I’m finally getting around to building a new rear wheel for the tandem.

Spank Stiffy rim with 530mm ERD.

Rohloff hub, which needs 234mm spokes.

Rose Bikes seem to be the cheapest for spokes with DT Swiss Competitions at £5.90 per 20

Rohloff recommend Pro Lock nipples, £5.55 per 40 from Rose again, either 12mm or 14mm length.

Now, looking at that Rohloff chart, a 234mm spoke is suitable for rims from 530mm to 533mm ERD.
As I’m using the smallest rim in that range, does that mean the shorter 12mm nipples are OK, or would a 14mm nipple give more thread engagement, which would be better for a tandem ?

AFAIK nipple length is to do with the thickness of the rim from spoke bed to inside edge. Used 14mm nips on a CXP33 as it was a deeper section, otherwise have used 12.

Regarding nip length and strength it’s my understanding that the majority of the load is taken by the first couple of threads so going longer purely for strength would not be beneficial.

Hi Graham
12mm would be fine.
cheers paul

OK, thanks both.
Spokes always seem to break at the point where they enter the nipple, I don’t think I’ve ever seen one strip its thread, so I’ll go for the 12mm then.

only time I’ve used 14mm by choice is when re rimming with a rim that has a slightly larger ERD.

CRC used to supply all their spokes with 14mm nipples, though, for some reason.

Yeah, I think it’s seeing 14mm as the only option on CRC, where I have always bought spokes in the past, that made me think that that must be the default length and 12mm was unusual.

I’ve never broken a spoke, but have snapped leads of nipples at the point they ‘flange out’.
It seems all the tension has been taken up by the nipple flange, so now I try to build wheels with the spoke thread nearly all the way through the nipple.

Is this correct??!!

DrP

XM819s need longer nips so there’s enough nipple to engage the spoke key outside of the insert. Others do if it’s a deeper section, generally 12s will be fine.

length of thread is the same on 12 and 14s – in DT anyway.

the spoke should reach the nipple base as a matter of course when wheel building – anything else is a bodge- not saying it wont work for a time but its not correct.

“so now I try to build wheels with the spoke thread nearly all the way through the nipple.”
If your finished build is all good, and the end of the spoke is around about at the end of the nipple. then you’ve got a good build with the right length spokes.
remember that you hang your weight off the top spoke.
cheers paul

remember that you hang your weight off the top spoke.

If by that you mean that the top spoke increases in tension to take your weight (and none of the other spokes do to any significant extent), then that’s completely untrue.

I used 14mm on a recent wheel build, purely as they came with the spokes.

Subsequently, 3 of the spokes snapped just at the top of the nipple, I presume because it was causing a slightly tighter bend than a 12mm nipple would have.

Replaced with Sapim Race spokes 12mm polyax nipples to reduce the bend in the spoke as much as possible.

remember that you hang your weight off the top spoke.

If by that you mean that the top spoke increases in tension to take your weight (and none of the other spokes do to any significant extent), then that’s completely untrue.

+1
If the wheel is tensioned correctly, the wheel should act as a single solid object. Reminds me of the theory cooked up by a mad German I knew that disc brakes wouldn’t work as they’d snap all the spokes.

I bunged that rim and hub into a spoke calculator and it comes up with 233.0mm. Now personally I always round down when selecting spoke lengths (especially if using butted spokes), as that measurement is for static spoke length. When tensioned spokes stretch, so the effective length of a spoke is more than it’s static length – with a 234mm spoke you run the risk of bottoming the nipple on the spoke threads before reaching optimum tension.

As mentioned above, the length of thread in a nipple is the same for 12mm and 14mm nipples anyway.

“If by that you mean that the top spoke increases in tension to take your weight (and none of the other spokes do to any significant extent), then that’s completely untrue”

did you take a long run up before you made that jump

“did you take a long run up before you made that jump”

No…he’s right. The spokes behave like loaded columns once they’ve been pre-tensioned. This means that your weight is supported by the lower spokes that experience ‘compression’. It’s like a pre-tensioned concrete beam in behaviour….in this instance as long as the ‘compression’ experienced is less than the pre-tension the wheel will be okay (ie. pre-tension = 1,000 N, load experienced = compression of -800 N spoke tension when exposed to load = 200 N. If there is any doubt on this you can look at Brandt’s book The Bicycle Wheel or HP Gavin’s paper on Spoke Fatigue where the wheel is treated as a radially loaded column on elastic foundations.

This is currently the area of study for my final year Mech Engineering degree dissertation. I am by no means an expert but the theory holds true in testing. Oli.

What calculator are you using, aracer ?
Rohloff themselves say 234mm.
I also used this one simply because it’s got the Spank and Rohloff dimensions already there so I don’t have to type them in manually, which gives 234.2mm.

Spokes bending at the nipple can be a problem with a Rohloff hub, especially on a 26er, because of the large diameter flanges. Another reason to go for 12mm nipples then.

Without sidetracking my own thread too much, I always thought the spokes near the 12 o’clock position were under the most tension and those near 3 & 9 o’clock more than those at 6 o’clock.
If you think about it, you could put a static load on a wheel with just one spoke at 12 o’clock.
Increase the load and the rim will try to go elliptical. Two more spokes at 3 & 9 o’clock would stop that.
A spoke at 6 o’clock would have no tension on it at all.

That’s just intuition though.
I’d be interested to see any evidence one way or the other.

Edit;
Cross posted with oliwb.

This means that your weight is supported by the lower spokes that experience ‘compression’

Hang on… if I put weight through a spoke, the spoke would simply slide out of the rim!
The wheelpro book, and science, would suggest that spokes work in tension, not compression!

DrP

someones making assumptions.

until the preloads exceeded its in compression – once the preloads exceeded you start hanging from the top spoke.

spokes near the 12 o’clock position were under the most tension and those near 3 & 9 o’clock more than those at 6 o’clock.

Brandt’s book has a breakdown of the tension distribution, but broadly speaking, the spoke tensions are practically equal over almost the entire wheel with just a few spokes (3 or 5) at the 6oclock position having a slight reduction in tension (that slight reduction is then balanced by an equal increase, but spread evenly over the rest of the spokes).

once the preloads exceeded you start hanging from the top spoke

nope, still “hanging” from all the other spokes not just the top one

sorry – missed an S – same difference to non pedants – your no longer compresing spokes.

If you think about it, you could put a static load on a wheel with just one spoke at 12 o’clock.
Increase the load and the rim will try to go elliptical. Two more spokes at 3 & 9 o’clock would stop that.
A spoke at 6 o’clock would have no tension on it at all.

You could, but that’s not how a bicycle wheel works. A bicycle wheel is a pretensioned structure on which you can superpose compressive loads. You can’t just simplify it by removing spokes. Brandt has a good explanation of this in his book, including a finite element analysis of a wheel which proves the point.

http://sheldonbrown.com/rinard/spocalc.htm is the spoke calculator I use – I know it’s using the right formulae, not necessarily so for anything web based. Looking at the one you link to, it appears to be using nipple seat diameter instead of ERD – the nipple seat is a couple of mm less than the ERD.