Okay, I'm wanting to move my lower shock mounts closer to the pivot bolt. Will this increase or decrease the load on my shocks?

The way I understand things, having the shocks at an angle (as opposed to perpiindicular to the swingarm) increases the load. Also, the wheel axle being located outside outside the lower mount increases the load on the shock.

Moving the lower shock mount two inches in would give the axle two more inches of leverage on the shock. However, moving the shock closer to perpindicular to the swingarm should decrease the leverage on the shock.

Is that right or am I misinterpreting things?

moving closer to the pivot means the lever puts more pressure on whatever you've moved, ya

when you make the shock (or whatever) more perpendicular to the ground (or more radial to the movement of the lever) ya, it decreases the pressure put on the shock.

the whole linear movement vs radial thing confuzzles me sometimes.

then add a worm + worm gear and we get into really fun stuff

oh well, i made it, it worked, i try to leave work at work

Is there an equation that can be used to figure out the ratios?  I would like the end result to be less stress on the shock.

Ask in here Mak.......
http://www.eng-tips.com/threadminder.cfm?pid=800

or here......
http://www.eng-tips.com/threadminder.cfm?pid=668

Just dont encourage them too much and ask them to keep it simple 

It's Newt's 2nd Law for rotational motion about a fixed axis! 
Net torque = moment of inertia x angular acceleration    (Where MoI = massXradius^2)

(Same as F=ma for a rigid body, except that the rigid body is rotating)

Now, I can't picture in my head these "lower shock mounts" that you're talking about.  If you can draw it, I can give you numbers on it, using just arbitrary numbers for the mass of the bike and the force of the shock on the swingarm - but, it's good enough for comparison. 
But, if you're talking about moving the shock more perpendicular to the swingarm, then:
  Ohgood, it's easy, just think about force applied through the moment of inertia (the MoI being an imaginary line through the shock) to the lever arm (the swing arm) which rotates around a single point of mass but not dimension (the frame-swingarm pivot joint).  The force of the shock (assuming no acceleration and no friction) will always give greater torque to the pivot point at 90 degrees than at, say, 30 or 120. 
It's like if you push a heavy door with your arm at 90 degrees, or if you push it with your arm at 30 degrees to the door.  Same force, but less torque applied through the door to the spring at the hinge.  So, it's harder to open. 
So, closer to perpendicular to the swingarm = more force applied to and coming from the shock.


However!  When the shock is pushing the swingarm, it's applying torque to the swingarm joint. 
When the swingarm is pushing the shock... it's applying torque to the shock. 
More torque one way = more torque in the opposite direction also. 
The swingarm can take it, but the shock might not. 


Plus, it's a matter of ROM (range of motion). 
When the bike is sitting on the sidestand, the shock isn't perpendicular.  But, check the angle when the shock is depressed.  How close is it to perpendicular? 
I'm not familiar with the bike's set-up, but the angle should get closer to perpendicular as the tire travel increases.  It effectively increases dampening torque, while the force applied through the shock stays the same. 

I wouldn't mess around with those angles and distances.  Just a slight delta theta can equal big, big changes in force output. 

Sorry, not force output.  Angle changes equal TORQUE changes.  Oops. 

If you want it explained:
Torque (how hard something is twisted) = [the mass of the thing doing the twisting (your hand, not the screwdriver) x how far your hand is from the center of the screwdriver] squared x how fast you accelerate your hand around it

Or:
Torque  = F x l
Torque = magnitude of the force times length of the lever arm.  (If you keep the angle of the force the same.)

Think of an imaginary line going through the shock, toward and through the swingarm, for infinity.  That's the "line of action".  Now, think of a line coming from the swingarm-frame joint and connecting to the "line of action" at 90 degrees, that's the lever arm.
See?  If you change the angle of the shock to the swingarm, the lever arm length changes. 
The closer you get to 90 degrees, the longer the lever arm.  The longer the lever arm, the higher the torque.  The higher the torque, the more work done by the force of the shock. 

(In physics, only done work if you've actually moved something.  Push all you want against a wall, but you've only done work if it actually moved.
Force of the shock stays the same, only the work and torque change.)


Hope that helps!



Granted, I haven't got a clue how the shock attaches to the swing arm.  I was drunk when I put mine back together.
But, if you take a good picture, and measure it for me, I can give you some numbers on it. 
If it was good enough for Cummins when I redesigned the water pump jacket on their 4-cylinder, then it's good enough for your bike. 

haha thanks I'll have to read all that here in a bit...lol...here's a pic, though...kinda...

Oh, I see.  I pictured it backwards.  I thought you were talking about angling the shock AWAY from the swingarm-frame joint. 
Either way, same answer.  The closer to perpendicular that the shock would be - the more efficient use of it's force. 
This is disregarding those those "dogbones". 
If they work in unison with the swingarm, it's a little different.  Same concept, just Newt's 2nd Law.  But, different torque distribution. 

Just think of it like pushing a door.  The swingarm is the door, your arm is the shock, and the door hinge is the swingarm-frame joint.  The wheel is over by the doorknob (no frame).  There's somebody on the other side, trying to push it open towards you.  You, being the shock, have to push it back, keeping it closed.  (For the sake of example, the guy on the other side always pushes with the same force.) (Guy on the other side is the weight of the bike.)

If you push 90 degrees to the door, it's easy.  If you stand at 30 degrees to the door, and push, it's much harder to keep him out.  And, the closer you are to the door hinge, the harder.  That's all. 
That's how torque works.  To get more torque, you can push harder, get a better angle (more perpendicular), or more away from the point of axis. 
Only, the shock can't use more force, according to my understanding of these shocks (very limited  ). 


Don't think in terms of "load".  Think in terms of force, it's much simpler.  Imagine the frame and the pivot as always staying in the same place, while the swingarm moves up as a bump "forces" the tire up and the shock "forcing" the swingarm back down. 

Looking now at a picture of the shock set-up, you'd have to move the top of the shock toward the rear of the bike.  The bottom would need to stay where it is, with the linkages being the way they are. 
It'd raise the rear of the bike a pretty fair amount, maybe up to about 3 inches.  And, you'd need the new bracketry to be STRONG.  Stronger than what's on there now.  The ride would be harsher, so you'd have to lower the shock setting. 

Not a very efficient use of your time, really. 
Not that I would know, as much time as I waste on this board.   

Here's what I'm working with:

http://www.kaleesphotography.com/photoartclub/Shocksproject/shocksproject.html

I'm entertaining ideas for stiffening the shock.  I'm looking into other things...primarily other spring options...but, in the end, I'll be using a different swingarm and may want to make some adjustments anyway.

Also keep in mind when you change the angle of the shock closer to parallel you not only get more leverage, ie a softer suspension, you also get a reverse progressive suspension because as the suspension compresses the lever gets closer to the shocks upper mount, ie shock gets even more "laid down". The ideal for a progressive suspension is at maximum compression you have 90 degrees between the shock and lever arm. This doesn't even take into account the differences that the dogbone and pivot introduce since those too create progressiveness not taken into consideration. Without completely measuring the GS's suspension it would be hard to say hoy the rear suspension would behave with a change in the shock angle.

something something something; shock more perpendicular to the link = damper takes on more load from the swingarm as the moment arm distance increases and it is translating a lot of that force into the vertical (y) direction.

give us some numbers and we can calculate the difference for you.

(lengths and applied forces; and if you want spring constant and resistance due to damper)

As stated before doing this will probably raise the rear end of the bike a few inches, but wouldn't that in turn shorten the wheelbase of the bike thus decreasing the rake?
Is it just me or does it seem like a terrible mess involved messing with all the angles and such? I would just trust the suzuki engineers and leave it be.
I would also think that the added leverage of the swingarm on the shock would be greater than the shock's mechanical advantage on the swingarm, but I've no college education in physics... yet.

+1 for trusting the suzuki engineers.  this isn't just a small change in fork oil or springs this is serious geometry your messing with.

The problem with trusting Suzuki engineers is that they never expected you to put an FZR600 swingarm, GS500 wheel, and knock-off piggybacks on a 1981 GS750.  All in the link above.

Quote from: makenzie71 on April 07, 2009, 04:18:05 PM
The problem with trusting Suzuki engineers is that they never expected you to put an FZR600 swingarm, GS500 wheel, and knock-off piggybacks on a 1981 GS750.  All in the link above.

are you just trying to get parts on the cheap, or weren't there some other 80's era shocks made for a similar configuration ?

No shocks for my particular situation.  Parts on the cheap is one way to put it...the swingarm was free and the wheel I have.  The shocks themselves are part of a bigger project explained in the link above.

This is a comment on makenzie's diagram.  Wladziu is absolutely right but I'll try to say this in layman's terms to make it more understandable.  Besides, I haven't been in Physics class for 28 years so most of the terminology and equations have left me, but the basic understandings remain.

The more you move the base of the shock toward the swingarm pivot, the harder the shock will need to work and the harder it will become for the spring to be able to keep the bike from bottoming out.  In other words, the more the shock mount moves away from the rear axle, the more load will be placed on the shock by the lengthening lever.  Keeping the mount near the axle keeps the shock load smaller by keeping that lever short.

In this case, the angle of the shock to the swingarm isn't extreme, not far from perpendicular, so it's not as important as the increased leverage put on the shock as it moves away from the rear axle, creating a lever of increasing length, which gives the weight on the rear wheel more mechanical advantage over the shock, which is bad, unless you're planning on putting in a beefier shock.

Having said that, there is a smoothness of operation factor to consider as well.  Keeping that lever I mentioned short allows the assembly to operate more smoothly than it would if there was a lot of leverage in the equation.  Leverage in a situation like this is best avoided unless needed.  That's why old dual-shock race bikes had long shocks standing up almost vertically right above the rear axle.  That's the ideal way to do it if you can.  A weaker shock with less leverage on it would operate more smoothly than a beefier shock with more leverage applied to it, even if the load carrying advantage of the beefier shock was equal to the increased load placed on it by the increased leverage.  The reason is the swingarm would be under less stress.  We don't know how strong the swingarm is.  Suzuki's engineers do.  Moving the shock mount away from the rear axle could cause the swingarm to flex significantly, bend, or even break, and all those things are BAD.  If it did flex, bend, or break, it would do so right behind the shock mount.

So to answer the question, my answer is moving the mount 2 inches will increase shock load more than the improved angle will reduce it because the angle isn't bad in the first place, and the assembly won't operate as smoothly as you'll be putting more stress on the swingarm, and no one here knows if you can get away with that.  My guess is you can if the shock is beefier than stock, as 2 inches in this example isn't very much, but expect the ride to be somewhat harsher.

I don't suggest moving the shock location without thorough consideration of the loading of the swingarm tube.  It appears to me that the swingarm was designed to accept and transmit the axle loading though the forging welded to the end of the swingarm.  Therefore, the tube is likely not of suitable dimensions to carry the load of the bike in what is essentially a supported at both ends, load at an asymmetrical point beam.

Simply welding a bracket on the tube in the new location will result in a fatigue crack in the heat affected zone of the weld within a fairly short time in service interval.  The crack will likely be circumferential due to a dramatic change in stiffness of the tube and the nature of the varying and reversing loads a suspension system faces. 

The crack will likely be located just aft of the end of the new bracket location, where the tube stiffness changes and the the forces focus on what has now become the fixed end of a fixed one end, load at the other beam section.

Looking at the weldment, I can't see an easy way to accomplish this without dramatically changing the stiffness of the tube, resulting in a fatigue crack or cracks.

Get some heavier springs. 

There's no welds at the end of the swingarm .  This wouldn't be the swingarm in the pic above...that's stock.  The FZR swingarm is boxed steel and will be braced.  It's going to have to have shock mounts welded to it either way because the FZR was a monoshock bike.

However, odds are I'm going to be sticking with a pretty close to stock geometry.  I may bring the shock mounts in just a bit, but it'll be more for the consideration of other parts clearances.  What I'm going to do to accommodate my shock length issue is to build a mount that'll put allow the lower eye of the shock fall approximately 1.5" closer to the upper mount, but on the same line.  When all is said and done, should these shocks be deemed unworthy, I'll simply cut the upper mount down and run my showas aout where they're supposed to be.