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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 29 Oct 2013
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raising the rear suspension

Hi Guys I have a 4pt, 99 model. an id like to raise the rear suspension a wee bit,,is their any dog bones out there that would do this,,or are they any bones from a different bike that would fit it... thanks...
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Old 29 Oct 2013
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Info here: http://www.horizonsunlimited.com/hub...spension-60728
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Old 4 Nov 2013
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This piece costed me nearly 1000euro this summer. It broke the top attachement of the suspension and let the gas out. This happent on the way to mongolia.

New rear suspension from wilbers 400euro + express shipment to Ulaanbator 550euro.
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Old 4 Nov 2013
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Quote:
Originally Posted by 2499 View Post
This piece costed me nearly 1000euro this summer. It broke the top attachement of the suspension and let the gas out. This happent on the way to mongolia.

New rear suspension from wilbers 400euro + express shipment to Ulaanbator 550euro.
I quess your top would have broken anyway, cant see that the piece can break of the top of suspension. You mount the suspension same way as it was in the frame, only difference is 2,5cm down.
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Old 4 Nov 2013
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Maybe, maybe not....

There is a lot of force in this connection. The swingarms ratio between the pivoting point , the full lenghs , and the fixation for the suspention is around 1:4
Lets say the rear wheel is under a 150kg load. 200kg bike + driver + lugage, divide between front and backwheel.

This make a 600kg load on the rear spring, 4x150kg. Just standing still without moving...

I dont think anything will break under normal driving, i broke my one driving to fast in kazachstan.
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Old 4 Nov 2013
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Quote:
Originally Posted by 2499 View Post
Maybe, maybe not....

There is a lot of force in this connection. The swingarms ratio between the pivoting point , the full lenghs , and the fixation for the suspention is around 1:4
Lets say the rear wheel is under a 150kg load. 200kg bike + driver + lugage, divide between front and backwheel.

This make a 600kg load on the rear spring, 4x150kg. Just standing still without moving...

I dont think anything will break under normal driving, i broke my one driving to fast in kazachstan.
Did it break in the welding of the top?
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Old 4 Nov 2013
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Mine has stood up to some pretty serious shit. I've taken motocross jumps, ridden shitty roads in Romania and Ukraine with foot-deep holes, and ridden offroad with panniers on.

I replaced the stock shock after over 100.000km. It worked fine, I just got an offer I couldnt resist on a Wilbers.
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Old 4 Nov 2013
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Just to be clear

Quote:
Originally Posted by 2499 View Post

This make a 600kg load on the rear spring, 4x150kg. Just standing still without moving...
Not so: that can't happen in accordance with the priinciples of physics/engineering.
In your example the force acting remains as 150Kg through a lever arm that would generate a bending moment if it were not for the fact that the swinging arm is jointed and unable to resist/generate a bending moment at it's fixing.

I do agree that substantial forces, in motorcycle terms, are generated in a rear shock absorber; for instance impact loading can double a static force (in your example, 150 Kg static could generate a more or less instantaneous, temporary force of up to 300 Kg while hitting the ground after jumping a bike).
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Old 5 Nov 2013
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Hi Dave

This is the calculation i did, i know it over simplified but it is just to give an idea of the static forces involved.

F1=Rearwheel
F2=Damper
Attached Thumbnails
raising the rear suspension-understanding-dynamics-towing-pt2-forces.jpg  

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Old 5 Nov 2013
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the top fixation point didn't break of completely. It just got slightly bended which made a crack in the top of the damper and the gas escaped.
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Old 5 Nov 2013
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Quote:
Originally Posted by 2499 View Post
Hi Dave

This is the calculation i did, i know it over simplified but it is just to give an idea of the static forces involved.

F1=Rearwheel
F2=Damper
Thanks for that graphic 2499!
Now I see what you were saying in your earlier post: I've just measured my XT225 swingarm, not exactly but near enough for this discussion.
The L1 to L2 ratio I have is 510/150 = 3.4 so I agree with you about the increased force acting through the shock; in my case increased by a factor of 3.4 or thereabouts.
For the dynamic forces produced in the shock, these should be much less than the theoretical maximum effect of doubling that I mentioned so long as the shock is doing it's job, but they would be worse than normally occurs if a shock absorber is not working properly.
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Last edited by Walkabout; 5 Nov 2013 at 13:59.
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Old 5 Nov 2013
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I dont get this, where do you add the tire, spring and shock in this?
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Old 5 Nov 2013
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Originally Posted by xtrock View Post
I dont get this, where do you add the tire, spring and shock in this?
It's a force diagram - a graphical representation of the forces acting.
The green triangle represents the fixing point of the swing arm - a pivot point for the black horizontal line which is the swinging arm.
The blue and red force arrows represent the action of the wheel and the shock absorber with respect to the swinging arm; now I look at it again, one of those force arrowheads needs to act in the opposite direction to the other for equilibrium purposes.

Hope that helps.
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Old 5 Nov 2013
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Quote:
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I dont get this, where do you add the tire, spring and shock in this?


Sorry the diagram is for a Australian XT driver (Upside Down)




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