New Cervelo Model

This is the new Cervelo model :

http://www.cyclingnews.com/photos/20...=live/DSC02027

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

-Amit

What about braking force? I guess that works out to a tension on the
stays?

In article . com, Mike
Reed wrote:

What about braking force? I guess that works out to a tension on the
stays?


If the seatstays are truly superfluous, why doesn't Cervelo mount the
rear brake on the seattube and rid itself of the vestiges?

Luke

In article ,
Luke wrote:

In article . com, Mike
Reed wrote:

What about braking force? I guess that works out to a tension on the
stays?


If the seatstays are truly superfluous, why doesn't Cervelo mount the
rear brake on the seattube and rid itself of the vestiges?

Luke

That is a question best directed to the UCI. In short: the rules require
a diamond-frame bicycle (with a bunch of dimensional restrictions that
are too boring to explain). The seat stays are required for that reason.

--
Ryan Cousineau http://www.wiredcola.com/
"I don't want kids who are thinking about going into mathematics
to think that they have to take drugs to succeed." -Paul Erdos

wrote:
This is the new Cervelo model :

http://www.cyclingnews.com/photos/20...=live/DSC02027

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

-Amit

I had a conversation w/ a local yet prominent framebuilder in CO,
regarding the use of carbon stays on otherwise non-carbon bikes. He
said that the reason no one expressed concerns over the potential for
bad glue jobs is that there's almost no stress on the seatstays and
therefore the junction doesn't have to be that strong.

It should follow that w/ sufficiently strong chainstays, the seatstays
are even less necessary if not completely superfluous.

In article
.com,
wrote:

This is the new Cervelo model :

http://www.cyclingnews.com/photos/20...=live/DSC02027

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

Where have you heard this?

Consider an axis through the rear axle, directed fore-aft,
and parallel to the ground. Torque at the axle about this
axis is normally resisted by seat stays. Remove the seat
stays and that torque must be resisted by the joint at the
chain stays and the bottom bracket.

More generally, the two chain stays, two seat stays, seat
tube, and rear axle form a tetrahedron. In a tetrahedron
with rigid members the joints could be pinned without
compromising the strength of the structure, making the
tetrahedron an efficient spacial structure. Analogously,
a triangle of rigid members can be pinned at the joints
and yet be very strong in its plane. Contrast this with a
pinned square; it will flop around when subject to stress.

In the real world the rigid members actually flex;
therefore the joints must be built to resist this flex. So
we put a bridge between the chain stays near the bottom
bracket, and a bridge between the seat stays near the seat
tube.

--
Michael Press

In article ,
Michael Press wrote:

In article
.com,
wrote:

This is the new Cervelo model :


http://www.cyclingnews.com/photos/20...hp?id=live/DSC
02027

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

Where have you heard this?

Consider an axis through the rear axle, directed fore-aft,
and parallel to the ground. Torque at the axle about this
axis is normally resisted by seat stays. Remove the seat
stays and that torque must be resisted by the joint at the
chain stays and the bottom bracket.

More generally, the two chain stays, two seat stays, seat
tube, and rear axle form a tetrahedron. In a tetrahedron
with rigid members the joints could be pinned without
compromising the strength of the structure, making the
tetrahedron an efficient spacial structure. Analogously,
a triangle of rigid members can be pinned at the joints
and yet be very strong in its plane. Contrast this with a
pinned square; it will flop around when subject to stress.

In the real world the rigid members actually flex;
therefore the joints must be built to resist this flex. So
we put a bridge between the chain stays near the bottom
bracket, and a bridge between the seat stays near the seat
tube.

How do you account for designs such those of Softrides[1]? I'm no
proponent of this approach; chainstays of dimensions equal to those of
motorcycle swingarms strike me as incredibly ugly. Is this a case of
simply over-engineering the chainstays and BB junction to handle the
torsional loads?

I'm unsure from the photo whether Cervelo's design utilizes CF
chainstays; perhaps advances in the application of that material may be
able to provide strength comparable to that Softride achieves with its
gargantuan aluminum stays.

Luke

1.
http://www.softride.com/product.asp?p=13

In article ,
Luke wrote:

In article ,
Michael Press wrote:

In article
.com,
wrote:

This is the new Cervelo model :


http://www.cyclingnews.com/photos/20...hp?id=live/DSC
02027

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

Where have you heard this?

Consider an axis through the rear axle, directed fore-aft,
and parallel to the ground. Torque at the axle about this
axis is normally resisted by seat stays. Remove the seat
stays and that torque must be resisted by the joint at the
chain stays and the bottom bracket.

More generally, the two chain stays, two seat stays, seat
tube, and rear axle form a tetrahedron. In a tetrahedron
with rigid members the joints could be pinned without
compromising the strength of the structure, making the
tetrahedron an efficient spacial structure. Analogously,
a triangle of rigid members can be pinned at the joints
and yet be very strong in its plane. Contrast this with a
pinned square; it will flop around when subject to stress.

In the real world the rigid members actually flex;
therefore the joints must be built to resist this flex. So
we put a bridge between the chain stays near the bottom
bracket, and a bridge between the seat stays near the seat
tube.

How do you account for designs such those of Softrides[1]? I'm no
proponent of this approach; chainstays of dimensions equal to those of
motorcycle swingarms strike me as incredibly ugly. Is this a case of
simply over-engineering the chainstays and BB junction to handle the
torsional loads?

Yes. Without seat stays there can be enough torque to
twist the chain stays sufficiently to induce
`auto-shifting.'

I'm unsure from the photo whether Cervelo's design utilizes CF
chainstays; perhaps advances in the application of that material may be
able to provide strength comparable to that Softride achieves with its
gargantuan aluminum stays.

The seat stays and seat stay joints do not need to be as
strong as the chain stays and chain stay joints. Still,
they must be strong enough to make the structure a
tetrahedron.

The bicycle frame is an elegant design. But there is
always someone to improve it. {:^)

Custom frame builders typically take the approach that a
good musician takes to Mozart: be skilled enough to
implement the design, then get out of the way.

--
Michael Press

In article
. com,
" wrote:

Michael Press wrote:
wrote:

from what I've heard the seatstays contribute very little to the
structure. the chainstays and seatube are strong enough that the bike
would be ridable without seatstays.

Consider an axis through the rear axle, directed fore-aft,
and parallel to the ground. Torque at the axle about this
axis is normally resisted by seat stays. Remove the seat
stays and that torque must be resisted by the joint at the
chain stays and the bottom bracket.

More generally, the two chain stays, two seat stays, seat
tube, and rear axle form a tetrahedron. In a tetrahedron
with rigid members the joints could be pinned without
compromising the strength of the structure, making the
tetrahedron an efficient spacial structure. Analogously,
a triangle of rigid members can be pinned at the joints
and yet be very strong in its plane. Contrast this with a
pinned square; it will flop around when subject to stress.

In the real world the rigid members actually flex;
therefore the joints must be built to resist this flex. So
we put a bridge between the chain stays near the bottom
bracket, and a bridge between the seat stays near the seat
tube.

Amit said that (he heard that) the bike would be rideable without
the seatstays. This is probably true. However, I believe it
would last longer with the seatstays. W/o seatstays, the chainstays
will flex more at the BB joint and fatigue quicker. I'm thinking
of torque about the crank axle that is applied when the bike
goes over a bump - that is what the seatstays resist. Torque
about the axis that runs from rear hub to the BB shell is applied
by pedaling force/chain tension, not by the rear wheel, and causes
torsion in the BB shell, independent of the seatstay arrangement.

Seatstays don't bear a lot of stress and this is why, even on a
classic bike, they can be made of pretty skinny lightweight tubing.

The seatstay and chainstay bridges are not there to resist pedaling
induced flex in the rear triangle.

First of all, for this analysis the model of a rear
triangle is insufficient. We need to consider the space
structure for what it is--a tetrahedron. The various
forces have components in three dimensions.

We have had several reports here of fatigue failure at the
chain stay bridge; enough to suppose that there could be
large stresses at this joint sufficient to require its
inclusion.

Finite element analysis shows that the bottom bracket and
bottom bracket joints are the most critical for reducing
frame flex.

I am puzzled how you think that the stresses here are so
small as to render the chain bridge superfluous. Could a
frame builder chime in here?


They are there to provide a
convenient place to attach fenders. The seatstay bridge is also
a useful place to put a rear caliper brake, and it does help reduce
flex of the stays with a rear cantilever brake. The bridges are
usually made of small diameter tubing that is not very stiff in bending
(much less so than the chainstays) and would not add much to the
stiffness of the rear triangle. Bicycles have been constructed without
seatstay or chainstay bridges, with no ill effects. Other than the
difficulty of attaching fenders (and getting the rear tire stuck
between the chainstays when removing the wheel).

--
Michael Press

Michael Press wrote:

First of all, for this analysis the model of a rear
triangle is insufficient. We need to consider the space
structure for what it is--a tetrahedron. The various
forces have components in three dimensions.

We have had several reports here of fatigue failure at the
chain stay bridge; enough to suppose that there could be
large stresses at this joint sufficient to require its
inclusion.

Finite element analysis shows that the bottom bracket and
bottom bracket joints are the most critical for reducing
frame flex.

I am puzzled how you think that the stresses here are so
small as to render the chain bridge superfluous. Could a
frame builder chime in here?



Possibly the chain stay bridge caused the failure by providing a stress
raiser.


--
Andy Morris

AndyAtJinkasDotFreeserve.Co.UK

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