Yellow Saddle
Guru
- Location
- Loch side.
In this thread (warning, it may hurt sensitive people), @Milkfloat posted a link to a DT Swiss web page talking about spoke tension.
This graph grabbed my attention.
DT Swiss apparently takes a "fingerprint" of each wheel as it comes off the production line. The fingerprint shows the tension, of that specific wheel, in each spoke. Also, in a very apt graph, which helps to understand what's going on.
This graph is of a 28-spoke wheel and represents the tension in either side. The red shows the tension on one side, the black on the other. As you can see, maximum tension is about 1200N. This could be rear or front wheel, provided, if it is a front wheel, it is a disc wheel, hence the difference between left and right.
The graph fits in nicely with my postulation that a wheel that's perfectly true cannot have equal spoke tension and conversely, a wheel with equal spoke tension cannot be equally true.
I used to teach that to students in my wheelbuilding classes. They usually have a question such as, "why don't we just make all spokes equal tension and then the wheel will be true?"
The answer lies in the rim. It is an extruded rail, bent into a hoop and welded at the one end. Then it is drilled for spokes and drilled for a valve. Extrusions are not homogeneous. Some places have more material, others less. Further, the valve hole makes it weaker in one place and the weld thickens it at the opposite end. This all means that different tensions all around the wheel are required to make it run true.
If you look at the graph you can infer where the valve is - at position (spoke) 6. The weld, which is always placed opposite the valve hole is at position 13. Strangely enough it is not exactly at the opposite end. That's because the welding doesn't heat the joint perfectly evenly and, there's a lug inside that may not be placed exactly centre inside the joint.
The other variations are due to extrusion irregularities.
I love it when I see a great graph that does what it is supposed to do.
Thanks Milkfloat.
This graph grabbed my attention.
DT Swiss apparently takes a "fingerprint" of each wheel as it comes off the production line. The fingerprint shows the tension, of that specific wheel, in each spoke. Also, in a very apt graph, which helps to understand what's going on.
This graph is of a 28-spoke wheel and represents the tension in either side. The red shows the tension on one side, the black on the other. As you can see, maximum tension is about 1200N. This could be rear or front wheel, provided, if it is a front wheel, it is a disc wheel, hence the difference between left and right.
The graph fits in nicely with my postulation that a wheel that's perfectly true cannot have equal spoke tension and conversely, a wheel with equal spoke tension cannot be equally true.
I used to teach that to students in my wheelbuilding classes. They usually have a question such as, "why don't we just make all spokes equal tension and then the wheel will be true?"
The answer lies in the rim. It is an extruded rail, bent into a hoop and welded at the one end. Then it is drilled for spokes and drilled for a valve. Extrusions are not homogeneous. Some places have more material, others less. Further, the valve hole makes it weaker in one place and the weld thickens it at the opposite end. This all means that different tensions all around the wheel are required to make it run true.
If you look at the graph you can infer where the valve is - at position (spoke) 6. The weld, which is always placed opposite the valve hole is at position 13. Strangely enough it is not exactly at the opposite end. That's because the welding doesn't heat the joint perfectly evenly and, there's a lug inside that may not be placed exactly centre inside the joint.
The other variations are due to extrusion irregularities.
I love it when I see a great graph that does what it is supposed to do.
Thanks Milkfloat.