Cycling UK Forum

I have a much loved 1930s Grubb tandem and have just discovered a broken spoke on the rear wheel.

It's a 40H SA "AT" hub from the 1930s with drum brake and three-speed hub gear, laced in a 4X pattern. It's a hefty thing- the wheel weighs 3.5kg! We use the bike for local rides and light no-tent touring.

Since the wheel was probably last rebuilt over 60 years ago, it's done quite well, but I'd like to take the opportunity to renew all the spokes rather than just one. The 26 x 1 3/8 rim looks fine, just surface rust.

I'd like to use Sapim 'strong' spokes (butted 2.3mm/2mm, 13/14G).

However, currently the old galvanised spokes seem to be 12G or 2.6mm, and the holes in the rim are quite large, at 5mm. I'll use spoke washers as the hub flange is thinner of course.

So my question is:

With such large rim holes is it safe to use modern narrower spoke nipples as long as I use nipple washers, or is it possible to buy thicker nipples that still fit 14G spokes but will fill out the holes better?

Where to start?.......

On a huge flange like that drum brake, I would use much fewer crossings.....this is so the spokes approach the rim at a better angle. An alternative is to give the spokes a permanent bend right by the nipple, to avoid the spokes being stressed (flexed) and fatiguing there.
40H 4x gets the spokes fully tangential to the hub flange on a small flange hub, I don't know if your spokes overlap the head of the next spoke in the SA flange.

I would check the rim very carefully looking for fatigue cracking round the spoke holes. The current wheel has very thick spokes, which have next to no "give" in them at all at sensible tension, and my guess is that the steel rim is more flexible around the spoke holes than an alloy rim, where the material will be thicker.
As you presumably have an un-dished wheel with 40 spokes at very similar tensions, i would be thinking about using double butted spokes which are more stretchy and will "share out" a load between more spokes, and more rim drillings.
i think you are right about rim and hub washers.

don't make 'em like that anymore!

x4 is full tangent which normally allows the same length spokes to be used each side of the wheel. There is a bit more working out to be done if you use (say) DSx3 and NDSx1 or x2. FWIW I have successfully used 2 spoke washers per spoke in some cases with SA steel hubshells. Also you can buy 'converter nipples'; these have a (larger) 13g body, but a 14g thread.

mig wrote: ↑12 Aug 2024, 1:28pm don't make 'em like that anymore!

Don't need to either. I have toured off road on handbuilt 36h Deore hubs carrying a heavy load with no issues at all.
I carry silly/serious loads on my cargo bike, again off road, on 32h Hope hubs. No issues.
Just build them well.

Thanks for your helpful replies. I have further questions...

Colin: Yes it's an undished wheel. Are you recommending a mixed cross pattern due to the larger flange on the hub brake side? I admit the existing pattern does leave some pretty extreme angles at the rim, but the wheel has held up fine for 60+ years that way, and the breakage occured at the elbow raqther than the rim... Further, I thought that sticking with a 4x pattern would be best for wheel strength, especially if I use thinner spokes. Unfortunately the only double butted spokes I can find are 2mm-1.8mm-2mm, which is too thin, unless you know of somewhere I can get 2.3mm ones?

Brucey: so would a 13g nipple body be ok in a rim hole that is 5mm?

Thanks as ever for the help. What was a simple spoke replacement in my head this morning is rapdily turning into a can of worms (but perhaps that's ok )

tenbikes wrote: ↑12 Aug 2024, 2:32pm

mig wrote: ↑12 Aug 2024, 1:28pm don't make 'em like that anymore!

Don't need to either. I have toured off road on handbuilt 36h Deore hubs carrying a heavy load with no issues at all.
I carry silly/serious loads on my cargo bike, again off road, on 32h Hope hubs. No issues.
Just build them well.

that's encourgaing to hear - I admit I wouldn't mind being able to get the weight down a little. 3.5kg for just the rear wheel is a lot uphill with only 3 gears!

RobC wrote: ↑12 Aug 2024, 2:38pm Thanks for your helpful replies. I have further questions...

Colin: Yes it's an undished wheel. Are you recommending a mixed cross pattern due to the larger flange on the hub brake side? I admit the existing pattern does leave some pretty extreme angles at the rim, but the wheel has held up fine for 60+ years that way, and the breakage occured at the elbow raqther than the rim... Further, I thought that sticking with a 4x pattern would be best for wheel strength, especially if I use thinner spokes. Unfortunately the only double butted spokes I can find are 2mm-1.8mm-2mm, which is too thin, unless you know of somewhere I can get 2.3mm ones?

Brucey: so would a 13g nipple body be ok in a rim hole that is 5mm?

Thanks as ever for the help. What was a simple spoke replacement in my head this morning is rapdily turning into a can of worms (but perhaps that's ok )

Yes, the fewer crossings is to attend to the angle the brake side spokes approach the rim. The only advantage of 4 cross is to get spokes tangential to the hub flange, this is best for torque transmission, but has no other purpose, and it doesn't apply to that massive brake flange.
.I was meaning 2/1.8/2 mm spokes (14/16/14 G).....this is to get the maximum "stored stretch" in the spoke, which means that more spokes will share a load applied to a single point on the rim.
To avoid spoke failure at the bend at the hub end, its necessary to
1. improve the spoke line.....so that the spoke goes straight, and doesn't bow away from the flange ....some pictures here search.php?st=0&sk=t&sd=d&sr=posts&keyw ... 8&start=60
2. stress relieve. Theres a thread on here which i can find.viewtopic.php?t=110419&hilit=screwfix&start=15

I'm not a fan of thick spokes. I think fatigue failure has 3 phases; crack initiation, crack propagation, and failure, and of these crack initiation is the long one. Thick spokes can only extend the time taken for crack propagation, and they are a pig to stress relieve properly.
I think Sapim do some spokes which go from 13G to 16G and back to 14G , but I don't think I have ever seen one!

Or, just replacs the broken spoke for now, and think about it. 1 failure in 60 years is pretty damn good!

Thanks Colin - I found a DT Swiss triple butted spoke in the shed of the right length, so I think I'll just replace the broken one, as you suggest, and ponder longer term solutions.

Of course, it's a lot thinner than the rest of them though, plus the nipple almost falls through the rim hole so I'll be using an oval nipple washer and hoping for the best...

RobC wrote: ↑12 Aug 2024, 2:38pm....Brucey: so would a 13g nipple body be ok in a rim hole that is 5mm?

yes, I think so