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Repeated broken rear spokes on Trek District 4 Equipped

I have about 4000 miles now on the Trek District 4 Equipped I bought new last year, and I think I've now had five or six broken rear spokes. It has a Shimano Alfine 8 rear hub laced to a Bontrager rim with 32 straight gauge spokes, and has 700C x 40 mm tyres.

The shop has been great at replacing them under warranty, and last time they even got Trek to give me a new rear wheel on the theory that maybe it was built wrong. Well, that was less than six months and 1500 miles ago, and I've just dropped it off again when I found another broken one. They all break at or just inside the nipple, with a few threads left on the spoke.

I bought the bike in late March of 2023, so I have about six weeks of warranty left. I am well, well under the weight limit for the bike at about 165 lb / 75 kg, have never used it for heavy loads, and about the roughest thing I do to it is slow rides up or down 6" dropped kerbs. I also don't put out massive power, especially when I ride this bike, which is mainly my commuter. Any thoughts? I'm not looking to return the bike. My thought was once it's out of warranty I'll just rebuild it myself with quality double butted spokes and upgrade to brass nipples, probably $50 (£40) per wheel if I do the labour myself. I told the shop owner that, and he assured me they "won't let it get that far."

My intent with this bike, with its belt drive, internal gears, and generator lights, is it would be an unstoppable 100% reliable pub bike to get me home at night without any mechanical issues, and to be fair it has been. Even with two broken spokes there was enough chain stay clearance to handle the wobble.

Any theories as to what the cause might be other than "maybe the spokes aren't strong enough?"

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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26 comments

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andystow | 1 month ago
3 likes

I got it back a few days ago. The new and old spokes measure right at 2 mm, so 14 gauge. They're built three cross, but the third cross is basically behind the flange.

I still haven't had a chance to check the tension.

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chrisonabike | 2 months ago
2 likes

I've one of these (also 32 spokes, Ryde sputnik rim (622x19c rim), not sure the spokes, 3 cross). Just by eye the alfine hub appears to have a thick flange not just a wide one (but haven't checked with a gauge). That wouldn't explain issues at the nipple ends though. As others say perhaps lacing pattern?

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chrisonabike replied to chrisonabike | 2 months ago
2 likes

Sounds like you'll just see how the new wheel works now.  I've not had issues but I've done much less distance.  Probably had somewhere north of 500 miles in the last build of this bike (theft, recovered it but needed a rear wheel rebuild) with no issues.  Couple of hundred this time round.

 RABBITHOLE ALERT!

I had a quick look online and the Alfine wheels of this diameter I could see all had the same spoke pattern.  The angles at rim do seem to be greater on this hub (because the wider hub flange?) though.

For deeper dives into wheelery-spokery there are of course SpokeCalc and FreeSpoke.  The latter gives you a nice visualisation with angles.  Plus a wealth of nerding from engineers, the late great Sheldon Brown etc.

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andystow | 2 months ago
2 likes

I stopped by today to buy a couple of things, and this is the state of my wheel. He's rebuilding it three cross with all new spokes.

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don simon fbpe replied to andystow | 2 months ago
2 likes

Which is all well and good, and hopefully built well, but we still don't know the cause of the previous failure.

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HoarseMann | 2 months ago
1 like

Looking at the photos on the Trek website, the angle that some of the spokes are leaving the nipple is quite extreme. I think Trek have made a mistake using a 2-cross pattern on a 32-hole hub - especially an internal geared hub that has wide flanges. (edit: if it is a 2-cross pattern, in some photos it looks like it might be 3-cross!).

On lower spoke count wheels with a smaller flange hub, the spoke angle is less. See below a rough example, the green triangle is the same size, you can see how much greater the spoke angle is on the 32 spoke wheel of the District 4 compared to a 24 spoke Domane.

I'd ask them to rebuild the wheels (or at least the rear) in a 3-cross pattern.

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hawkinspeter replied to HoarseMann | 2 months ago
1 like

HoarseMann wrote:

Looking at the photos on the Trek website, the angle that some of the spokes are leaving the nipple is quite extreme. I think Trek have made a mistake using a 2-cross pattern on a 32-hole hub - especially an internal geared hub that has wide flanges. (edit: if it is a 2-cross pattern, in some photos it looks like it might be 3-cross!).

On lower spoke count wheels with a smaller flange hub, the spoke angle is less. See below a rough example, the green triangle is the same size, you can see how much greater the spoke angle is on the 32 spoke wheel of the District 4 compared to a 24 spoke Domane.

I'd ask them to rebuild the wheels (or at least the rear) in a 3-cross pattern.

Interesting - I wouldn't normally think that 2-cross vs 3-cross would make much difference to the spoke angles. Also, I would expect the nipple to deform slightly to accomodate that if they (more likely the nipple flanges) aren't sitting flush with the rim. I'd say that 3-cross would be stronger than 2-cross, but mainly for resisting sideways forces on the wheel (including the forces when braking/pedalling).

A rebuild to 3-cross is a good idea though as it'll force them to use a different set of spokes due to the longer length required.

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don simon fbpe replied to hawkinspeter | 2 months ago
2 likes

I would guess that multiple recorded failures would point at design flaws and one or two instances of failure pointing at manufacturing or QC failure (spoke tension).

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HoarseMann replied to hawkinspeter | 2 months ago
2 likes

I might be wrong about it being 2-cross, but the spoke angles do look quite high, this one in particular:

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andystow replied to HoarseMann | 2 months ago
1 like

HoarseMann wrote:

Looking at the photos on the Trek website, the angle that some of the spokes are leaving the nipple is quite extreme. I think Trek have made a mistake using a 2-cross pattern on a 32-hole hub - especially an internal geared hub that has wide flanges. (edit: if it is a 2-cross pattern, in some photos it looks like it might be 3-cross!).

On lower spoke count wheels with a smaller flange hub, the spoke angle is less. See below a rough example, the green triangle is the same size, you can see how much greater the spoke angle is on the 32 spoke wheel of the District 4 compared to a 24 spoke Domane.

I'd ask them to rebuild the wheels (or at least the rear) in a 3-cross pattern.

Thanks, good point. I see what you mean about the angles. The only other bike I've broken spokes on was my cheap Chinese Bickerton folder, and due to the short spoke length it had some very extreme angles. They also always broke at the nipple.

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andystow replied to HoarseMann | 2 months ago
1 like

Here's a recent photo of my actual rear wheel. I haven't kept track of which spokes broke, but the first time it was definitely one of the two adjacent to the valve.

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HoarseMann replied to andystow | 2 months ago
0 likes

I still can't work out if it's a 2-cross or 3-cross lacing, but it's something to check. The angles of some of those spokes do look like they are bending quite a bit at the nipple.

https://www.purecycles.com/blogs/bicycle-news/156387911-speaking-of-spok...

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David9694 replied to andystow | 2 months ago
2 likes

It's a regular enough pattern, but I don't like the way the spokes run in pairs to (?) adjoining holes on the rims.  3x (the only method I've used) is always better. I'd recommend Sapim Strong for for DS and Sapim Race for NDS if you go the rebuild route. 

I assume the breaks are happening at the J? 
 

ive never got to the bottom of spoke tension on rear wheels.  Even on each side, ping on the NDS and pong on the DS. 

I know you said "don't tell me the spokes aren't strong enough", but for whatever reason(s) you've got too much flex (e.g. weight, riding surface, less likely - riding style) and the spoking you've got cannae take it, Captain.

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andystow replied to David9694 | 2 months ago
1 like

David9694 wrote:

I assume the breaks are happening at the J?

Nope, just inside the nipple.
 

David9694 wrote:

ive never got to the bottom of spoke tension on rear wheels.  Even on each side, ping on the NDS and pong on the DS. 

I know you said "don't tell me the spokes aren't strong enough", but for whatever reason(s) you've got too much flex (e.g. weight, riding surface, less likely - riding style) and the spoking you've got cannae take it, Captain.

75 kg, maybe 200 W on a good day, and this bike gets used almost entirely on smooth surfaces except for the occasional kerb hop at low speed.

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hawkinspeter | 2 months ago
0 likes

I had a similar issue years ago when I bought my first road bike - a Cannondale Synapse. However, I had rear wheel spoke breakages at the usual place where the spoke bends near the hub and it's unusual to get spokes breaking near the nipple as that's a stronger part of the spoke. The bike shop replaced the factory supplied rear wheel with one that they considered to be an upgrade to fix the issue, but that was even worse and noticeably went out of true after a short ride.

The shop kept trying to fix the wheel and it kept going wonky, so I got bored of leaving my bike with the shop to fix, so I tried to true the wheel myself and found that the rim was distorted and so the spokes had to be very uneven in tension to make the wheel round. Once I realised the rim was unusable, I built up my own wheel instead (the shop hadn't agreed to me trying to true the wheel as they thought I'd been tinkering with it previously and had caused the problem).

With your problem, I wonder if maybe the spokes were under tensioned so that some of them were becoming unloaded during a revolution and that could explain the breaking near the nipple end.

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don simon fbpe | 2 months ago
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Given you have the ability to build a wheel, have you (or even the shop) put it in a stand to check out the build quality/spoke tension? Even if just to eliminate that.

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andystow replied to don simon fbpe | 2 months ago
1 like

don simon fbpe wrote:

Given you have the ability to build a wheel, have you (or even the shop) put it in a stand to check out the build quality/spoke tension? Even if just to eliminate that.

I've never built one from scratch, but I've replaced spokes before and have access to a truing stand (I sometimes volunteer at the local bike Co-Op.) The spokes on this wheel have always seemed extra tight to me by feel, and they are really thin (I'll measure them when I get it back this time.) At some point the tensiometer at the Co-Op walked off, unfortunately, but the mechanics at the Trek store are the most competent in town, so I imagine they've checked the obvious.

The wheel is very true both radially and axially when all the spokes are there.

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don simon fbpe replied to andystow | 2 months ago
1 like

They're unlikely to be extra tight, you'd have a particularly hard ride and potentially many punctures, unless short spokes have been used and we go back to their QC dept. Again the wheel being true radially and axially doesn't really mean that much if the spoke tension isn't within tolerance. I'll assume that when spokes have been added that attention has also been paid to other spokes across the wheel.

First port of call for me would be checking spoke tension.

It'd do no harm to strip it down and rebuild it, if Trek can't sort it out under warranty, there's nothing to lose.

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andystow replied to don simon fbpe | 2 months ago
1 like

don simon fbpe wrote:

They're unlikely to be extra tight, you'd have a particularly hard ride and potentially many punctures, unless short spokes have been used and we go back to their QC dept.

It did have the harshest ride of any of my bikes, but I attributed it to the aluminium frame (the rest are steel.) I actually put a ShockStop stem on it to stop the harshness at the bars.

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don simon fbpe replied to andystow | 2 months ago
1 like

It's possible that they ran out of correct length spokes and had to overtighten a shorter spoke or resort to 2 cross and overtighten, but having seen production wheels being built, I can't see this sort of thing happening. Might be the frame material, might be a tightly laced wheel causing harshness. Easiest way is to eliminate the possibilities and get that tensionometer to do its thing.

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Creakingcrank replied to don simon fbpe | 2 months ago
4 likes

Scared to get into an engineering debate, but:

I don't think spoke tension has much of an effect on wheel stiffness/ride feel, provided the spokes are tight enough that the bottom ones don't lose all their tension under load.

The stiffness of a spoke depends upon the Young's Modulus of the material and its cross section, neither of which change that much in "normal" operating/assembly conditions. Here's a link to some experiments.

There's a slim chance the wheel was built with the rim backwards, so the nipples come out at the wrong angle and the spokes have to bend a long way to compensate.

Overall, however, I'm betting on a root-cause of "crappy spokes"

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don simon fbpe replied to Creakingcrank | 2 months ago
0 likes

Creakingcrank wrote:

Scared to get into an engineering debate, but:

I don't think spoke tension has much of an effect on wheel stiffness/ride feel, provided the spokes are tight enough that the bottom ones don't lose all their tension under load.

The stiffness of a spoke depends upon the Young's Modulus of the material and its cross section, neither of which change that much in "normal" operating/assembly conditions. Here's a link to some experiments.

There's a slim chance the wheel was built with the rim backwards, so the nipples come out at the wrong angle and the spokes have to bend a long way to compensate.

Overall, however, I'm betting on a root-cause of "crappy spokes"

I maybe misunderstood teacher.

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hawkinspeter replied to don simon fbpe | 2 months ago
0 likes

don simon fbpe wrote:

They're unlikely to be extra tight, you'd have a particularly hard ride and potentially many punctures, unless short spokes have been used and we go back to their QC dept. Again the wheel being true radially and axially doesn't really mean that much if the spoke tension isn't within tolerance. I'll assume that when spokes have been added that attention has also been paid to other spokes across the wheel.

First port of call for me would be checking spoke tension.

It'd do no harm to strip it down and rebuild it, if Trek can't sort it out under warranty, there's nothing to lose.

I also share CreakingCrank's scepticism of how much spoke tension contributes to the ride feel. I'd expect tight spokes to put extra force on the rim which can lead to rim failure (it goes from a circle to a (mathematical) saddle shape) but does it really affect how much the spokes stretch?

Also, how does spoke tension affect the numbers of punctures - I haven't heard that theory.

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Creakingcrank replied to hawkinspeter | 2 months ago
2 likes

Correct length spoke - ends up roughly flush with top of nipple. Spoke overtightened - sticks out of nipple on the inside - pierces rim tape - punctures tube. Less likely on a box section rim, but potentially a problem on a "basic" shaped one.

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hawkinspeter replied to Creakingcrank | 2 months ago
1 like

Creakingcrank wrote:

Correct length spoke - ends up roughly flush with top of nipple. Spoke overtightened - sticks out of nipple on the inside - pierces rim tape - punctures tube. Less likely on a box section rim, but potentially a problem on a "basic" shaped one.

Aha - that makes sense now.

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andystow | 2 months ago
1 like

I will add that I've never had a broken spoke, or even had to true, my Mason X Hunt 650B Adventure Dynamo Disc Wheelset. I ride it much harder and over chonky gravel, and have nearly 15,000 miles (24,000 km) on them. They do have a slight advantage with supple 48 mm tyres vs. fairly harsh Bontrager 40 mm, but they also only have 28 spokes per wheel, and since they use a cassette I'd imagine they have a steeper driveside angle than those on the Alfine 8.

Per Hunt:

  • J-bend cold drawn.
  • Made from high grade T302 (18/10) stainless steel wire by Sapim.
  • Triple butted 2.0-1.6-2.0 (then 2.2 at the head for the patented Pillar Spoke Re-enforcement).
  • 28 spokes laced 2-cross front and rear.
  • Black stainless treatment.

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