spokes and rims

General Discussion about electric bicycles.
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Chalo   100 GW

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Re: spokes and rims

Post by Chalo » Jan 07 2018 7:21pm

Plain steel spokes used to be stronger than stainless steel. There were other reasons to prefer stainless, like the fact that it didn't corrode and stick to the nipples. 14ga spokes typically have static tension on the order of 1/4 of their yield stress. So they don't need to be stronger. But the fact that plain steel spokes were stronger led to peculiar customs like Dutch bikes using plain steel spokes with stainless steel rims.

Stainless alloys and processing used for spokes have gotten better over time, and now it's no longer accurate to characterize plain steel spokes as consistently stronger than stainless steel spokes.

Most spoke breakages are due to low-cycle fatigue and can be prevented by proper stress relieving of good quality spokes. Cheap nasty Chinese spokes are made of whatever stuff, and the metal contains inclusions and flaws that promote crack precipitation and breakage even in spokes that seem too thick to break in normal use.
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amberwolf   100 GW

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Re: spokes and rims

Post by amberwolf » Jan 07 2018 11:03pm

Just to drop in some more experience info, both on normal bicycles loaded heavily and ridden on potholey roads, and normal bicycles loaded with just me on decent roads and potholey ones, and then hubmotor wheels built both with heavy gauge spokes and with normal bicycle-gauge spokes (all used on heavy-duty cargo haulers on those poor roads).

When I rode the normal bikes with just me on them, and later for much of my normal bikes with heavy cargo, I didn't really know anything about the mechanics of bikes, I just rode them till they broke or fell apart beyond my ability to deal with, and then got a different (used) one (often from a thrift store or yard sale), sometimes swapping wheels or tires but not much else. I did this sort of thing most of my life; I didn't really start seriously learning about bike maintenance and building-bike-type-stuff until about when I started on my ebike quest. :oops: and nly then because i had to in order to figure out how to do what I wanted with whatever bits I could find.

Anyway, I had problems with certain kinds of wheels, and though I didn't really know why at the time, when I did learn about the issues, I remembered enough of the problems to see the pattern, which is essentially what Chalo has pointed out, about thicker spokes (or spokes that don't keep their tension for other reasons) allowing/causing a wheel to fail. Mostly the spokes would be dull, or with chrome plating that peeled off showing dull underneath, once the spokes got loose and bendy. What I'd usually see is rims that (though I didn't know what it was called then) wouldn't stay true, would become all bendy and warped, and spokes would start breaking. And since I used rim brakes, I'd have all sorts of problems with those too.

The wheels that didn't have this problem usually had thin shiny spokes that didn't appear to be plated, and that were nice and tight (almost musical in their tone if I twanged them vs "plunky" on the problematic wheels).

So thickness had something to do with it, thicker usually meaning more problematic (though I didnt' know why then), and metal type did, too. I could have thin dull spokes that would be very easy to bend that would be in wheels that would fail early, while thin shiny spokes that were hard to bend would be in wheels that didn't fail, or not as soon. I don't know what the metal composition actually was for any of those spokes, but I suspect the problematic ones (dull) were some form of mild steel that stretched a lot easier than the shiny ones, which were probably stainless. (not counting the chromed ones as "shiny")

Since learnign how to rebuild wheels, and then build from scratch, I've built some with thicker spokes and both steel and aluminum rims, after having problems with thinner spokes and the same rims, and found the thicker-spoked wheels generally failed faster than the thin ones, because they'd break the rim itself (cracks around the nipple holes in the aluminum rims, and deforming the nipple hole area on the steel ones) or on occasion they'd break the hub's spoke flange on aluminum ones, if I tensioned them enough to keep the wheels true (and would get loose if I didn't tension them that high, usually resulting in broken spokes at the elbow).

The problems I had with the thinner spokes usually ended up being insufficient tension, rather than insufficient thickness--if I tensioned them enough to start with they didn't break from getting loose. Sometimes it was crappy spokes, that kept stretching more each time I'd tension and true them (again, usually dull easily-bendable ones vs shiny hard-to-bend ones).

Once I started using hubmotor wheels, especially smaller ones like 24" and then 20", I *really* started seeing the difference between thicker and thinner spokes, and also with eyeletted vs non-eyeletted rims.

The latter would crack sooner than the former with thick (12g) spokes, if I tensioned them enough to not come loose with the loads and roads I use them between.

With thinner (14g and smaller) spokes, I only had problems when I either excessively loaded the wheel, or hadn't tensioned them sufficiently to start with. (when I first started buildng smaller wheels, especially hubmotor wheels, I didn't realize they'd generally need to be tighter for the shorter spoke lenght to get them to behave the same as the longer spokes did, but I found it out the hard way).

With 13g/14g butted spokes, I had less problems than with 12g by far, and less than with just plain 13g spokes. The butted spokes are what I've now been using with eyeletted wide rims and big tires with the SB Cruiser trike for more than a year (I don't remember exactly when I started with the bigger tires, but it migh tbe as long as a year and a half), without wheel problems, even from impacts that have broken a hubmotor axle. AFAICR I haven't ever gone that long without a wheel problem (at least requiring periodic retensioning/truing) with these kinds of loads / roads on short spokes in the time I have been doing this.

The rims definitely make a difference, because I've also used the 13g spokes on small bike rims, and those broke (cracked nipple holes) when the spokes were tensioned sufficiently to not loosen over a few rides, and then start breaking spokes (at the elbow). If they'd been eyeletted rims they'd've survived longer. If they were high-quality rims designed for strength, maybe they wouldn't have broken on 13g,

But the best has been the 13/14g butted on the eyeletted wide rim so far. Might be even better if I tried out 14/15g for the short spokes on hubmotors in 20" wheels, and if I ever have to rebuild one due to spoke or rim (nipple hole) problems on the 13/14g butted spoke wheels, I'll try that next. :)

So far, though, no need.

FWIW, I had less problems with the thicker-spoked wheels whenever they were only used on lightly-loaded bikes (and better on the front than the rear by far). However, even after I began building my own wheels and rebuilding existing ones, thicker spokes would usually still be more problematic than thinner ones, all else the same.

I've never tried stuff in the 10g range, and probably havent' had any above 12g (might've been one hubmotor with something thicker than 12g but I don't remember now), but I don't imagine the problems I had would get better with thicker ones, unless I also used rims that could survive the much higher tensions they'd need--I'm pretty sure none of the generic stuff I have here would.

augidog   10 W

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Re: spokes and rims

Post by augidog » Jan 08 2018 12:07am


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