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Just as the woodsman said, that design has no more flexible junctions then the original stock setup, the heim joint connections are only there to make the geometry of the whole thing adjustable. Probably because the creator was faced with the same questions as yourself; what spring, travel and shock absorption rates are required to make it function. The Kinetic kit really isn't a mono-shock conversion, it's a rear shock relocation conversion only if it still utilizes 2 shocks simply mounted higher and forward on the frame. Handling is probably not improved in the least considering the shocks they are using, probably handles like a pogo-stick.
They do say they have a mono kit as well.
 

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Discussion Starter #42
Not sure where or why you think the junctions are flexible. It follows the same basic design that most are using for the modification, simply reinforcing the existing swing arm. It'd be money better spent getting XB33BSA or one of the Brit experts that frequent the site to build you a proper set of shocks for the rear.

You said earlier that you had a plan. So far you have stripped a non running bike, hacked the rear frame off and now are seeking advice on chopping and welding it into a mono shock. How is your back end modification going to affect front end geometry, are you changing forks? Are you sticking with the 18/19 rims, if so it limits tire choice or are they changing. Are you trying to improve the performance of the motorcycle or is this an exercise in what you think looks cool?
Thanks for the input.

If the intention is/was to reinforce the original swing arm, why retain the flexible junction where the original shocks mounted ahead of the rear axle?

Isn't the result at odds with the intention - flexible not strengthened?

I assume this is to allow easy/multi-fit rather than tailored to suit.

Could we agree a stiffer swing arm to be a good thing when converting to mono-shock?

Every intention of retaining 18/19" rims - I'll be back for tyre advice in due course.

Ditto front end, retaining current (rebuilt) forks although I'm not a big fan of gaiters.

Still looking for 500T tank.
 

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Discussion Starter #44 (Edited)
Just as the woodsman said, that design has no more flexible junctions then the original stock setup, the heim joint connections are only there to make the geometry of the whole thing adjustable. Probably because the creator was faced with the same questions as yourself; what spring, travel and shock absorption rates are required to make it function. The Kinetic kit really isn't a mono-shock conversion, it's a rear shock relocation conversion only if it still utilizes 2 shocks simply mounted higher and forward on the frame. Handling is probably not improved in the least considering the shocks they are using, probably handles like a pogo-stick.

One of the key design criteria in a performance monoshock suspension is to locate the shock absorber mounting points as low as possible in the frame. This is why the linkage type monoshock suspensions are superior to the non-linkage type setups. Honda's latest and greatest linkage setup moves the mounting points even lower then their previous setup by eliminating the top frame connection completely:

The swingarm pivot and the lower linkage dog bone carries all of the stress.

Something else to note is that modern performance monoshock spring/damper units are light years more advanced in their construction and design then the original spring holders on your antiquated CB. ... If you can't figure out that Kinetic design, this one will drive you crazy.


Thanks, this reply/info is exactly what I'm after, lovin the banter but much prefer the tech.

Re your comments on Kinetic and as my reply to Woodsman, I can't fathom the flexible mount by the axle particularly as the c/l prop appears welded to the swing arm plate in other photos of their kit. The rest I get.

Any thoughts on appropriate shock, oriented as my earlier sketch and with related compression ratio to suspension movement?

Also I've got to figure the logic of this site. Can I get a chain of linked messages running without the other messages in between?

Sorry last one probably not a question for you.

Thanks
 

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... Any thoughts on appropriate shock, oriented as my earlier sketch and with related compression ratio to suspension movement? ...
To that I would refer you to the now 43 year old Yamaha dirt bike design that started the whole monoshock trend:

Note that the shock body is very long, large and incorporates a nitrogen gas reservoir, the advantage of all that being cooling. Shock absorbers basically quit working once they get hot. The triangulated swingarm design creates leverage because of the shape of the triangle, travel at the axle is increased and travel in the shock body is decreased. This means the spring needs to be more then even double the original spring rate and the same goes for the shock absorbers rebound and compression characteristics, they must increase more then double over the original twin shock design. Also note the effort to redirect the forces towards the steering head instead of the riders spine ;) good idea at the time, but it is now nearly a half century old concept. Present thought on rear suspension is not to redirect the forces towards the steering head as that actually disrupts the bikes handling, now the designs are aimed more towards carrying the centralized mass of the rider and bike instead of pushing all the rear suspension force towards the other end of the bike, hence in a modern monoshock the travel is almost vertical and the entire mass is shifted towards the centre and strongest part of the frame.

Personally if I was going to redesign an old motorcycles suspension, I would pattern it after the present day best, not mimic the concepts that were explored decades previous.
 

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Discussion Starter #50
To that I would refer you to the now 43 year old Yamaha dirt bike design that started the whole monoshock trend:

Note that the shock body is very long, large and incorporates a nitrogen gas reservoir, the advantage of all that being cooling. Shock absorbers basically quit working once they get hot. The triangulated swingarm design creates leverage because of the shape of the triangle, travel at the axle is increased and travel in the shock body is decreased. This means the spring needs to be more then even double the original spring rate and the same goes for the shock absorbers rebound and compression characteristics, they must increase more then double over the original twin shock design. Also note the effort to redirect the forces towards the steering head instead of the riders spine ;) good idea at the time, but it is now nearly a half century old concept. Present thought on rear suspension is not to redirect the forces towards the steering head as that actually disrupts the bikes handling, now the designs are aimed more towards carrying the centralized mass of the rider and bike instead of pushing all the rear suspension force towards the other end of the bike, hence in a modern monoshock the travel is almost vertical and the entire mass is shifted towards the centre and strongest part of the frame.

Personally if I was going to redesign an old motorcycles suspension, I would pattern it after the present day best, not mimic the concepts that were explored decades previous.
Terrific info again many thanks. Looks wonderful.

At the risk of causing offence to others, a solid, triangulated swing arm with no left over 'flexible'/rubber junctions - unlike the Kinetic. IMHO.

I'm clear on the need to uprate the spring in my proposed alignment, just need to figure the new compression rate and related damping.

And find something to match.

I take your point about vertical alignment, need to think on that.

Certainly points to serious reinforcement at the head of the mono-shock.

Many thanks
 

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Discussion Starter #52
LOL.

I'm not goin' anywhere, I'm waiting to be converted to the value of the idea, until the vision is revealed. We'll see where things end.
Excellent.

A couple of photos

1. Broken tach drive/cable retainer - gorilla glue holding

2. Swing arm in process. Committed to rigid triangulation.

The question is am I a day nearer or a day further from collecting $5 from cyclocrossfool?

image.jpeg
image.jpeg
 

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At the risk of causing offence to others, a solid, triangulated swing arm with no left over 'flexible'/rubber junctions - unlike the Kinetic. IMHO.
I think some of the disagreement may be around the use of the word "flexible". I wouldn't consider a joint to be flexible just because it can pivot. Flex in this context implies to me that the material itself will yield. I wouldn't call the joint where the swingarm mounts to be flexible for instance. By design, springs flex and swingarms pivot.

That said, I'd prefer a solid structure over the Kinetic offering too.
 

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Discussion Starter #59
I think some of the disagreement may be around the use of the word "flexible". I wouldn't consider a joint to be flexible just because it can pivot. Flex in this context implies to me that the material itself will yield. I wouldn't call the joint where the swingarm mounts to be flexible for instance. By design, springs flex and swingarms pivot.

That said, I'd prefer a solid structure over the Kinetic offering too.
I'd assumed/hoped as much.

On the basis the original twin shock set up has 4 non-rigid links (2 top and 2 bottom of shocks), and the shocks are inherently 'flexible', are they adding any strength to the swing arm?

Or, does the swing arm rely entirely on its own integrity to resist twisting at the axle?

Thanks
 
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