Concept for suspension hoop

[Bitza]

OK probably not something I'm about to make but have been thinking about. A lightweight version of the suspension hoop as per early Monsters, 851/888s, to be used in conjunction with the Corsa rocker with height adjustment.
The standard rod end adjusters are to be replaced with fixed mounts for spherical bearings, and the bearing for the hoop/rocker pivot is set into the hoop.
I would also consider having bobbins fixed between the plates for stiffness. Components could be bolted together or welded.
While I was initially thinking of using aluminum, the possibility of carbon fiber does seem to be a possibility?
It's just for fun all comments welcome.

 

[Nickj]

The idea is a construction of composite pieces or some kind of one piece forged CF ?

 

[Mr Gazza]

This gave me some brain food. Very good prototyping BTW, a man after my own heart.

The hoop is pretty much in compression all the time unless you are given to aviate at any time!
I think it would take a lot of attention to the bonding if it were to be made in carbon, particularly the joint of the top bearing to the hoop.
My hoop is different to yours as it has two ears either side of the (standard) rocker.

I'd prefer an Ally construction only because I think welding would be stronger.
I'd like to see a web between the hoop flanges, to make it into an "I" beam, which would add huge strength and maybe make it possible to reduce the width of the "flanges". Maybe machine the hoop from solid to create the "I" beam and eliminate any possible weld failure, but weld the ends on for ease of manufacture?
Spherical bearings are rather heavy and since you have adjustment at the rocker, I wonder if simple solid bushes would be better, lighter and simpler?

 

[utopia]

I've looked (albeit rather casually) at alternative hoop designs (both the available aftermarket ones and also imagined redesigns) in the past and I have always arrived fairly rapidly at the conclusion that the original design takes some beating.
Alloy alternatives on the market always look rather complicated in form compared to the simple elegance of the plain steel tubing of the original and provide unnecessary dirt traps (and a heavy visual appearance) without contributing to a significant weight reduction.
Personally I wouldn't trust a carbon fibre design in such a failure-critical area, particularly a homespun design which had not undergone stress analysis or significant testing. Aluminium alloy would at least tend to fail gradually if overstressed whereas carbon fibre tends to fail suddenly/totally. I would also be dubious of using adhesives in such an application unless their use was under closely controlled assembly conditions and again only after extensive analysis and testing.
I would stick with spherical bearings of some sort because they soak up any out-of-parallel alignment between the rocker mount and the swingarm mounts. There must be fairly big scope for accumulative errors in manufacture here when you consider the tolerances in frame manufacture, engine installation, crankcase machining, swingarm construction etc and there needs to be no play in the linkage to compensate for these otherwise suspension action is compromised.

 

[Mr Gazza]

With you on the original design Jeff. I think an ally tube version would be perfectly fine, maybe with a very slightly beefier gusset?
There's a good pattern for sure and it's been proven over many miles and bikes.

I still think it would be worth persevering to eliminate the spherical bearings even though it might require a bit more measuring.
One way to check the present alignments might be to fit the hoop on the bike with some old rod ends and then super glue the balls in place in the ends.
If carefully removed everything should be as it sits on the bike. Rods checked for straightness could then be passed through both rod ends, if it will go through both? If not at least you now know which way each ball is pointing.
Then pass another suitable straight rod through the top bearing and check that rod is on the same plane as the lower one which hopefully is going through both bottom eyes.
That could turn into an exercise in massaging the swinging arm mounts to get everything aligned, or serve as a pattern to ream the proposed solid bushes to match.
The revised bottom ends would consist of a pair of hardened steel top hats pinched into the mounts with a Ti bolt, running in a phosphor bronze or oillite bush seized into the hoop, complete with grease nipple of course.

 

[Dukedesmo]

OK probably not something I'm about to make but have been thinking about. A lightweight version of the suspension hoop as per early Monsters, 851/888s, to be used in conjunction with the Corsa rocker with height adjustment.
The standard rod end adjusters are to be replaced with fixed mounts for spherical bearings, and the bearing for the hoop/rocker pivot is set into the hoop.
I would also consider having bobbins fixed between the plates for stiffness. Components could be bolted together or welded.
While I was initially thinking of using aluminum, the possibility of carbon fiber does seem to be a possibility?
It's just for fun all comments welcome. View attachment 201View attachment 202View attachment 203

Suspension maybe a bit 'wooden' (sorry)

Reminds me of;

 

[Nickj]

I have a vague memory of there being a bike that had a ply main spar frame, not at all sure what the motor was? called redshift or something like that?

 

[Bitza]

Have to agree that the original hoop is hard to improve upon, having said that the two rose joints do weigh alot. (Total weight say 630gms minus rose joints 500). I'm thinking that spherical bearings are a good idea to allow for the swinging arm flexing.
Bearing in mind that the forces are primarily in compression, my idea is to have the bearing carriers pushing on the two plates that in turn push onto the hoop/rocker pivot. In this way any fasteners are basically simply functioning to hold the pieces together, rather than to transfer force. This principle would I'm thinking be particularly handy in the CF version, where I was planning a kevlar sandwich with the two plates for added stiffness. Finally have to say I would be very cautious about actually fitting a self made CF version, more of a mental exercise.
Re the wooden bike.......... why?

 

[Nickj]

For the one I remember I think it was someone proving a point and also not wanting to spend out on a one off alloy casting. At the time the alloy spar frames were very rigid = handled badly as the Japanese engineers hadn't quite got the hang of the construction, the ply had enough flex to give better handling and there wasn't a huge mass difference as I remember.

 

[Bitza]

Ahh I assume you're (Nick) talking wooden bikes?