Inpoke — Part 1

Alright, another long post.
Today I'm talking about inpokes.
Not spokes—inpokes.
When you search Google for it,
it shows "Did you mean: spokes?"
So there's definitely no homonym in common terminology.
Well, that makes sense—this is my own made-up term.

First thing: unless otherwise noted,
in my diagrams and photos,
the right side represents the direction of travel.


When building a wheel, you thread spokes through the hub flange, but

when you thread spokes from the inside of the hub outward,

↑this state I'll call inpoke from now on in this blog.
I'm just being lazy—writing "spokes threaded from the inside" every time gets tedious.


Similarly, when you thread spokes from the outside of the hub inward,

↑I'll call this state outpoke from now on.
I could call it "reverse inpoke," but outpoke is easier to type.


Normal wheels come in two main lacing patterns.
A pattern where spokes don't cross from the hub center is called
radial lacing because the spokes appear to radiate outward.

I suspect the very first spoked wheels were probably radial-laced,
but radial lacing has both pros and cons (I'll explain later—this is already long),
and until materials and designs emerged around the late 1980s that could overcome those issues,
tangent lacing (like in the photo above) was the standard.


With tangent lacing, the spokes going through the hub flanges
alternate between inpokes and outpokes (except for special two-spoke patterns).


Two spokes emerging from adjacent hub flange holes that extend
in directions where they don't touch each other look like this in a diagram,


and this direction is close to tangent to the circle,
which is why this lacing pattern is called tangent lacing.


As I mentioned at the start,
everything that follows treats the right side as the direction of travel.

With all those spokes it gets confusing and hard to see,
so in the photo above I'll keep only the four spokes
whose red nipples are visible and clear away the rest.
Normal wheels have these four spokes as one group—
six groups makes 24H, seven makes 28H, eight makes 32H, and so on.

Before that, though...

I've prepared colored spokes. I'll thread them through as inpokes.
Red is the inpoke closer to me,
and blue is the inpoke farther from me—let me thread them through the hub.


↑When the two inpokes in the back relative to the direction of travel are
Italian lacing.


↑I flipped this around from before.
Now the inpokes are in front relative to the direction of travel.
This is reverse Italian lacing.


↑By contrast, when the four spokes have inpokes in front and back
relative to the direction of travel, that's
JIS lacing.
The red inpoke is the same as Italian, but
the blue inpoke is reversed.


↑With JIS lacing, flipping it over doesn't change the inpoke positions.

Whether inpokes extend forward or backward
relative to the direction of travel is extremely important.


Here's a 16H tangent-laced wheel with only the inpokes drawn.
Showing the near inpoke in red and far inpoke in blue,
Italian lacing looks like this diagram.


JIS looks like this. I'll say it again:
whether Italian or JIS, the red inpoke position is the same.


↑This is the direction they extend.


This, "when looking at the top half of the wheel, the inpoke points backward"—
this is crucial for rear wheels.
I'm calling this the "porcupine direction."


↑So here's a "right-inpoke-only wheel."
To belabor the point again: whether Italian or JIS,
the right-flange inpoke is always porcupine direction.


↓

During riding, the freewheel body has a sprocket on it,
the chain wraps around that, and when you press down the pedal
via the crank arm from above, there's intense twisting force forward.
Expressing that by hand looks something like this.

The freewheel won't let you see the hub flange,
so I'll hold the hub body and twist it forward.
To see how the force is applied, spoke tension is slack—
basically untensioned.

↓

See how the spokes become even more tightly compressed?
In an actual properly built wheel it won't deform this much,
but it shows the kind of load the spokes constantly endure.


So what happens if the right inpoke is pointing anti-porcupine direction?
This happens with reverse Italian or reverse JIS lacing, but...


↓

The spoke tension goes in the loosening direction instead.


Without tire pressure, the spokes would bulge out from the rim
like they're popping out.
When you're hammering down on the pedals hard,
which direction do you think better transmits that force
to the outside of the rear wheel?
Obviously the porcupine-direction inpoke, right?

"Well, that's obvious," you might say, but some complete bikes have hand-built wheels
in reverse Italian lacing, and some complete-wheel systems have
straight-spoke hubs where the rightmost spoke is anti-porcupine direction.
So it's worth keeping an eye out for that.
The specific examples get long, so I'll detail them later.


Say you have a rubber cylinder with evenly-spaced markings...

and you grab the end and twist it—the twist magnitude is larger
the closer you are to where the twist originates. Imagining this on a rear hub...

↓

it works out like this. The spoke taking the largest load from pedaling force
is the right inpoke, so the right inpoke should be porcupine direction.

Next is the rim-brake case.

A wheel with porcupine-direction inpokes is rolling.

I hit the brakes hard.
The rim stops instantly, but

the hub doesn't stop instantly, so the spokes
get compressed further in the porcupine direction.

That phenomenon happens.
With Italian lacing, this compression is equal on both sides,
but with JIS, only the left-side inpoke (relative to direction of travel)
gets the tension-relieving force.
I just find that left-right asymmetry really uncomfortable.


Let me look at it from a different angle.
On low-profile rims, the nipple holes alternate side-to-side.


↑Built, it looks like this.


Actually, this wheel is a Campagnolo Neutron, but


as the rim decal shows, Neutron has internal nipples.
The Neutron with external nipples is...
it gets long, so I'm cutting it. Not detailing this later either.


So, a rim with hole offset

gets built like this.


↑This blue marker here—for our purposes, imagine it's
"a magic knife that cuts through anything like tofu."


So I slice along the hole offset, nice and easy.

Around the valve hole I cut like this.


One more thing. For the hub flange,

↑I'll mark inpokes like this,

↑and outpokes like this.

And if I unfold the previous wheel into a flat pattern,

↑Italian lacing looks like this.
Red is right inpoke, blue is left inpoke.
The notches at the corners are where the valve hole was.
Read exactly, this is an 8H wheel with one group of inpoke/outpoke pairs,
but this is just a conceptual diagram for understanding force distribution,
so don't worry about whether such a wheel could actually be built.


Then showing just the inpokes:


↑JIS lacing looks like this.


Then showing just the inpokes:

↑By the way, "JIS stays JIS when flipped" can also be
expressed this way.


So "braking at the rim" or
"twisting the freewheel body forward on a rear wheel" amounts to
grabbing the hub section and pulling straight up in the diagram above.
Let me actually demonstrate.

Technical archive

Original Japanese post: のむラボ日記 #19