Shorter Fork Springs?

[Tonerjockey]

Anyone ever make/buy/find fork springs for V7 Sport that are about 305mm? I am considering lowering the front end by about 1.75" and need shorter, custom length, springs.

The front end of the oil pan is a bit higher than the rear end of the oil pan.

I'll hafta make shorter shock rods as well but that doesn't seem much of a show stopper.

Cutting a standard set of springs seems problematic. Tempering, shaping, hmmm.

next step is working on the human sail on top of the bike...
Alex

 

[kiwi dave]

Rather than shortening your springs, why not reduce the preload? If there's no adjustment, perhaps there's a slug in there that you can shorten or remove.

A shortened spring will be stiffer than the original.

 

[GTM®]

I'm guessing you don't care about the negative movement of the fork then? Post the OD, ID and coil thickness along with the length, and I'll see what I can find for you. Per what Dave posted above, if their is a preload spacer, that is an easy option.

 

[Tonerjockey]

The top mount of the cartridge was shortened as much as possible. That's the piece that attaches the cartridge to the fork.
I am not overly concerned with increased tension... the track this thing runs on is smooth (Bonneville).
Not sure what you mean by negative movement and not sure what a preload spacer is.
This V7 Sport has stock fork internals (pretty much). The cartridge has a rod (shock rod) that connects the cartridge plunger rod to the end cap... the spring is captured between the cartridge and the end cap.

This diagram of a T3 is very similar to the V7 Sport parts:

32 is the locating cup, 35 bottom spring retainer, 31 shock rod, 30 plastic buffer, 28 cartridge are stock. #2 top mount are shortened.

This piece has been shortened (short piece not displayed).

Whatcha think?

Alex

 

[Tonerjockey]

I 'll take measurements and post them here.
Looking thru MG cycle, Harper, Stein-Dense, and everyplace else that Yahoo could find indicates that no GUZZI uses the length I am searching for.

Alex

 

[Tonerjockey]

Spring OD = 1.016" 25.88mm
Metal thickness 0.190" 4.77mm
ID .642" 16.3mm
Unloaded Length 16.25" 412.75mm (must have compressed a bit in 43 years...)

Looking for length about 14.75" or 374.65mm

 

[kiwi dave]

Another method to achieve your lower front end is to raise the staunchions through the top yoke (triple-tree). I have no idea whether this is possible or not, just another suggestion.

 

[Tonerjockey]

Hey Dave,
That's how I figured the needed final length of the springs etc.

Unfortunately, the result (above) is obvious. Inspection would never let this pass. In the class we run, Production, All modifications must not be visible. Even though the desired effect is just to level the bike out... it would appear as a modification (lowering below stock).

Thanks for the note though.

Alex

BTW are you folks having summer now?

 

[kiwi dave]

Yes, summer is meant to be here, but it hasn't really happened yet where I live. Very soon I hope.

Remember if you shorten your spring, you will increase your spring rate, resulting in a harsher ride. If that's acceptable, OK but otherwise you will need a lighter spring at that shorter length to maintain the same spring rate.

I guess you've already thought about jacking up the rear to achieve your objective.

 

[Tonerjockey]

We have a mild winter here in San Jose Ca. USA... but it IS upon us now.
The harsher ride will be acceptable... until I don't like it
Rising the rear would bring the entire bike up and I am trying, in every " improvement" made, to "not let the wind see me."

Today I go to the shop and attempt to shorten a spare set of springs... or maybe wind up with some new wall art.

Alex

 

[Tonerjockey]

86 the search for shorter springs. I cut down a couple spares.

Now gotta find some 18mm OD by I dunno what ID steel tube...

Alex

 

[kiwi dave]

86 the search for shorter springs. I cut down a couple spares.


Now gotta find some 18mm OD by I dunno what ID steel tube...

Alex

So you're gonna replace some spring length with steel tube? All you will achieve is a greater spring rate at the front end.

Surely you just want to reassemble with the shorter spring alone to achieve the lowering in height.

 

[Tonerjockey]

I am going to replace the shock cartridge extension rod with a self made one that is 1.5" shorter... as the experimental springs now are.
Part # 31 in above parts explosion.
The rod connects the shock cartridge plunger to the bottom of the spring and lower fork slider.

Alex

 

[Tonerjockey]

OK I think I'm there.

Made a cartridge rod 1.5" shorter than stock. Used solid round rod instead of the factory style tube. Each rod is 40 g heavier than stock... but I think a good portion of that gained weight will be offset by the weight loss of the shorter spring... anyway 40g is about what .. an order of fries at McDonalds?

Thanks all for the responses and ideas.

Alex

 

[GuzziMoto]

Glad it is working out for you. I do find the subject of springs to be interesting. Cutting down springs is a interesting way to modify the suspension. It has several affects, it clearly makes the spring shorter but it also makes the spring stiffer at the same time. In some applications making the spring stiffer would be a bad thing, but in many cases it is actually a useful result of shortening a spring. If you are making the spring shorter to lower the bike you likely also need the spring stiffer, otherwise you may find that the lower ride height results in too much bottoming out of the suspension. In some cases, making the spring stiffer is actually the point of shortening the spring. It can be a cheap way to stiffen the suspension, or in some cases stiffer springs aren't available.
Way back in the early '90s we used a similar trick to lower the front end of our Ducati 750 race bike. What we did, as I recall, was to cut off an inch or so of the spring and actually re-install that inch under the damper tube so that it forced the forks to be shorter while at the same time it acted as a top out spring (which at the time was not something that was common, now it is fairly common).

 

[Tonerjockey]

Huh. Never heard of that. Sounds like ya ID'd an important area of focus.
Regarding a stiffer front, in my application I don't think that should be a show stopper. It actually might be an enhancement.
As a LSR buddy/Guru sez "suspension costs power."
Bottoming... the bike needs to be ridden some to check for that. I can shorten (trim bottom) of the fork tubes as needed to address any bottoming.
Hoping for "no further action needed," of course but time will tell.

Next area of activity; The Wonderful World Of Pistons.... oh yeah and rider needs to loose another 20 pounds to get back into that old skinny suit.

Happy New Year
Alex

 

[Shrek]

Glad it is working out for you. I do find the subject of springs to be interesting. Cutting down springs is a interesting way to modify the suspension. It has several affects, it clearly makes the spring shorter but it also makes the spring stiffer at the same time. In some applications making the spring stiffer would be a bad thing, but in many cases it is actually a useful result of shortening a spring. If you are making the spring shorter to lower the bike you likely also need the spring stiffer, otherwise you may find that the lower ride height results in too much bottoming out of the suspension. In some cases, making the spring stiffer is actually the point of shortening the spring. It can be a cheap way to stiffen the suspension, or in some cases stiffer springs aren't available.
Way back in the early '90s we used a similar trick to lower the front end of our Ducati 750 race bike. What we did, as I recall, was to cut off an inch or so of the spring and actually re-install that inch under the damper tube so that it forced the forks to be shorter while at the same time it acted as a top out spring (which at the time was not something that was common, now it is fairly common).

Hi
Please excuse my ignorance,but i am very interested in suspension stuff and spring rates etc
How can shortening a spring,increase its rate or make it stiffer?
My understanding is the spring rate is determined by the wire diametre and the coil spacings.
Given a set wire diametre,a closely wound spring(less gap between coils) will make it softer or a lower rate.
Springs which are wound more open(larger gap between coils) will be stiffer or a higher rate.
Can you please explain why as i am currently experimenting with different types,lengths and rates of springs on my Lemans V
Shrek

 

[GuzziMoto]

A coil spring is really a straight piece of spring steel of a given length and thickness coiled up. The length and thickness of the piece of spring steel are what determines its rate. For a straight rate spring, length and thickness is the only thing that determines its rate. A thicker piece of spring steel would have a firmer rate than a thinner piece if each piece is the same length. Conversely, a longer piece of spring steel has a softer rate than a shorter piece of spring steel if both are of the same thickness. The fact that they are coiled up, and how they are coiled up including the spacing between the coils, is not a factor in their rates unless they are coiled up in such a way as to cause some of the coils to touch while others are still open. That is typically how a progressive rate spring works. I will get back to those later. For now, assume we are talking about straight rate springs. A longer length of spring steel in the same overall size package may appear to have coils that are closer together, but it is not that the coils are closer together that influences its rate. It is that the length of spring steel is longer. The fact that the coils are closer together is just a side effect of the length of spring steel being longer. The opposite is true when the coils are further apart, the real difference is that the length of spring steel is shorter and so the rate is stiffer. Those are visual clues, but they are not cause and effect.
So, if a springs rate is determined by the thickness and length of the piece of spring steel it is made from, well I can't really change the thickness. Once it is made of a given thickness that aspect is set. But I can change the length, I can make it shorter. Making it shorter makes it stiffer. Think of something as simple as a pencil, if I take a brand new pencil at full length I can bend it with some effort. Now, if I try the same thing with a pencil that has been re-sharpened over and over and is now half as long I probably would have a hard time bending it. So, if I shorten a piece of spring steel of a given thickness I have made that spring stiffer. I can only shorten it, I can't make it longer, so I can only make a given spring stiffer by cutting it. Once cut, the spring is now both stiffer and shorter. In a typical situation I would be replacing the section I cut out with a spacer made from a non-compressible material. That brings me back to the original, or desired, length but with an increased rate. If you want to lower or shorten a spring and you cut it as mentioned you are both shortening it and stiffening it at the same time. In that case you may not want to replace the missing part of the spring with a spacer.
If I have a progressive spring, they typically use a variation of this concept to achieve the progressive rate. A progressive rate spring typically has coils on one end wound closer to each other than they are on the rest of the spring. These closer coils are not harder or softer than the others, but as the spring compresses and the coils get closer to each other these coils (that started out closer to each other than the rest) begin to touch. Call that coil bind. Because they started out closer together they will touch before the rest of the coils touch (a spring does not compress from one and or the other, all the coils compress together equally). When they touch they have the effect of shortening the piece of spring steel as they can no longer compress further. Once they touch, once they coil bind, that part of the length of spring steel is in effect out of the equation. It can no longer compress. The remaining length of spring steel continues to compress, but as it is now, in effect, a shorter length of spring steel the effective rate of the length of spring steel has gone up. It now acts like a shorter piece of spring steel. If you cut a progressive rate spring shorter, which end you cut has an effect on the result, but it is not as simple as one end is the softer and and one end is the stiffer end. If you cut from the end where the coils are closer together you are removing some of the progressiveness out of the spring, while also making what is left stiffer as a whole. But the difference between the lower rate and the highest rate (the progressive curve) would be reduced. If you cut from the other end you are leaving the progressive curve alone and removing from what might be called the base rate of the spring. The progressive curve would still be there, the amount of rate increase from the beginning rate to the ending rate would not change much, but the whole spring rate curve would be moved up a few notches in stiffness,
You can make a progressive rate spring that uses a variable thickness for the length of spring steel, but I have never seen that on a motorcycle and I am not including that in this discussion.
I hope this helps, please feel free to ask questions or disagree with any of this.

 

[Shrek]

A coil spring is really a straight piece of spring steel of a given length and thickness coiled up. The length and thickness of the piece of spring steel are what determines its rate. For a straight rate spring, length and thickness is the only thing that determines its rate. A thicker piece of spring steel would have a firmer rate than a thinner piece if each piece is the same length. Conversely, a longer piece of spring steel has a softer rate than a shorter piece of spring steel if both are of the same thickness. The fact that they are coiled up, and how they are coiled up including the spacing between the coils, is not a factor in their rates unless they are coiled up in such a way as to cause some of the coils to touch while others are still open. That is typically how a progressive rate spring works. I will get back to those later. For now, assume we are talking about straight rate springs. A longer length of spring steel in the same overall size package may appear to have coils that are closer together, but it is not that the coils are closer together that influences its rate. It is that the length of spring steel is longer. The fact that the coils are closer together is just a side effect of the length of spring steel being longer. The opposite is true when the coils are further apart, the real difference is that the length of spring steel is shorter and so the rate is stiffer. Those are visual clues, but they are not cause and effect.
So, if a springs rate is determined by the thickness and length of the piece of spring steel it is made from, well I can't really change the thickness. Once it is made of a given thickness that aspect is set. But I can change the length, I can make it shorter. Making it shorter makes it stiffer. Think of something as simple as a pencil, if I take a brand new pencil at full length I can bend it with some effort. Now, if I try the same thing with a pencil that has been re-sharpened over and over and is now half as long I probably would have a hard time bending it. So, if I shorten a piece of spring steel of a given thickness I have made that spring stiffer. I can only shorten it, I can't make it longer, so I can only make a given spring stiffer by cutting it. Once cut, the spring is now both stiffer and shorter. In a typical situation I would be replacing the section I cut out with a spacer made from a non-compressible material. That brings me back to the original, or desired, length but with an increased rate. If you want to lower or shorten a spring and you cut it as mentioned you are both shortening it and stiffening it at the same time. In that case you may not want to replace the missing part of the spring with a spacer.
If I have a progressive spring, they typically use a variation of this concept to achieve the progressive rate. A progressive rate spring typically has coils on one end wound closer to each other than they are on the rest of the spring. These closer coils are not harder or softer than the others, but as the spring compresses and the coils get closer to each other these coils (that started out closer to each other than the rest) begin to touch. Call that coil bind. Because they started out closer together they will touch before the rest of the coils touch (a spring does not compress from one and or the other, all the coils compress together equally). When they touch they have the effect of shortening the piece of spring steel as they can no longer compress further. Once they touch, once they coil bind, that part of the length of spring steel is in effect out of the equation. It can no longer compress. The remaining length of spring steel continues to compress, but as it is now, in effect, a shorter length of spring steel the effective rate of the length of spring steel has gone up. It now acts like a shorter piece of spring steel. If you cut a progressive rate spring shorter, which end you cut has an effect on the result, but it is not as simple as one end is the softer and and one end is the stiffer end. If you cut from the end where the coils are closer together you are removing some of the progressiveness out of the spring, while also making what is left stiffer as a whole. But the difference between the lower rate and the highest rate (the progressive curve) would be reduced. If you cut from the other end you are leaving the progressive curve alone and removing from what might be called the base rate of the spring. The progressive curve would still be there, the amount of rate increase from the beginning rate to the ending rate would not change much, but the whole spring rate curve would be moved up a few notches in stiffness,
You can make a progressive rate spring that uses a variable thickness for the length of spring steel, but I have never seen that on a motorcycle and I am not including that in this discussion.
I hope this helps, please feel free to ask questions or disagree with any of this.

Thanks for the very detailed reply.Much appreciated.
I understand everything you are saying and i agree or cant disagree as i dont know better.
My brain just has trouble digesting it.
I was taught that the spacing between each coil determines its rate given a fixed wire diametre.
Which is correct,as you state a heavier weight spring will have less wire which means more gap and and less coils for a given length.
I always thought that the angle of the wire,being less for a lighter rate,would allow it to bend bend easier.
Example of a progressive spring,
I thought the closer coils on a progressive spring would bottom out first before the the wider wound coils moved at all.
Are you saying that they all compress at the same rate but the closer ones bind first effectively raising the rate.

If so,i wish i new this two sets of springs ago.

My Lemans V came standard with two springs per leg.
The small soft one,with more wire or less gap,was way too soft.
I could feel it bottoming halfway through the stroke riding out of my driveway.
I removed the soft spring and replaced with pvc pipe.
It felt better at speed but too hard for everyday riding.(Your explanation explains why)
So i purchased a pair of progressive springs.
These were also way to soft for most of the stroke.
So i thought i was being clever by cutting the heavy end of the progressive spring and mating it with the heavy Guzzi spring.
It was a vast improvement but still a little light when hard charging.
Occasionally bottoming and sliding the front.
Not knowing what rate i needed/wanted,i fitted a pair of linea rate springs of 0.95kg of the same total length.
That has made me happy.
However,i could have achieved what i wanted by simply shortening the springs i had,with a bit of experimentation.
Not so clever. I guess i should ask first.

Thanks again.
Shrek

 

[GuzziMoto]

Cutting springs to make them stiffer does work. But it is not something I would do unless I could not buy the correct springs of the correct rate. I would rather buy straight rate springs of the correct weight and go with them. Cutting springs is usually either something you do because they don't make the desired spring or you are too poor to afford them. I have been in both situations.

As to the way a progressive spring compresses... Yes, the whole spring compresses as one (it is, after all, one spring). Since the thickness of the spring wire determines its rate, along with the length of the wire, and the entire spring wire is the same thickness, the entire spring should compress at the same rate. When the coils that are closer together to begin with coil bind they can't compress anymore and the rest of the now shorter spring continues to compress. As the effective length is now shorter the effective spring rate is now higher.

A basic measurement for spring rate is to measure sag. Comparing the three different sag measurements should tell you how you are doing with the rate of your springs and whether you need stiffer, softer, or you are already on the money.

One last concept to through into the mix. Adding preload to a spring does not make the spring stiffer. Removing preload does not make a spring softer. Adjusting preload changes the ride height, not how hard or soft the spring actually is.
Preload does have an effect on progressive springs, it can't actually make the spring stiffer or softer but it can effect what part of the rate curve you are using.