When building a wheel, you need to calculate spoke length,
and the information necessary for that includes rim support length (the distance between tire-bearing surfaces),
hub flange width, and hub flange diameter — three things in total.
Today I'm writing about the left-right difference in rear hub flange width.
First, about flange width.
Flange width is the dimension from the outside of one flange to the outside of the opposite flange.
In the diagram above, I'm calling the distance from the center of the entire hub to the right flange edge R,
and to the left flange edge L.
As a tangent, the spoke length that comes out of this calculation is the length of radial spokes.
For crossed spokes, strictly speaking the dimension should be measured to the inside of the flange,
but in practice the difference is absorbed by the nipple thread length,
so you don't need to calculate two different spoke lengths from one side of the flange.
Taking Shimano's FH-6700 as an example.
In Shimano's catalog (more on that later), the FH-6700 lists
flange width as 59.2mm and
ochoko amount as 8.9mm.
The 59.2mm flange width is L plus R in the diagram above.
But what exactly is the 8.9mm ochoko amount?
We need to determine L and R from these two figures,
but the definition of the term "ochoko amount" is unclear,
so actually you can't determine it from these numbers alone.
Since I know the answer beforehand, I can work backwards from the answer to determine
what measurement Shimano actually means by "ochoko amount"
through calculation.
First, let me mark the midpoint of the flange width (L+R).
Since it's half of 59.2mm, it's at 29.6mm from the flange edge.
"Shimano's ochoko amount" is the amount by which L exceeds 29.6mm.
This is shown as the blue line in the diagram above.
Half the flange width is (L+R)/2.
Subtracting "Shimano's ochoko amount" from that gives R,
and adding it gives L.
The calculation itself is straightforward, but is Shimano's 8.9mm
really a valid measurement to call "ochoko amount"?
The concept of ochoko amount arose from the fact that you need to fit many sprockets
on the rear freewheel side, so the freewheel-side flange is offset toward the center.
When this happens, L is always greater than R,
and L−R becomes a positive number.
I believe this "L−R" is what the term "ochoko amount" should refer to.
Now let me calculate L−R. Since I know the values of L and R,
it comes out easily: 17.8mm.
17.8mm is exactly double "Shimano's ochoko amount."
So "Shimano's ochoko amount" is (L−R)/2.
Whether "ochoko amount" refers to (L−R) or (L−R)/2,
as long as you understand the scope of the definition, it's just a matter of calculation either way,
↑Shimano listed R and L dimensions directly until 2011.
(The 20.7/38.5 in the table above represents that)
↑This is from the 2013 catalog,
and from 2012 the notation changed to flange width and (alleged) ochoko amount.
(The 59.2 and 8.9 in the table above represent that)
Why did they adopt such confusing notation?
Spoke tension imbalance increases with larger ochoko amounts, but assuming the right flange width stays the same,
a larger flange width means greater lateral stiffness.
Spoke tension imbalance can be compensated through building technique,
but there's nothing you can do about the lack of lateral stiffness from a narrow flange width—
this is something I've mentioned repeatedly.
Basically, rear hubs with larger ochoko amounts are better, I think.
The FH-9000 has an ochoko amount of 9.75mm, up from the FH-6700's 8.9mm.
At face value this is a welcome development, but
let me calculate the actual widths of R and L.
↑Actually, the FH-6700 has the wider left flange.
↑This 18.7mm on the freewheel side is the problematic part.
For up to 10-speed, most hubs have around 21mm,
but for 11-speed the freewheel-side flange was narrowed by about 2mm,
so the apparent ochoko amount increased even though
the actual flange width narrowed.
Is it cynical to suggest they changed the notation from direct R and L measurements
to flange width and (alleged) ochoko amount to obscure this?
Separately, the FH-7900 hub comes in only 28H with the
right flange narrowed by 0.4mm.
I don't see any rational reason for narrowing it by 0.4mm,
and what's strange is that 24H uses the same dimensions as 32H and 36H,
while only 28H is different.
This is speculation, but when manufacturing hub shells,
they probably don't do it as "make the shell"→"drill holes later,"
but rather "drill the holes while making the shell."
Perhaps when manufacturing 28H hub shells, they made
a large batch with freewheel-side dimensions 0.4mm different
from other spoke counts by mistake.
Rather than remake all those shells, I suspect they figured it paid
to just note the difference clearly in the catalog.
The FH-9000 is also different in 28H only.
With flange width 56.5mm and (alleged) ochoko amount 9.95mm,
calculating gives
FH-9000 (28H): R=18.3mm, L=38.2mm
FH-9000 (other than 28H): R=18.7mm, L=38.2mm.
So the FH-9000 appears to be basically an FH-7900 shell finished differently
with an 11-speed freehub body attached.
↑This is an excerpt from Shimano's hub dimension reference covering
Dura-Ace, Ultegra, and 105. It's a bit old, going back to the 7900 era,
but I was looking for it specifically to judge "high lateral stiffness hubs" not by flange width
but by how far the left flange extends.
The full document is a PDF. Details here→here
I linked to it to show it's a primary source, Shimano's official documentation.
The link will probably break eventually, so I captured it as the image above.
This thing is pretty messed up.
• FH-7900 has left-right flange widths reversed
It shows L=20.15mm, R=36.35mm, which doesn't make sense at all.
• FH-7900 and HB-7900 flange diameters are wrong
FH-7900 shows left 52.8mm, right 53.8mm, and
HB-7900 shows 48.4mm on both sides,
which falls somewhere between a Dura-Ace track bike large-flange hub
and a road hub. Impossible.
• FH-6500, thought to be an Ultegra hub, appears in the Dura-Ace group.
That's a new fact.
• The 105 Hub 5500 and its successor 5501
have different hub dimensions, yet
HB-5500 (207g)→HB-5501 (148g),
FH-5500 (286g)→FH-5501 (348g)
show these weight differences.
Upon investigation, the correct figures for 5500 are actually front 148g, rear 348g too.
With so many problems, rather than trust this, I want to pull flange width
specifications from a catalog with reliable data.
↑Dura-Ace
↑Ultegra
↑105
Only the three hubs shown in the diagram above have right flange width of 20mm or greater
and left flange width of 38mm or greater.
Of these, the FH-6600 was a fantastic hub that came in 24H and 28H as well,
but with the nearly identical FH-6700, the lineup changed to only 32H and 36H.
Nomu Lab Wheel No. 33 will use the 6700 hub.
↑The FH-6700 manual appears to be a copy-paste of the FH-6600,
with the 24H and 28H entries forgotten in the deletion process. Annoying.
If the FH-6700 came in 24H, I'd buy 10 or even 20 of them.
Apart from spoke count availability,
the FH-6700 is one of Shimano's most extended-left-flange rear hubs in history—
this is what I wanted to say, which is why I was looking into all this.
and the information necessary for that includes rim support length (the distance between tire-bearing surfaces),
hub flange width, and hub flange diameter — three things in total.
Today I'm writing about the left-right difference in rear hub flange width.
First, about flange width.
Flange width is the dimension from the outside of one flange to the outside of the opposite flange.
In the diagram above, I'm calling the distance from the center of the entire hub to the right flange edge R,
and to the left flange edge L.
As a tangent, the spoke length that comes out of this calculation is the length of radial spokes.
For crossed spokes, strictly speaking the dimension should be measured to the inside of the flange,
but in practice the difference is absorbed by the nipple thread length,
so you don't need to calculate two different spoke lengths from one side of the flange.
Taking Shimano's FH-6700 as an example.
In Shimano's catalog (more on that later), the FH-6700 lists
flange width as 59.2mm and
ochoko amount as 8.9mm.
The 59.2mm flange width is L plus R in the diagram above.
But what exactly is the 8.9mm ochoko amount?
We need to determine L and R from these two figures,
but the definition of the term "ochoko amount" is unclear,
so actually you can't determine it from these numbers alone.
Since I know the answer beforehand, I can work backwards from the answer to determine
what measurement Shimano actually means by "ochoko amount"
through calculation.
First, let me mark the midpoint of the flange width (L+R).
Since it's half of 59.2mm, it's at 29.6mm from the flange edge.
"Shimano's ochoko amount" is the amount by which L exceeds 29.6mm.
This is shown as the blue line in the diagram above.
Half the flange width is (L+R)/2.
Subtracting "Shimano's ochoko amount" from that gives R,
and adding it gives L.
The calculation itself is straightforward, but is Shimano's 8.9mm
really a valid measurement to call "ochoko amount"?
The concept of ochoko amount arose from the fact that you need to fit many sprockets
on the rear freewheel side, so the freewheel-side flange is offset toward the center.
When this happens, L is always greater than R,
and L−R becomes a positive number.
I believe this "L−R" is what the term "ochoko amount" should refer to.
Now let me calculate L−R. Since I know the values of L and R,
it comes out easily: 17.8mm.
17.8mm is exactly double "Shimano's ochoko amount."
So "Shimano's ochoko amount" is (L−R)/2.
Whether "ochoko amount" refers to (L−R) or (L−R)/2,
as long as you understand the scope of the definition, it's just a matter of calculation either way,
↑Shimano listed R and L dimensions directly until 2011.
(The 20.7/38.5 in the table above represents that)
↑This is from the 2013 catalog,
and from 2012 the notation changed to flange width and (alleged) ochoko amount.
(The 59.2 and 8.9 in the table above represent that)
Why did they adopt such confusing notation?
Spoke tension imbalance increases with larger ochoko amounts, but assuming the right flange width stays the same,
a larger flange width means greater lateral stiffness.
Spoke tension imbalance can be compensated through building technique,
but there's nothing you can do about the lack of lateral stiffness from a narrow flange width—
this is something I've mentioned repeatedly.
Basically, rear hubs with larger ochoko amounts are better, I think.
The FH-9000 has an ochoko amount of 9.75mm, up from the FH-6700's 8.9mm.
At face value this is a welcome development, but
let me calculate the actual widths of R and L.
↑Actually, the FH-6700 has the wider left flange.
↑This 18.7mm on the freewheel side is the problematic part.
For up to 10-speed, most hubs have around 21mm,
but for 11-speed the freewheel-side flange was narrowed by about 2mm,
so the apparent ochoko amount increased even though
the actual flange width narrowed.
Is it cynical to suggest they changed the notation from direct R and L measurements
to flange width and (alleged) ochoko amount to obscure this?
Separately, the FH-7900 hub comes in only 28H with the
right flange narrowed by 0.4mm.
I don't see any rational reason for narrowing it by 0.4mm,
and what's strange is that 24H uses the same dimensions as 32H and 36H,
while only 28H is different.
This is speculation, but when manufacturing hub shells,
they probably don't do it as "make the shell"→"drill holes later,"
but rather "drill the holes while making the shell."
Perhaps when manufacturing 28H hub shells, they made
a large batch with freewheel-side dimensions 0.4mm different
from other spoke counts by mistake.
Rather than remake all those shells, I suspect they figured it paid
to just note the difference clearly in the catalog.
The FH-9000 is also different in 28H only.
With flange width 56.5mm and (alleged) ochoko amount 9.95mm,
calculating gives
FH-9000 (28H): R=18.3mm, L=38.2mm
FH-9000 (other than 28H): R=18.7mm, L=38.2mm.
So the FH-9000 appears to be basically an FH-7900 shell finished differently
with an 11-speed freehub body attached.
↑This is an excerpt from Shimano's hub dimension reference covering
Dura-Ace, Ultegra, and 105. It's a bit old, going back to the 7900 era,
but I was looking for it specifically to judge "high lateral stiffness hubs" not by flange width
but by how far the left flange extends.
The full document is a PDF. Details here→here
I linked to it to show it's a primary source, Shimano's official documentation.
The link will probably break eventually, so I captured it as the image above.
This thing is pretty messed up.
• FH-7900 has left-right flange widths reversed
It shows L=20.15mm, R=36.35mm, which doesn't make sense at all.
• FH-7900 and HB-7900 flange diameters are wrong
FH-7900 shows left 52.8mm, right 53.8mm, and
HB-7900 shows 48.4mm on both sides,
which falls somewhere between a Dura-Ace track bike large-flange hub
and a road hub. Impossible.
• FH-6500, thought to be an Ultegra hub, appears in the Dura-Ace group.
That's a new fact.
• The 105 Hub 5500 and its successor 5501
have different hub dimensions, yet
HB-5500 (207g)→HB-5501 (148g),
FH-5500 (286g)→FH-5501 (348g)
show these weight differences.
Upon investigation, the correct figures for 5500 are actually front 148g, rear 348g too.
With so many problems, rather than trust this, I want to pull flange width
specifications from a catalog with reliable data.
↑Dura-Ace
↑Ultegra
↑105
Only the three hubs shown in the diagram above have right flange width of 20mm or greater
and left flange width of 38mm or greater.
Of these, the FH-6600 was a fantastic hub that came in 24H and 28H as well,
but with the nearly identical FH-6700, the lineup changed to only 32H and 36H.
Nomu Lab Wheel No. 33 will use the 6700 hub.
↑The FH-6700 manual appears to be a copy-paste of the FH-6600,
with the 24H and 28H entries forgotten in the deletion process. Annoying.
If the FH-6700 came in 24H, I'd buy 10 or even 20 of them.
Apart from spoke count availability,
the FH-6700 is one of Shimano's most extended-left-flange rear hubs in history—
this is what I wanted to say, which is why I was looking into all this.