The Bicycle Wheel (pt. 1): Principle Behind the Wheels

Uploaded by Google on 11.01.2008


PIAW NA: I'm Piaw, and this is Pardo.
Pardo will probably do most of the talking.
And well, without much further ado, we'll hop on into
First of all, we promised that some of you will get books,
and yes, we have books.
We'll hand them out at the end of this class.
Stick around.

For those who are building wheels in the workshop two
weeks from now, we'll provide tools, we'll provide supplies,
we'll provide oil.
What your responsibility is is to buy hubs, rims, and enough
spokes to get yourself built.
Don't worry, by the end of today, you will know exactly
what to buy and how to go about making the computations.
In the lab, we'll have two students each build one wheel,
so if you're not building a wheel, partner with
somebody who is.
And we'll have two demo wheels we're going to build so we can
have up to four people who completely don't
want your own wheel.
Historically, about half the people who sign up for the
workshop typically want to build something of their own.

So that's it for administrivia.
There's a sign in sheet going around.
Please try to sign it so that our sponsors know how many
people actually make it to these things.
OK, Pardo?
D. PARDO: So I guess as a starting point, why would you
want to build your own wheels?
Well, I like doing it because it's fun and interesting.
It can be cheaper than hiring somebody else, and sometimes
you can get things done that you can't otherwise.
Bike shops, for good reason, won't put a new rim on old
spokes, because they don't know the history of the
spokes, and they don't want to be liable when you go out the
door and your old spokes start snapping.
But if you're comfortable with the spokes, wear out a rim,
just put on a new one, keep riding, no problem.
Sometimes you can get a better built wheel than you can by
getting somebody else to do it.
And it's also useful to know how the wheel works so that if
you're out in the boonies somewhere and something
breaks, you can just stop, tweek, tweek, and on your way
instead of being stuck.
The flip side of that is for a lot of people, building wheels
is kind of scary.
There's a lot of myth and lore about it, and how you have to
have everything just right and so on and so forth.
So a lot of people won't touch it.
For a long time, I personally worked on every part of the
bicycle except for the wheels.
And then one day, I was sitting on a bus going
somewhere, and I was chatting with a fellow there.
And it turned out he wouldn't work on any part of his bike
except the wheels.
He built his own wheels from scratch, but he hadn't heard
that they were mysterious and difficult.
So he just went ahead and built them.
And so I decided that well, I could probably do it.
And with the mystery gone, you can too.

For this class, we're mostly going to be talking about what
I'll refer to as ordinary wheels.
There's all sorts of fancy things that you can get.
But basically we're talking about things like 36-spoke
road wheels, 32-spoke mountain bike wheels, fairly normal
rims instead of ones that are the super wide arctic SnowCat
or the super deep aerodynamic ones, and so on and so forth.
Some of the things here apply just fine to
those sorts of wheels.
Some of the things don't apply very well.
For instance, if you have a carbon rim, you don't want to
keep tightening the spokes until it starts to go out of
true, because it will probably snap before it starts going
On the other hand, you can still build those, but you'll
just want to be careful about it and make sure you have all
of the appropriate information.
But there will be a lot of useful background here that
will help you [INAUDIBLE].
As Piaw mentioned, the general structure is a couple of
lectures plus a workshop.

Piaw said you'll have everything you need to know in
order to buy exactly what you want.
And I would say nobody ever has all the information they
need in order to get exactly what they want, because
there's so many variables involved.
But we hope you'll be well along your way.
And I hope that as things go along, you will ask questions
early and often.
First of all, I'm forgetful.
And I'm also sometimes unclear.
Also, if you're interested in something and I haven't talked
about it, chances are there's 10 other people sitting in
here who are also interested in it and
haven't asked about it.
So if you ask one question, you'll get to make a whole
bunch of people happy.
The lectures are going to be organized sort of along the
lines of theory and practice.
And I'll try to step through things in a linear fashion.
But one of the funny things about bike wheels is that
everything is connected to everything else.
And so everything is its own prerequisite.
So it's a little hard to just start at one end
and go to the other.
So I'll actually make a couple passes through the
information, and there will be a certain amount of skipping
around as we go.

And in keeping with the spirit of an end to a mystery of
building wheels, just because we say something, don't
believe it.
We sometimes make mistakes and sometimes make simplifications
and things like that.
I mean, it's OK if you believe something, but don't believe
it just because we've said it.
All this stuff is understandable.
You can understand the principles involved, not just
a set of rules that you're supposed to follow or
something like that.
And a lot of this stuff is stuff that you can demonstrate
to yourself from the comfort of your own home or garage, or
wherever you're working on wheels.
There's no need to go out and buy $1 million of equipment to
understand it.
And once you do understand it, having the principles in mind,
you'll be able to build better wheels than if you're just
following a set of rules.
So without much further ado, into the wheels.

I'll start by talking about the individual pieces, and
we'll probably get at least today through talking about
spoke length.
Then we'll talk about putting everything together.
And part of putting everything together is going to be
figuring out what it is that you
actually want to put together.
So I've got this little section called requirements to
help you think about what it is that you really want to
accomplish with your wheels.
And from requirements, then, you can figure out what the
parts are that you actually want to have.
So the basic parts of a wheel.
there's lots of pieces here.
I'll pass things around.
Feel free to look at things.
That's a rim that is symmetrical, and this other
one is a rim that is asymmetrical with the spoke
holes off on one side.
There's lots of different spokes.
Here's two of them.
One's a straight gauge spoke, and the other one has a little
bit of a neck at either end, which is called either a
butted or a swaged spoke.

The nipples that connect the spokes and rim together, and
the common things are aluminum, which are the
colored ones in here, and chrome-plated brass, which is
the silver one in there.
And at the middle of it all, hubs.
Here's a somewhat funny [UNINTELLIGIBLE].
Hubs deserve a little extra commentary.
We're going to be talking about hubs here as basically
just a lump.
Hubs are actually pretty complicated.
They've got bearings and moving parts
and things like that.
And that's probably the least structurally important part of
the wheel, but the most service-intensive part of the
wheel in the sense that bearings go out of adjustment,
bearings need lubrication, bearings need this, bearings
break, axles break, things like that.
So we'll talk about the things you care about for building
the wheel, but if you actually go to buy a hub, you'll
probably want to hear about a bunch of stuff that we're not
talking about here.

Along with the parts, in order to build the wheel, the most
important thing that you need is a spoke wrench.
And there's lots of different kinds of spoke wrenches.
They turn the nipple, and tighten and loosen the spokes.

Make sure you get them for the right size.
There's a couple different sizes of nipples.
And if you get the wrong size one, you'll round off the
nipples and then you won't be happy.
There's a bunch of other tools.
Here's an example of a truing stand.
You put the wheel in and spin it, and it helps guide you to
get things precise.
If you don't have a truing stand--
and we'll provide them for the lab section of this-- but if
you don't have one, you can actually use your bicycle and
the brake pads as a truing stand.
It's just a little less convenient.
I didn't bring one, but there's also dishing tools
that you use for trying to get the side to side location
exactly centered.
Again, you can fake that if you don't have one.
It's just a little less convenient.
There's also a thing called a tensiometer, or a
spoke-tension meter, which you put onto the spoke, clamp in
onto the spoke, and let the spring go.
And the spring is calibrated, and it tells you how
tight the spoke is.
And again, with aluminum rims, you can fake it.
If you don't have one, you can get within a few percent of
the right spoke tension for all the parts that you have.
You'll also want oil.
Basically, any kind will do.
Sometimes people build wheels using some sort of an
extra-friction compound, either boiled linseed oil or
Wheelsmith Spoke Prep or something like that.
And that's sort of an attempt to get around wheels that are
built on the edge.
The spokes can unscrew themselves as you ride if the
spokes are getting really loose.
But if the spokes are getting really loos, the wheel is also
getting close to collapse.
So by and large, the better the wheel is, the less
important it is that it's built with something like
boiled linseed oil or spoke prep.

You also want rags.
Where there's oil, there's rags.
Gloves are important because when you get to the stress
relieving part of it, you'll need to squeeze the spokes
hard enough that if you're not wearing gloves,
it hurts your hand.
That's the definition of how hard to squeeze the spokes.
So you'll want gloves.
And spokes are not very likely to break, but they're under a
lot of tension, and you're looking right at the thing
while you're building the wheel.
So you also want eye protection just to be sure to
be sure to be sure.
There's also intellectual tools for wheel building.
It's good to have knowledge and we hope to get you most of
that that you need in here.
We also recommend, and for at least some of you, we'll be
handing out a copy of The Bicycle Wheel.
I brought one along, but I forgot to bring it here to
pass around.
Jobst Brandt, the author of it, says, everything is in
there that you need to know.
Well, he's a mechanical engineer, and it's written
pretty densely.
And I'm pretty sure that he's correct.
But after 500 years, I'l still rereading it.
Everything is in there, but you might have as much trouble
as I do understanding it, hence this class.
I also personally like a book called Building Bicycle Wheels
by Robert Wright.
It's maybe 30 pages long.
So it's a pretty simplified overview of things, but it's
also pretty straightforward in this sense of just do this, do
this, do this, do this, do this, voila, wheel.
And because it's simplified, you might be a little more
likely to get into trouble with it.
On the other hand, because it's simplified, it's a lot
less of a challenge to get through it.
Another part of knowledge is knowing what it is you know
and knowing what you don't know.
There's a lot of myth and lore about bicycle wheels.
People say, oh, you have to do exactly this.
Or you better not ever do that.
Or all sorts of stuff that it's right, or it's right in
the wrong ways, or it's wrong, or it misses the
point, things like that.
This is engineering.
It's not mysterious.
There is a right answer.
You don't necessarily want to go to all the trouble that you
need to go to get exactly the right answer, but it's not
some sort of an arcane practice for which you need
boiled toads, or something like that in order to make
good bicycle wheels.

Was there a little bit more?
Oh, yeah.
And there's a book, The Art of Wheelbuilding.
I don't want a book on the art of wheelbuilding.
I can figure out colors myself.
So don't worry too much about the art of it.
In going through this class, we'll spend a fair amount of
time talking about two things, strength and durability.
And in common use, they're often interchanged.
But they actually mean slightly different things.
Actually, they mean dramatically different things.
Strength is how much weight can you put on something
before the wheel collapses?
And that's a one time event kind of thing.
You can take a brand new wheel and pile more and more weight
on it, and it will eventually collapse.
That's strength.
There's also durability which is the year after year after
year after year and then things start snapping and
popping and crackling.
And that can happen even if you never put a lot
of load on the wheel.
Just repeated cycles on it can eventually cause destruction.
And the reason these two things are important is
because there's a lot of trade-offs in building wheels.
And sometimes there are trade-offs that we'll build a
stronger wheel that's less durable, or a more durable
wheel that's less strong.
And so you want to know what those things are and make some
sort of a conscious decision about, well, I tend to go out
and ride lots and lots of miles, but I don't beat up on
the bike a lot.
Or I tend to ride off the roofs of small buildings, and
I don't do that very often.
But I only need to collapse a wheel one time before I'm
upset that the wheel collapsed.
So you want to understand and keep those things in mind.
I heard a cough.
Was that a question?
OK, ask questions.

Oh, yes.
As an example of that, if you use thinner spokes, it often
increases the wheel's durability but decreases its
lateral strength.
So that's a particular example, but it's one that
you'll see over and over again.
People will say, I built this wheel and it was totally
Well, that's bomb-proof against the kind of riding
that they were doing.
And that same wheel with a different rider, in a
different riding situation might be trouble from day one.

So let's see.
Parts-- rims, nipples, spokes, hubs.
We'll go through these more or less in that
order at a high level.
And then some more, coming back next time, we'll talk
about lots and lots of little details.
So from the standpoint of this class, what you hear about is
what does a rim do, what's a good rim, how's it failed?
Because ultimately, when something fails, that's
reached the limit of its usefulness.
Well, a rim holds the tire in place.
And you want it to be the right size, dimensions,
whatever, for the tire that you're using.
Rims have a little drop section in the middle.
The tire bead goes down in that drop section.
When you're mounting a tire, you've got a round rim.
It might not be really obvious, but you kind of get
the tire off center to the whole rim in order to get the
thing in there.
And there are some rims that have a deeper center which is
good if you want to get the tire on and off easily, but
it's bad if you tend to ride in certain ways that the tire
wants to come off by itself.
PIAW NA: And then there are some rims that are designed
just a little bit too big.
D. PARDO: Manufactured.
They were designed the right size and they were
manufactured the wrong size.
PIAW NA: And then what happens is you break a few tire levers
while getting the tire off.
D. PARDO: While you're off on a hill in the middle of
Switzerland somewhere.
That's not the time you want it.
AUDIENCE: Are you going to talk more about tire sizes?

D. PARDO: I'll talk a little bit about it.
I guess the basic overview is if the rim is very wide and
the tire is very narrow, then it will tend to blow off.
And if the rim is very narrow and the tire is very wide,
then it tends to be kind of unstable.
And you can correct that a little bit by using higher
tire pressures, but only up to a point.
And especially if you're riding off-road on a bicycle
that doesn't have any suspension on it, so you want
to have the tire pressure down low, you can really have an
unpleasant ride with an [INAUDIBLE] tire.
I don't know if that--
do you have a specific question?
AUDIENCE: OK, my specific question is I kind of like
wider tires, just because they're right
on gravel or something.
But it seems that the fancier wheels tend
to be narrower ones.
Am I wrong on that?
D. PARDO: Well, I think you might be using somebody else's
definition of fancy.
I happen to be with you on the use of wide tires.
This is a road tire which is about halfway to the width of
a mountain bike tire.
And I like that because I can go riding and my friends stop
and repair their flat tires, and I don't.
You just need to get a rim that's wide enough, so that's
part of the requirements--
which is you want to run fat tires, make sure that you get
a wide enough rim.
It's certainly the case that there is a different selection
of tires, or a different selection of rims depending on
the width of it.
But there are good rims that are wide.

The rim is a structural element.
Basically every part of the wheel serves some sort of a
structural role.
And the rim is one part of that.
You want it to be strong to support a load.
You also want it to be durable.
That thing I mentioned, rotation after rotation after
rotation puts cyclic stresses into the rim.
And eventually bits and pieces of it can crack and fail,
leaving you unhappy about it.
Also, when you slam into the edge of a pothole or something
like that, it can cause a ding in the edge of the rim.
And some of the lighter rims, they're nice and light, but
they're also thinner in order to achieve that lightness.
And it takes a remarkably small difference in the
thickness of the wall of the rim to make a pretty
substantial difference in the dent resistance of it.
The rim is sort of shaped like this.
And the dent resistance is a function of
that thickness here.
But it's a little bit funny.
If you double this thickness, you roughly eight times
increase its strength.
So relatively small differences can make a pretty
substantial change in how dent-firm things are, if
that's a problem that you have.
For a lot of riders, for a lot of bicycles, the rim is also
an important component of the brakes.
That's one half of how you develop the brake force, the
other half being the brake pads that rub on the rim.
Among other things, the rim serves as a radiator to help
keep the brakes cool.
And if the brake pads get too hot, you can
have a brake failure.
And if the brakes aren't quite hot enough to fail, you can
still have failures where the tire blows off the rim and
that's both a brake and a steering
failure when that happens.
I've had it happen.
I don't recommend it.
Breaks also wear out the rim over time, making this side
wall here thinner and thinner and thinner.
And very often what will happen is the rim will develop
a concave shape.
Well, it's concave on the outside, but it's still
usually pretty straight on the inside.
As it gets thinner and thinner, it
gets more dent prone.
And eventually as you keep using it, that part of the rim
will get so thin that the air pressure in the tire just
blows off the side of the rim, leaving you stranded out in
the middle of the woods.
This has happened to me also.
I don't recommend it either.
So that's a consideration.
If you ride a lot someplace where you tend to wear out the
brake track on the rim, you might want to consider a
heavier wheel with a thicker brake track.
On the other hand, if it never happens to you, then maybe you
want a lighter one.
Many rims have some sort of a wear indicator built in.
However, many do not.
The usual sorts of wear indicators include either a
little groove which is manufactured into the rim.
And when that groove disappears, it's time to
replace the rim, at least according to manufacturer.
Another strategy is they make a little
hole in the back side.
And when that little hole appears in the breaking
surface, it's time to replace the rim.

Of course no cycling discussion would be complete
without at least a brief discussion of weight.
So rims obviously weigh something.
They also contribute to the aerodynamics, or lack thereof,
of the bicycle.
This is a kind of tricky thing in that a lot of the
aerodynamic wheels have their best function when you're
going straight ahead with no cross wind.
And in a lot of real cycling, an aerodynamic rim will
actually give you less aerodynamics than a less
aerodynamic rim.
So if this is something that's important to you, you probably
want to be very, very close attention to it.
And if it's something that's not important to you, then you
don't want to be sold by the guy at the corner bike shop
saying, oh, this is an aerodynamic rim, because well,
it might not actually be one even though it seems to be.

There's two basic styles of rims. The ones that I passed
around before are so-called clincher rims, where the tire
casing sits down inside of the rim.
I guess I should draw a tire casing.
The other kind, and this is a little section of the tubular
rim, is one where the tube is basically just a doughnut, and
it sits on top of the rim and air pressure keeps it there.
Air pressure and maybe a little bit of glue.
This was sort of the old, original way of doing things.
And it becomes less and less popular every year, especially
because it is a royal pain to patch flats.
You still them some, because they do have advantages.
Specifically, they weigh less.
But for the purposes of this class, we'll just be talking
about clinchers because they are by far the
most common and popular.

Rims can be made of lots of different materials.
Usually, and for the purposes of this class, we'll be
talking about aluminum, or if you prefer, al-u-minium.
You can also get steel, which is often chrome-plated to keep
it from rusting.
But you mostly see this on lower-quality rims, so you're
not likely to want to go into a bike shop and buy a steel
rim to build up your own wheel, especially because
there are both heavy and the chrome-plating is a lousy
braking surface when it's wet.
So they stop OK when they're dry, but that one time that it
rains and you're riding down the road and the light turns
red, you don't want to wind up in the middle of the
There are some stainless steel rims. They're better.
Carbon fiber is increasingly popular, again, because it's
very low weight.
But it has some special build properties that you don't want
to do exactly the same things as you do when
you're building aluminum.
And for simplicity, we're going to
pretty much ignore that.
And I will say also that some of the rims are a composite of
both carbon fiber and aluminum.
For the purpose of this class, treat them as carbon fiber.
The fact that it's got aluminum in it does not mean
you want to build it like an aluminum rim.
There's also all sorts of other things, magnesium,
titanium, wood-- the original carbon fiber.
Again, they have special build properties, so you want to be
careful with that.

Yeah, I guess that's it.
Rim dimensions.
There's lots of different dimensions to a
wheel, or to a rim.

There's the dimensions of the rim as it connects to the
tire, as it connects to the spokes, and as it connects to
the brakes.
So one of the dimensions is how big is it where the tire
connects to it.
And that's known as the bead seat diameter.
The part of the tire that connects to it is
known as the bead.
And it's also known as the E-T-R-O, or ETRO number, which
is the European Tire and something Organization.

Another pair of dimensions is the section width, which is
how wide is the rim.
And in general, a wider rim is going to
be stiffer but heavier.
There's also the section depth, and in general a deeper
rim is going to be stiffer and stronger, but also heavier.
The aforementioned center drop for changing tires.

The nipple bed diameter for where the spokes and the
nipples attach.
And that's known as the spoke bed, or the ERD, for Effective
Rim Diameter.
And historically, what happened was people sized
tires according to the outside diameter of it.
And so if you wanted a 27 by 1 and 3/8 inch tire, you bought
a different rim than if you wanted a 27 by 1 and 1/4 or a
different rim than if you had a 27 by 1.
And they eventually figured out this was a terrible
headache and switched to the ERD.
For some rims, such as this offset one that we passed
around, the spoke holes are a little bit off to one side.
And that's useful when you're building an asymmetrical wheel
which was dished.
So that would look something like that, with all of the
spoke holes offset to one side.
That's useful because it builds a better wheel.
But it's another dimension, or at least another
characteristic to keep in mind when you're choosing a rim.

The brake track height is a kind of tricky thing.
The brake pads are available in a couple different heights.

And you would sort of think at least at some level that
everything is just obvious.
But it isn't.
One reason is some rims, this is very small.
Even when it's large, if you adjust the brake pad--
so it's say, there--
and if you're using a big tire--

so it's up here--
as things wear, part of the brake pad
can go into the tire.

This tends to cause a flat tire.
I've had this happen.
I don't recommend it.

So you say, OK, well, I'll put the brake pad down low.
And then also if I ding the rim or something like that, I
won't have that problem.
Well, especially if you're using cantilever brakes, and
by cantilever brakes, I mean both the classic ones and
V-brakes, the pivot is not very far away this way
compared to how far away it is this way.
So as the pad rotates inward, it tends to move down.
And one thing that happens is just the brake pad doesn't
wear very usefully.
So you're wasting your money because you bought all this
rubber and then you're not using it.
But worse than that, as it wears away up here, it can
actually go underneath the edge of the rim.
This tends to lead to a loss of braking.
It can also lead to the brake pad winding up in the spokes,
which leads to something which might be
termed a loss of brakes.
I've repaired bicycles that have had that happen.
I don't recommend it.

Another thing that happens is when you put the brakes on and
apply an actual braking lube, the pads move around.
There might be a little bit of looseness in the bearings.
But even if you don't have a looseness in the bearings, as
Grant likes to say, in the real world,
everything is made of rubber.
You apply a load to it, it flexes.
And depending on the brakes you have, that amount of
motion can be fairly small or it can be fairly large.
And it can lead to problems like the brake pad moving up
and into the side wall of the tire.
I have a friend who's quite heavy, and he can climb on
most bicycles fitted with conventional brakes.
And if he brakes really, really hard, just riding along
next to him, I can actually see the brake arms springing
up and into the side wall of the tire.
Most people aren't that heavy, but if you're riding a tandem
or something like that, it's definitely a consideration.
And even if you're not, if you wind up with a rim that's got
a really, really, really narrow brake track on it,
well, you might be unhappy.
Because you put the pad right at the edge of things, and
then it swung up just a little bit into the tire.

AUDIENCE: When talking about rim sizes, which dimensions
are represented?
Is that something--
D. PARDO: Which dimensions?
AUDIENCE: Like, which measurements?
You were talking before-- you said a 27 and 1 and 1/2.
Which dimensions are there?
So 27 is the nominal--
not actually, but the name everybody uses--
for this size here, the bead seat diameter.
27 is kind of on the way out.
26 is common.
700C, which is about the same size as 27.
But not quite.
They're not interchangeable.
700C is another common size.
Tires range from probably six inches or something like that,
up to around 36.
The 1 and 3/8 or 1 and 1/4 or whatever is actually a nominal
tire dimension.
But you care about that for the rim in the sense that you
don't want to run a really wide tire with a really narrow
rim or a really narrow tire with a really wide rim.
AUDIENCE: Can you be a bit more precise about that?
Like if you want x width, what size rim you should have?
Or it doesn't matter that much?
D. PARDO: It's not super precise.
But you probably don't want to run a 20 millimeter tire on a
rim that's designed for 40 millimeter tires.
And you probably don't want to run a 2 and 3/8 inch tire on a
rim that's designed for 1 and 1/4 inch tires.
AUDIENCE: So does the rim say what range of tires it's
designed for?
D. PARDO: Really, but often times, the folks at the bike
store will be able to point you at, this is a pretty
workable combination, this is one that you really have to
keep the tire pressure up or else you're going to be
unhappy, things like that.
I have a wheel that I ride fairly frequently which
violates that principle, and I just have to make sure I keep
the tire pump out.

So I mentioned brake track thickness before.
That's an issue of how long the rim will wear.
And that depends tremendously on your riding and your riding
conditions and things like that.
Gobst, who wrote The Bicycle Wheel is in the habit of going
to the Alps every year for a couple year cycling trip.
And one year, he put on a brand new rim
and went on his trip.
And he came back, and he put on another brand new rim
because the brand new one that he put on when he left was
worn out after a few weeks of riding.
That's a pretty extreme case, but I've certainly worn out
rims, I know other people who have worn out rims. A friend
who was an experienced road rider started mountain biking.
And while she was learning more and more about how to
ride without braking, she was wearing out rims about every
three months.
These things happen.

PIAW NA: In general, the rule of thumb is if you're wearing
out break pads, you're also wearing out the rims.
D. PARDO: Yes Yes.
So the person who was wearing out rims every three months
was wearing out brake pads every two weeks.
PIAW NA: Not every ride.
D. PARDO: Well, no, every four rides.
D. PARDO: Go back up just a little, Piaw.
This depends tremendously on your riding habits.
If you ride only in dry weather around here, you might
have a rim that's still basically brand new from a
wear point 20 years after you started riding it.
So it has a lot to do with what abrasives you pick up and
stick to the rim while your brakes are in operation.
So if it hasn't been a problem for you so far, maybe the past
is a predictor of the future, and it's not something you
need to worry about.
On the other hand, if you have already replaced rims due to
wear, or if you really hope to be riding the rim for a very
long time without touching it, then brake track thickness
might be something you want to worry about.
AUDIENCE: You had said that offset rims
build better wheels.
D. PARDO: They build better dish wheels.
AUDIENCE: Better dish wheels.
So better rear wheels.
D. PARDO: Or front if you're running disc brakes.

AUDIENCE: So speaking of disc brakes, if you use those, rims
don't wear out?
D. PARDO: They can still fail, but they don't wear out on the
brake track, because you're not using the
brake track for anything.
And in fact, some rims are disc-specific rims. They don't
have any brake track on them.

I'll have a lot more to say about nipples later.
But for the purpose of right now, basically they're the
thing that connects the rim to the spokes and holds
everything together, adjusts the spoke tension.
There's basically two materials that are common,
chrome-plated brass and aluminum.
And for the purposes of this class, and except for special
circumstances-- and I'll explain why later--
I'd say brass nipples are the way to go.

There'll be lots more to say later, but I'll say a fair
amount right now.
They connect the rim and the nipple to the hub.
They're also an important part of supporting the wheel loads.
When you get on your bike and apply some weight to the
wheel, there has to be structure that connects
everything together.
And it's a little tricky how it all works.
I'll explain it.
But although a spoke, if you just pick one up and grab a
hold of it and try and stretch it, it doesn't
feel like it's elastic.
But again, as Jobst says, "in the real world, everything is
made of rubber." It actually bends quite a bit when it's
supporting a load.
And basically, it's just a long spring.
Some attributes of spokes.
For the wheels that we're talking about here, we're just
talking about tension-only spokes.
So there's tension in this.
And if you apply enough load to it, this spoke will go
slack, at what point it's doing you no good.
There are also plenty of wheels like wagon wheels where
they might not support any tension at all, but when you
put a load on it, they get more and more
compression on them.
So bicycle wheels, if you take a spoke and you try and
compress it from the ends, what's going to happen?
It's going to bend.
I'm pushing on this with maybe a half pound of force.
There's no weigh it's going to support my weight in
It's all done using tension.
AUDIENCE: [UNINTELLIGIBLE] the fancy cars with the spoke
wheels that have both tension and--
D. PARDO: It's pretty rare to build a wheel that uses both
tension and compression to a great degree.
Probably a bunch of the cast wheels do, but most of the
multi-part wheels--
not all of them-- but most of the multi-part wheels, they're
either tension wheels or compression wheels.

lots of choices.
For our purposes, stainless steel.
For other purposes, it's fairly common these days to
see aluminum.
There's also carbon fiber and other sorts of plastics.
And they tend to have a lot of special properties, some of
which you don't like.
And also, things like the aluminum spokes are sold built
into wheels, but they're not generally available for use
after the fact.
So even though you probably don't want them, you can't buy
them anyway.

Because the spoke connects the hub and the rim together, it
has to be the right length to bridge that gap.
The length of the spoke is measured from the crook of the
elbow to the end of the threads.
And when you go into a bike store and say, I want spokes,
you can either tell them that length, or you can go in and
say, these are the parts that I'm using, and they should be
able to compute the length for you.
We'll say later how you can compute the length yourself.
The diameter of this spoke.
Oh, and the length also depends on the lacing pattern.
We'll talk more about lacing pattern in a little bit.
The diameter of the spoke is something you get to choose.
As a rule of thumb, if it's thinner, it's more
aerodynamic, it weighs less, it tends to build a more
durable wheel.
But it also, when you tighten the nipple on it, it tends to
wind up the spoke.
And if it's really thin, you can damage the spoke with the
amount of twisting that's on it.

And a thinner spoke may build a wheel that
is laterally weaker.
So if you tend to go and crash a lot, which some of us do,
you might be concerned about having the wheel do something
unpleasant, not because you just put a static load on it,
like you're riding in a straight line, but because
you're doing lateral loads to it.
Sorry, a radial load, like you're going
in a straight like.
A lot of spokes-- and some of the ones I passed around
before, wherever they are-- are thicker at the ends and
thinner in the middle.
And the reason for doing that is the ends tend to have a lot
of residual stress in them from the
manufacturing processes.
So they're weaker as a result of making the elbow and the
threads and all that sort of stuff.
So you want them thicker so they don't break at the ends,
but you don't want it the whole length thicker.
You want it thin, typically, so [UNINTELLIGIBLE]
the middle.
There's also all sorts of funny shapes of spokes, not
just round.

Here's a round spoke.
One thing they do is they'll make an oval spoke that
basically fits within that profile, but it's
thinner this way.
So this round might be two millimeters, and the oval
might be 0.9 millimeters.
The total area of this is big enough--
spokes are typically strong enough for anything you're
going to put at them.
So the fact that it's thin isn't a problem, but it tends
to wind up even more easily than a regular reduced
diameter spoke.
So again, it's harder to build a wheel with that.
Some other ones are made with a bladed profile that's
actually bigger than the outside diameter
of the round spoke.
And that can lead to all sorts of troubles building the wheel
because at some point, you have to put the spoke through
the hole in the hub.
And if the spoke is bigger than that hole, it doesn't go
through very well.
Bladed spokes also tend to suffer from the problem I
mentioned earlier about aerodynamic rims, which is
they may be better when you're going in a straight line, but
in a cross wind, you may actually have
more drag from it.
So again, it's a very special purpose kind of thing.
People do use them.
You can go to your corner store and buy one.
But for the purposes of this class, round spokes.
PIAW NA: And the other problem with spokes that are not round
is that your hands hurt even more than the--
D. PARDO: When you squeeze?
So just keep that in mind.
AUDIENCE: So when you say harder to build, is it because
you have to be much more careful about [UNINTELLIGIBLE]
getting turned?
D. PARDO: Yes.

AUDIENCE: I was just wondering if it was that the material
was harder or something like that.
D. PARDO: Well, when you twist the nipple, there's friction
and a slightly angle between the nipple and the
threads on the spoke.
And it tends to make a candy cane out of the spoke.
If it gets too bad, that will damage the spoke.
And then you'll have all sorts of problems a little later on.

Your transaction is being processed.
AUDIENCE: So why do thinner spokes make the
wheel radially stronger?
I missed that.

D. PARDO: I'll talk more about this later, but briefly what
happens when you apply a load to the wheel--
you've got your wheel, you press down on it.
What happens?
Well, the ground is down here pushing up, and you're pushing
down on the hub here, these spokes get looser.
And the more load you apply, the looser they get.
When these spokes down here go slack, you've lost some
support for the rim.
And in particular, these things not only get looser as
you apply a radial load, they also help support the wheel
against lateral loads.
So if they go slack and you apply a lateral load, there's
not very much keeping the wheel from collapsing.
So basically, spokes go slack, that's bad.
Now, how do thin spokes help with that?
When they're thin, they're basically more springy.
And so as I press down on the bicycle, these get less
tension in them, but you have to displace the rim further
before they go slack.
What happens when you displace the rim further is some load
gets carried off to the sides through the rim.
The rim is kind of rubbery, but it's also kind of stiff.
So it transfers more load to the spokes that
are on either side.
So for a given weight, you're less likely
to get these slack.
So for a given weight, you're less likely to lose the
lateral support.

AUDIENCE: Basically, it makes it more flexible?
D. PARDO: It makes this part of it more flexible so that
when you're at high load, there's a little bit of
tension left in these spokes to resist the lateral forces
on the wheel.
AUDIENCE: So are you saying that you take thinner spokes
and put them under higher tension when
you build the wheel?
D. PARDO: No, same tension.
AUDIENCE: But they stretch more.
D. PARDO: Yeah, they stretch more when you tension them,
which means when you apply a load, you have to move the rim
further before it goes slack.
And because you're moving the rim further, there's more
opportunity for the load to get carried off forward and
back into the spokes that are on either side of it.
So this also depends on the stiffness of the rim, which is
one of the reasons that I'm saying, well, we're talking
about ordinary wheels here.
AUDIENCE: And also the number of spokes in the rim.
D. PARDO: Yes.

AUDIENCE: So why doesn't everybody use 40 or 50 spokes,
besides the obvious hassle of more spokes?
D. PARDO: It's a hassle.
It costs more.
It weighs more, typically.
There's effectively lower limits to how skinny you can
make the spoke.
So having an infinite number of hair thickness spokes is
not a practical alternative.
Basically, there's a race between a whole bunch of
different compromises.
And then last of all, I think most consumers are not very
discerning about what they buy.
And so people will go out to their corner store, and say,
well, I want a bike for going grocery shopping.
And the guy selling bikes will say, oh, you want to buy this
racing bike with 24/16 wheels.
So that's what they buy.
And it doesn't happen all the time, but it's more common
There have been times in history, for instance, the old
traditional sit-up-and-beg English tourist cycle has 40
spokes per wheel.
Used to be common.
There's a couple of reasons for that.
Some good, some bad.
But we've sort of gotten away from that.

So then the last element in all of this is the hubs.
And again, I'll have more to say about this later.
But a hub is basically axle bearings and the flanges The
flanges have the holes in it where the spokes go in.
And we'll be talking about the flanges and the center spool
that sets the distance between the flanges.
I'm not going to be talking about the bearings very much,
I'm not going to be talking about the axles.
Those are things you definitely care about because
they're high-maintenance items, relatively speaking.
But that's outside the scope of what we're
talking about here.
The goal of the flange is basically
to support the spoke.

And as with rims having lots and lots of different
measurements, a seemingly simple hub flange has lots and
lots of different measurements.

You've got basically a circle, a bunch of holes in it, and an
axle in the middle.
So one dimension is the radius of the spoke holes.

If you look at the hub sideways, another dimension is
the distance between the flanges.

For dish wheels, which is to say rear wheels with a bunch
of sprockets on one side or disc brakes, this is actually
offset with a big thing on one side, and a little
thing on the other.
So the center line is off to one side.
So we actually in that case, it's not just the distance
between the flanges, it's the distance, for instance, from
the center line to each one of the flanges, which can be
pretty different numbers.

There's a couple of slightly subtle things.
One is the thickness of the flange.
So as comparison--
I'll pass these around again-- look at the difference in
thickness between these two flanges.
More material obviously weighs more, but it also builds a
stronger flange.
You have to be a little bit careful, you can't make too
thick of a flange because then the spoke
elbow won't go through.
So what they've done on the black flange there is to
actually relieve the hole slightly.
So if that's the flange, they've radiused in the hole,
so that when you put a spoke in it, it
can all fit in there.
But because the flange is much thicker, you have a lot more
material supporting it.
I actually forgot one dimension from here.
Another dimension that's relevant is what's the
distance from the edge of the hole to the outer-most
diameter of the hub?
The spoke has a lot of tension that's trying to basically rip
the hub apart.
And if this distance is small, then you'll
tend to have hub failures.
If this distance is large, then you won't tend to have
hub failures.
And this kind of tear-out is especially an issue with
radially-spoked wheels to the extent that some of the
manufacturers will specifically state their hubs
are not rated to be built into radially-spoked wheels,
because they're not strong enough without.

Those are pieces.

Oh, I forgot to mention with the hubs, there's also the
diameter of the hole.
The diameter of the hole tends to be pretty standard, but
there are some variations.
And you don't want to have a little teeny spoke in a big
fat hole, and you can't have a big fat spoke in a little
teeny hole.
So it probably won't be a problem for you, but it's
something to keep in mind, especially if you decide to
build with unusual parts.

So those are parts.
The next thing is to build up a wheel.
How does it all go together?
People often talk about a wheel being radial, or one
cross, two cross, three cross.
Radial is when a spoke goes in a straight line from the hub
out to the rim.
Cross is when it goes off at an angle and it crosses over
some other spokes.
And it's usually counted up as the number of times that a
spoke crosses over other spokes that are on the same
side of the wheel.
So this one here comes out of the hole in the hub and
immediately crosses over this other spoke
going the other way.
It doesn't touch it.
They're actually on other sides of the hub flange, but
that counts as one of the crosses.
And then there's another one where, again, it doesn't touch
it because it's still that flange thickness apart.
But it counts as another cross, and then actually goes
under, called interlacing, and touches here.
That's a third cross.
This is a three-cross wheel.

What do you want?
Well, typically three cross or four cross.
There's a bunch of little details here.
Shorter spokes weigh less, so if you get a fewer cross, then
you can build a lighter wheel.
But there are some disadvantages.
The crossing spokes tend to support each other when you're
carrying loads, and especially when carrying torsional loads.
Ideally, if you're carrying a lot of torsional load, you
want the spoke to come pretty tangent to the hub flange.
It doesn't make so much difference for a front wheel
and a rim brake, but for a rear wheel where you're
driving it, or especially for a front wheel where you have a
disc brake on it, you'd like to get the most leverage that
you can for your wheel.

Cross actually depends on the number of spokes involved.
A rule of thumb for the maximum that you can achieve
is take your spoke count and divide by nine.
You can sensibly build a four-cross or a five-cross
wheel with 48 spokes in it.
You cannot sensibly build a four-cross wheel with 16
spokes in it.

So it's actually the angles that are
involved that really counts.
But it's easy to count cross.
And it's hard to say, well, that looks like about a 69 and
1/2 degree angle of intersect, so people talk about cross.
PIAW NA: Do we want to go into Spocalc now?

D. PARDO: Yes.
PIAW NA: So Spocalc is the spreadsheet that is posted on
the web for calculating spoke length.
Generally, when you are computing what you want to
get, you want the full-strength version.
You open it in Excel and it's very important that you use
Excel, because it's entirely driven with macros.
AUDIENCE: No Google Docs.

It uses these fancy macros.
And this is the first thing it says, is well, hey, you've got
a security alert.
Let's enables the macros.
There are four tabs here.
There's an instruction tab, there's the calculator where
you can input everything that Pardo just talked about.
And then there's a rim database and a hub database.
And the rim database is very nice because you can just say,
well, hey, I'm building a Velocity Aerohead rim, and I
will just use this thing and say--

there's a tool here that says, hey, enter the front rim
And it will enter it for you.
You can look at a hub database and say, hey, I'm building a
Phil Wood field serviceable hub that's 100 millimeters
wide, and I can say, well, that's the front hub.
And now when you go back to the calculator, it will have
entered all that data for you.
Front hub is field serviceable, front rim is
that, you can enter in how many spokes you've got.
Let's see, we've got 36 spokes.
And now it computes.
Hey, for a three cross front wheel with 36 spokes, you want
290 and 1/2 millimeter spokes.
And so you go to your bike shop and you say, please give
me 36 290 and a 1/2 millimeter spokes.
And the bike shop employee laughs at you because they
don't make them in half millimeter sizes.
I don't know why.
D. PARDO: Spokes are usually two millimeter increments.
Sometimes one.
AUDIENCE: Are they even or odd?
Typically even, or--
D. PARDO: Typically even.
PIAW NA: Wheelsmith will sell them in evens, Sapim will sell
them in odds.

And in general, what we'll do is we'll tell you to round up
to the next size that's longer than what your
computer with Spocalc.
In general, the problems are pretty obvious.
If your spokes are too short, you won't even be able to put
the wheel together.
If the spokes are too long, what will happen is eventually
the spokes themselves poke through these spoke holes and
you end up with 36 flats the first time you
ride down the hill.

And that's not desirable either.
But it's easier to deal with too long spokes than to deal
with too short spokes.
One of the other things you can do with the spreadsheet is
you can play around with both front and rear rims and have
combinations and try to get all the lengths in one so if
you're touring somewhere, you only have to carry one type of
spoke, or one length of spoke.
The other important thing is they also do offset spoke bed
So let's say you have a Velocity off-center rim, then
you can say, here's the rear rim, and let's try a Shimano
nine-speed hub here.
Here we go, a Shimano Dura-Ace 10 speed, and it's a real hub.
And what the calculator will tell you is here's are the
different lengths on each side.
Notice that they're different between the
left and the right.
And with the offset spoke bed, the tension on the right side
of the wheel is going to be 77% that of the
left side of the wheel.
If you have an asymmetrical rim in this case, what happens
is that just by changing that offset spoke bed number,
you'll see that the balance between the left and right
side of the wheel dropped dramatically from
77% to under 60%.
And that's a significant number when it comes to how
strong your rear wheel is.
So this is a very useful tool for figuring out, hey, how
much strength am I actually going to get by going to an
offset rear wheel versus a straight rear wheel?
D. PARDO: The offset rear wheel also helps keep the
loose spokes from going slack, or rather the outside rim
helps keep these loose spokes from going slack, which helps
keep the nipples from unscrewing and the wheel going
out of true.
So it tends to build not only a stronger wheel, but a
PIAW NA: If you're buying parts for the workshop, send
me and Pardo an email.
We'll hook you up with suppliers that we know of that
can get you some decent prices.
D. PARDO: We're also happy to entertain questions about,
well, this is what I think I want to do.

I can't solve mysteries.
I can't build you a one-gram wheel set.
AUDIENCE: Well then the two of you can fight over it.
D. PARDO: Right.
Thank you.
That ends the first session.
And if we owe you a book, come up here and we'll make you
sign for it, and we'll hand you the book.