Rear Springs

[ET43]

Sorry Howard, In order to increase the pre load on a spring you need to put a packer under the spring inside the covers. KTB lists the spring rates and from this a linear inch/weight chart can be drawn up. By winding out the SP4, one is increasing the ride height. Some people think that if you increase the pre load, the spring becomes stronger. What it does in fact is, allows more weight to be put on the machine before the spring starts to be compressed, resulting in less travel of the unit.
All this knowledge comes about by respringing umpteen 'undred sidecars, and working out the spring rates for my own outfit, and now the trike. Cheers, ET43

 

[Robert Watson]

Alyn
You will find that a piece of a front spring from a triumph (as in say a 70's Bonneville) will slip inside a rear spring and when you hit that hard bump, will pick up the extra load. Had them in the woolly for a long time before I switched to Thornton stuff. Experimentation will find the length. Start with one that will just squeeze in under the claw and if too stiff, shorten it a bit. You will have to unscrew the claw to put it in! Repeat until a bit too soft and start again!

 

[Albervin]

It seems the easiest solution is the Thornton system. I could waste a lot of riding time by playing with my rear end! There doesn't appear to be an agent in the Australasian area so I guess it is a toss up with
exchange rates & freight.. Thanks to all who supplied input.

 

[Howard]

Sorry Howard, In order to increase the pre load on a spring you need to put a packer under the spring inside the covers. KTB lists the spring rates and from this a linear inch/weight chart can be drawn up. By winding out the SP4, one is increasing the ride height. Some people think that if you increase the pre load, the spring becomes stronger. What it does in fact is, allows more weight to be put on the machine before the spring starts to be compressed, resulting in less travel of the unit.
All this knowledge comes about by respringing umpteen 'undred sidecars, and working out the spring rates for my own outfit, and now the trike. Cheers, ET43

ET43
As I said, I'm not an expert on Vin cycle parts, but check again. The maximum ride height is limited by the amount of travel in the damper. If you put a spacer under the spring (not easy with the claw arrangement?) you effectively increase the mounting hole centre distance on the spring box in its free state, just like screwing out the SP4s. That means you have to compress the spring more to fit it on the mounting shafts, which increases the preload.

On a Girling spring/damper unit you could pack the spring and increase the preload (against the damper rod) which is in effect how Girling do it with their cam thingymajig.

The ride height is changed by increasing the preload (by adjusting SP4), but it's the spring condition that decides how high the back of the bike is.

As you say, increasing the pre load does not make the spring stronger, it increases the weight the bike can take stationary. It only results in less travel if the spring becomes coil bound before full travel is reached. The trick on a short spring like the Vin's is to get a spring strong enough, with wire diameter small enough to give full suspension travel.

Shoot me down, I don't mind, this is my interpretation having used springs on many machines designs, but never vehicle suspension.

H

 

[ET43]

Oh dear,
If a suspension system travel is limited by a damper and where the damper is fully extended, by placing packing pieces under the spring, the spring is then pre loaded. This does not alter the distance between the mounting eyes as the damper rod is the limiting factor. The SP4 eyes are for adjusting the ride height only. If one winds them fully out, or winds them fully in, the spring will still work at the same rate, and from this , if one has preloaded the spring, then the machine's ride height can be brought back to it's previous height by adjusting the SP4's. It may well be that springs set up so that the damper rod is fully extended will be to hard for a comfortable ride, so a certain amount of compression of the system by the machine's weight and the weight of the rider is required. If the machine settles too much with rider aboard, then stronger springs are required. This should be able to be accommodated by the various rates of springs available. I personally would not fit unequal strength springs on a solo. The standard Rapide springs ( pair ) are rated at 378lbs/inch, so a 1/8th inch packer would inrease the preload by around 48lbs. My last post was wrong in as much that spring rates can be found in the appendix of Paul Richardson's book and not KTB. It is so long since I had a Vin with normal suspension, that I take your point about is being difficult to preload, with packers, a Vincent set up, so therefor it seems the only way to go is to fork out and obtain some different rate springs. It is not all that difficult to find a spring manufacturer in the U.K. as I had special rate springs made for W.C.S., and they were not all that expensive. ET43

 

[Howard]

Oh dear,
If a suspension system travel is limited by a damper and where the damper is fully extended, by placing packing pieces under the spring, the spring is then pre loaded. Agreed, but if you put spring packs in, all you are doing is making the spring box longer, so that when you fit it to the bike you have to compress the spring more to fit it - that gives you the extra pre load, so why not just open the SP4s so that you have to compress the spring more?
This does not alter the distance between the mounting eyes as the damper rod is the limiting factor. You misread what I wrote - I said in the free state ie detached from the bike.
The SP4 eyes are for adjusting the ride height only. You can only lower the ride height with the SP4s by compressing damper and losing suspension travel (at least travel compressing the damper). You can't raise the ride height past the damper travel.
If one winds them fully out, or winds them fully in, the spring will still work at the same rate, and from this , if one has preloaded the spring, then the machine's ride height can be brought back to it's previous height by adjusting the SP4's which compresses the spring more, increasing the pre load - if the bike settles on the springs you can only increase the height by increasing the force supplied by the springs.
It may well be that springs set up so that the damper rod is fully extended will be to hard for a comfortable ride, so a certain amount of compression of the system by the machine's weight and the weight of the rider is required.
If the machine settles too much with rider aboard, then stronger springs are required. Higher pre load, not necessarily higher spring rate. If you fit a higher spring rate you may not get full suspension travel, and there's little enough travel on a Vin. Pre load for ride height, spring rate for ride comfort.

This should be able to be accommodated by the various rates of springs available. I personally would not fit unequal strength springs on a solo. The standard Rapide springs ( pair ) are rated at 378lbs/inch, so a 1/8th inch packer would inrease the preload by around 48lbs. My last post was wrong in as much that spring rates can be found in the appendix of Paul Richardson's book and not KTB. It is so long since I had a Vin with normal suspension, that I take your point about is being difficult to preload, with packers, a Vincent set up, so therefor it seems the only way to go is to fork out and obtain some different rate springs. It is not all that difficult to find a spring manufacturer in the U.K. as I had special rate springs made for W.C.S., and they were not all that expensive. ET43

Over to you

H

 

[ET43]

Howard, You cannot alter the spring rate by winding out the SP4's. All you will do is to use the same amount of travel of the spring given that the same weight is applied. I thought that the quest here was to stiffen up Albervin's suspension so that it would not bottom out. He therefor needs to increase the preload, and if that is not possible, then he needs stronger springs. I have been sat at this computer for almost three hours trying to think of a polite way to respond to your glorious statements in red. As diplomacy is not a word I am familiar with, I will not respond with answers that will prolong this thread. I know that what I have postulated, works for me, and at least I understand it if nobody else does. Thank You, Phil Primmer.

 

[Howard]

Howard, You cannot alter the spring rate by winding out the SP4's. All you will do is to use the same amount of travel of the spring given that the same weight is applied. I thought that the quest here was to stiffen up Albervin's suspension so that it would not bottom out. He therefor needs to increase the preload, and if that is not possible, then he needs stronger springs. I have been sat at this computer for almost three hours trying to think of a polite way to respond to your glorious statements in red. As diplomacy is not a word I am familiar with, I will not respond with answers that will prolong this thread. I know that what I have postulated, works for me, and at least I understand it if nobody else does. Thank You, Phil Primmer.

Phil

No offence was meant - I only used red to differentiate between your writing and my comments. I still think you're missing something, but lets discuss it over a pint sometime.

Howard

 

[vince998]

Phil

No offence was meant - I only used red to differentiate between your writing and my comments. I still think you're missing something, but lets discuss it over a pint sometime.

Howard

Packing out the springs, or increasing the overall length of the spring box (unit) is going to have the same effect as far as i see it and this is pre-load. This may effect ride height if the spring was compressing at a standstill with the riders weight (this will obviously not be compressing quite so much so giving you a higher starting point.)
This will not however affect the spring rate, or the point at which the suspension bottoms out. All you´re doing is postponeing the point at which the spring starts to compress and not stiffening the spring. This usually leads to a harsher ride on bumpy roads because the suspension starts to move later.
To alter spring rate, you have to change the spring.
I achieved both a ride height increase and a change of (effective ) spring rate on my yamaha through fitting shorter "dogbones"(or links) to the suspension linkage, and so reducing the effective leverage caused by weight transfer to the spring. This however is not possible on any Vincent as one end of the suspension is fixed (UFM) whilst the other end is directly attached to the prime mover (RFM).
As for different spring rates on each side, as long as there is no play between the UFM mount, RFM mount and the through bolts, i don´t think you´ll have enough leverage to twist the UFM

 

[vince998]

Packing out the springs, or increasing the overall length of the spring box (unit) is going to have the same effect as far as i see it and this is pre-load. This may effect ride height if the spring was compressing at a standstill with the riders weight (this will obviously not be compressing quite so much so giving you a higher starting point.)
This will not however affect the spring rate, or the point at which the suspension bottoms out. All you´re doing is postponeing the point at which the spring starts to compress and not stiffening the spring. This usually leads to a harsher ride on bumpy roads because the suspension starts to move later.
To alter spring rate, you have to change the spring.
I achieved both a ride height increase and a change of spring rate on my yamaha through fitting shorter "dogbones"(or links) to the suspension linkage, and so reducing the effective leverage caused by weight transfer to the spring. This however is not possible on any Vincent as one end of the suspension is fixed (UFM) whilst the other end is directly attached to the prime mover (RFM).
As for different spring rates on each side, as long as there is no play between the UFM mount, RFM mount and the through bolts, i don´t think you´ll have enough leverage to twist the UFM

Correction,
After a bit more thought, if you moved the RFM suspension mounting point forward (effectively reducing the leverage) you´d achieve a rise in ride height whilst effectively "stiffening" the spring.
Not quite sure if this would affect the spring "rate" though as it´s still the same spring?