Mark Beaumont: slacker spokes good?

[SA_SA_SA]

Mark Beaumont mentioned that his wheel broke a spoke early in his world crossing, and a Polish wheelbuilder fixed it , mentioning that the spokes had been too tight, after Mark Beaumont mentioned that the spokes seem alarmingly slack:

how slack is bad, how tight is bad?

[Freddie]

Spokes should be tightened until the rim bows, then you back off the rim straightens itself out and this is optimum tightness, essentially as tight as possible. Different rims will take differing amounts, thus tightness depends ultimately on the rim.

[531colin]

Spa work to an average spoke tension of 100Kgf (kilograms force) per spoke.
So fronts are 100Kgf, rears are 120 driveside and 80 nearside.
This is using a tension gauge, of course. They are pretty tight, but then I have never known spokes to get tighter in use, only slacker.
Building (and maintaining) your own wheels you could build slacker than this.

Spokes are too loose if riding loads can result in a spoke momentarily having no tension, when that bit of rim is momentarily unsupported from that side and the nipple is liable to unscrew itself.. Bumpy roads, heavy loads, 80 Kgf per spoke seems to offer a margin of safety. Tandems, mountain bikers doing drop-offs, still seems to work. (Most tandems almost dishless rear, 145mm. dropouts)

As freddie says, spokes are too tight if tension causes the rim to "pringle" - 4 smooth waves, 2 to left 2 to right. Its actually a double twist, reducing the "diameter" of the rim, thereby reducing the tension. Average 100Kgf can be pretty close to "pringle point" on very light or damaged rims. I have never yet "pringled" a sputnik!
More tension will decrease fatigue life, as the spokes are taken closer to yield point each revolution. For many applications, this is a theoretical problem only. However, bumpy roads, heavy loads....Spa use thicker rear driveside spokes!

[Mick F]

Just been thinking about getting a spoke tension meter.
I think I'll think again!

Have you seen the price?
http://www.sjscycles.co.uk/product-Park ... -11191.htm

[robc02]

According to Roger Husson in his book:

http://www.wheelpro.co.uk/wheelbuilding/book.php

Tension gauges have to be calibrated to the specific spokes (diameter) being used and that small variations in spoke diameter, due to production tolerances between batches/manufacturers, cause large variations in readings. Therefore the main benefit is in comparing tensions between spokes in the same wheel, and that you can do by plucking them and listening to the note. The latter method is remarkably sensitive.

I have paraphrased Roger, of course.

That still doesn't help in setting the tension in your first wheel. Its probably as well to compare, by feel, to the tension in a known good wheel.

[CREPELLO]

Spokes should be tightened until the rim bows, then you back off the rim straightens itself out and this is optimum tightness, essentially as tight as possible.

I wouldn't attempt this with rims such as the Sputnik as Colin aludes too. It's alright as a practise with lighter rims, but there is a risk of rim fatigue around the eyelets if certain rims are over tensioned.

Mark Beaumont's problems were with a Rohloff hubbed wheel, so a little different in construction from your average touring wheel. The 32 hole Rohloff hub does seem susceptible to flange fractures, from what I've heard. Sorry, what was his wheel failures again? I don't have the magazine to hand.

(Incidentally, is the magazine available online yet?)

[PW]

I tension mine by stress relieving, as recommended by Brandt. Squeeze parallel pairs of spokes, hard, (you need gardening gloves to do it properly) starting and finishing at the valve hole so you don't miss any. If the wheel Pringles as described by Colin back every spoke off 1/4 turn and true the wheel, job done. If it doesn't pringle give the spokes another round of tightening 1/4 turn each and try again until it does.

[hubgearfreak]

there is a risk of rim fatigue around the eyelets if certain rims are over tensioned.

i've found that the spokes snap off at the start of the thread before damage is done to a sputnik.
they don't get to be that weight without some stoutness

[531colin]

Just been thinking about getting a spoke tension meter.
I think I'll think again!

Have you seen the price?
http://www.sjscycles.co.uk/product-Park ... -11191.htm

Now you know why wheelbuilding pays (almost) national minimum wage!

[531colin]

According to Roger Husson in his book:

http://www.wheelpro.co.uk/wheelbuilding/book.php

Tension gauges have to be calibrated to the specific spokes (diameter) being used and that small variations in spoke diameter, due to production tolerances between batches/manufacturers, cause large variations in readings. Therefore the main benefit is in comparing tensions between spokes in the same wheel, and that you can do by plucking them and listening to the note. The latter method is remarkably sensitive.

I have paraphrased Roger, of course.

That still doesn't help in setting the tension in your first wheel. Its probably as well to compare, by feel, to the tension in a known good wheel.

My Park Tools tension gauge reads a deflection. To get to Kgf you use a conversion table. According to that table, deflections representing 100Kgf are as follows;

2.3mm spoke reads 28
2.0mm spoke reads 24
1.8mm spoke reads 21
1.6mm spoke reads 19

Manufacturing tolerance would be how much? Surely less than 0.1mm, ie less than one deflection unit?

[531colin]

Mark Beaumont's problems were with a Rohloff hubbed wheel, so a little different in construction from your average touring wheel. The 32 hole Rohloff hub does seem susceptible to flange fractures, from what I've heard. Sorry, what was his wheel failures again? I don't have the magazine to hand.

(Incidentally, is the magazine available online yet?)

I would be interested to know the exact failure, too. Rohloff wheel spokes commonly fail at the rim, as the flange is so big the spokes approach the rim at an unusual angle. special rims are made with angled holes.

[rogerzilla]

I tension mine by stress relieving, as recommended by Brandt. Squeeze parallel pairs of spokes, hard, (you need gardening gloves to do it properly) starting and finishing at the valve hole so you don't miss any. If the wheel Pringles as described by Colin back every spoke off 1/4 turn and true the wheel, job done. If it doesn't pringle give the spokes another round of tightening 1/4 turn each and try again until it does.

The trouble with JB's tensioning method is that some rims exist, especially in sub-700c sizes, that will not pringle until the nipples snap or the tension is so high that eyelets pop or the rim cracks a year later. DT XR 4.1, or whatever they're called now, spring to mind. In these cases you have to start with well-lubricated nipples (dipping them in oil works better than lubricating the male threads on the spoke, and helps them turn in the rim too) and just tighten until you fear for the integrity of the nipple. A 4-sided spoke key (I think Pedro's make the best one) is much safer - the nipple will actually snap before it rounds off.

With Brompton rims the spokes are too short and stiff for the "squeezing" method of stress relieving, so wedging an old crank into the spoke crossings and levering hard does a better job. And if you really want to be sure that you've got the twist out of them, extreme measures are needed.

[PH]

Mark Beaumont's problems were with a Rohloff hubbed wheel, so a little different in construction from your average touring wheel. The 32 hole Rohloff hub does seem susceptible to flange fractures, from what I've heard. Sorry, what was his wheel failures again? I don't have the magazine to hand.

(Incidentally, is the magazine available online yet?)

I would be interested to know the exact failure, too. Rohloff wheel spokes commonly fail at the rim, as the flange is so big the spokes approach the rim at an unusual angle. special rims are made with angled holes.

If I remember right - The original wheel was breaking spokes almost straight away. On the television program it was said the wheelbuilder couldn't get the right length spokes so cut a thread into some others and it was this cut thread that was the problem.
The wheel was completely rebuilt, with the right spokes, by the Polish wheelbuilder with the ideas about not using too much tension. Something he wasn't happy about, but gave surprisingly little trouble considering the roads it was used on.
He did question whether he'd made the right choice using a Rohloff, more to do with being unable to simple swap a wheel than the hub itself.
In over 35,000 miles on my Rohloff I haven't broken a spoke, though I have had a flange crack.

[531colin]

If I remember right - The original wheel was breaking spokes almost straight away. On the television program it was said the wheelbuilder couldn't get the right length spokes so cut a thread into some others and it was this cut thread that was the problem.
The wheel was completely rebuilt, with the right spokes, by the Polish wheelbuilder with the ideas about not using too much tension. Something he wasn't happy about, but gave surprisingly little trouble considering the roads it was used on.
He did question whether he'd made the right choice using a Rohloff, more to do with being unable to simple swap a wheel than the hub itself.
In over 35,000 miles on my Rohloff I haven't broken a spoke, though I have had a flange crack.

Spoke threads are rolled, rather than cut with a die. Cut threads are a smaller diameter than the original spoke as metal is removed. rolled threads are actually bigger (overall) than the original spoke as the metal is not removed but pushed about a bit. AFAIK nipples for cut threads are no longer available. Shops have a little hand - cranked machine for rolling threads.
I think thread rolling may be the sort of thing which can "work harden" steel, but I am outside my comfort zone here. In any event, this is precisely the area where I have seen spokes fail in Rohloff wheels.
35,000 miles.... wheels properly built, then!

[rogerzilla]

Rohloffs do give a bad spoke/rim angle, which is made slightly worse by smaller 26" wheels. There are ways round this, such as ensuring the spoke has a kink rather than a bend, or choosing a rim and nipples (e.g. Sapim Polyax) that can orient themselves better.

I know someone who has broken several Rohloff flanges. Thorn can supply a reinforcing ring which is supposed to reduce the chances of this. I don't know if the flanges are canted inwards (they should be), but if they're not, there is a lot of inwards bending force on them from the spokes.

Ultimately I think everyone would be happier if Rohloff just offered a 36 or 48 drilling for the Speedhub; there are enough variations of it already that surely one with more holes wouldn't be too much to ask?