Brake Question.....

Harry Brogan said:

I would like to try and go from a dual pull hydraulic system to a
single pull system.

Does anyone have any web sites that they know of that would help in
this endeavor?

well, it's not a matter of simple plumbing - the first thing you need to
think about is how to proportion the force between front and rear. it's
completely non-trivial to implement. especially as the c.o.g. on a bike
is variable, unlike a car.

jim beam said:

Harry Brogan said:

I would like to try and go from a dual pull hydraulic system to a
single pull system.

Quoted message said:

Does anyone have any web sites that they know of that would help in
this endeavor?

well, it's not a matter of simple plumbing - the first thing you need to
think about is how to proportion the force between front and rear.  it's
completely non-trivial to implement.  especially as the c.o.g. on a bike
is variable, unlike a car.

Yo, Jim, if only that were true. But even statically a car's cenre of
gravity is only fixed on certain conditions. Its CoG almost always
changed front to rear by filling or emptying the fuel tank. Something
that is often overlooked is that the centre of gravity also has a
lateral component, which can be quite grossly changed by adding a
passenger. That is one reason why a certain class of
pseudo-"production" racing car (now more honestly called a prototype)
once had a driver's seat in the centre of the width of the car, with
the compulsory passenger seat split in two and one half placed to each
side of the driver... Note that a combination of these deviations from
the assumptions under which even the static CoG is calculated can lead
to a diagonal movement of the CoG across the plan view of the car.

I don't imagine I need to say that in a vehicle on springs (even a
rubber tyre on a solidly fixed axle is a spring already), the moment
it starts moving, the centre of gravity shifts and keeps shifting.

That's not the only problem of the centre of gravity in an automobile.
A very large component of force acting on (against, with) the controls
of an automobile is the CoP, the centre of aerodynamic pressure, a
substantial force you may imagine as pressing against the side of the
car at a point which alters with speed and ambient factors; do not for
a moment believe the force acts simply perpendicularly to the length
of the car, or even at a constant angle. Trying to make the CoP
coincide with the CoG even some of the time, or at least fall at a
critical transition (in a fast corner of known radius) in an
advantageous position to it, can drive strong men to drink; it is one
of the reasons many racing drivers just purely love estate cars or
large sedans for fast transcontinental journeys, because they have so
much side elevation behind the driver.

So, claiming that "especially as the c.o.g. on a bike is variable,
unlike a car" is such [censored] that I imagine the magisterial Jobst
Brandt is pupping Palo Alto as he reads that. A car's CoG is simply
not simple.

I haven't particularly thought about the mass shifts on a bicycle, nor
about its aerodynamics, but I suspect they will be simpler than those
of automobiles. For instance, compared to a car a bicycle with its
rider is very narrow indeed. The CoG can shift laterally only to a
very limited extent before the rider and bike fall over and interest
ceases as the machine no longer moves. (The purpose of calculating the
CoG is to determine how weight will shift in a suspended machine in
motion; if it has fallen over and its operator is crying for his
mommy, it no longer moves, and the calculation becomes moot, see?) As
another instance, a bicycle is full of holes for the air to blow
through, so that CoP element of mass shifting around is probably less
than on a car, and on a bike, if sensibly designed, for instance as a
Dutch city bike with coat protectors on the rear wheel, or as a
touring bike with panniers and a rack pack, it is quite easy to catch
the wind more on the rear quarters than the front, with positive
benefits. Another obvious instance (to me, if not to the fellows who
design "racing" bike helmets) is the pointy end of racing helmets
behind the pointy heads of racing bicyclists; the innocent might think
that design "feature" is to blend the air flowing over their heads
along their backs (technically to avoid separation at the boundary
layer) but it's [censored], as Professor Kamm showed a gazillion years
ago -- one would think long enough ago to have penetrated the thick
skulls of cycling helmet designers. What those pointy helmets are
actually good for is moving the centre of pressure back a little; a
smart designer would turn it into a flat vertical fin, the bigger the
better, and the rider can then, by merely turning his head a little,
gain extra weight transfer onto whichever wheel he desires (or,
equally, off the other wheel) by adding the force of aerodynamic
pressure to the mass transfered by him and the bike in motion. As it
is, those pointy "racing" helmets are most probably useless fashion
accessories, but don't get me started on the excessive drive to
conformity of cyclists.

I thought everyone knew that. It is in all (minus the bicycle bits but
plus the pianful math I'm presently sparing you) in my book "Designing
and Constructing Special Cars" published by Batsford in the UK and
Bentley in the US.

HTH.

Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

In article
<[email hidden]>,

Andre Jute said:

but don't get me started on the excessive drive to
conformity of cyclists.

Since it is equalled in any association of human beings.

--
Michael Press

jim beam said:

Harry Brogan said:

I would like to try and go from a dual pull hydraulic system to a
single pull system.

Does anyone have any web sites that they know of that would help in
this endeavor?

well, it's not a matter of simple plumbing - the first thing you need to
think about is how to proportion the force between front and rear. it's
completely non-trivial to implement. especially as the c.o.g. on a bike
is variable, unlike a car.

I suspect that Harry Brogan want to brake the two front wheels of a
tadpole trike with one lever.

The center of gravity of a car varies with live load distribution.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Tom Sherman said:

"jim beam" wrote:

<snip for clarity>

Quoted message said:

The center of gravity of a car varies with live load distribution.

e.g. passenger count, not as a function of driver position like a bike.
and a car's c.o.g. does /not/ move as a function of braking as is a
popular misconception.

jim beam said:

Harry Brogan said:

I would like to try and go from a dual pull hydraulic system to a
single pull system.

Quoted message said:

Does anyone have any web sites that they know of that would help in
this endeavor?

well, it's not a matter of simple plumbing - the first thing you need to
think about is how to proportion the force between front and rear.  it's
completely non-trivial to implement.  especially as the c.o.g. on a bike
is variable, unlike a car.

I was right with you until the "unlike a car" comment. Proportioning
is a big deal with cars, too, as there's significant weight transfer
under braking especially with vehicles with a high cg. Some vehicles
have load-sensitive prop valves tied to the rear suspension, so that
they cut pressure to the rear brakes as the rear suspension unloads.

nate

jim beam said:

Tom Sherman said:

"jim beam" wrote:

<snip for clarity>

Quoted message said:

The center of gravity of a car varies with live load distribution.

e.g. passenger count, not as a function of driver position like a bike.
  and a car's c.o.g. does /not/ move as a function of braking as is a
popular misconception.

the actual center of mass may not change, but the normal force on the
various tires most certainly does - under braking, cornering, and
acceleration. Ever see a drag car hike the front wheels completely
off the ground?

nate

N8N said:

jim beam said:

Tom Sherman said:

"jim beam" wrote:

<snip for clarity>

Quoted message said:

The center of gravity of a car varies with live load distribution.

e.g. passenger count, not as a function of driver position like a bike.
� and a car's c.o.g. does /not/ move as a function of braking as is a
popular misconception.

the actual center of mass may not change, but the normal force on the
various tires most certainly does - under braking, cornering, and
acceleration. Ever see a drag car hike the front wheels completely
off the ground?

nate

of course - that's why we use vectors when doing the math on this stuff.
but some people are unclear on the concept, hence they confuse force
with c.o.g.

N8N said:

jim beam said:

Harry Brogan said:

I would like to try and go from a dual pull hydraulic system to a
single pull system.
Does anyone have any web sites that they know of that would help in
this endeavor?

well, it's not a matter of simple plumbing - the first thing you need to
think about is how to proportion the force between front and rear. �it's
completely non-trivial to implement. �especially as the c.o.g. on a bike
is variable, unlike a car.

I was right with you until the "unlike a car" comment. Proportioning
is a big deal with cars,

of course - that's why this is a non-trivial problem.

Quoted message said:

too, as there's significant weight transfer
under braking especially with vehicles with a high cg.

unless it's something like a liquid load, you're not getting "weight
transfer", you're getting a force vector equation.

Quoted message said:

Some vehicles
have load-sensitive prop valves tied to the rear suspension, so that
they cut pressure to the rear brakes as the rear suspension unloads.

of course. and that's probably the only non-computerized solution that
works really well. cars that use valves with fixed proportioning are
much more rudimentary, but it's simpler to implement. and it's arguably
safer for many vehicles that operate within a given weight range because
an incorrectly adjusted load-sensitive proportioning valve is a damned
dangerous thing. ask me how i know.

getting back to bikes though, given that the rider moves around and thus
the c.o.g. moves, the only mechanical way to implement proportioning
would have to be with a load sensitive valve. and that would in turn
require rear suspension. as i said, it's non-trivial.