R1100GS fork swap & more or my HPF build

[larryboy]

Originally Posted by Fab418

No engineer either but if it's a pivot doesn't it just transfer that load to the upper mount?

Well maybe an engineer will stumble across this post and sort this out

Or maybe time will tell.

Yup, time will tell.


I do have TIG envy.

[mousitsas]

Originally Posted by larryboy

I'm a little concerned about the strength of what you have going on there. I've done considerably more structurally and I've gotten comments questioning the strength and you haven't done anything to strengthen structurally.

The swingarm/wishbone thing had half the load or so in the original suspension. I can't imagine that the two little struts that the coil bolts to will be enough to keep the front end from just folding over on itself.

Correct! The top frame mount is not designed to carry torsional loads or axial loads other than those of the direction of the suspension movement, all these are taken care of by the A telelever wishbone. It is necessary to use the A mounts too to strengthen it, as well as adding material to the existing four braces (if possible in an X-configuration).
It is dangerous as it is now.

[Fab418]

I've been riding the bike today for a little test drive.

The thing is awesome! Much lighter and stable in the sand. IMO what the GS should've been from the start for someone coming from an offroad background. I'm currently running the .43 stock springs and it soaks stuff like crazy. .52 springs on order so it's more balance and capable.

To Larryboy and mousitsas: You guys both have a point as to be worried about stiffness and the forces implied. Unfortunately, I need some numbers before taking a decision on what is good with the current setup and what needs improvement.

So far my thinking (with the help of a fellow adver) as been toward the forces involved. Mainly, the compression forces (pushing up toward the frame, leaving the rake alone since it's the same and for the sake of simplicity), the braking forces (front to back of the bike) and torsional forces (side impact or when leaning the bike in a turn).

Today I've gone through the compression forces. Here's what I have to say: The important here is to focus on the forces going to the frame and to compare the stock setup vs the new one. In stock config, the force transmitted to the upper shock mount is roughly 156% of the force coming from the fork tubes thanks to the lever effect you get when positioning the shock behind the forks. In the new setup, the force are going straight through the fork tube so it's 100% transferred to the frame. On the stock setup, the upper shock mount is position 16% closer to the pivot point or fulcrum(lower front frame mount) than with the new setup (the top of the triple tree is now the leverage point). so, simply put, there is about 40% less upward force with the new setup.

The other 2 forces (braking and torsional) are more problematic and need some more measurements to be able to compare stock vs new. More on that later but it's going somewhere.

Did I mentioned I'm stocked on riding this thing? Braaaap!

More to come.

[larryboy]

Originally Posted by Fab418

I've been riding the bike today for a little test drive.

The thing is awesome! Much lighter and stable in the sand. IMO what the GS should've been from the start for someone coming from an offroad background. I'm currently running the .43 stock springs and it soaks stuff like crazy. .52 springs on order so it's more balance and capable.

To Larryboy and mousitsas: You guys both have a point as to be worried about stiffness and the forces implied. Unfortunately, I need some numbers before taking a decision on what is good with the current setup and what needs improvement.

Awesome!!!

I'm putting .49 springs in for my conversion, gonna have to be close enough for now.

Go over to my thread for a look on what I've done to mine. I weld and wrench for a living, have built a tube chassis rock crawler and have been welding/fabbing for 25 years. I'm doing what there is room for and what I feel comfortable with from a safety viewpoint...probably overbuilt.

[mousitsas]

Originally Posted by Fab418

Today I've gone through the compression forces. Here's what I have to say: The important here is to focus on the forces going to the frame and to compare the stock setup vs the new one. In stock config, the force transmitted to the upper shock mount is roughly 156% of the force coming from the fork tubes thanks to the lever effect you get when positioning the shock behind the forks. In the new setup, the force are going straight through the fork tube so it's 100% transferred to the frame. On the stock setup, the upper shock mount is position 16% closer to the pivot point or fulcrum(lower front frame mount) than with the new setup (the top of the triple tree is now the leverage point). so, simply put, there is about 40% less upward force with the new setup.

I think your reasoning is flawed. The compression forces to the 4 mounting points of the subframe to the engine case are the same (more or less) in both cases. In the original setup you have a greater force acting with a lower leverage whereas in the second the force is less but the leverage is greater. [What I forgot to mention in the beginning of my sentence, is that you have to think in terms of torque rather than absolute force]. However, in the second case this torque produced by the fork springs and valving is applied in a way that will tend to compress the two rear legs of the subframe and extend the forward ones. But even so, I believe the main issue has to do with the lateral and torsional forces which cause torque reactions the subframe has no way of dealing with. Look closely the Baker approach and you will see what he deemed necessary doing, and he did so in stainless steel rather than aluminum! Also there is a reason the telelever wishbone is such a sturdy piece of metal. I want by no means to cause panic and I do like your built, but please please, in the current state this is a major structural liability!

[Fab418]

Originally Posted by mousitsas

I think your reasoning is flawed. The compression forces to the 4 mounting points of the subframe to the engine case are the same (more or less) in both cases. In the original setup you have a greater force acting with a lower leverage whereas in the second the force is less but the leverage is greater. [What I forgot to mention in the beginning of my sentence, is that you have to think in terms of torque rather than absolute force].

Torque formula: T=RxF where T=torque R=radius from fulcrum to end of lever and F=force. This is a direct relation so if you double the force with the same radius the torque simply doubles. Also, every part is mounts on pivots and can rotate to an extent so torque is not really relevant IMO.

Originally Posted by mousitsas

However, in the second case this torque produced by the fork springs and valving is applied in a way that will tend to compress the two rear legs of the subframe and extend the forward ones.

Absolutely right but since the compression forces are more or less the same, this is a non-issue.

Originally Posted by mousitsas

But even so, I believe the main issue has to do with the lateral and torsional forces which cause torque reactions the subframe has no way of dealing with.

There is actually 2 main issues: the one you mention plus the braking force. Since the fulcrum is moved to the bottom bearing mount the force acting on the frame (now pulling the steel braces and pushing the alu ones) is 2,48 time higher than in the original setup so it have to be looked at too. Edit: it's 1.84 time higher, I was using the bottom bearing as the pivot in the first calculatio but the actual pivot is the bottom mounting point of the alu frame.

The lever relation is the same for torsional forces or torque (which apply here) as the pivot point is the same so are the lever lengths. 2.48 (Edit: 1.84; see above)time more stress on the frame than in the original config. This needs to be addressed too.

Originally Posted by mousitsas

Look closely the Baker approach and you will see what he deemed necessary doing, and he did so in stainless steel rather than aluminum!

My thought on Bakker chosing SS: Tougher looking than full steel and MOSTLY, easier to manufacture than an alu/steel combo and to put in medium scale production. 1 jig and only one material supply, no trouble melting and casting alu with all the high energy costs involved and the multiple steps in the manufacturing process. Ask me, I've been casting aluminium for the last 13 years.

Originally Posted by mousitsas

Also there is a reason the telelever wishbone is such a sturdy piece of metal.

Still, Bakker did not use it (isn't it the point: getting rid of that brick?) and even more strange, it mounts in the same original 4 holes with the original hardware (I presume). This is where my attention is going to now. Making sure that the hardware and the steel mounts can handle the additional loads.

Originally Posted by mousitsas

I want by no means to cause panic and I do like your built, but please please, in the current state this is a major structural liability!

Every comment here is just stirring more thoughts and this will eventually lead to a better/stronger/safer design.

Thanks for the input!

[Whale Rider]

Originally Posted by Fab418

No engineer either but if it's a pivot doesn't it just transfer that load to the upper mount?

Well maybe an engineer will stumble across this post and sort this out

Or maybe time will tell.

Hay Fab Looking Good I agree with you about the way the forces are taken on the front end I see it as all the weight is taken up through the top of the shock absorber but the back and forward forces taken from the front wheel are spread through the telelever wishbone and the the top fork mounts The reason a standard Oilhead doesnt dive under braking Keep the photos coming.
WR

[Deadly99]

[Fab418]

As stated before by many, the week points in this build are the braking and and torque or twisting forces applied to the neck. Those forces ar acting mostly by pulling on the back frame mounts that are made of steel tubing and by twisting these tubes mounting bolts and the aluminium arch.

By boxing the aluminium arch lower than it was originally, I think I do have enough strength there. The force is now acting on the mounting bolts wich are M12. M12 bolts of any grade have great shear resistance, way more than needed to hold a 500lbs bike even when it's hung on the forks.

The back frame mounts are made of steel tubing and are designed IMHO to flex a bit under compression and tension(mainly tension that occurs under braking). But here, we have to deal with higher tension than with the stock configuration. 1.84 times more. To strengthen these tubes, I welded some 1inch pipe to the top and connected the bottom with the old bearing carrier of the telelever.

Cutting the telelever:


The welded arms:


This make the bottom fairly strong. One likely weak point is the upper mounting bolt of these arms. It's an M10 10.9 graded bolt and from what I understand, it would take a ridiculous amount of force to damage it in shear. But still, I will have to watch it closely as I begin testing this setup more and more.

I've also moved the battery holder back a bit to make room for a cross brace for the back tubes if it becomes a necessity. That brace would have to be bolted on one side in order to remove the arms.

I've been riding the bike in tight trails and sand pit a bit before this last mod and I still can't believe how much better it is from stock. Next run is going to be a littler further away and more demanding on the bike to gradually test it.

I also placed 2 orders recently:

Custom 0.65kg/mm forks springs from Sonic Springs. Thanks to Rich who has been really kind and patient in answering all my questions and providing genuine help! BTW, ktm's 950R used .62s according to racetech's spring selector so this should provide a really decent setup.

I also ordered a super motard rotor and caliper braket from EBC to stop this thing. It can go really fast in the woods now :

That's it for now. Waiting for parts and then some testing and hopefully some action pics or video.

[MotoKaw]

Originally Posted by Fab418

*** That's it for now. Waiting for parts and then some testing and hopefully some action pics or video.

Fabrice,

Nice work and thanks for sharing your project. I've been following your progress closely as I gather parts to start one of my own. I'll be really eager to hear more about how it performs compared to stock. A video would be nice too!

Bob

PS: My lazy mockup. The victim/donor bike was a '99 R1100RT:

[larryboy]

Fab, that looks much, much better. Nice work!!!

[Fab418]

Originally Posted by larryboy

Fab, that looks much, much better. Nice work!!!

Thanks man. It's ridding great too. Can't wait to get the stiff springs. Did you ride your bike yet?

[larryboy]

Originally Posted by Fab418

Did you ride your bike yet?

Not yet, one more week of work on it, should be riding by Sunday.

[Fab418]

Here's a teaser:

[Deadly99]

Cant help noticing the 800 couldnt keep up to you....