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Discussion Starter #21
......ok

Don't go under...
50mm=1.96"
1.2mm=0.047"

May not need to go over
75mm=2.95"
2.0mm=0.078"

The thicknesses sound about right... I almost always use 16g tubing which is 065. occasionaly 18g tubing for subframes or bracing which is 049.

084 is 14g, 095 is 13g. Like Teazer said those typically are not in the realm of sport chassis building.


Harley's maybe...

but whatever, nobody comes here to listen anyway...



I meant comparing a thinner walled tubing at one larger size diameter.

Okay thanks for clarifying, i didn’t understand, i haven’t run the tests with thinner walled tubing yet.

I will run it with the .065 wall and see what it looks like.
Maybe with the weight savings of using the .065 the frame can be triangulated from the outside of the pivot up to the neck. Although this probably won’t be necessary.
Thanks for the advice.
 

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1400ft/lbs really isn't that much, I simulated frame designs using a solid rod extending to the contact patch and put 500lbf inline with travel and perpindicular to it, basically as a reference, you shoudn't in my opinion, see anything close to your safety factor anywhere on the frame with those loads, if you do, I would redesign. while it's unlikely a bike would experience that kind of loading continuously, you have to realize that those loads can easily by experienced periodically, leading to fatigue and failure
 

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Discussion Starter #23
1400ft/lbs really isn't that much, I simulated frame designs using a solid rod extending to the contact patch and put 500lbf inline with travel and perpindicular to it, basically as a reference, you shoudn't in my opinion, see anything close to your safety factor anywhere on the frame with those loads, if you do, I would redesign. while it's unlikely a bike would experience that kind of loading continuously, you have to realize that those loads can easily by experienced periodically, leading to fatigue and failure
Likewise i loaded 750lbs on the front axle and the frame displaced the axle by a whole 42mm
That means the spin twisted 3.6 degrees
I think once the engine is bolted in, it will help strengthen this dimension.
Other than that, the lateral flexing 12mm is easy to correct with a minimum of triangulation from the exterior of the pivots to the neck.
 

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none of those foale basckbone frames use the engine as a stressed member
the engine is basic aly just hanging and gives zero added structural ridgidity
 

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ii seel this myth often,in forum discussions,that the rear shock loading is going to the stearing head
with the mono shock pointed at the seerring head
complete horseshit
the loading that the shock/spring impasrts to the frame is all going into the swinger pivot
 

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Discussion Starter #26
ii seel this myth often,in forum discussions,that the rear shock loading is going to the stearing head
with the mono shock pointed at the seerring head
complete horseshit
the loading that the shock/spring impasrts to the frame is all going into the swinger pivot
That may be true, but you know as well i that every action has an equal and opposite reaction. You can angle the rear shock appropriately so that the upper shock mount and SA pivot are facing equal magnitude forces with opposing directions.
So if the sa pivot is perfectly in line with the backbone, it is purely under tensile stress. The upper shock mount however will need to be placed higher up on the backbone and will be at a steeper angle to the spine.

When you try to bend a pipe, do you push on it end to end to compress it until it bows out?
No, you push at 90 degrees to it. Well here i want to minimize the flexing, so the forces must be directed along the spine.

The goal is to align the forces along the spine as best as possible because would be a purely compression and tensile stress. This is not possible with a standard SA rear suspension as the shock mount of the SA would need to be as close as possible to the pivot, so compromises must be made.

I never claimed i was aiming the forces from the rear to the steering head, i said i wanted to have them aimed as close to parallel with the spine as possible to minimize the strain of the spine.
 

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Discussion Starter #27
none of those foale basckbone frames use the engine as a stressed member
the engine is basic aly just hanging and gives zero added structural ridgidity
I had assumed as much, which is why they were not included in the simulations.
 

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I had assumed as much, which is why they were not included in the simulations.
I don't buy that, the rear mounts connect to the pivot, and the front mounts connect to the neck. I'll give you that they probably don't add a lot, but I'd be damned if they don't add something - even in a cradle frame the engine adds some rigidity.
 

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Discussion Starter #29
I don't buy that, the rear mounts connect to the pivot, and the front mounts connect to the neck. I'll give you that they probably don't add a lot, but I'd be damned if they don't add something - even in a cradle frame the engine adds some rigidity.
In the original frame designs the front mounts were just bolted to the spine.

It will do little to reduce the torsional strain as they are mounted so close to the axis of rotation in comparison to the length of the forks. I would rather not rely on it for rigidity, but if it adds any that will be a bonus.

For the lateral strain it may help, but the mount on the engine is about 18” below the spine. That means i am asking the front motor mount and the down tubes to resist a significant amount of torsional stress.

It might help the longitudinal strain, but even in that case the spine only bowed by 1.3mm so it’s not really a concern.

The best bet would be some additional triangulation from SA to neck
 

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I don't buy that, the rear mounts connect to the pivot, and the front mounts connect to the neck. I'll give you that they probably don't add a lot, but I'd be damned if they don't add something - even in a cradle frame the engine adds some rigidity.
the weight of the front of the engine is hanging from a non structural flexing mount
the rear of the engine indeed it can add to thAt areras strength so me say zero was wrong
i am only joining in here to ad what i fead in foales book ,but its obvious to a designers eye what is happening or not
in his book he states the front tubes support the weight of the engine
and no more mention of it and he certainly would mention if it did contruibute
in oreder for them to add structural and tuie the engine into that kit needs to be aan actual structutral type of design ,needing substancial triangullation and a substational mount up at the neck
thats all i like the frames
 

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That may be true, but you know as well i that every action has an equal and opposite reaction. You can angle the rear shock appropriately so that the upper shock mount and SA pivot are facing equal magnitude forces with opposing directions.
So if the sa pivot is perfectly in line with the backbone, it is purely under tensile stress. The upper shock mount however will need to be placed higher up on the backbone and will be at a steeper angle to the spine.

When you try to bend a pipe, do you push on it end to end to compress it until it bows out?
No, you push at 90 degrees to it. Well here i want to minimize the flexing, so the forces must be directed along the spine.

The goal is to align the forces along the spine as best as possible because would be a purely compression and tensile stress. This is not possible with a standard SA rear suspension as the shock mount of the SA would need to be as close as possible to the pivot, so compromises must be made.

I never claimed i was aiming the forces from the rear to the steering head, i said i wanted to have them aimed as close to parallel with the spine as possible to minimize the strain of the spine.
you could never bend that pipe you speak of the top shock mount is not pushing beyond the mount with any significant force
you need to educate yourself the forces are strictly into the pivot
you are not grasping the concept
iyou have some weight transfer but not the huge leverage multiplied forces of suspension
 

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for example lets take a 1981 yz465 the top shock mount way up by the steer tube
if your horseshit theory was correct then any time the mx racer was ion the throttle hard ,front wheel not touching dirt much just skimming
while attacking nasty whooped out bumps ,the goddam bumps ,each one that deeply activates rear suspension,would make the front end drop
this iis not the case in fact the rider would feel it if so and that would have been a reason to never put tilkens design into production at all 1980 yz 465.jpg
 

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Discussion Starter #33
you could never bend that pipe you speak of the top shock mount is not pushing beyond the mount with any significant force
you need to educate yourself the forces are strictly into the pivot
you are not grasping the concept
iyou have some weight transfer but not the huge leverage multiplied forces of suspension
I must be missing something.

Do you agree that when the frame a load such that the rear tire is under 450lbs of load, if the SA is a cantilever with a 2:1 length ratio, the rear shock is under 900lbs of load?

Well what is the direction vector of that load? It points straight along the shock body, from sa mount to frame mount. So if this vector point perpendicular to the spine, there will be more bending force on spine from this than if it was pointing parallel to the spine.

What point of this stick has the greatest load?


This is the same situation as if the top hand is the sa pivot, inline with the neck.
The shock pushes into the spine as opposed to pushing along it.

The reason you want the pivot inline is that you also have the chain pull and other forces to worry about. So yes the pivot is the most important part, but the angle the shock is mounted at is also important to consider.
 

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Discussion Starter #34
for example lets take a 1981 yz465 the top shock mount way up by the steer tube
if your horseshit theory was correct then any time the mx racer was ion the throttle hard ,front wheel not touching dirt much just skimming
while attacking nasty whooped out bumps ,the goddam bumps ,each one that deeply activates rear suspension,would make the front end drop
this iis not the case in fact the rider would feel it if so and that would have been a reason to never put tilkens design into production at all View attachment 87385

Look at the angle of that shock though
It runs parallel to the imaginary line between the neck and pivot.
 

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you could never bend that pipe you speak of the top shock mount is not pushing beyond the mount with any significant force
you need to educate yourself the forces are strictly into the pivot
you are not grasping the concept
iyou have some weight transfer but not the huge leverage multiplied forces of suspension
the load goes into the pivot on a more verticasl shock as well
the fulcrum is bottom shock mount and it is levraging the swinger pivot point in a direction opposite of shock
iot is tryingn to rip then frame apart between top shock mount and swinger pivot
on a more verticasl shock ther load is downward at pivot
the stlyle like foale and yamaha used is basuicallyrotated close to 90 degrees for the other style
hence the load at swinger pivot more rearwards
that i describe above IS for every action there is a reaction
 

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for example lets take a 1981 yz465 the top shock mount way up by the steer tube
if your horseshit theory was correct then any time the mx racer was ion the throttle hard ,front wheel not touching dirt much just skimming
while attacking nasty whooped out bumps ,the goddam bumps ,each one that deeply activates rear suspension,would make the front end drop
this iis not the case in fact the rider would feel it if so and that would have been a reason to never put tilkens design into production at all View attachment 87385
Hang on a minute. If a force is applied to the rear wheel on a bump, it will tend to push the front wheel down even though most/much of the force is dissipated in the shock. If the shock upper mount is free to move as when the front wheel is in the air, it must move. Yes? There are all sorts of other factors at play including inertia, but it must move.
 

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Discussion Starter #38
“on a more verticasl shock ther load is downward at pivot”
Yes, and depending on the geometry, a 2:1 leverage ratio of wheel to shock travel means the pivot sees the same (but opposite) force as the wheel does.

“the stlyle like foale and yamaha used is basuicallyrotated close to 90 degrees for the other style”

Kind of, except that with the same 2:1 ratio the rear pivot sees 2.25x the force on the rear wheel.
Say you have force F pushing up the wheel,
You have then 2F at the shock.
The resulting force vector has a magnitude such that F(pivot)^2=2F^2+F^2
So F(pivot)^2= 5F
F(pivot)=2.25


“the fulcrum is bottom shock mount and it is levraging the swinger pivot point in a direction opposite of shock”

Yes and no. It depends on the angle of the shock. You can angle the shock downwards towards the front wheel, depending on the leverage ratio of the SA (2:1 means 30* off horizontal) you can balance out the vertical load of the sa pivot so that the load is straight back. This is not practical however as you transfer that load to the spine in a direction so the frame is under the same stresses. In your statement you seem to be implying that the fulcrum of a lever sees no forces, this is incorrect. If the pivot is under load, this load must have an equal and opposite load somewhere else on the SA. Part of it is transmitted by the wheel, but the rest comes through the shock. But what holds the shock? The frame. Thus the magnitude of the load on the SA pivot is geometricly related to the load on the frames rear shock mount.
 

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Discussion Starter #39
Hang on a minute. If a force is applied to the rear wheel on a bump, it will tend to push the front wheel down even though most/much of the force is dissipated in the shock. If the shock upper mount is free to move as when the front wheel is in the air, it must move. Yes? There are all sorts of other factors at play including inertia, but it must move.
Exactly
I would love to see a rear suspension setup that doesn’t impart a force downwards on the front wheel.
The best way to picture it is to replace the shock with a solid strut and ask yourself “what’s going to happen now?”
 

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Hang on a minute. If a force is applied to the rear wheel on a bump, it will tend to push the front wheel down even though most/much of the force is dissipated in the shock. If the shock upper mount is free to move as when the front wheel is in the air, it must move. Yes? There are all sorts of other factors at play including inertia, but it must move.
We needs a physics teacher and a force vector diagram...


Actually, I think solidworks or autocad's FEA program might be able to calculate how much load in each direction.

Edit- But seriously, there are definitely forces transmitted through the frame.

Remember Honda's unit pro link rear suspension? No? google it. Rossi won on the Honda with it and it finally made it to production on the 600rr in 2010 (?)
 
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