the inertia that the springs are subject to having the 'most compressible' element of the springs toward the bottom. In other words, the whole of the springs are not being pushed up & down with small suspension movements when just the 'softest' part of them is doing the work.

I hope that makes sense :D
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Re: Progressive springs - which way up

Postby phil23fair » Sat Oct 10, 2020 7:04 pm

WT1 that make absolute sense. Thanks
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Re: Progressive springs - which way up

Postby bsso78 » Sat Oct 10, 2020 9:16 pm

Personally I think they are as much use as tits on a bull. Standard springs every time for me.
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Re: Progressive springs - which way up

Postby dickie » Sat Oct 10, 2020 10:10 pm

bsso78 wrote:Personally I think they are as much use as tits on a bull. Standard springs every time for me.

I found the "ultimate" progressive springs to be far too soft and hated them. I use BGM ones now and really like them. However, they're not right for everyone. It depends what kind of roads you ride, weight, riding style etc.

Anyway, they should be installed with tight coils at the top to reduce unsprung weight. That said, you'd need to be some kind of special rider in extreme riding conditions to notice the difference. I'm talking about GP standard when running at least mid pack. An unlikely scenario for a Lambretta :lol:
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Re: Progressive springs - which way up

Postby Andyf » Sat Oct 17, 2020 9:07 am

Would a racer prefer the predicability of a linear spring over a progressive?

Also, if the effect only manifests itself at 'racing' activities, wouldn't it be preferable to have the least mobile end (tight) at the end where you prefer least movement (wheel)?
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Re: Progressive springs - which way up

Postby Warkton Tornado No.1 » Sat Oct 17, 2020 1:10 pm

Andyf wrote:Would a racer prefer the predicability of a linear spring over a progressive?

Also, if the effect only manifests itself at 'racing' activities, wouldn't it be preferable to have the least mobile end (tight) at the end where you prefer least movement (wheel)?


There is a lot of "smoke & mirrors" associated with suspension & the control of the springs.

The springs @ both ends are constantly working absorbing surface imperfections. The dampers in turn control the springs to prevent the kind of oscillation that springs alone would default to.

Progressive springs have parts of them working all of the time whilst the machine is being ridden. Obviously, the softer element does the majority of the work until it becomes overcome in the suspension/wheel deflection, whereupon, like a tubular pushrod, any further forces are then passed on to & absorbed by the harder spring element.

My conclusion is that with the harder element placed low, the bottom part will then be constantly going up & down for no real gain. Potentially, the spring inner pushrod is subject to more wear & unsprung weight is increased. I cannot see any benefits to inverting the springs, but it's all theory in any case :D

'Feel' is important & the only Lambretas that I have ridden where I personally felt that feedback was lacking was on front ends with no damping or those equipped with the Kawasaki type dampers. As for anti-dive, I much prefer dive as it sharpens up the suspension for the inevitable hairpin bend that is about to be negotiated, effectively preparing rider & machine in advance.
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Re: Progressive springs - which way up

Postby SmudgeDog » Sat Oct 17, 2020 9:55 pm

I see this differently. The spring never contributes to "sprung" or "unsprung" weight. It is the link between the two...ish. It does not even matter if you have them different, you still get the same amount of spring resistance. Physics. I think the only common sense advice in real world conditions is to put the tighter coils downwards as it may help keeping shit out. Weight down for a lower centre of gravity...well you or I will never be able to sense that miniscule difference.
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Re: Progressive springs - which way up

Postby bsso78 » Sat Oct 17, 2020 11:23 pm

I refer you to my earlier comment me’lud
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Re: Progressive springs - which way up

Postby Warkton Tornado No.1 » Sat Oct 17, 2020 11:29 pm

SmudgeDog wrote:I see this differently. The spring never contributes to "sprung" or "unsprung" weight. It is the link between the two...ish. It does not even matter if you have them different, you still get the same amount of spring resistance. Physics. I think the only common sense advice in real world conditions is to put the tighter coils downwards as it may help keeping shit out. Weight down for a lower centre of gravity...well you or I will never be able to sense that miniscule difference.



Healthy, differing opinions about the best way up.

The rates of a pair of springs stays the same, either way, & any scientific measurable differences would be minuscule.

I dare say there are many forks fitted with mismatched springs which would be difficult to detect by the ride. However a pair is to be preferred IMO fundamentally as the wheel/axle/fork links are not that rigid an assembly. Otherwise we would be able to fit a double rate spring in just one fork leg.

I will confess to assembling forks with one SII (175) & the other SIII. It took me ages to realise my mistake, even though the wheel was angled over to one side :oops:
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Re: Progressive springs - which way up

Postby dickie » Sat Oct 17, 2020 11:58 pm

@wt1. There isn't really a hard and soft part of the spring. The tight coils just get coil-bound first, so that the spring in effect becomes shorter and consequently harder. Like you say, the whole spring is working and at the same N/mm rate, UNTIL, the tighter coils are fully closed. It's at this point that there is a transition into a firmer rate.

I don't know how to say the next bit without being total nob, so forgive me, it's wholly unintentional. The suspension will perform better with the tighter coils at the top as they are denser and therefore would increase unsprung mass (inertia), consequently reducing the ability of the suspension to react as quickly to undulating in road surface. This really isn't opinion, just physics (that was the nob bit). However, note that this effect is tiny so you'll never know the difference; it's just an interesting bit of physics if you like that sort of thing.
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Re: Progressive springs - which way up

Postby Warkton Tornado No.1 » Sun Oct 18, 2020 2:40 pm

dickie wrote:@wt1. There isn't really a hard and soft part of the spring. The tight coils just get coil-bound first, so that the spring in effect becomes shorter and consequently harder. Like you say, the whole spring is working and at the same N/mm rate, UNTIL, the tighter coils are fully closed. It's at this point that there is a transition into a firmer rate.

I don't know how to say the next bit without being total nob, so forgive me, it's wholly unintentional. The suspension will perform better with the tighter coils at the top as they are denser and therefore would increase unsprung mass (inertia), consequently reducing the ability of the suspension to react as quickly to undulating in road surface. This really isn't opinion, just physics (that was the nob bit). However, note that this effect is tiny so you'll never know the difference; it's just an interesting bit of physics if you like that sort of thing.


Thank you & I had got the element of the spring that reacts first the wrong way around, but somehow, it appears that the preferred manner in which the dual rate springs should be fitted is as you & I had already said.

This is a really good explanation:

https://www.google.com/search?q=how+do+ ... oZzjk3vmpM
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Re: Progressive springs - which way up

Postby cookieman66 » Mon Oct 19, 2020 8:47 am

I would ask the place you bought them from .
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