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Old 09-21-2010, 04:57 AM   #21 (permalink)
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I think an odd number of spokes is more appealing to the human eye.

I see 3-spoked alloys every so often, mostly on Mercedes. I believe they are not good for larger diameter wheels because the distance between spokes is big enough to allow denting/bending. I hate 4-spoke wheels, though.

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Originally Posted by CapriRacer View Post
I've heard that using prime numbers has the effect of isolating vibrations. So 5, 7, or 9 are common used when the number of "X" is chosen.
Um, 9 isn't a prime number.

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Hey, that's cheating!!

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How about the 8-spoke DaVinci wheel?


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Old 09-21-2010, 10:06 AM   #22 (permalink)
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Quote:
Originally Posted by Piwoslaw View Post
Um, 9 isn't a prime number.
Prime numbers are desirable here because they have few divisors, and the ones they have are large. A 9-spoke wheel may have resonant vibrations at 1, 3, and 9 times wheelspeed, while a 6 spoke wheel may at 1, 2, 3, and 6 times wheelspeed.

Sometimes, resonant vibrations don't matter. e.g. if there's enough damping for the vibration to die out before the next excitation arrives, if excitations at that frequency are exceedingly unlikely, or if the frequency of vibration is too high for humans to perceive.
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Old 09-21-2010, 07:23 PM   #23 (permalink)
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Originally Posted by RobertSmalls View Post
Sometimes, resonant vibrations don't matter. e.g. if there's enough damping
for the vibration to die out before the next excitation arrives, if excitations at
that frequency are exceedingly unlikely, or if the frequency of vibration is too
high for humans to perceive.
Robert,

I'm trying to understand this whole matter.

I have seen wheels with 3, 4, 5, 6, 7, 8,9, 10 and 11 spokes.

Beyond this it's too hard for me to count the spokes as they spin.

Presumably, all of these arrangements will run safely from 0 MPH, well up
beyond the highest legal Posted Speed Limit.

Since I haven't heard of any X numbered spoke wheel recall, can I presume
that whether through intentional design or blind luck, none of the issues you
have identified are likely to come up.

I tried to find an Internet site, blog, document, whatever discussing
wheel/spoke design, spoke cross section vs. number, etc.
Couldn't find anything.

Do you have any idea's for self-paced learning on this?
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Old 09-21-2010, 08:08 PM   #24 (permalink)
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Rokeby,

All the wheels on the road are safe. Some are heavier than they need to be, and some transmit more NVH than they ought to. The number of spokes is a very minor point, but lacking small divisors in your symmetry is generally a good way to avoid resonant vibration at lower frequencies.

An even-numbered spoke count is a sign that designers and stylists came up with something, then told the engineers to make it work. An odd-numbered spoke count indicates the process went the other way around.

Further reading? Nah. The math behind NVH is boring, and since it's so far beyond the scope of the DIY'er, there's not much written on it.
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Old 09-21-2010, 10:12 PM   #25 (permalink)
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...here's the DaVinci wheel I can relate to:

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Old 09-21-2010, 11:36 PM   #26 (permalink)
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AFAIR, the only two wheels that were engineered rather than styled were the tension-spoked (bicycle) wheel, which was actually developed for the still unsuccessful aircraft of the mid-1800s. At higher loadings and smaller diameters, the spokes get thick enough to take compression loads, and the end fittings become useless weight.
In the 60s, the Minilite was designed as a superior alternative for sport and racing cars, with some actual calculations.
While unsprung weight is one of the biggest factors in ride and handling, the nature of wheels is almost unresponsive to fine-tuning of the structure. You need so much material for the hub and rim, almost anything can connect the two with reasonable success. These days, with FEA readily available, better wheels could probably be designed, but the performance increment would be easily overcome by BS and styling preferences. Cars are about image, not engineering goals. Nobody Needs fancy rims to drive around urban decay, but that is where you find them most often.
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Old 09-23-2010, 01:44 PM   #27 (permalink)
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Any number that divides evenly into 360 is a easily usable number of spokes, as they can be spaced evenly around the circle.
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Old 09-23-2010, 04:14 PM   #28 (permalink)
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Any number of spokes, even one, can be spaced evenly around a circle.
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Old 09-23-2010, 07:23 PM   #29 (permalink)
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Just an observation on the question of "why do most wheels have 5 spokes?" Most vehicles also have 5 wheel lugs as well. One lug per spoke seems visually appealing.
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Old 01-15-2011, 01:39 AM   #30 (permalink)
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I wonder what fuel economy advantage there would be in saying having
- 3 spoke light weight wheels that are easier for the engine to accelerate but have more openings hence cause more aero dag
- vs heavier disk wheels which are harder for the engine to accelerate but have less or no openings resulting in less aero drag

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