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History

Bought a new Diamondback Haanjo Comp in mid July, 2016. Rode 220 miles on trails and broke a spoke. I rode another 190 miles on combination of trails, paved and gravel roads, including about an hour's worth of cyclocross practice on a new course that was rather bumpy, then broke another spoke.

I'm about 300lbs. I don't ride over or down curbs, and am generally careful, but I do hit some bumps and things harder than I would like on occasion.

I am currently running WTB Nano comp tires in 40C at about 50 psi rear and 40 psi front.

I did contact HED about this issue, and had a good email exchange with Andy Tetmeyer, but ultimately it was just an offer to build me a set of wheels on the side, and no suggestions for improving these wheels.

Question

Is there anything I can do to make these wheels (primarily the rear) stronger? Can I change the spoke lacing to a 3 cross? Perhaps changing the spokes themselves to something else?

I don't want to spend money on "clydesdale" custom wheels that cost close to what I paid for the bike.

Am I destined to just get a new rear wheel with 36H or are there other inexpensive things I can try?

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    I doubt you can do anything about the existing wheel sets -- cheaping out on the wheelset is part of the way they were able to offer the bike at the price it costs, and at 300 lbs you really should not be running 24 spoke wheels (esp. cheaper ones). Unfortunately, you're going to need to get new wheels. – Batman Sep 4 '16 at 21:29
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    Also, you need significantly higher pressures than 40 or 50 psi for a 300 lbs rider. – Batman Sep 4 '16 at 21:47
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    If the tire bottoms out and you strike the rim that places much more stress on the rim and spokes than if the force were distributed more evenly. So you need high enough tire pressure to prevent bottoming-out. But 24 spoke wheels on any sort of off-roadish bike is stupid, and the 300 pound rider only adds to that. You need better wheels. – Daniel R Hicks Sep 5 '16 at 0:06
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    You bought the bike new? So you'll have the owner's manual - could you check it for any sort of maximum weight limit? 136 kilograms is above the maximum for most bicycles. As someone who was 110, I used to break spokes monthly, 4 in one trip. Now down to ~90 and I can ride a normal road bike. Try carrying less stuff to help lighten the load. – Criggie Sep 5 '16 at 0:43
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    This video shows what happens to your tyres as you go over bumps. Notice how close the rim comes to striking the ground on the 23mm tyres on the left. That's why you need higher pressure in your tyres. – David Richerby Sep 5 '16 at 8:49
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When building a wheel, there are two main things the builder does to prevent spoke breakage: set the spoke line at the hub flange and rim when the spokes have little or no tension, and stress relieve the spokes once they're at nearly full tension.

Setting the spoke line means to cold set the material into the final shape it would otherwise be pulled into by the tension on it. This reduces fatigue, which is the most common cause of breakage. It also helps keep the wheel true.

To do it, ideally the spokes would have little or no tension. Jobst Brandt in "The Bicycle Wheel" favors doing it with a little tension. I find I can tell what I'm doing better if they're pretty slack. At the hub end, push each outside spoke hard against its flange. You're trying to get them to lay flat against the flange when not under tension, as opposed to bowing out. (There are other techniques, but doing it with your fingers works fine). At the rim/nipple end, you're trying to prevent any bowing where the spoke enters the nipple. Many wheels don't need any attention here, i.e. the rim hole allows the nipple to swivel naturally into an angle that allows the spoke to run straight, but for the ones that do, just grab pairs of consecutive pushing and pulling spokes that make a "V" (the intersection of the V being the spoke crossing nearest to the rim) and squeeze them together hard to cold set the spoke. I like to do this once the wheel is near its final tension, so that there's only minimal thread movement left to go and you're not pulling the section you just bent up into the nipple.

Stress relieving is a process of temporarily overloading the material to eliminate residual stresses left in the spoke elbows. Most breakage is caused by these stresses putting the elbow area above its fatigue limit in use as the wheel rolls along, each spoke getting loaded and unloaded. To stress relieve the spokes on a cross-laced wheel, find pairs of nearly parallel pushing and pulling spokes on each side of the wheel and squeeze them together hard, as though you're trying to break them. (Brandt's terminology). I would recommend doing this at around 80-90% of final spoke tension.

Because your spokes are having fatigue problems already, these steps are no guarantee because they can't fix fatigue that's already accumulated. But if there's a way of getting the wheel to stop breaking spokes without replacing all of them, this is it. Also, make sure the final tension is nice and high.

In the end these wheels are probably not strong enough to be trouble-free for a 300lb rider, on-road or off. That's due to what kind of loads they can structurally take. Whether the spokes are operating within their fatigue limit is a separate concern, and that's what determines whether you'll break spokes. It's also true that the margin for error in how well internal stresses have been relieved is going to be little if any here, possibly to an extent that exceeds practicality.

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    Nice answer. Interesting perspective. I really like this contribution. – andy256 Sep 5 '16 at 2:11
  • Can you elaborate on what it means to have a final tension "nice and high"? I may have a shop replace it this time specifically to handle the tension part, but don't know exactly what I'd be asking for. – Craig Treptow Sep 5 '16 at 2:50
  • 110-120kgf right rear and left front, or whatever Hed tells you is correct. – Nathan Knutson Sep 5 '16 at 2:53
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Am I destined to just get a new rear wheel with 36H ... ?

In the end, yes.

See What is the maximum weight that "normal" racing wheels can withstand?

And also this Bicycle Weight Limits article.

You may get away with riding very carefully on perfect roads, but doing cyclocross practice puts a whole different level of stresses on the wheels.

So I recommend wheels with a more "traditional" spoke count (36) and rims built to take the loads you're going to apply. High flange hubs (as you mentioned) are worth considering too, especially if you use heavier guage spokes.

To put it in perspective, this bike is at a "medium" price point; not cheap, but not expensive. But you're asking it to do a heavy duty job. The frame may or may not stand up to the workload, but you could easily spend the original price again to get a wheelset (yes, both wheels) that will do the job safely. And that's the bottom line: having a wheel fail under you can be dangerous.

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