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Old 2016-11-21, 06:21 AM   #1
pirsquared
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Yet another "which 36er" thread

I want to get back into riding after 30-some years, and want a 36er.

After reviewing the other "which 36er" threads, I have plenty of data on the various 36ers, interchangeability, features, etc, so I want to boil this down to one question:

I'm 240-250 lbs, many of the "roads" around here are more like "off road", lots of 2-tracks, and then there are tons of hardpack orv trails, and other non-technical off road opportunities. Nothing gonzo, not crazy drops, just riding trails and dirt roads. Considering there is always the unexpected, am I considerably better off with a 48 spoke 36er? Please disregard the issue of the extra weight. Let's keep it to "am I likely to hurt a 36 spoke 36er" considering my size and intended use?

Thanks in advance.
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Old 2016-11-22, 05:42 PM   #2
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all of the 36ers use relatively "cheap" spokes. You're fine with a 36 spoke wheel. If you're super worried about it, I would contact Silva Cycles. He was trying to get some DT-swiss level spokes made in the 36er size, but I don't know if that ever happened. It would be quite an expensive wheel build though. Personally I think you're fine with an off-the-shelf 36er. Broken spokes happen. If you ride hard, they are really difficult to avoid on a unicycle. The extra weight isn't worth the marginal increase in strength.
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Old 2016-11-22, 06:44 PM   #3
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Current 36" rims are all quite strong. A symmetric 36 spoke wheel should be just fine.

If you like anecdotes i have ridden a 36 with the rim cut in three (then re-pinned) laced up with only 24 spokes off-road for a couple months and it held up just fine. Im about 190 lbs.

Edit: there was a bad batch of spokes that were used pretty much across the industry. It was a while ago and shouldent be a problem anymore.
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Old 2016-11-22, 07:55 PM   #4
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Do true and tension the wheel properly when you get it though. Most uni wheels seem to ship with the spoke tension a little low, which can cause breakages.
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Old 2016-11-27, 06:32 PM   #5
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Thanks for all the input. I'm beginning to think the 48 spoke wheels we used to build for tandems were more for torque (pedaling and braking) than for payload.

Thanks juggleadict for the following:

Quote:
Originally Posted by juggleaddict View Post
.....The extra weight isn't worth the marginal increase in strength.
It put it into perspective, but then got me thinking (always a bad idea, sorry, geek-speak ahead). For a spoked wheel, all other things being equal, the cyclic load amplitude (superimposed over the preload tension) on any spoke in inversely proportional to the number of spokes. 48 vs 36 spokes results in 25% less load amplitude for the cyclic portion of the load on each spoke. As far as weight is concerned. The extra weight for 12 spokes (14 ga) about 16" long, is about 4 ounces (550g). For the effect on accelerating or turning a rotating mass, the polar moment of inertia of the wheel is a function of the mass, and the radius squared. So the effect (on the polar moment of inertia) of 550g at one-half the wheel radius = the effect of 1/4 as much weight (110g or so) at the tire. As this is less that the typical difference between the claimed and actual weight of a tire/tube/rimstrip, and I plan to collect more than 110g of crap in the tread, and I've never considered the weight of my shoes (also part of the rotating mass of the wheel), I might lean toward "the increase in strength is worth the marginal increase in weight".

Thanks again for all the replies, all the engineering in the world wouldn't help me at all without the real-world baseline data.
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Old 2016-11-27, 07:19 PM   #6
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550g for the 12 extra spokes sounds pretty heavy to me.
Am I wrong?
Also for each spoke, the part that is close to the hub has much less rotative inertia than the part that is close to the rim. (inertia is proportional to the square of the radius, maybe that's what you mean).
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Old 2016-11-27, 11:27 PM   #7
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My back of the napkin math puts a spoke for a 36er at just under 10g each. But I thought we were disregarding the issue of extra weight
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Old 2016-11-27, 11:41 PM   #8
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I THINK [qualifier there], you can use the "r" value for the centroid of the spoke, considering the really small mass contribution as compared to the total....my brain hurts.....if you break each spoke in two:

1/2 the mass (weight) at 1/4 r, and 1/2 the mass (weight) at 3/4 r:

contribution to J (mr^2) = m/2 * r^2 /16 + m/2 * 9r^2 /16 = mr^2 /32 + 9mr^2 /32 = 10mr^2 /32 = 5/16 mr^2

for the spoke as a whole: m at 1/2 r
contribution to J (m r^2) = m * r^2 / 4

oh nuts.....if I did it right, breaking it into discreet parts does make a (small) difference: 0.25 mr^2 vs 0.3125 mr^2 (unless I made an 8th grade algebra mistake, entirely possible).

This will converge at some point, but it's gonna take someone who still does integration (that's SO far back in the cobwebs of my mind I'm not going there).....

Juggle? you're still young(ish) whatcha got? :P

I still think the contribution to J, for the extra spokes, is on the order of the dirt collected in the tread.

This makes me wanna get a bottle out of the freezer, but I shouldn't "drink and derive"
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Old 2016-11-27, 11:48 PM   #9
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oh nuts....if Sask is correct about the weight I burned out these brain cells for no reason.....

I used 0.075" diameter for the spokes, 16" long, 0.2836 lbs.cu inch for density =

0.0375 x 0.0375 x pi x 16 x 0.2836 = 0.020 lbs each = 44g each = 528g for 12
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Old 2016-11-28, 12:37 AM   #10
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Quote:
Originally Posted by pirsquared View Post
= 0.020 lbs each = 44g each = 528g for 12
NB: 0.020 lbs * 454 g/lb = 9.08 g each, which seems more likely given that 12" DT Swiss spokes are between 5 and 6 grams depending on the model.

(Guessing that you multiplied by 2.2 to go from lbs to kg when you should have divided... It happens.)

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Old 2016-11-28, 01:19 AM   #11
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head----->desk desk desk desk

in that case, I'm getting a 60 SPOKE WHEEL
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Old 2016-11-29, 09:42 PM   #12
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Not going to go too much into math. When you're talking spoke numbers and straight strength, you're missing the whole picture. (sorry pirsquared if this is repeating some of the PM I sent you :P)

Three things to consider:

- Rim stiffness has a lot to do with wheel strength. Note the stealth 2 is an excellent rim, and much siffer than the original stealth. Note the coker rim hasn't changed since they started making it... I haven't owned one so I can't speak for it's strength.

- Spokes, typically, do not break in the middle because of the force on the saddle. Spokes tend to break at the head or the bend unless there has been some unusual factor thrown in, such as a faulty spoke/alloy, a severe drop, or an improperly tensioned wheel. According to what I've read, which is by no means comprehensive, spokes break primarily because of fatigue caused by the spoke moving around while it's supporting weight.

- 48 spoke wheels use a different spoke length than a 36 spoke wheel, meaning the spokes are not interchangeable. I believe (unless this has changed) that coker doesn't sell individual spokes as of a few years ago, so you cannot buy replacements if you did happen to need one, though you may be able to get custom spokes made.

I did quite a lot of research on wheels when I was building my touring bike wheelset. I ended up going with 32 in the front, and 36 in the back, even on a bike that is meant to support weight like a truck. The 32 spoke wheel is still probably the stronger of the two because it isn't dished, despite it not having to support as much weight as the 36. It's been plenty strong and I had no issues on my 5000 mile trek, even with 50+ lbs of gear and my 175 lb self. Granted, a bike has both wheel supporting the weight, and a 26" wheel is stronger than a 36" one, just because a smaller wheel is inherently more stiff. . . Still I think it's not as simple as more spokes = stronger, and I still think a 36 spoke 36er is plenty strong.

Hub flange width also plays a role! A wider hub makes for a more stiff wheel, which, again in theory makes for a wheel that is stronger/less prone to failure. Note that there are 36ers with 100mm hubs and 125mm hubs... I have the wider of the two, for what it's worth. This affects q factor as well though, and comfort is also a whole big topic to consider.
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