Rough-stuff touring wheels - frequency of re-truing

[axel_knutt]

wind up is completely harmless, you just get a bit of tinkling for the first couple of yards

The nipple is free to rotate on the spoke, so if the spoke suddenly recoils with a ping, inertia will cause the nipple to get left behind, the same way wine glasses do if you suddenly snatch a tablecloth from under them, and so you end up with an unwanted adjustment.

you can't always be entirely certain of what was and wasn't turning.

Yes you can, all it takes is ~90 seconds to mark the end of each spoke with a felt tip pen before you start, then you can see how much the spoke turns relative to the rim, and how much the nipple turns relative to the spoke. No guesswork, no feeling for anything, you know exactly how much actual adjustment you've made.

[531colin]

How much wind up do you reckon you can get?
Quarter turn ?
A wound-up spoke recoils when it passes the bottom of the wheel and it’s relatively un-loaded.
So the slippage between spoke and nipple is what fraction of a turn?

[Carlton green]

How much wind up do you reckon you can get?
Quarter turn ?
A wound-up spoke recoils when it passes the bottom of the wheel and it’s relatively un-loaded.
So the slippage between spoke and nipple is what fraction of a turn?

H’mm, I wonder about all this wind-up.

What nice and new spokes do for a full time and experienced wheel builder might be different to what happens to me - and, indeed, some others too. When I can then I reuse any old stuff that I can lay my hands on (got loads of salvaged spokes) and it’s not always in the best of condition; it’s rare for me to get a spoke breakage though and if I do then I’ll likely just fit another spoke from the reclaimed parts store. The second to last wheel I built up-set me a bit, I had to buy new spokes ‘cause none in my store would fit . I can’t help my meanness, old habits, life can be tough and it’s made me thrifty - suppose they’re all wealthy in posh places like Harrogate .

I’m puzzled about marking-up spokes on the end with a pen. Perhaps it’s on the side next to the nipple (?); I suppose just a dab would do and it doesn’t need perfect accuracy. It’s easy enough, well I suspect it might be so with old stuff, to turn a nipple and likely all you’re doing is twisting the spoke rather threading the nipple further down the spoke.

A long time back someone said to me: “In theory, theory and practise should be the same, but in practise they’re not”. That information has stuck with me and it seems remarkably true over much we do, always some subtle differences, well that’s what I mostly find.

[531colin]

Carlton;

Are you on a wind up?
I made a detailed reply to you on the previous page, did you read it?

[Carlton green]

Carlton;

Are you on a wind up?
I made a detailed reply to you on the previous page, did you read it?

Deliberately winding other folk up-tight is not for me, sorry if my post had that effect on you. The most I try to do on forums is a bit of humour from time to time, coupled with a smiley face or similar.

I did read your reply to me and it was helpful, thank you. Beyond that there’s been so much to and fro on the topic that I’ve stopped following it closely. Your replies are always interesting and informative to read, but as with all stuff on-line only some of what’s written applies to any individual reader’s particular needs and circumstances. My habit is to question things, though mostly mentally rather than out loud or in writing.

All of my earlier post might appear to be addressed to you but only part of it was meant to be, the other part of the post was looking towards axel_nut’s earlier comments. I try pretty hard to make clear and constructive posts, but despite such efforts I don’t get everything right - few people do.

[Brucey]

you can't always be entirely certain of what was and wasn't turning.

Yes you can, all it takes is ~90 seconds to mark the end of each spoke with a felt tip pen before you start, then you can see how much the spoke turns relative to the rim.....

if I was going to male a mark there I'd probably use something that goes on easier and doesn't just wipe off at the first sign of oil or grease. Why not use a vibro-etch? It could be even quicker [having arranged the spokes in a line with their heads all hanging the same way] a single sweep with the vibro-etch would do it.

[Brucey]

What nice and new spokes do for a full time and experienced wheel builder might be different to what happens to me - and, indeed, some others too. When I can then I reuse any old stuff that I can lay my hands on (got loads of salvaged spokes) and it’s not always in the best of condition; it’s rare for me to get a spoke breakage though and if I do then I’ll likely just fit another spoke from the reclaimed parts store. The second to last wheel I built up-set me a bit, I had to buy new spokes ‘cause none in my store would fit . I can’t help my meanness, old habits, life can be tough and it’s made me thrifty - suppose they’re all wealthy in posh places like Harrogate .

spokes normally fail by fatigue, and fatigue comprises three steps;

1] crack initiation
2] crack growth
3] sudden failure [fracture]

Either of the first two can dominate the overall life of a part. If step 1 dominates, steps 2 then 3 follow fairly quickly.

A lot of cyclists think they broke a spoke because of a pothole or something. Well, 99 times from 100 that spoke will have already been badly cracked for some time and in fact nothing would have saved it.

My original research into this [which involved dismantling several thousand old wheels].showed quite conclusively that in bicycle wheels step 1 usually dominates the life and step 2 quickly follows.

Practically this means you are fairly safe in reusing old spokes provided that they were made without defects and you accept that any spokes that are already cracked [which is usually not many and even in the worst case is unlikely to greatly exceed the number of spokes that ever broke in the old wheel] will [pretty much whatever you do] go on to fail probably in the first few hundred miles. Normal stress-relief of the built wheel will usually ensure good service thereafter.

[CJ]

[Brandt] writes "The rim is divided into 36 short structural beams that reach from spoke to spoke." He surely means his calculations are based on those "short" beams acting as a single structure, he can't mean they are able to move relative to each other, like a hinge joint?

No, he is not stupid, so he cannot have meant that. Beams do not necessarily just rest upon things, they can be built into walls or welded onto other components at one or both ends. Those 36 short beams are obviously 'welded' one to another at each node and have the same twist, pitch and yaw as the next beam at that point. And across that point - or rather that imaginary welded cross-section - are reflected the same moments of torsion and bending, radial and lateral, which in concert with the spoke tension acting upon that point, result in different amounts of twist and bend at the opposite ends of this pair of short beams. And so on. The analysis of this interconnected web of forces and deflections, where everything has an influence upon everything else, is what makes it necessary to use a computer to crunch the numbers, over and over again, in a complex iterative process called finite element analysis, to predict how the wheel deflects as a whole.

In the 1930s, when cars and particularly aircraft had tension-spoked wheels, Professor A.J. Sutton-Pippard, acting for the British Aeronautical Research Committee, rendered the analysis solveable (obviously without computers) by the clever trick of imagining each bank of similarly aligned spokes replaced by a continuous sheet having an identical distribution of material: thinner at the rim, thicker at the hub and with the identical property of transmitting only tension - in only one direction. By this elegant means he calculated similar behaviour in a tension-spoked wheel to that obtained by Brandt much later, thanks to the mathematical mincing machine we call a computer!

I came across Sutton-Pippard's papers in the late 70s when working in Raleigh's Development Department, which had done a literature survey. The Department gave me the nice job of applying Sutton-Pippard's equations to bicycle wheels, so as to assess the relative effects of spoke and rim stiffness, which Raleigh was keen to optimise. It soon became very clear that the properties of the structure comprising the network of spokes is an order of magnitude more important in determining the deflections of a bicycle wheel, than the typical properties of its rim. In simple terms, for the properties of the rim to be just as important as the spokes, it would need to be something like ten times stiffer than any rim available at that time. And at that time it was inconceivable that customers would welcome such an increase in the bulk and weight of a rim. It is nevertheless possible that some of today's very deep aerodynamic rim sections may be ten times as stiff radially, as a typical 1970s rim. And that'll be how those wheels get by with so few spokes.

So when Brandt's book came out in 1981 his diagrams came as no surprise to me, but as a nice corroboration of Sutton-Pippard's work. I thought it was a shame that Brandt didn't mention this earlier work, but perhaps - like the cycling world in general - he never imagined there might be any existing science worth looking for!

[Brucey]

[Brandt] writes "The rim is divided into 36 short structural beams that reach from spoke to spoke." He surely means his calculations are based on those "short" beams acting as a single structure, he can't mean they are able to move relative to each other, like a hinge joint?

No, he is not stupid, so he cannot have meant that.....

maybe I'm stupid then [it would not surprise me in the slightest] because IIRC that is exactly what I thought he meant..Hence my earlier description of 36 freely hinged segments.
.FWIW I rather suspect that some modern rims are much more than ten times stiffer vs. some older designs..

[CJ]

.FWIW I rather suspect that some modern rims are much more than ten times stiffer vs. some older designs..

FWIW I agree, SOME may be more than ten times stiffer. The cube root of ten is only 2.15 after all, and some aero sections are 3 or 4 times deeper, but perhaps also half as thick, which will take their stiffness down a notch, in simple proportion only. These extreme aero sections however, have not hitherto been available in widths and drillings useful to touring cyclists. Three factors have changed that:

1. Disc brakes, so we don't have to worry anymore about how thin the sides of rims are, so they can be made deeper and fatter without necessarily becoming that much heavier.
2. Roadies' realisation that wider tyres and rims are a good thing, so what they want to ride is more like what we have always preferred.
3. And finally the gravel bike, which has made touring sexy and created a mass market for equipment that's optimised for going places that are sometimes a bit rough, with economies of scale that makes such equipment affordable.

Thats why my current 'road' bike is light enough to keep up with the clubrun but also makes a very capable touring bike, since it's built on a carbon gravel frame for which I have two pairs of wheels (and two pairs of mudguards): narrow and wide. The wide ones (and the frame) comfortably accept tyres up to 42mm. These wheels are nevertheless very light, thanks to straight-pull spokes and not many of them, distributed 2:1 between the dished-in side versus the other. So I'm happy to load up the bike and ride these very light wheels reasonably fast over quite horrible surfaces!

[531colin]

Just a reminder where this thread started; it started with "Slowster" saying his back wheel had "gone off" after very little riding.

Third post, page 1;

.................
In an ideal world, every wheel should be thoroughly stress-relieved, and then its my practice to go through a final repeating cycle, which is;
stress the wheel, true the wheel, balance the tension.....repeat this cycle until the wheel doesn't "go off" when stressed, and you get an acceptable balance between evenness of tension, trueness, and stability.
"stressing the wheel" in this situation means putting the axle end on a block of wood on the floor and pressing down on opposite sides of the rim with a fair proportion of my bodyweight....going all round both sides of the wheel....hard enough to feel the difference in stiffness on either side of a dished rear wheel, with a light rim.
.................

My aim in this "stressing the wheel" is to subject the wheel to the sort of loads the spokes will see in service, and this causes the wheel to "go off". It is self-evident that if the wheel is not subjected to loads until the customer starts riding it, then the wheel will "go off" as the customer starts riding it.....even if the spoke line is optimal, the spokes are at correct and even tension, the spokes are stress-relieved, and the wheel is round, true and correctly dished.

In my quoted post above, I mention that my "stressing" the wheel uses sufficient force "to feel the difference in stiffness on either side of a dished rear wheel, with a light rim"
This takes me to the discussion on the current page, that modern rims might approach TEN times the stiffness of the rims Brandt was considering.
Its a long time since I was building numbers of wheels. At the time Rigida Chrina was a popular narrow rim; double eyelets, quite narrow, with a shallow box section under the bit where the tyre fits. That was one of the rims where I could feel the difference in stiffness between the 2 sides of the wheel; the right spokes have a much shallower bracing angle than the left spokes, and leaning on the right side of the rim you could feel much more flex than leaning on the left side, where the spokes have a better bracing angle.
Rigida Snyper rims were I think slightly wider, single eyelet, but with a deeper U shaped box section under the tyre. With these rims, or with Sputniks there was very much less difference in stiffness of the 2 sides of a rear wheel.
If you picked up a Chrina rim like an archer holds a longbow, and made to "draw" it like an archer "draws" a longbow, you could feel the rim flex. Snyper and Sputnik rims were much harder to flex like this.
I formed the opinion that the difference in stiffness of the wheels was due to the difference in stiffness of the rims....not a great leap of imagination, as the spoking is essentially similar; 36 spokes, double butted right side, either plain gauge or 13/14g single butted right side.

On page 3, CJ talks about an instantaneous load of 500Kg moving the rim 3.6mm sideways due to unequal tensions in the left and right spokes, if built with the same gauge spokes both sides. I think that was for a "Brandt" rim, not a modern rim. How far sideways might a modern rim move, if it was ten times as stiff? or even just three times as stiff?

CJ maintains that using thicker (stiffer) spokes on the tighter right side will ensure your wheel doesn't go out of true; however, "Slowsters" wheel was spoked 13/14g single butted right side and 14/16g double butted left side, and it “went off” after very little riding. This means that making a durable stable wheel is more about the building than the spoke gauge.

If you want your wheels to stay true when the customer starts riding them, my recipe is....
1 Make sure the first time the wheels see some stress isn't when the customer starts riding them, but when you are finishing building them.
2 Use a stiff rim, particularly for a heavy rider or heavy use

However, I think the most common complaint about wheels is spoke breakage.
If you don't want spokes to break, here is my recipe for that....
1 Use a stiff rim but light spokes, this shares out any load between the maximum number of spokes
2 make sure the spoke line is optimal, this reduces flexing when tension changes in any spoke, and its flexing which fatigues spokes
3 Stress-relieve the spokes to take out as much "residual stress" as possible (from spoke manufacture, wheel-building, etc)

13/14g single butted spokes "look right" for highly-loaded right spokes. However, spokes fail due to fatigue, and crack initiation is the longest phase of fatigue, and it won't alter due to thicker spokes. Thicker spokes will only ensure that any crack has more steel to go at during the (shorter) crack propagation phase. (and thicker spokes are actually more difficult to get an ideal spoke line)

A brief explanation of what some terms mean (to me)
Optimal spoke line means any bend in the spoke is a set, permanent bend, so that the spoke runs straight to the hole in the flange, and straight to the nipple. Any curve in the spoke at these points is likely to mean the spoke is flexed, not permanently bent, and flexing causes fatigue. improving the spoke line must be done with slack spokes, because the metal needs to be flexed past the point where you want it in order to set the bend at the point you want it.
Stress relief means loading individual spokes more than any load they are likely to see in service. This means stress-relief is best done when spokes are at final tension, and you briefly increase the load.
Stressing the wheel means when the wheel is "finished" going round the wheel giving spokes the sort of load they will see in use, so that the wheel doesn't "go off" as soon as it is ridden.

[hoogerbooger]

(I have found this thread very useful.........I now realise that on the wheels I've made, I stress relieved the spokes......but not the wheel !! 2 out of 10 have stayed as straight as I made them....one on Sputnik..)

[Brucey]

I agree with colin's post save for one thing; actually spokes that are already under tension more easily take a new set than otherwise. so you don't have to over-bend them so much; in fact I suspect that with some rims, Brandt's favoured technique for spoke squeezing may actually be counterproductive in terms of spoke line for this reason.

FWIW I still believe Brandt meant freely hinged segments [we can hardly ask him now] because otherwise why would he have bothered to mention 36 beams rather than just one?
However it matters not because when that work was done, no rim would have contributed very much to the stiffness of the wheel, and I think he knew that.

[531colin]

Re reading Brandt; for “improving the spoke line” he grasps 2 spokes just above their last crossing.
For stress relieving he grasps 2 near-parallel spokes, which is going the wrong way for spoke line at the nipple.

Brucey, we have discussed this before, I believe I may have got it confused back then!

[CJ]

FWIW I still believe Brandt meant freely hinged segments [we can hardly ask him now] because otherwise why would he have bothered to mention 36 beams rather than just one?

Do you really believe that? Please think again. A rim comprising 36 freely hinged segments could never be built. Free to flex sideways at each spoke attachment 'node', that is exactly what it would do as each spoke was tightened, adopting a zig zag shape where each node is centred over the flange to which its spoke is attached, still with no significant tension on any spoke. Any futher attempt at tightening only results in an easy collapse into the Pringle shape, to which there is no resistance if the rim has no lateral stiffness at each node. The classic bicycle wheel is not a perfectly triangulated structure. It needs the stiffness of its rim just to stand up, to hang together at all.

Pringle collapse is also what would happen - but without the initial zig-zagging and only once a certain amount of spoke tension and rim compression had built up - in a wheel like this, that is a perfectly triangulated structure, thanks two spokes meeting at each node.
. In real world wheels do not spontaneously 'Pringle' until tensioned very highly, and that is thanks to the rim's inherent stiffness. But tighten those spokes too much and they do!

Rims may have only one tenth the resistance to deflection of the spoke structure, but what stiffness they do have plays a vital part in the structural integrity of the wheel and was certainly part of Brandt's analysis. He writes about the importance of the rim's torsional and bending stiffnesses on pp57-58 and these properties are necessary inputs to any mathematical model of how a wheel behaves.

I could not have applied Sutton-Pippard's equations to bicycle wheels without the torsional and bending stiffnesses of rims, which I calculated from their cross sections (drawn very large on paper with very small squares). Ask any engineer and he'll tell you: No structural analysis of a wheel even begins to be possible without taking account of rim stiffness.