I investigated the spoke specific gravity of Hoshi's Aero SB3 spokes.
"Spoke specific gravity" is a term I coined for this blog—
it's the ratio of how much a spoke weighs per 1mm of length compared to a 2.0mm plain spoke,
expressed as a percentage where the plain spoke equals 100%.
I've written this many times before, but as spokes get longer,
the proportion of the butted section relative to the overall spoke length
generally increases (whether round or flattened).
So theoretically, a butted spoke of 100mm versus one of 100000mm would show
a difference in spoke specific gravity,
but within the practical range of 240–310mm used for 700C wheels,
the variation isn't significant.
I use a scale that can measure to 0.1g.
Since the maximum measurable weight is 300g,
when testing multiple spokes, I adjust so the total doesn't exceed 300g.
It's always better to have more samples,
but for some lengths I have limited stock on hand.
Here's what I found:
282mm × 20 spokes = 135.1g
280mm × 44 spokes = 295.6g
278mm × 44 spokes = 294.4g
276mm × 38 spokes = 251.8g
266mm × 13 spokes = 83.0g
258mm × 33 spokes = 204.4g
I have more samples, but I'll stop here.
When I tabulate it, it looks like this.
There's one place with a dashed line, and there's a reason for it:
The Aero SB shows that below a certain length (around 270mm?),
the manufacturing process or jigs change, and the non-butted section becomes longer.
When this happens, the proportion of the 2.0mm plain (100% specific gravity) section increases,
so the spoke specific gravity would be expected to increase.
I calculated the weight per 1mm of length.
Contrary to what I just said, even crossing the dashed line,
there's no significant difference in the numbers.
The reason 276mm and 258mm show the same value marked "essentially the same"
is that when rounding to seven decimal places, the first six digits came out identical.
The reference value for 100% spoke specific gravity is 0.0257,
so I calculated the specific gravity from there.
The difference in decimals between the 276mm and 258mm results
is due to rounding at different decimal places before calculation.
From these results, I'm setting the spoke specific gravity of the Aero SB3 (No. 14) at
93.4%.
What's surprising is that even with just 13 spokes at 266mm,
we get nearly an average value.
If the scale resolution were 1g instead of 0.1g,
I'd want to increase the sample size about tenfold.
This spoke specific gravity number is quite useful in several ways.
First, it helps estimate finished wheel weight.
For example, if you have 24 spokes of 290mm Aero SB3,
you calculate: 290 × 24 × 0.0257 × 0.934 = 167.06g,
so the spoke weight is about 167g.
This is quite accurate.
Then you just add the weights of the hub, rim, and nipples (preferably measured, or use published specs),
and you can estimate the wheel weight pretty well.
By the way, if I calculate the highest measured value—278mm × 44 spokes × 294.4g—
using the spoke specific gravity of 93.4%, I get 293.6g.
You'd rarely use 44 spokes in a single wheel,
but even with 44 spokes, the error is only about this much.
The other use is when doing asymmetrical builds,
calculating spoke tension differences left and right through computation.
In my case, I use "the cross-sectional area ratio of a virtual plain spoke with that spoke's specific gravity."
This treats Aero SB3 the same as a plain spoke with 1.868mm diameter
because "they have the same specific gravity, so their behavior regarding spoke tension is the same"—
but in extreme terms, you could theoretically have a round-butted spoke that's 2.0–1.0–2.0mm
with 93.4% specific gravity, and you'd have to question whether it really behaves identically.
However, I've had no practical problems (empirical results match the calculations reasonably well),
so I use this as the basis for certain calculations.
As for why you need to convert butted spokes into plain equivalents—
that's proprietary information, so I can't write about it here.
Since this blog also serves as my personal notes,
I'm writing the Aero SB3 spoke specific gravity here for quick reference.
I could just write the number, but I wanted to document the method for measuring spoke specific gravity
and show that you can get reliable results even with surprisingly few samples,
so I included the photos.
This Aero SB3 isn't a current product.
It's discontinued, and I'm hoping for a re-release,
but I'm sure an identical Aero SB3 will never be available again.
Someone recently left a comment asking why I don't use Hoshi spokes,
so I'll answer that here.
Hoshi spokes used to have spoke head stamps without exception:
"H" for Starbright, and "☆" for stainless.
(Starbright is technically a stainless spoke, but here "stainless" refers to the product name.)
Currently, these stamps are apparently mixed on some products,
but I can't see a rational reason to make a product harder to distinguish when it's already difficult to tell visually.
It's no longer a product I can trust to sell to customers.
Also, the magnetic response differs significantly between the current Starbright
and this older Starbright.
Spoke magnetism is extremely important to me in assessing material properties.
If that's very different, it means the material or manufacturing process (work hardening, etc.) has changed significantly,
so I can't consider them the same thing.
Frankly, they're different products.
If Starbright had stayed the same as before,
especially for plain spokes, it's actually a spoke I prefer over DT Champion,
so I'd certainly be using it for my regular wheel builds.
"Spoke specific gravity" is a term I coined for this blog—
it's the ratio of how much a spoke weighs per 1mm of length compared to a 2.0mm plain spoke,
expressed as a percentage where the plain spoke equals 100%.
I've written this many times before, but as spokes get longer,
the proportion of the butted section relative to the overall spoke length
generally increases (whether round or flattened).
So theoretically, a butted spoke of 100mm versus one of 100000mm would show
a difference in spoke specific gravity,
but within the practical range of 240–310mm used for 700C wheels,
the variation isn't significant.
I use a scale that can measure to 0.1g.
Since the maximum measurable weight is 300g,
when testing multiple spokes, I adjust so the total doesn't exceed 300g.
It's always better to have more samples,
but for some lengths I have limited stock on hand.
Here's what I found:
282mm × 20 spokes = 135.1g
280mm × 44 spokes = 295.6g
278mm × 44 spokes = 294.4g
276mm × 38 spokes = 251.8g
266mm × 13 spokes = 83.0g
258mm × 33 spokes = 204.4g
I have more samples, but I'll stop here.
When I tabulate it, it looks like this.
There's one place with a dashed line, and there's a reason for it:
The Aero SB shows that below a certain length (around 270mm?),
the manufacturing process or jigs change, and the non-butted section becomes longer.
When this happens, the proportion of the 2.0mm plain (100% specific gravity) section increases,
so the spoke specific gravity would be expected to increase.
I calculated the weight per 1mm of length.
Contrary to what I just said, even crossing the dashed line,
there's no significant difference in the numbers.
The reason 276mm and 258mm show the same value marked "essentially the same"
is that when rounding to seven decimal places, the first six digits came out identical.
The reference value for 100% spoke specific gravity is 0.0257,
so I calculated the specific gravity from there.
The difference in decimals between the 276mm and 258mm results
is due to rounding at different decimal places before calculation.
From these results, I'm setting the spoke specific gravity of the Aero SB3 (No. 14) at
93.4%.
What's surprising is that even with just 13 spokes at 266mm,
we get nearly an average value.
If the scale resolution were 1g instead of 0.1g,
I'd want to increase the sample size about tenfold.
This spoke specific gravity number is quite useful in several ways.
First, it helps estimate finished wheel weight.
For example, if you have 24 spokes of 290mm Aero SB3,
you calculate: 290 × 24 × 0.0257 × 0.934 = 167.06g,
so the spoke weight is about 167g.
This is quite accurate.
Then you just add the weights of the hub, rim, and nipples (preferably measured, or use published specs),
and you can estimate the wheel weight pretty well.
By the way, if I calculate the highest measured value—278mm × 44 spokes × 294.4g—
using the spoke specific gravity of 93.4%, I get 293.6g.
You'd rarely use 44 spokes in a single wheel,
but even with 44 spokes, the error is only about this much.
The other use is when doing asymmetrical builds,
calculating spoke tension differences left and right through computation.
In my case, I use "the cross-sectional area ratio of a virtual plain spoke with that spoke's specific gravity."
This treats Aero SB3 the same as a plain spoke with 1.868mm diameter
because "they have the same specific gravity, so their behavior regarding spoke tension is the same"—
but in extreme terms, you could theoretically have a round-butted spoke that's 2.0–1.0–2.0mm
with 93.4% specific gravity, and you'd have to question whether it really behaves identically.
However, I've had no practical problems (empirical results match the calculations reasonably well),
so I use this as the basis for certain calculations.
As for why you need to convert butted spokes into plain equivalents—
that's proprietary information, so I can't write about it here.
Since this blog also serves as my personal notes,
I'm writing the Aero SB3 spoke specific gravity here for quick reference.
I could just write the number, but I wanted to document the method for measuring spoke specific gravity
and show that you can get reliable results even with surprisingly few samples,
so I included the photos.
This Aero SB3 isn't a current product.
It's discontinued, and I'm hoping for a re-release,
but I'm sure an identical Aero SB3 will never be available again.
Someone recently left a comment asking why I don't use Hoshi spokes,
so I'll answer that here.
Hoshi spokes used to have spoke head stamps without exception:
"H" for Starbright, and "☆" for stainless.
(Starbright is technically a stainless spoke, but here "stainless" refers to the product name.)
Currently, these stamps are apparently mixed on some products,
but I can't see a rational reason to make a product harder to distinguish when it's already difficult to tell visually.
It's no longer a product I can trust to sell to customers.
Also, the magnetic response differs significantly between the current Starbright
and this older Starbright.
Spoke magnetism is extremely important to me in assessing material properties.
If that's very different, it means the material or manufacturing process (work hardening, etc.) has changed significantly,
so I can't consider them the same thing.
Frankly, they're different products.
If Starbright had stayed the same as before,
especially for plain spokes, it's actually a spoke I prefer over DT Champion,
so I'd certainly be using it for my regular wheel builds.