Spoke tension

[jamesofyorkshire]

Anyone know what tension the spokes should be on a heavy-duty touring wheel built around a Schmidt dynamo? I've scoured the internet but without result.
Schmidt/Sapim race spokes/Andra 30 rim.

[531colin]

If it was me building, it would be 100kgf.
I have only built Andras with angled spoke holes to suit very big hubs, I guess there is another sort?

[jamesofyorkshire]

OK. Thanks Colin. I have the same Andras.

[thecycleclinic]

1100N is normal for the drive sise of a rear weheel, NDS tension depends on the dish of the wheel which in turn is determined by the relative diameter of the flanges. The non drive side should be around 700N. If the drive side is set to 1000N you may not be able to get sufficent tension on the NDS. A front wheel should have around 1000N tension for normal sized hubs. With large flanges this can be reduced a bit. Keep the tension as high as you can. With Sapim spokes they take tension wery well and the nipples do not distort at high tensions ~1300N.

As an example my road wheels on one of my bikes uses a cheap rigida Chrina rim with a 130mm OLD miche RC2 hub aand sapim race spokes + nipples and the DS rear tension is ~1300N with about 800N (I forget the NDS tension but its quite high) drive side. The wheels has done ~2.5K miles and remains sound. The fronts built using the same rims, hubs and spokes have 1000N and these also remain fine and so has every other whell I have built.

[jamesofyorkshire]

All good stuff!

The dishing bit doesn't apply to me as I'm running SON front and Rohloff rear.



To most people, a pushbike is such a simple contraption.......but to us folk who have a bit more interest in it, it's incredibly technical and interesting.
It constantly amazes me how much there is to cycling......frame geometry, crank length, spoke tension, gear inches, tyre sizes, chain widths........the list goes on......

.......and this and other forums allow those with greater knowledge to pass it on. Love it.

[531colin]

cycleclinic....
I think that we are in agreement, pretty much, within the accuracy of measurement given to us. I have only used a Park spoke tension gauge, which relies on deflecting the spoke, so the thickness/stiffness of the spoke is in there to muddy the waters....I googled Newtons, they say about 9.8N=1Kgf, is that about right?
You say 1100N driveside, (=112Kgf), I reckon 120Kgf
I like to see 80Kgf NDS, you say 700N (=71Kgf)
likewise, Chrina rim, Sapim spokes I have had driveside over 130Kgf with no problems (about 1300N)
Only thing, the difference in tension between the 2 sides is because the hub is offset relative to the frame, the rim needs to be almost over the driveside flange, NDS flange is further from the midline.

[mouldfield]

Hi jamesofyorkshire and all,

I have a Rohloff Speedhub too.

It’s on a hard working, heavy weight carrying, motorised, Yuba Cargo bike. I bought a used rohloff for it and I'll be building a wheel with an Andras30 rim and Sapim Race spoke (when they arrive in a few weeks). In the meantime, it arrived built into a Rhino Lite rim with 14 gauge spokes and I need to keep it going. It's needed truing a few times and now I've just swapped out two broken spokes. You can hear that the spokes are clearly in need of tightening, and the recommended tightness is 1000N.

Two things though. Rohloff are now producing Flange Support Rings to reduce flange damage on tandems, ebikes, cargo bikes, and heavy-rider-owned bikes. All new Rohloffs are now shipped with these rings and Rohloff has told it’s dealers to retrofit rings when rebuilding any earlier Speedhubs.. My hub came from a Tandem, and is now on an ebike/cargo bike with a heavy rider, so if any Rohloff flange is going to suffer, mine will.

With my new wheel components on their way, I am concerned that my speedhub will be damage before I get to build that new wheel. It already has a small chip on one flange. So I figure that, to avoid flange-damage in the meantime I’ll keep the loads lighter than I previously had, reduce tyre pressure a bit (which is a recommendation anyway) and keep the spokes a bit looser which might lead to some more spoke wear but that’s preferable to buying a new casing for my speedhub, isn’t it?

But how loose and how will I measure it apart from by appearance (of trueness) and feel, which is how I’ve always trued and tightened my wheels and spokes.

I have a tension meter on it's way but I thought maybe I can do this with an instrument tuner. A wheelbuilder I know uses a tuning fork but I’m not confident that my hearing is good enough (tinnitus).

Any helpful suggestions would be greatly appreciated.

Cheers,

Rik

[rfryer]

I'd think carefully before loosening the spokes. There's a good chance it could make matters worse, by increasing shock loads on localised parts of the flange.

[jamesofyorkshire]

I'm not technially knowledgeable enough to offer advice, but common sense tells me that you should fit the biggest tyre that your frame can handle if you want to keep impact on the hub to a minimum.

[Brucey]

unless the flange reinforcement rings are shrink-fitted onto the flanges, they may not so much prevent flange breakage entirely as mitigate the consequences of it when it does occur, by holding the bits together when a crack occurs.

I would counsel caution if the wheel is only to last a few weeks before being rebuilt; loosening spokes is exactly the sort of thing that can make a wheel fall apart PDQ whilst providing little or no benefit of the kind you seek. Most forms of normal wheel loading cause large tension reductions in a few spokes at a time and small tension increases in the remainder. That rims start to fatigue in slack wheels, spoke holes wear, spokes are more likely to break etc tells you that slack wheels have less predictable loadings at least, if not worse ones.

When the wheel is apart, the hub flanges should be inspected carefully (at least using a magnifying glass) for cracks and if any are found then the hubshell should be renewed.

BTW whether you have flange reinforcement rings or not, it is worth noting that winter use in the UK is not at all kind to any aluminium rear hub with stainless spokes through it. Anodised hubshells are almost certainly worse than polished ones, too. Splashing salty water over this mixture of metals can mean that the aluminium will suffer stress corrosion cracking at much lower stresses than normal.

To prevent this, I'd recommend cleaning thoroughly (with hot soapy water, a hot rinse and thorough drying) then running some corrosion-inhibiting treatment (such as waxoyl) into the spoke holes (and behind the flange reinforcement rings when they are fitted) by heating the assembly to ~60C (eg using a hairdryer) when the waxoyl is applied. An unsightly excess can be wiped away, provided the crevices are suitably protected.

Despite revised seals etc Rohloff used to have "an oil leakage problem" (that wasn't really a problem for rim-brake users and only occasionally a real problem for disc brake users) and as a consequence they have gradually reduced the oil fill level inside their hubs, to the point at which there is often little if any liquid oil sloshing around inside their hubs in normal service. The outside of such hubs stays cleaner and drier for sure, but mysteriously they now have "a flange breakage problem" that they presumably didn't notice before. I think these two things are not unrelated; the oil seepage almost certainly helped to prevent stress corrosion cracking (SCC) of the flanges.

[Note also that the oil seals will only work properly/not wear if they are kept wetted with lubricant; where they are situated inside the hub, the main oil seals are the first parts that are likely to run dry if there is no oil sloshing around inside. I have seen water behind the seals in a dry-running Rohloff, before the seal lips were badly worn; there is a clue there about the sequence of events IMHO.]

The flange reinforcement rings may, if anything, accelerate the effects of SCC on the hub flanges, by providing a larger cathode and providing a larger crevice in which strength-sapping corrosive residues can lurk. I would suggest that with rings fitted, the need for some kind of additional corrosion protection may be greater than ever.

cheers

[NATURAL ANKLING]

Hi,
I would of thought that a stronger hub even larger spokes and rim would be on the cards for such a system, some of the spoke configuration I see on this hub look a bit lightweight?
oh I found this post
viewtopic.php?t=104463
"

Despite the glib Outer Mongolia comment I'm genuinely interested in rohloffs reasoning. If a possible weakness had been found surely it would be better to redesign the hub shell rather than the 'after the horse has bolted' reinforcements?

If they did redesign the hubshell it would probably make it heavier too, which might put some people off.

In point of fact it might be difficult for a small company like Rohloff to design a 'much better hubshell'. It is also possible that they do not understand the nature of the problem well enough. There are plenty of engineers who would automatically assume that 'a stronger grade of material is always better' in hubshells.

In a single race (or something) they might be right, too, but in many kinds of prolonged service it is a false assumption; many stronger aluminium alloys are also more susceptible to SCC (stress corrosion cracking). Worse than that, such alloys may be used in billet form; which leaves any part vulnerable to inclusions and other inhomogeneities there might be in the material.

Many would argue that the best hubshells are forged, not machined from billet material, because this gives a more favourable structure to the material. However tooling up for forged hubshells is very expensive for small volume manufacture. Similarly others would argue that the best hubshells are [i]not made in the hardest material available. The argument goes that if the hubshell deforms to allow a larger contact area between the hubshell and the spoke, it is kinder to both, with less severe local stresses in either.

If the wheel is correctly built, i.e. with stress relief applied, it is possible that the hubshell material is strained beyond its ductility limit (in a high strength low ductility material), which could lead to cracks starting to form prematurely. If there is no yielding in the hub, well you might as well have a steel flange, and no-one would recommend that for a strong wheel these days, because it is so difficult to build a durable wheel (in which the spokes don't break) with such a flange material.

The other thing that is worth a mention is the subject of anodising. Without this, many high strength materials are not corrosion resistant enough for even 'normal hubshell service' leave alone any winter road salt etc. However its use in bicycle hubshells is rather questionable; the reason being that the wheel cannot be built without the anodising being breached where the spokes are fitted. Once the anodising is breached the hubshell is subject to extremely localised corrosive attack, i.e. potentially worse than if the anodising wasn't there. Since the breaches are at the points of highest stress, and have a (naturally cathodic) stainless steel spoke in there as well, this makes for a 'perfect storm' of highest stress and localised corrosive attack.

Some other hubshells that arguably break too often include Hope hubs and several other 'bijou' brands made in 7xxx and 2xxx grade materials.

FWIW I think that many hubshells can be made more crack resistant if a corrosion inhibiting material is used in the spoke holes; I quite often run a little waxoyl into the spoke holes of a freshly built wheel and this seems to stop them from going white and furry in that area; this ought also to mean a reduced cracking risk.

So Rohloff's approach of 'belt and braces' means that they can carry on making the same stuff as before ('we have not made a mistake') whilst offering an 'improved product'. I suspect that they do not willingly embrace certain forms of change; after all it took the fact that third parties were starting to offer 36hole hubshells for their hubs to finally force Rohloff to make them themselves, and it is only after decades of user-irritation that they have finally offered an alternative to the 'world's most annoying sprocket retention system'.

cheers

[/i]"

[Des49]

unless the flange reinforcement rings are shrink-fitted onto the flanges, they may not so much prevent flange breakage entirely as mitigate the consequences of it when it does occur, by holding the bits together when a crack occurs.

When I fitted the support rings to my Rohloff they just fell into place, not sloppy but certainly no interference fit. However they may be a tighter fit when the spokes are all tensioned and effectively pulling the flange outwards a touch.

So, I suspect their purpose is indeed to hold the flange together more in case of failure.

I am happy I fitted them and cannot see a downside. They do not appear to interfere with the lay of the spokes at all.

[mouldfield]

Thank you all for your comments. I'll be careful to keep the spoke tension higher and just reduce the load a little till I've sorted my wheel rebuild.