Understanding Wheel Building

Tom Reingold wrote:

reason given is that braking generates higher loads on spokes (as
much 10 times greater than pedaling)

Wanted to comment on this also... since it isn't true. The limits
of torque will be either loss of traction or an endo. If you do
the basic force balance you will see that it is possible to
generate as much rear wheel torque via stomping in a low gear, as
what you could achieve via braking on the front.

If this is true, and I have no reason to disbelieve it, then none of
this matters. 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.

You might find answers to your assumptions in "the Bicycle Wheel"
where these effects are analyzed. The main effects are that tension
barely increases for any kind of loading, but that tension decrease
from vertical loads on bicycle wheels is the main effect one must
consider.

Results of loading are shown graphically and numerically for all modes
of loading.

http://tinyurl.com/22v535

Jobst Brandt

Phil wrote:
"Ron Ruff" wrote in message
...
HKEK wrote:
reason given is that braking generates higher loads on spokes (as much
10 times greater than pedaling)

Wanted to comment on this also... since it isn't true. The limits of
torque will be either loss of traction or an endo. If you do the basic
force balance you will see that it is possible to generate as much
rear wheel torque via stomping in a low gear, as what you could
achieve via braking on the front.

FWIW, the torque follows a sine wave over time during pedaling, whereas it
exists through the full 360 of rotation during braking. It seems that
fatigue is more of an issue at that point and would be more of a concern for
the rear than the front wheel, especially if the rear is disc also.

I'd say it is fatigue in any case. Where the rear disc wheel is
concerned, pedaling torque *can* be high but doubt it is very often...
you need a very high force plus a low gear. Braking torque on the rear
will be limited by traction, which will be low as the weight is thrown
to the front. The front wheel though can see pretty high braking
torque on a regular basis. It will depend on the rider, but I'd guess
the front disc wheel sees the highest torque loads the most.

Tom Reingold 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.

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

Braking torque with a disc 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.

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,
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.

Jobst Brandt

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!

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.

Jobst Brandt

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.



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.

Jobst Brandt

Brian Nystrom wrote:
HKEK wrote:
I gave that some thought, not interlacing the spokes. That would seem
to achieve all of the design objectives. I just have not seen it in
practice nor have I seen it stated in any of the wheel building
guides. Why isn't it commonly done?

On Jan 1, 4:25 pm, Brian Nystrom wrote:
There is a third alternative, which is to not interlace the spokes. If
they clear the derailleur and/or brake calipers when static, they will
clear it regardless of the spoke load.

You could also do what Mavic does on their MTB wheels. They use a hub
designed for straight pull spokes with the paired flanges offset, so
that crossing spokes go directly to the rim without touching each other.

Interlacing helps spread to maintain tension in the spokes that are
detensioned by the torque load, by putting a side load on them as the
spokes bearing the try to straighten. If the wheel is built with high
enough spoke tension relative to the torque load, it shouldn't matter
whether the spokes are interlaced or not. The Mavic wheels I spoke of
have low spoke counts and relatively high spoke tension, which works
well. I don't know if this would be a reasonable idea for a typical
32/36 spoke wheel or not. Although I've seen wheels built that way, I
don't recall if I've ever built one myself. Perhaps Jobst could speak to
this.

jobst's "book" anwser is that interlacing "supports" the spokes.
however, you need to ask yourself how this is supposed to work given
that he then goes on to poo-poo tying & soldering on the basis that it
/doesn't/ work [notably using the incredibly flawed process of jumping
from "method" to "conclusion", omitting "results"] - a total logical
disconnect.

so, is there a benefit? there is a slight difference in spoke tensions
from heads-in and heads-out spokes, and interlacing mitigates this
slightly, but the effect is small. if you want to see numbers, you can
calculate bracing angles, or check out the latest version of damon
rinard's spokecalc which i believe has relative spoke tensions for
dished wheels. you should be able to put in numbers for each side of
flange spacing and see how small is the difference.

Tom Reingold wrote:
On Jan 2, 2:36�pm, Ron Ruff wrote:
HKEK wrote:
reason given is that braking generates higher loads on spokes (as much
10 times greater than pedaling)
Wanted to comment on this also... since it isn't true. The limits of
torque will be either loss of traction or an endo. If you do the basic
force balance you will see that it is possible to generate as much
rear wheel torque via stomping in a low gear, as what you could
achieve via braking on the front.

If this is true, and I have no reason to disbelieve it, then none of
this matters. 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.

Tom Reingold
Noo Joizy



braking torque increases spoke tension more than pedaling torque.

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. 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. 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.

someone wrote:

The weight of the rider plus bike creates more tension in the
wheel than pedaling torque. Â*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. Â*The rest are basically unaffected.

Braking torque with a disk wheel is not a trivial matter... Â*there
is a reason why they use large flange hubs. Â*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.
Interlacing spokes is also analyzed.

Jobst Brandt