S&S couplers on a recumbent

[Cletus Lee]

In article <[email protected]>, [email protected] says...
> I have a 2 inch monotube Volae and I've been eyeing the idea of a coupling as well. I'm somewhat
> baffled as to why a monotube frame is off-limits for a coupler. The frame itself is probably
> 0.035 - 0.045 wall thickness. It should be easy to make a coupling that is stronger than the
> frame. I imagine that some attention should be paid to ensuring that there aren't stress
> concentrations at the joint between the coupling and the tubing. I have a 30+ year old Raleigh 20
> folder that is a monotube folder. It's heavy, of course, but it is a monotube.

I will bet that your 30+ Raleigh folder doees not use S&S Couplers. The problem as I see it is in
the strength of the join between the Stainless Steel Coupler and the tube itself. It does not appear
that the coupler is welded to the frame tube. The Coupler itself is very strong. It amounts to
little more than a fancy pipe union that you might find in the plumbing department of your local
hardware store. With a Monotube two things become critical. One, vertical aligmment of the two must
be exact. You can easily see that it would be possible to align the two wheels 90 degrees with
respect to each other. This would represent an extreme case but clearly you can see the potential
for problems. Second, Without a doubt, the joint will hold under any reasonable loade and stress
placed upon it. However, the area where the S&S Joint connects to the frame tube would over time and
torsional loads be subject to failure. You do not want to be riding down the road at 20 mph, hit a
bump and have oyur bike fall apart.

IIRC, a year or so back, Vision had a recall on their Double Vision because of a BB weld failure.
This is the kind of failure that S&S does not want to risk.

Now, I don't think a Monotube is off-limits to a coupler, just couplers of the S&S type. In fact, I
think the Teardrop shape of the Bacchetta affords an opportunity to overcome the torsional stresses
and maintain its rigidity with a sleeve type of joint.

--

Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
- Bellaire, TX USA -

 

[John Riley]

Cletus Lee <[email protected]> wrote in message news:<[email protected]>...
> In article <[email protected]>, [email protected] says...
> > I have a 2 inch monotube Volae and I've been eyeing the idea of a coupling as well. I'm
> > somewhat baffled as to why a monotube frame is off-limits for a coupler.

Apparently there is a possibilty they will work themselves loose in a monotube.

John Riley

 

[Tom Sherman]

Cletus Lee wrote:
>
> I will bet that your 30+ Raleigh folder doees not use S&S Couplers. The problem as I see it is in
> the strength of the join between the Stainless Steel Coupler and the tube itself. It does not
> appear that the coupler is welded to the frame tube. The Coupler itself is very strong. It amounts
> to little more than a fancy pipe union that you might find in the plumbing department of your
> local hardware store. With a Monotube two things become critical. One, vertical aligmment of the
> two must be exact. You can easily see that it would be possible to align the two wheels 90 degrees
> with respect to each other. This would represent an extreme case but clearly you can see the
> potential for problems. Second, Without a doubt, the joint will hold under any reasonable loade
> and stress placed upon it. However, the area where the S&S Joint connects to the frame tube would
> over time and torsional loads be subject to failure. You do not want to be riding down the road at
> 20 mph, hit a bump and have oyur bike fall apart.
>
> IIRC, a year or so back, Vision had a recall on their Double Vision because of a BB weld failure.
> This is the kind of failure that S&S does not want to risk.
>
> Now, I don't think a Monotube is off-limits to a coupler, just couplers of the S&S type. In fact,
> I think the Teardrop shape of the Bacchetta affords an opportunity to overcome the torsional
> stresses and maintain its rigidity with a sleeve type of joint.

Here is a picture [1] of a monotube frame bicycle with a de-facto coupler. The frame is joined with
a slotted outer tube and pinch bolts (pretty much standard for SWB adjustable length booms).
Alignment could be a problem since there is no guide pin on the "female" tube to insure proper
alignment (one of my two [2] real complaints about the bike).

[1] <http://www.ihpva.org/incoming/2002/sunset/Sunset001.jpg>
[2] The other is the lack of chain retention devices on the mid-drive step-up jackshaft.

Tom Sherman - Quad Cities