Determining Spoke Material and Measurements: Truth and Facts

The spoke tension needed to build a bicycle wheel or properly true a wheel depends on both the material and certain dimensions of the spoke.
Most spokes are composed of aluminum, steel, or stainless steel. There are some made from exotic materials such as carbon fiber and titanium. Again, proper tensioning to the spoke is dependent on knowing the material used.
Calvin Jones got a lot of comments when he used a small kitchen magnet to distinguish spoke material including stainless steel.
Before we get into this, let’s first talk about what steel and stainless steel.
Steel is composed of Iron atoms with carbon spaced between giving the iron durability and strength.
Stainless steel is actually a broad term used to refer to iron/carbon-based alloys containing chromium, nickel and other materials.
There are more than 100 grades of stainless steel. These are differentiated by the percentage of chromium, nickel, and other alloying elements.
Although similar in nature, these stainless steels do display some significant differences.
Each grade is used for specific purposes and comes with its own advantages and disadvantages.
When specific components are combined and processed, some will produce what we call austenite steel.
A face-centered cubic solid has atoms at the corners and, as the name implies, at the centers of the faces of its unit cells.
The term austenite is used to describe a face-centered cubic (FCC) iron or steel alloys that have this type of structure. It was named after Sir William Chandler Roberts-Austen, an Englishman known for his studies of the physical properties of metals.
Austenitic stainless 304 and 316 are the most commonly used types because of their exceptional resistance to heat and corrosion, it's used extensively in many industries. Grades 304 and 316 are high austenite stainless and should be non-magnetic.
But I must point out that any process such as cold working (forging) as well as welding can change the crystal structure of stainless steel can cause austenite to be converted to the magnetic forms of iron. These processes include cold working and welding. It is also possible for austenite to spontaneously convert to martensite at low temperatures. To complicate matters further, the magnetic properties of these alloys depend on the alloy composition. Within the allowed ranges of variation of Ni and Cr, significant differences in magnetic properties may be observed for a given alloy.
Now remember, stainless steel comes in over 100 grades and not only varies in added components but also in the degree of austenite when formed.
Can we use a magnet to distinguish between the composition of various spoke material.
Aluminum
Carbon Steel
Wheel Master
DT spokes
CN spokes
Sapim spokes
Carbon spokes
Magnets may give us a clue but are not overly helpful in differentiation. Some stainless-steel spoke are magnetic and some not.
So, what can we go by:
• Try a magnet realizing it limits:
a. probably carbon / iron (ferric) steel
b. weakly magnetic - some stainless spokes
c. non-magnetic doesn’t help us - could be stainless but may be titanium, aluminum, other
• It’s look, i.e., physical appearance (aluminum is often a bit “frosty” looking)
• Scraping (aluminum is soft and scratches easily)
• Brand - sometimes marked on the end of the spoke may give us a clue
• Finally, search the internet for wheel manufacturer or contact them
Finally, with experience, you can make an educated guess.
Next measurement using calipers:
1. Round Spokes:
• Measure diameter toward mid-point of the spoke and closer to the spoke nipple
• If same, you have a straight gauge spoke and mark down the diameter
• If you note a 2 mm difference, you have a double butted spoke. Mark down each number.
2. Flat Spokes:
• Measure the width and record
• Measure the thickness and record
With a good guess as to the material and the measurement of the spoke diameter, width and thickness, one can now proceed to use the correct spoke tension chart.