silverbullet132
Well-known member
On a twin shock application, where is most of the load? Swingarm side or where it bolts at the top?
question on twin shock
- Thread starter silverbullet132
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It will help if you clarify the question. The question that you asked, might not be the question that you intended to ask.
If you are considering static forces being applied to the shock then omnivore has the right answer. The static loads at top and bottom must match (differing only by force of gravity on the shock itself).
If you are considering static forces being applied to the swingarm then normally, given that the shock mounts are normally out near the axle end of the arm, the shock mounts will see higher static loads than the swingarm pivot. Draw a free-body diagram to understand why and by how much.
Dynamic loads are a whole different ball game. Torsional loads applied at the axle end can only be absorbed by the swingarm pivot alone.
If you are considering static forces being applied to the shock then omnivore has the right answer. The static loads at top and bottom must match (differing only by force of gravity on the shock itself).
If you are considering static forces being applied to the swingarm then normally, given that the shock mounts are normally out near the axle end of the arm, the shock mounts will see higher static loads than the swingarm pivot. Draw a free-body diagram to understand why and by how much.
Dynamic loads are a whole different ball game. Torsional loads applied at the axle end can only be absorbed by the swingarm pivot alone.
silverbullet132
Well-known member
Should have clarified, I meant to ask which mount will take more load.
If an adapter plate is made up to go in place of the passenger pegs, of nice thick steel (1/4in?) would a newer gsxr subframe be able to handle the load?
If an adapter plate is made up to go in place of the passenger pegs, of nice thick steel (1/4in?) would a newer gsxr subframe be able to handle the load?
I would say probably not
I think he means:
swingarm side = bottom of shock
where it bolts at the top = top of shock.
I don't think he is asking anything about which end of the swingarm sees more forces, but whether the shock will see more force applied to it where it bolts to the subframe beneath the seat, or where it bolts to the bosses on the swingarm.
swingarm side = bottom of shock
where it bolts at the top = top of shock.
I don't think he is asking anything about which end of the swingarm sees more forces, but whether the shock will see more force applied to it where it bolts to the subframe beneath the seat, or where it bolts to the bosses on the swingarm.
The spring and dampening load is equal at both points.
Here's the real question that should have been asked at the beginning.
Can the passenger peg mounts of a GSXR subframe handle the load of a mounted shock?
Did the GSXR support a shock with the subframe? My uneducated guess is that your support bracket will have to extend from a solid mounting location (likely the rear of the frame) to the top of the shocks. The subframe would just support the seat and hide the support you built.
silverbullet132
Well-known member
Ahh, looks like I'm fk'd. Was going to use a Bandit 1200 swingarm with twin mounts welded on mated to a 06 gsxr 600 subframe.
We are still fishing for the correct question. Only when the correct question is asked is there a hope for the correct answer to be given!
If the question is one of using a dual-rear-shock rear suspension on a GSXR subframe (is it?) then there are a couple things to keep in mind.
Rear suspension designs that use a shock linkage (most modern sport bikes) or which don't have a linkage but have a single shock mounted up near the front of the swingarm, have a substantial mechanical advantage between the movement of the rear wheel and the compression of the shock, typically in the 2.5:1 - 3:1 range. This results in a need for much higher spring and damping rates and very high forces being transmitted through the shock and linkage. Those high forces have an equal and opposite reaction ... a portion of it gets used to push down on the rear axle, but a BIGGER portion of it pushes down on the swingarm pivot. The shock linkage and shock mounts on a bike with a monoshock rear suspension have very high loads imposed on them.
The old twin-shock suspensions have little mechanical advantage between axle travel and shock, and also, the load is split between the two sides. So the forces at the shock pivots (and at the swingarm) are much lower with this design. That's why a lot of the older twin-shock bikes have spindly, thin swingarms by modern standards.
But there is still a need for the suspension to transmit bump impact loads which the GSXR subframe was not designed for. Those peg brackets were designed to have someone standing on them (pushing down) and there is quite a bit of cushioning between bump impact loads and the rider's legs/butt. There is NO cushioning between the shock and its pivot points. Subframes on modern bikes were not designed to handle bump impact loads pushing upwards. That doesn't necessarily mean that they can't handle it, only that they weren't designed for it. Someone would have to do a proper structural analysis. I wouldn't do it without doing at least some structural analysis on it.
Now the related question: why? Presumably that GSXR subframe is attached to a perfectly good GSXR frame and with a perfectly good GSXR swingarm on it. Why retrograde to a dual-shock design?
If the question is one of using a dual-rear-shock rear suspension on a GSXR subframe (is it?) then there are a couple things to keep in mind.
Rear suspension designs that use a shock linkage (most modern sport bikes) or which don't have a linkage but have a single shock mounted up near the front of the swingarm, have a substantial mechanical advantage between the movement of the rear wheel and the compression of the shock, typically in the 2.5:1 - 3:1 range. This results in a need for much higher spring and damping rates and very high forces being transmitted through the shock and linkage. Those high forces have an equal and opposite reaction ... a portion of it gets used to push down on the rear axle, but a BIGGER portion of it pushes down on the swingarm pivot. The shock linkage and shock mounts on a bike with a monoshock rear suspension have very high loads imposed on them.
The old twin-shock suspensions have little mechanical advantage between axle travel and shock, and also, the load is split between the two sides. So the forces at the shock pivots (and at the swingarm) are much lower with this design. That's why a lot of the older twin-shock bikes have spindly, thin swingarms by modern standards.
But there is still a need for the suspension to transmit bump impact loads which the GSXR subframe was not designed for. Those peg brackets were designed to have someone standing on them (pushing down) and there is quite a bit of cushioning between bump impact loads and the rider's legs/butt. There is NO cushioning between the shock and its pivot points. Subframes on modern bikes were not designed to handle bump impact loads pushing upwards. That doesn't necessarily mean that they can't handle it, only that they weren't designed for it. Someone would have to do a proper structural analysis. I wouldn't do it without doing at least some structural analysis on it.
Now the related question: why? Presumably that GSXR subframe is attached to a perfectly good GSXR frame and with a perfectly good GSXR swingarm on it. Why retrograde to a dual-shock design?
silverbullet132
Well-known member
It is going on my 78 GS750 project bike
silverbullet132
Well-known member
Cutting off the current subframe to run the gsxr subframe, nothing wrong with them just want to run the newer subframe.
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silverbullet132
Well-known member
Would love to do that if I could.
At this point it looks likes I am going to end up taking it to speedworx so they can do a proper chassis setup and weld on a monoshock mount.
The early 80's Katana resto-modders often use the Bandit 1200 swingarm with twin shocks...however, it is paramount that you keep the OEM steel subframe. If ou just want the GSXR tail fairing, why not graft just the plastic or fibreglass onto the OEM steel subframe. That way you can achieve the look you want with a subframe that can handle the loads as it was designed with shock support in mind already.
