By Bill Dobson
As arranged on the ICEBIKE mailing list, I volunteered to perform hardness tests on a
few studs from winter bicycling tires. Several others agreed to send samples of
studs and shortly I received studs from 3 different studded tires: Nokian, IRC, and
Nashbar, to measure their hardness.
At last I have the stud hardness test results! The following is my report.
A little background first...
In a hardness test, a small indenter (in this case made of diamond) is pressed into the
surface of a metal sample with a known force. The result is a small impression, and the
size of the impression is an indication of hardness. The smaller the impression, the
harder the material. The term "Hardness" is really a measure of the ability of a
sample to resist indentation, and in itself it is meaningless, and only becomes useful
when compared to the hardness of something else. There is a definite relation between
hardness and strength and wear resistance. Harder materials are stronger and more wear
resistant.
To measure the hardness, the sample must be properly prepared. Standard metallographic
technique is to embed the sample in a plastic "mount" which allows the
technician to hold the sample in proper alignment for preparation. In this case, the studs
were laid on their side in the mount. The face of the mount was ground down, and in the
process the studs themselves were partially ground away, In this case, we ground the mount
until about half the studs were ground away, revealing a cross-section through the stud
centerline. This surface is then polished to a mirror smooth finish, since the hardness
impressions are microscopic and surface imperfections could affect the result, thus the
need for a flat smooth surface.
| Here is an image of the the prepared mount with the ground and
polished studs showing their cross sections. Click on the image for a
close-up view. It can be seen that the studs have a "T" shape cross
section. There is a head at one end (like a nail head), a body, and a tapered end, which
is the "business" end of the stud that makes contact with the ground. |
Photo Credit: Bill Dobson.
|
Now the results:
It is immediately obvious that the Nokian and IRC
studs are made from two pieces: the stud body which is steel, and
an insert brazed into the center of the stud. It is the brazed insert that is in contact
with the ground, and the body is simply a holder. The Nashbar stud is a single piece of
steel.
The Nokian insert had a hardness of 1700 KN (Knoop hardness scale). The IRC insert had
a hardness of 1400 KN The Nashbar had a hardness of 350 KN (corresponding to about 57 HRC
for those who care about such things).
The Nashbar stud is by visual examination and hardness testing, simply hardened steel.
It was harder on the surface than in the center, which implies a low alloy and/or low
carbon steel (ie: less expensive steel), as something this small should harden throughout
its thickness when heat treated - there should be no hardness gradient. I made no
attempt to identify the composition of the IRC or Nokian inserts (that would have been a
bit expensive), but my best guess is they are "carbide", a very hard, wear
resistant material commonly used for high wear applications like metal working tools, saw
blade edges, and so on.
A word of caution: Don't try to attach a "value" to the relative hardness of
the studs. The Nokian is not "5 times better than the Nashbar" nor will it
"last 5 times longer". All that can be said is that the Nokian and
IRC are "substantially harder and will be much more wear resistant" than the
Nashbar.
| UPDATE: The
Nashbar tires tested in this article are NOT the current tires
offered by Nashbar and reviewed here.
The tires mentioned here were an earlier variety than the current
tires, and by all reports the current tires are of much better
quality and have much better studs. |
As a metallurgist, and knowing the environment these tires run in, I would be very
surprised to see significant wear on a Nokian or IRC stud, whereas on road surfaces, I
would expect wear on the Nashbar. Running on dirt or ice the Nashbar may hold up
much longer.
On a personal note, I am impressed with the degree of technology exhibited by the
Nokian and IRC tires. There is considerably more cost involved in preparing the stud to
receive the insert, and then going through the brazing process, compared to the Nashbar
stud which is simply machined and then heat treated. I can understand why the Nokian tire
is so expensive! .
Background reading:
Microhardness
Testing
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