Let's Talk Threads - for spoke nerds only

December 06, 2015 6 Comments

My fellow spoke nerds deserve something to chew on, even at the risk of boring other worthy readers.

Disclaimer: I’m going to share some magnified images of threads. Some of you may find these unexpectedly ugly and not representative of the named brands. Mind you, none of this post is intended to evaluate brands. Let’s just explore the details.

To begin, who are spoke nerds?

(1) They do not simply choose spokes with unquestioning brand loyalty, indifferent to details. Good news, we have spoke choices that make this mind set safe for riders.

(2) You only need to care to join the club. It starts with intention. We’re few in this niche and welcome anyone who wants to know more about physics, materials, economics, and design of spokes.

The saga of spokes is not over, just because nothing obvious has occurred for a few decades. the spokes of the future will be improved by spoke nerds of today.

(3) Many recent recruits are among the growing numbers of spoke machine users. Of course, spoke nerd orientation is not required for spoke machine use, but it is a great vantage point to observe and learn.

Thread form is guided by international standards: ISO, DIN, JIS, etc. to ensure good design and interchangeability. Early years of cycling did not benefit from global embrace of these standards. Today, DIN 7902 is the most important standard.

Here are glimpses of 3.

While there are other standards, these three are instructive. In particular, JIS is historically important as they were key as JP rebuilt its economy, post WWII, embracing the best engineering traditions available. As the upper end of the cycling industry migrated from JP to TW, JIS were the first standards to hold sway and as the migration continues to the mainland, they are still influential.

Notice how the peaks and valleys of DIN and ISO threads are blockish. Peaks are thick and sturdy. JIS puts more emphasis on the larger, smooth radius of the thread root (valley base). This makes sense for wire as the biggest danger in spoke threads is not thread stripping but fatigue fracture in the thread root.

Stripping is not much issue even with loose nipple-spoke fit because this fine thread has so much surface area and is designed for 4mm engagement (serious wheels serve up nearly twice).

Let’s look at some actual threads, at about 50X magnification.

Below are two cut on a Phil spoke machine. These are not meant to characterize Phil function but examples of thread form.

Last are two images from the spoke machine we sell. My bias is obvious, yet please do not assume too much. The discussion is the variety of thread form.

You can record such images yourself with a basic digital microscope or observe with a handheld magnifier. You should as you'll stunned from time to time.

Here is a commercially bought spoke whose supplier decided to shorten. Original threads on the right, botched threads on the left. Was one reason for this builder to buy his own machine.

Manual spoke machines have the advantage of slower speed so the thread is likely to be more uniform. Industrial threading occurs in a fraction of a second.

I am partial to the dies used in our machine. You can see they favor a larger radius in the thread root. The peaks become thinner, sometimes pointy, but the contribution to fatigue life has been measured. These dies are guided by JIS but take the root radius even further. It is a proprietary design.

Take away points:

(1) All threads showed are going to give outstanding performance during building and hard riding. We’re talking subtleties. Even the botched thread would likely succeed. That's how rugged the spoke thread system is.

(2) Common thread forms from ISO and DIN do not favor the largest root radius so useful to wire spokes.

(3) Manual spoke machines benefit from slower rate and can offer better finish as well as custom thread shape.

(4) The 14G spoke thread is incredibly effective and in such widespread use some have declared it the World’s Most Used Thread (next to last paragraph).

While a more effective thread solution for wire wheels is unlikely, we need to study the variables, improve our practice, and keep learning. Better components = better wheels, so do your part!

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