What's happened here?

[melville]

Am I seeing LWB swingarm and SWB subframe, or is there more to it? Looks kinda folded up in the middle. Bike for sale locally, $1800.

[Deleted User 287]

Is that a Duct Tape® brand seat?

[Jean]

How about an ST swingarm/rear end (single side) with some other engine (other than R80ST) fitted into the frame?
I don't SEE a LWB swingarm there.

[melville]

How about an ST swingarm/rear end (single side) with some other engine (other than R80ST) fitted into the frame?
I don't SEE a LWB swingarm there.

No, it's still twinshock:



Being sold as 1972 R75/5. Something's wrong/different back there, but I can't figure out quite what.

[vanzen]

Using a long SA and a short sub-frame
will create a situation, quantified by the specific angle of the shock,
of adding a "progressive" response to the action of the shock.
Maybe a good thing, or maybe not – I haven't done the math.

[Deleted User 287]

Only one way to tell for sure, Mel, go see it.
I suppose it is possible to mount longer shocks and lengthen the lower diagonal sub-frame members.

[twist]

Maybe a good thing, or maybe not – I haven't done the math.

geometry? quantum mechanix? sub frame mechanix?

[vanzen]

Only one way to tell for sure, Mel, go see it.
I suppose it is possible to mount longer shocks and lengthen the lower diagonal sub-frame members.

The rate of action of a shock will be determined by the angle of that shock.
Grossly simplified, a vertical shock's action will be linear.
Beyond that, as the angle of inclination increases, the action becomes more progressive,
but there will be a certain angle where the shock's action then becomes regressive.
Hence, my statement, ' I haven't done the math', as these reactions can easily be calculated
as a function of shock angle, distance from the shock mounting to the SA pivot, and length of the shock.

The situation of a SWB sub-frame and a LWB SA –
Might very well result in a more responsive road suspension.
Or not.

The consideration of 'longer shocks' would be entirely reasonable.
However, the specific length chosen would need to be studied
in order to determine how it will effect ride height, suspension travel, and rake & trail ...
as well as the very real consideration of allowing the tire enough room to enjoy it's full range of suspension travel
without grinding into the fender.

My suspicion is that if a "stock" length shock was used on this LWB SA & SWB sub-frame example –
rake & trail would be (if slightly) increased, reducing "flickability",
as well as defining a new and limited rear suspension travel.

[Deleted User 72]

Seems to me that a shock spring's geometry is neutral (vs progressive) when the length from the SA pivot to the lower shock mount equals the length from the SA pivot to upper shock mount (isosceles triangle.) Moving the upper shock mount laterally either forward or aft changes the geometry to progressive (vs neutral) with the spring rate (due to geometry) decreasing with further compression.

[richard t]

damm! a airhead bobber, I seen a airhead chopper once, but never seen a bobber before now