dashdotrobot
commented
6 years ago Hi Bart,
The reasoning for putting the forces on nodes 1 and 35 as well is that the tire has some equivalent stiffness which effectively spreads the load across some length along the rim. This can especially be seen in measurements of the bending moment of the rim directly where the force is applied. If the force were applied at a single point, the bending moment would have a discontinuous slope (and be very high) at the point of application. Instead, experiments by Burgoyne and Dilmaghanian indicate that the bending moment more closely matches that which would be expected from a distributed load on the rim.
Here's the citation: https://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9399(1993)119:3(439)
Sorry for the engineering jargon... I don't know what your background is.
To your second question, (how many spokes?), I would say it depends on what you are trying to optimize. If you want a strong wheel, indeed you should add more spokes. But that adds weight, rotational inertia, and air drag. The conventions around how many spokes is "enough" have shifted over the years, and don't seem to be based on rigorous theory. If the number of front and rear spokes is to be different, it makes sense to put more spokes on the rear wheel, since the rear sees more weight and is usually asymmetric (leading to lower tensions on the non-drive side).
I am quite interested in these questions (How strong will a wheel be? What is the optimum tension? etc). If you are interested and care to wade through some math and mechanics jargon, my publications, many of which are related to the wheel, are here: http://dashdotrobot.com/pages/curriculum-vitae.html
Take care, ~matt
Dear Matthew,
I got your code to run properly and find the results interesting.
In your example "example_stand_on_spokes.py"
What is the reasoning to add forces to node 1 and 35.
Wouldn't it be closer to "real world" to just put the force on node 0?
FYI, I'm interested in this is because I cannot find any quality reasoning for the spoke count in commercial available bicycle wheels and the information supplied by wheel builders. Wheel builders on their websites have this dropdown box to select front/rear wheel spoke count. Why choose 20/24, 24/28 or 28/32? If you are a heavier rider, put more spokes. Seems logical, but how much exactly? These are the kind of questions I like to find an answer to. Besides that, bicycle wheels are an amazingly complex mechanical structure. It's intriguing :-)
Regards
Bart