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wheel strength and diameter

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wheel strength and diameter

Old 06-30-08, 12:23 PM
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wheel strength and diameter

Question: Has anyone quantified how much stronger a 26" wheel (ERTO 559) is relative to a 700c wheel (ERTO 622)? Will it be 11% stronger (622/559 - 1)?

For simplicity, we should assume that the spoke, rim, and tires are the same; i.e., suppose that both wheels are 36 spoke, sun rhynolite rims, with big apple tires.
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Old 06-30-08, 01:40 PM
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Depends on what you mean with stronger. A smaller dia wheel will be laterally stiffer, but that's usually not a problem for a bike wheel and doesn't say much about either durability or vertical strength. Damon Rinard has a wheel test somewhere which might quantify the difference.
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Old 06-30-08, 03:07 PM
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Originally Posted by dabac View Post
Depends on what you mean with stronger. A smaller dia wheel will be laterally stiffer, but that's usually not a problem for a bike wheel and doesn't say much about either durability or vertical strength. Damon Rinard has a wheel test somewhere which might quantify the difference.
Well ... I am no engineer nor physicist ... I had one year of physics where I generally concentrated on the girls in the following music course. I think that both lateral and vertical (compression) strength is largely a function of the number of spokes in the contact area. At least that is what I recall from Brandt's book the Bicycle Wheel. Consequently, I figured that the relative strength would be proportional to diameter ... which is proportional to circumference.

I would think that in this case, by stronger, we are talking about the ability to resist catastrophic failure. But I figure that this must be highly correlated with durability too.
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Old 06-30-08, 03:24 PM
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It would be hard to quantify. Physicists like to invoke similarity arguments, but strictly speaking they don't work here because the wheels aren't "similar" in a mathematical sense. A 26" wheel similar to a 700c wheel would have 11% thinner spokes, 11% thinner rims, 11% narrower hub flanges, ...

In the similar case, one could possibly work out a power law relating strength simply to size, but I'm too sleep deprived right now to actually work that out and get it correct. The reality would probably be that the 26" wheel would be stronger than the similarity argument predicts since the elements (spokes, rims, hubs) are chunkier for their size.

Also, since strength in a bicycle wheel is anisotropic (i.e. the wheel is stronger parallel to its plane than perpendicular to its plane), one has to be careful how he or she defines strength.

In any case, I am fairly confident that strength is not proportional to the inverse of wheel diameter. Experimental results are probably the way to go in this case, and I'd love to see them if anyone has measured such wheels.
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Old 06-30-08, 09:34 PM
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Give me two wheels to crush and I'll "quantify them" for ya.Put them in the press at work and see how much it takes to crush them.Is that what you have in mind?
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Old 07-01-08, 03:13 AM
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The problem here is getting two identical rims in 26" and 27" and 700c sizes, in order to rule out the rim's strength in the test.
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Old 07-02-08, 03:30 PM
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Originally Posted by DannoXYZ View Post
The problem here is getting two identical rims in 26" and 27" and 700c sizes, in order to rule out the rim's strength in the test.
Well that is why I picked the Sun Rhynolites. From what I could gather, the rims in the two different sizes are quite similar in character other than their diameter.

The vice or press would be a good start. Maybe we can put a 200 lb dummy on a bike running on a "rough" treadmill to experiment.

In case you wonder, I am pondering a new build for a commuter/utility bike. Most non-suspension roadish bikes are 700c nowadays. I am wondering what is the payoff to doing something a little unusual and working with 26" tires. At the moment, if the budget is there, I am thinking of a Big Dummy (26"). But if reality sets in, I might find an early 90's MTB -- the geometries were pretty close to road bikes -- and build that up. I don't know what the geometry consequences would be from using a more modern MTB with a rigid fork and giving it a more roadish feel (drop/moustache bars, bars ends, etc.). Otherwise, I could just find a decent hybrid (700c), Crosscheck, LHT, etc., and work with that. Anyway, it seems that going with the 26" wheels would mean more work/risk. I am trying to assess whether it would be worth going for 26" wheels.
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Old 07-02-08, 03:54 PM
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Aside from causing brake reach challenges, a smaller wheel will bring everything closer to the ground, affecting handling and making pedal strike a bigger issue while turning. My personal opinion is that the effect on wheel strength is small compared to these issues.

A 700c wheel with Rhyno Lites, 36 spokes, and Big Apples, built well, sounds pretty darn tough to me.

The LHT, I know, uses ISO 559 (26" ) wheels on the sizes up to 54 cm. Don't know your size, but if you are a 54 cm or less, the LHT is purpose-built for the wheels you want. Judging from hearsay (I've never owned one), it would probably be a fantastic commuter/utility bike. The Big Dummy sure looks cool...like a pickup truck that you pedal!

I'd say it's not worth worrying about. People beat the crud out of 700c wheels and come up smiling all the time. Pick the frame you like best and can afford, spec the wheels for the recommended diameter and with stout, high quality parts, build it up nice and tight, and enjoy the ride!
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Old 07-03-08, 08:37 AM
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Originally Posted by FLYcrash View Post
Aside from causing brake reach challenges, a smaller wheel will bring everything closer to the ground, affecting handling and making pedal strike a bigger issue while turning. My personal opinion is that the effect on wheel strength is small compared to these issues.

A 700c wheel with Rhyno Lites, 36 spokes, and Big Apples, built well, sounds pretty darn tough to me.

The LHT, I know, uses ISO 559 (26" ) wheels on the sizes up to 54 cm. Don't know your size, but if you are a 54 cm or less, the LHT is purpose-built for the wheels you want. Judging from hearsay (I've never owned one), it would probably be a fantastic commuter/utility bike. The Big Dummy sure looks cool...like a pickup truck that you pedal!

I'd say it's not worth worrying about. People beat the crud out of 700c wheels and come up smiling all the time. Pick the frame you like best and can afford, spec the wheels for the recommended diameter and with stout, high quality parts, build it up nice and tight, and enjoy the ride!
Interesting points.

I would not use 26" wheels on a 700c bike for the reasons discussed above.

A 54 cm bike is definitely on the small side for me.
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Old 07-03-08, 09:29 AM
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Lets look at it this way, where are the most common failures?

Taco

Big dent towards axel

Spoke nipple pulls through rim

Spole breaks on nipple end

Spoke breaks at head end


Any way my rule of thumb is the distance between spoke holes on a 559 should be the same as a 622 rim for duribility from the big dents which is how I lose rims, so a 36 spoke 622 is about equal to a 32 559 if memory serves, I need to go out and measure some CR18s I have in the shed,
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