I’ve been trying to learn more about this wheelbuilding lark, and so have just spent a few hours putting my shiny new onza hub in the muni wheel. I think I’m getting the hang of it; this time I’m going to try to finish the whole thing rather than take it to a bike shop, under the careful supervision of Sheldon Brown’s dead useful web page.
He talks about “trailing” and “leading” spokes… presumably this means a wheel does have a “forwards” and a “backwards”? I’d never really thought about it before, but looking at it all the inside spokes go one way, and all the outside spokes go the other.
Does it matter? Could this be why I seem to have had an unusual number of spokes (ie. any at all) break on me in the last few months? They have all been when putting back pressure on the pedals, either when doing an overenthusiastic rollback mount, slowing suddenly or going down steep hills.
Must get the muni humming over nicely for BMW at the weekend…
which spokes are leading, and which are trailing isn’t an issue on a unicycle wheel, or shouldn’t be.
It can be an issue with rear wheels on bicycles, due to the way drive is applied.
Last I checked I disagreed with Sheldon as to which spokes should be trailing, and which should be leading for a rear wheel any how, and all the wheels I’ve bought agree with the way I think they should be laced. Have to check again at some point, I may have misinterpreted him.
If you think about a bicycle wheel on a bicycle, all the torque about the axle is essentially in one direction, whether accelerating or braking – assuming the bicycle has rim brakes. So if you were insane about lightening things up you might use lighter components on the spokes that don’t bear that load. So it makes sense to have different terminology. If you remember that the rear wheel is dished, you see that most of the torque of acceleration is handled by 9 spokes on the rear wheel. These are called “trailing” spokes because from the spoke head, the spoke trails behind the head like the tail of a comet, during forward motion. Brown’s definition: "In the case of a rear wheel, the trailing spokes are those which become tighter when the rider applies pressure to the pedals. "
For a unicycle wheel, the torque is balanced because we are accelerating and decelerating via the hub with an undished wheel. In addition, we do things like idle and ride backwards. So the terminology is of little use to us.
I imagine that the reason you are breaking spokes is because the wheel is overall too soft and the spokes have been fretting for a while, wearing a notch in the spoke near the head. The hard back pressure puts the tension harder on spokes that haven’t broken yet, and so they break.
One way to stop the carnage is to rebuild the wheel with new spokes, and ensure that the tension is high enough from the start so that the spokes won’t fret. If the rim is of good quality, then you should be able to do this.
Although Sheldon Brown’s website is helpful in many ways, I think you’d find the Schraner and Brandt books clearer and more instructive.
Thanks Mike, I got your PM… I’ll be taking all the spares I have, about 7 or so, which should hopefully get me through the weekend even if I make a thorough mess of the wheel… See you at the weekend!
Previously the wheel has creaked when putting backwards pressure on it; I presume that means it’s been a bit loose. However I’m not sure how much more I can tighten the spokes without rounding out the nipples or breaking a spoke in the process, which happened on one attempt. I presume it must have been a spoke weakened by being loose for a while.
Some of them don’t half creak when tightening them up, and that’s rather offputting when trying to tighten them up. Would a blob of grease or something on the spoke threads help this, or would that just make the spokes come loose even faster?
Andrew: I was on MSN very rarely over summer due to not being able to go on the internet for much or very long (my post count here plummeted, too…) but now I’m on a bit more. Not, however, mid-morning (GMT), which was when you were on sometimes; now I’m at work then…
Well, that’s something I’ve never done before. The neighbours probably think I’m (even) strange(-r than before)… some hunched figure in the darkness of the road, attacking a unicycle frame with a car jack. The onza hub is wider than the suzue…
Next challenge in the neverending uphill that is Muni Maintenance (besides finishing the wheel) is fixing the damage from Sunday, somehow…
Spokes seem to make creaking sounds when there is a minute amount of movement at the the crank. strip, grease & repeatedly tighten and hammer the cranks until they stop moving further on. (take care not to damage the extractor threads)
Sound like you may be getting them excessively tight?
I use grease, some people prefer linseed oil because it dries.
I have recently rebuilt the Bontrager wheel on the unibike due to a defective rim that kept spreading at the weld seam (a very noticeable problem when relying on rim brakes). The spoke holes are slightly off center, so I simply laced the new rim with the widest portion towards the cassette like the original. After a few rides (probably 50 miles), a slight ping was followed by a major brake rubbing wobble, and yet another surprise test of my safety wheel. A leading spoke snapped near the nipple, a couple of threads in from the spoke shaft. Are these spokes likely to be lightened enough to be unusable after re-lacing and re-tensioning? If one spoke failed while cruising along with no more than the usual strain, I assume there will be more to follow.
More paranoia to consider before reverting to forkless mode.
Usually when one spoke goes for no reason the’re all ready to go. Sorry to say it, but you’re better off replacing the whole lot now.
What you describe is a classic fatigue failure. I presume the spokes are non-butted spokes; probably 14 straight gauge? Replacing them with 14/15 butted spokes will strengthen your wheel. I know it’s counter-intuitve, but the thinner center section is more elastic which allows the contact load to be distributed over more spokes. This reduces the cyclic load on the threads which are prone to fatigue failure.
I’ll have to check it to make sure, but ASYM rings a bell.
The spokes are non-butted. I don’t know what gauge they are, but they’re thinner than those on the wheel I replaced, which never had a problem. I replaced the wheel two years ago for the addition of the disc brake. I would hope that a new wheel would last more than two years, but as I mentioned, the rim has already failed. Maybe I bought the wrong wheel.
I can’t find anything ASYM with respect to Bontrager. Perhaps it isn’t a current model.
If your rim is asymmetric, then the “bulge” should be away from the cassette. This allows the spokes to have a less extreme dish and thus strengthens the rear wheel.
If the wheel were constructed with the “bulge” on the wrong side, this would weaken the wheel considerably. Constructing the wheel this way may not even be possible clearance-wise; I don’t know.
However, the likelihood, like cyberbellum said, is that your reused spokes were already fretted and weakened; in the new wheel with higher tension they simply broke even more quickly. An aggravating factor would be not placing each spoke in the exact same position on the new wheel.
Check your spoke thickness right next to the nipple. If it is 1.8mm, it’s 15 gauge. 2.0mm means its 14 or 14/15 gauge. The former (15 alone) would be underkill for your usage. It sounds as though your best bet would be to replace the spoke set with new 14 or 14/15 gauge spokes. And, as always, use all the best wheel-building methods, including getting the tension as high as possible.
Or perhaps there are other factors due to characteristics of the wheel that we haven’t seen yet in this thread.
Rim - ASYM Maverick E.R.D. 542
Spoke O.D. - 0.070” (in between 14 and 15 gauge, I think).
Nipple O.D. – 0.153”
Rim eyelet I.D. – 0.173”
Hub hole I.D. – 0.110”
The spokes in the old wheel are 14 gauge (0.078”) with the same size nipple as the new smaller spokes. Upon closer inspection, there is a label on the Maverick rim that points to the drive side (leaving the bulge on the left), so it doesn’t seem to be an installation problem. If the carnage continues and I have to replace all the spokes, the hub holes and rim eyelets are large enough to accept 14 gauge replacements, which will hopefully prevent this problem in the future.
This may just be an additional quirk of loading a bicycle wheel with twice the weight that it was designed to carry. Yes, I’m still getting shortened life out of tires and tubes, due to valve and sidewall/bead failure. I still haven’t tried the heavy tubeless tires.
Any recommendations are welcome.
Thanks again for the assistance.
Sounds like you’re on the right track, Jeff. Personally I’d replace all the spokes now before you chance ruining the rim. The rim looks like it would be quite strong, and the reviews of it on mtbreview are generally good. Perhaps the next wheel should use a beefier, wider rim for more strength and less tendency for the rear tire to fold over. Cyber was correct to suggest 14/15s, which are just as strong as 14s, but help ensure that the “stretch” takes place within the body of the spoke, and not at the spoke head. Your wheel is taking a higher than designed-for continuous radial load, which is perfect for fretting spokes at the head. However, that rim is good for resisting same because it has a taller sidewall.
Are you using two brakes, if I remember correctly, a disk and a rim brake, both on the rear wheel?
I wonder about using a very small safety wheel on the front, even 16 or 12". You couldn’t brake it but it would let you do emergency stops using the rear brake(s). Moreover, it would be much lighter and less of a sail in windy conditions. You’d have to use a wider hub, though, to fit the fork, I suppose, and build the wheel from scratch.
Yeah, I concur. Bite the bullet now before you trash your new rim.
You are loading the wheel with more that twice the weight. All those side loads from balancing and getting on are REALLY hard on the wheel. If you can find a hub with very wide flanges then the side loads won’t stress the spokes as much. Offhand I can’t think of any good candidates. Perhaps a giraffe hub?
Actually, I’m using three brakes. Two rim brakes and the disc (operated by a gear shift lever and only used on downhills).
I already have a 16” safety wheel for windy days. However, on long one way rides like I have coming up with Lewis (Animation), it’s real uncomfortable to ride if I have a problem that requires me to ride back on two wheels (like a broken spoke). This mini wheel catches much less wind, but the pedals almost drag the ground when it’s not in the air. A 12" wheel would cause pedal dragging and probably wouldn’t offer a noticeable benefit over the 16".
I’ll plan on rebuilding the wheel, but I don’t have time before the rides with Lewis. I’ve taken it on a 10-mile test ride up to 35kph with no more than a little creaking as the spokes settled in. Hopefully, it will survive a few rides. Wish me luck. If it breaks, I’ll have a lot of walking time to kick myself and think about the warning I’ve received.