Understanding Wheel Building

_ wrote:
On Sat, 03 Jan 2009 10:53:12 -0800, jim beam wrote:


braking torque increases spoke tension more than pedaling torque.

Wow.

Another revalation from the master.

There are now (at least) *two* kinds of torque, and one inceases tension in
spokes more than the other.

Like to see then math on that - so many inch-pounds of torque increasing
tension by x% if it's from braking, y% if it's from pedaling.

How did those spokes get so smart, that they can tell braking torque from
pedaling torque.

Maybe they're magic Mavic spokes...y'know, modern materials and superior
technology or something.

Kind of like Doug's two kinds of being dead.


are there two kinds of being stupid?

wrote:
someone wrote:

The weight of the rider plus bike creates more tension in the
wheel than pedaling torque. Therefore, there is no reason to
consider braking torque, because it's less than the tensions of
coasting, and wheels are already adequate to sustain coasting.

As Jobst said, spokes near the bottom of the wheel *lose* tension
when coasting. The rest are basically unaffected.

Braking torque with a disk wheel is not a trivial matter... there
is a reason why they use large flange hubs. Pedaling torque isn't
trivial either if you are riding a low gear (like the common
22/34) with high force and have good traction.

The reason I suggested looking into the graphs and numbers in "the
Bicycle Wheel" is that pedaling and braking torque is insignificant
and far smaller than the tension cycles coasting on level ground
produces.

II have the first edition and I don't remember reading anything in
it specific to disc (or drum) brake hubs although, from this
discussion, it seems that the tension changes due to braking are not
really a major issue. What I would like to get you (Jobst) to weigh
in is the subject of spoke interlacing. What is the downside of
running the spokes directly from the hub to the rim without
interlacing them? I know your book does touch upon this subject but
would you please provide a bit more of the mechanics of taking up
slack and reducing shock? Do these issue vary in degree for mountain
bikes with disc brakes vs. road bikes with rim brakes?

Go back and read about loads and look at the diagrams showing relative
distortion. All diagrams are based on the same load and torque is for
climbing a theoretical vertical wall to put loads into perspective.

why don't you spell it out jobst? you don't analyze disk [or hub]
braking per se, but you do analyze pedaling torque. pedaling torque
increases and decreases spoke tensions. braking forces operate ont he
same principal, but more so since braking forces exceed pedaling forces.



Interlacing spokes is also analyzed.

numerically??? where?

Jay Beattie wrote:
On Jan 3, 10:41�am, jim beam wrote:
HKEK wrote:
On Jan 3, 4:35 am, wrote:
Ron Ruff wrote:
The weight of the rider plus bike creates more tension in the wheel
than pedaling torque. Therefore, there is no reason to consider
braking torque, because it's less than the tensions of coasting,
Jobst I have the first edition and I don't remember reading anything
in it specific to disc (or drum) brake hubs although, from this
discussion, it seems that the tension changes due to braking are not
really a major issue. What I would like to get you (Jobst) to weigh in
is the subject of spoke interlacing. What is the downside of running
the spokes directly from the hub to the rim without interlacing them?
I know your book does touch upon this subject but would you please
provide a bit more of the mechanics of taking up slack and reducing
shock? Do these issue vary in degree for mountain bikes with disc
brakes vs. road bikes with rim brakes? Thanks!
jobst won't say because he doesn't really know.

anyway, here's your reason: shimano's lacing advice is to give a small
degree of relief for the spokes that "pull" against braking forces.
while a lot of this is academic, in theory, the heads-in spokes can have
very slightly less tension than the heads out because their position on
the outside of the hub flange affects their bracing angle. �the wider
the bracing angle, the less the spoke tension. �thus, theoretically, you
get the lowest total stress [and thus fatigue loading] by ensuring the
spokes getting braking loads are those with the lowest tension from
pre-stress. �in practice, especially since modern branded spokes are
highly fatigue resistant, you'll have a hard time ever being able to
differentiate spoke life on this basis, but in theory, that's how it works.

enjoy.

I would assume that with drum or disc brakes, the stresses are
different than with rim braking.

of course.


Stopping the hub shell must affects
spokes differently than stopping the rim, at least intuitively (to the
non-engineering mind). How do tortional (rotational?) forces fit in
here? With a rim brake, the caliper becomes another anchor point, and
it seems that most of the force of stopping would be seen at the
contact patch and mainly by the tire. You don't have that anchor
point with a disc brake.

disk [and drum] brakes are a different matter entirely. all torque is
spoke transmitted. with rim brakes, spokes don't participate in torque
differentials.



You stop the hub shell, and assuming
infinite traction, it seems to me that the wheel would "wind up" or
that it would see wind up forces of some sort. -- Jay Beattie.

the braking torque is transmitted through the hub to the spokes. some
spokes experience an increase in tension, others a decrease. increase
or decrease depends on whether they're "pulling" or "pushing" the
braking torque.

On 2009-01-04, Jay Beattie wrote:
On Jan 3, 7:39*pm, Andre Jute wrote:
Ron Ruff wrote:
Tim McNamara wrote:
Do you have a copy of _The Bicycle Wheel_? *You'll find the analysis of
the effects of braking and pedaling on spoke tension in there.

You weren't addressing me, but in my version (2nd edition) disc and
hub brakes are not considered.

Is someone claiming that in the 3rd (latest) edition disc and hub
brakes are considered? I don't see anything specific about disc and
hub brakes.

But I do wonder if you cannot take the "drive force" indicated as a
proxy for a disc or hub brake. The brake force applied on the hub
would be the same as the drive force but in reverse, and the spokes on
each side are symmetrical backwards and forwards, not so?

Be tricky to handle this if you insist on realism (you don't always
stop pedalling fully before you brake -- will the spokes enunciate an
S and hiss sibilantly?) but it might do for a theoretical
approximation.

Andre Jute
Where are you when we need you, Dr de Bono?



Several
factors are involved, one of them being the much higher deceleration
that can be achieved by braking compared to acceleration by pedaling.

That is not true. Traction and endos will limit the forces due to
braking. And as I've shown in a much earlier thread on this forum,
even on a road bike if you have low gears, and apply maximum force to
the pedal, traction is likely again be the limiter... and they end up
being very close... and *not* trivial. Anyone with an understanding of
gear ratios and geometry can calculate this themselves.

Preamble to avoid flames: I am not an engineer and don't even play
one on T.V. With that said, this is how I see it. When I put force
to the rear wheel, the bike moves -- the force is turned in to forward
motion.. When I lock up my front disc, the force is transmitted in to
the wheel and is relieved only when the tire loses traction. It seems
to me that rear drive torque is different from front braking torque.

You can get a higher torque, either braking or accelerating, if the
wheel isn't locked or spinning. This is because for most materials the
coefficient of static friction is higher than the coefficient of dynamic
friction-- in other words once things start sliding they offer a bit
less resistance.

With my considerable weight, and on the steep hills that I descend on
my disc brake bike, I can put a lot of braking force in to the front
hub. -- Jay Beattie.

When riding away the bicycle's acceleration is only limited by the
maximum torque you can get through the rear wheel for the first few
metres. After that the power output of your body becomes the limiting
factor. There's no such limit on braking power, which means braking
torque is not necessarily higher, but probably lasts longer.

John Henderson wrote:
_ wrote:

On Sun, 04 Jan 2009 11:25:33 -0600, Tim McNamara wrote:


Torque is torque. Not having seen "jim's" entire post, I
don't know
where you got the "two kinds of torque" from. Torque from
pedaling and torque from a hub brake will be the same as far
as the spokes are concerned.
Not according to beamo (this was quoted in the post to which
you replied):

"braking torque increases spoke tension more than pedaling
torque."

To say that more than one phenomonen produces X in no way
implies that there is more than one kind of X (in other than
the question-begging sense of there being a difference in X's
history or origin).

John

you're wasting electrons - he doesn't understand the principles so he
won't understand any further differentiation.

Jay Beattie wrote:
On Jan 3, 7:39�pm, Andre Jute wrote:
Ron Ruff wrote:
Tim McNamara wrote:
Do you have a copy of _The Bicycle Wheel_? �You'll find the analysis of
the effects of braking and pedaling on spoke tension in there.
You weren't addressing me, but in my version (2nd edition) disc and
hub brakes are not considered.
Is someone claiming that in the 3rd (latest) edition disc and hub
brakes are considered? I don't see anything specific about disc and
hub brakes.

But I do wonder if you cannot take the "drive force" indicated as a
proxy for a disc or hub brake. The brake force applied on the hub
would be the same as the drive force but in reverse, and the spokes on
each side are symmetrical backwards and forwards, not so?

Be tricky to handle this if you insist on realism (you don't always
stop pedalling fully before you brake -- will the spokes enunciate an
S and hiss sibilantly?) but it might do for a theoretical
approximation.

Andre Jute
Where are you when we need you, Dr de Bono?



Several
factors are involved, one of them being the much higher deceleration
that can be achieved by braking compared to acceleration by pedaling.
That is not true. Traction and endos will limit the forces due to
braking. And as I've shown in a much earlier thread on this forum,
even on a road bike if you have low gears, and apply maximum force to
the pedal, traction is likely again be the limiter... and they end up
being very close... and *not* trivial. Anyone with an understanding of
gear ratios and geometry can calculate this themselves.

Preamble to avoid flames: I am not an engineer and don't even play
one on T.V. With that said, this is how I see it. When I put force
to the rear wheel, the bike moves -- the force is turned in to forward
motion.. When I lock up my front disc, the force is transmitted in to
the wheel and is relieved only when the tire loses traction. It seems
to me that rear drive torque is different from front braking torque.

magnitude may be different, but principle is exactly the same.




With my considerable weight, and on the steep hills that I descend on
my disc brake bike, I can put a lot of braking force in to the front
hub.

you can exert more rear braking force than traction force too.

HKEK wrote:
I would like to get back to the central issue that started this
thread. Shimano has specific instructions as to how spokes are to be
laced to their disc brake hubs. Take a look at their spoke lacing
instructions on one of their Technical Service Instruction sheets:

http://tinyurl.com/7sf8ac

1) Take a look at Shimano's requirement for the drive side of the rear
hub. This lacing pattern differs from one that has been recommended in
Jobst's book. Shimano has the pulling spokes on the outside of the
flange whereas Jobst recommends the (drive side) pulling spokes be on
the inside of the flange. The stated reason for having pulling spokes
on the inside is to cause the interlaced spoke crossings to move
inward under pedaling torque.

2) Take a look at Shimano's requirement for the non-drive side of the
rear hub and their requirement for each side of the front hub. If it
is always better to have the interlaced spoke crossings move inward
(rather than outward) under braking torque, then Shimano has it
backwards for the brake torque as well.

I guess Shimano is saying that movement of interlaced spoke crossings
is not important; what is important is simply that the spokes that
experience increased tension due to torque from either pedaling or
braking should be on the outside of the flange.

Might this be because the spoke line on the outside of the flange is
better and fewer fatigue failures occur on spokes outside the flange?

from torque loading, all other factors being equal, yes.

Ron Ruff wrote:
HKEK wrote:
Might this be because the spoke line on the outside of the flange is
better and fewer fatigue failures occur on spokes outside the flange?

I don't see it. And considering Shimano's poor reputation with their
factory wheels,

whoa there ron - that's massive [and somewhat inflammatory] presumption.
i've had no problems with factory shimano wheels, and i'm a
clydesdale, so i'm not exactly going easy on them.



I wouldn't put too much stock in their recommendation.
If they can't be bothered to explain their rationale, then I can't be
bothered to follow directions that don't make sense.

they don't bother to explain their rationale for cold forging dura-ace
brake calipers either, but there is a reason, and that reason is well
known to anyone sufficiently knowledgeable.



BTW I didn't realize the post above was made early (thought I was on
the 2nd page). My apologies.

Ron Ruff wrote:
Tim McNamara wrote:
In 40+ years of riding bike, Ron, despite being 200+ pounds and quite
strong I've never spun a tire on clean pavement by pedaling, even in my
racing days when I was at my peak strength and fitness.

But have you tried? Lowest gear, going slow or stopped... now stomp on
the pedal with full force. This isn't "normal" pedaling, but then
locking up the front wheel and/or doing endos isn't normal braking on
a road bike either.

On a MTB where these things go to extremes, the gears are much lower,
and flirting with endos and front wheel skids are more common.

even on an mtb, you can brake much faster than you can accelerate.
therefore, by definition, braking force torque [and therefore tension]
on a disk braked spokes exceeds pedaling force torque [tension].

wrote:
Jobst on hub brake and pedal effect:

"Pedaling causes nonuniform torque that varies during the pedal stroke
and with rider effort. A hub brake, on the other hand, produces
uniform torque, but its torque still causes dynamic changes as the
wheel rolls. For a small-flange hub, torque from strong pedaling or
braking causes tension changes as large as plus and minus 5%."

Way more than 5% is possible... even typical. It isn't difficult to do
this calculation. A steady seated climb at 300W in a 34/27 at 70rpm
will produce a 24kg tension change in a wheel with 28 crossed spokes
(see below). Triple the power... which most of us could do for a few
seconds if we try... and that goes up to 71kg... hardly trivial. If
the initial tension is 100kg, we are looking at a 71% tension change.

On another forum one of the members was complaining about how his
supposedly "bombproof" 32 spoke rear wheel kept breaking DS spokes.
Turns out he was doing sprint intervals on a 20% grade, so it didn't
surprise me.

Effective flange radius (mm) 20
Crank length (mm) 175
Front sprocket teeth 34
Rear sprocket teeth 27
Crossed spokes on drive side 14
Rider power (W) 300
Cadence 70
Peak torque/ avg 2
Peak torque (N-m) 82
Peak force (N) 468
Peak force (lb) 105

Spoke tension change +-(Kg) 23.7