Sapim Race Spokes in a Rohloff Wheel with Andra 30 Rim - What Tension To Use?

[Slammin Sammy]

Greetings Thornoids!

I trust you're all well and those of you in northern climes are enjoying your springtime.

I know this question has been batted around before, but although I've done a reasonable amount of researching past discussions on this and other forums ("fora"?), I am still none the wiser. Let me describe my dilemma:

When cycling a rail trail in central Victoria week before last, I broke a spoke in Attila the Nomad's rear wheel (32h Andra 30 which I had laced myself only last July with 238mm Sapim Race black spokes). When last I checked, the wheel was running quite true, with spoke tension between about 80 and 105 Kgf (average about 94) as read on my Park Tool TM-1 Tension Meter. The spoke was more or less opposite the valve hole, and broke right in the middle, after hitting a sharp bump (buckled pavement) while I was going downhill at speed with lightly loaded panniers. I must say I was surprised, because I thought the wheel would be far stronger than that.

Later in the week, clumsy old me actually tripped over the bike, inadvertently stepping on, and breaking another spoke (same side, next adjacent to the original broken one). Also snapped in the middle.

No worries, says I, as I had 6 spokes left over for each wheel from my original build. Upon returning home, I pulled the wheel, replaced the spokes, and whilst tightening them up to tension, a third spoke snapped!, this time opposite the two others (valve side). This bothered me, as these spokes ought to be able to withstand at least double the tension, especially while static.

My question is this (apologies for being long-winded): As the Andra 30 is considered one of the strongest rims on the market, and the TM-1 tension chart shows a range up to 167Kgf for 1.8mm diameter steel spokes, why shouldn't I be able to tension up the wheel to say, 130 Kgf, +/- 20% (104 - 156)? I would think that would give me a stronger wheel, no? But if that is true, why did the third spoke break so easily?

I also note that the tension measured on my wife's Raven (same wheels, silver spokes, presumably Sapims?) built by Thorn in August are the same as mine (all very close to 94Kgf, or 20 on the TM-1 scale). Making the obvious assumption that Thorn knows a lot more about building this wheel that I do, I'm wondering what I'm missing? My wheel was true, the tensions were pretty tightly grouped around the average, so why did a spoke break on what should be the strongest wheel going?

I will try to take a macro-photo of the third spoke break surfaces, to see if the spokes were defective, but I would think there's a fairly low chance of that having been the case. I'm just trying to ensure I get good reliable service out of these wheels when fully loading them up on future tours.

Thanks in advance for your always well-considered responses,
Sam

[Slammin Sammy]

Update - I realise a mistake I made when comparing the tension on my wife's Raven (built by Thorn) to mine (built by me) in that I measured hers with a Marathon Dureme inflated to 45 or 50 psi still attached. Mine is a raw wheel measurement. So hers would be much higher tension prior to tyre inflation.

Here's a couple of photos of the break:



and

[url=https://flic.kr/p/ntaWez]

I believe the colours may be misleading (looking like rust in a crack), as I inspected the ends with a hand lens (like a jewellers' loop) which is 20x, and I don't see the red colour in that view.

[triaesthete]

Hi Sam

Roger Musson  http://www.wheelpro.co.uk/wheelbuilding/book.php  puts the following in bold for emphasis   "For a reliable wheel it is important to have all the spokes sharing the tension equally."  I think yours have a tension range of some 20% and this may be the issue. From your evidence it would seem (and I'd expect)that the Thorn wheel is built to a narrower tension tolerance. You also have just about the stiffest and most unyielding rim out there which may exacerbate this.

I've done my tensions by ear/tone only and it is possible to get them nice and even. The spokes carrying excess tension sound much brighter than the others and are easily backed off. Thanks to Roger's tips I have not EVER had to adjust or true  any wheel I've built and some of them have seen considerable off road use. You can download the book now for £9, I can't recommend it enough.

Did you also pay attention to spoke torsion (wind up) during your build?

Happy twanging
Ian

[mickeg]

I think some variation in spoke tension will be normal, I would not worry about your variation.

I would contact Sapim and find out if they want to send you a new batch of spokes to replace all of yours.  I can't remember if I have ever heard of a bunch of spokes on one wheel snapping in the middle - not at the end.  But with the bad luck you are having with this wheel, if it was me, I would not want to get too far from home until I could replace the spokes.

In USA, Sapim spokes are hard to find.  I used Wheelsmith spokes and Sapim nipples on my Nomad with Rohloff.  I wanted to use butted spokes but the length is so unusual that all I could find were straight gauge spokes, which is what I eventually decided to use.  On my other touring bikes I use Wheelsmith DB-14 spokes without incident.

[Slammin Sammy]

I finally got a chance to complete my repairs and cleaning of our bikes after our tour to Victoria.

Mike, now that I've had a good look and cleaning of both my wife's spokes and my own, I'm liking your suggestion of going back to Sapim for a replacement. My black spokes (both wheels) are definitely pitted by rust, whereas my wife's silver spokes are fine. Bear in mind I built my bike about June 2013 (my wife's Raven was built in August).

We live near the beach, but the bike has never been in salt water, and has been cleaned regularly. I am now convinced the spokes are substandard, and the pitting has weakened them sufficiently to cause breakage under sharp stress. I have replaced the broken spokes and have re-tensioned and re-trued the wheel. I am satisfied the wheel is well built, and if another spoke breaks, I will be replacing them all - front and back. But I won't be using Sapim spokes again until I get a satisfactory explanation from them for this phenomenon.

[Slammin Sammy]

Hi guys,

I thought an update on this topic was in order. I have been busy, and so haven't brought the story up to date.

My rebuilt rear wheel managed to go another three weeks before spoke number 4 let go. Same problem, breakage right in the centre:





I rebuilt again, this time using extreme care and checking tensions and trueness on a high end Park Tool truing stand and PT tension gauge. I recorder the tensions for each spoke and they were within 5% of each other, at about 100 Kgf (~1000 Nmm2?). This was one well-built wheel, and went pretty well right through June.

In the meantime, I copped a broken front spoke! This time, it broke near the rim end. I replaced it and carefully trued up that wheel to the same specs.

I finally decided to take mikeg's suggestion and contact Sapim - here's my message and the prompt response from them:

Hi,
I built a Thorn Nomad Mk2 in June 2013, with 238mm Sapim Race spokes (black) in back on a Rohloff speedhub, and 260mm up front on. SON 28 dyno hub. Both wheels are Andra 30 by Ryder (Rigida).
The spokes have been a big disappointment. I have already broken five in the rear, and one in the front, even though the wheels were well built and strong. The spokes have exhibited pitting (rust), and have broken in the middle, not at the hub or rim end, in almost all cases. These spokes have broken under relatively light load - far lighter than the rating for this bike and wheels.
I want to replace all of the spokes with new ones, since I feel they were poorly made. Are you prepared to provide 36 of each length under warranty? I purchased the spokes from SJS Cycles (Thorn) in the UK, and can send photos and documentation of the sale.
I look forward to your response.
Thank you,
Sam


Dear sir,

Sorry to hear that you had troubles with our spokes.
You have all the right to ask for a replacement in case of problems and in this case we will take our responsibility and replace your spokes by a higher quality of spoke.
You will receive a force spoke which match better with your hubs.

The problem of the rust is rarely noticed but it can happen. We process yearly +/- 47.000.000 km of wire, and a small problems might happen.

Please give me your address and we will send you the spokes free of charge.

Best regards
Wim

Now that's what I call service! I was unaware that the Force spokes were more appropriate, although I would have thought the Race model would certainly be strong enough. I think they're rated 1300 Nmm2, while the Force are rated for 1400. The difference appears to be an extra 0.18mm thickness in the hub-end butt.

And what about 47 MILLION km of wire!? How many spokes is that? At four spokes per metre, that's 188 BILLION SPOKES per year! Can that really be true?  

PS - Just yesterday, another rear one let go, this time at the rim-end. The replacement spokes are still in the mail, so I'll replace this one with a Race spare, but I'm getting mighty tired of this. They seem to always give way after about 40km of riding too, not first thing.

Anyway, TBC!

[Danneaux]

Wonderful followup report, Sammy. I've followed this one from the beginning with great interest.

Different mechanism of course (and different materials) but I'm reminded of my experience in the 1970s with Robergal Trois Etoille spokes. They were plated but had not been heat processed properly so were hydrogen embrittled and would break spontaneously even with the bike at rest.

I find the location of your breakages particularly interesting.

Following with greatest interest and empathy -- repairing those wheels and even rebuilding them gets old quickly.

All the best,

Dan.

[Dave Whittle Thorn Workshop]

I wouldn't use Force spokes in a Rohloff hub, IIRC they are more than 2.0mm at the bend, this will make flange failure more likely.  We had this problem on some Sapim spokes, since this we have always spec'd Swiss wire from Sapim when ordering our Race spokes and have never had an issue since.

[jags]

anyone got a link to a good video on how to dish a rear wheel.
cheers
anto

[Slammin Sammy]

I wouldn't use Force spokes in a Rohloff hub, IIRC they are more than 2.0mm at the bend, this will make flange failure more likely.  We had this problem on some Sapim spokes, since this we have always spec'd Swiss wire from Sapim when ordering our Race spokes and have never had an issue since.

Thanks, Dave. I wondered about that! I have double checked and found that both Rohloff and Schmidt specify 2mm spokes. I will respond to Wim with this information.

I realise that sometimes, manufacturing errors can occur in wire, as well as in subsequent spoke formation. I'm surprised that Sapim would use special wire for SJS spokes rather than build to one standard, but in any case, I presumed that since I bought the Race spokes from SJS, they would be identical to what was used in new Thorns. Would this be correct?

I don't want to cause hub flange problems using the larger spokes, and I want to use blacks, so I will persevere.

Regards,
Sam

[Dave Whittle Thorn Workshop]

I presumed that since I bought the Race spokes from SJS, they would be identical to what was used in new Thorns. Would this be correct?

For silver yes, we don't use anywhere near enough black ones to order direct from Sapim and specificy certain criteria like we do with the silver.