Need help figuring out what my spokes are made of
 

I recently broke a spoke that was mounted on the Bontrager AT-750 rims that came with my new Trek 2016 7.2FX bike. I was about to install a new steel spoke I'd bought, but while watching this video ( ) about the Park Took Wheel Tensioning App, I realized I hadn't thought to check the material my old spokes are made of before buying replacements.

As that video suggested, I checked whether the old spokes react to a magnet and found they don't at all, so they don't seem to be steel. The new spokes, on the other hand, react very strongly to a magnet. This leads me to believe the old spokes are likely to be aluminum.

On the other hand, it's my understanding from that video that aluminum spokes are likely to have a larger diameter than steel spokes, but the old and new ones are both 2 mm. This seems to contradict my earlier guess that the old spokes are likely to be aluminum.

I'm guessing titanium is a more expensive material, such that a manufacturer wouldn't install spokes made from it on such a low-end rim.

I looked on the web and couldn't find information on what kind of spokes Trek installed on these rims when shipping this bike.

Not sure where to go from here when it comes to determining the material the spokes are made of. Any suggestions?

In case it's relevant, the old spokes are about the same weight (7 g) as the new steel spokes of the same size (292 mm).

Most spokes today are SS and non-magnetic so you should use the same type of material to get correct tension on all spokes. Another difference in spokes is diameter. Some spokes are the same diameter for the entire length from the "J" hook at the hub to the end of the threaded area at the nipples. Other spokes have one thickness at the ends, the hub or the rim, and have a thinner section between those points. This type are called butted spokes and their purpose in life is to provide the necessary thickness at the ends where needed and the thinner section, since it can stretch a bit more, will distribute tension more evenly to the rim which in turn produces greater durability of both rim and spokes. It is best to be consistent in spoke material for any one wheel. I hope tis helps.

Your old spokes are undoubtedly stainless steel. All makers of good spokes like DT, Wheelsmith, Sapim, etc. use stainless steel and even reasonably low cost wheels use them.

Aluminum and Titanium are used only on specialty (read expensive) wheels and rarely then.

Thanks for clearing that up, folks. A bit misleading that the Park Tool video suggests stainless steel spokes must be magnetic.

Some versions of stainless steel are slightly magnetic. I'll also add that a built wheel has it's own tension meter, the rim. When the rim is centered and true the replacement spoke is the correct tension. Andy

Normal magnets are not strong enough to have a noticeable attraction to most alloys of stainless steel. However if you use a neodymium magnet which is many times more powerful than a normal magnet, then it will attract most types of stainless with seemingly the same force as it does regular steel.

Don't know what to say though about your example though. However if you call or email Trek, I'm pretty sure they'd answer your question as to what the spokes are made of. Maybe even tell you where to get identical replacements if that is what you want.

I'm not certain how accurate tension meters for spokes are when the spokes are not the same. That might be something to ask a wheel builder.

There are both magnetic and non- or weakly-magnetic corrosion-resistant steel alloys, so a magnet is of limited use.

Alloys of metals are assigned Numbers, those will offer insight
to what the various minerals in an alloy are, by %..

Tension meters generally don't read outright tension. The Park for example reads an "index" value, that you then pull out a conversion chart based on the material and butting/profile of the spoke. Take for example the table for the Park TM-1:

https://www.parktool.com/assets/doc/...conv-table.pdf

Now...the TM-1 being basically a spring scale measuring flex, is as precise/accurate as a spring scale gets and prone to the same drift-with-use a spring scale is. Enterprising people on RBR open-sourced a home-built digital spoke tension gauge which is far cheaper than the Park:

https://forums.roadbikereview.com/co...er-366447.html

$25 USD and a bit of your time plus access to a 3D-printer

And someone else came up with a relatively cheap calibration rig for a tension-meter:

https://forums.roadbikereview.com/co...ce-366842.html

$80 in parts plus some of your time.


Which makes the $80USD Park TM-1 look like a waste of money on a quite frankly underwhelmingly engineered and cheaply built gadget....seriously Park Tool got owned by a couple random people on the internet here.