Is replacing single spokes by a different spoke type harmful?

Question

Since one of my rims will to need replacement somewhere in the nearer future I was contemplating rebuilding the wheel myself. While researching information concerning which type of spokes to use I came across an article that stated that, when building a wheel for long-distance touring/traveling, it is better to use conventional (i.e. non-bladed) spokes. The rationale was that it might be easier to get a replacement in local bike shops since conventional spokes are more common and the chance is higher that the shop will have the appropriate spokes available.

That statement made me think whether replacing a limited number of bladed spokes with conventional round ones does have any negative impact on the performance of the wheel – minimal aerodynamic changes set aside. Or is this basically addressing an esthetic aspect? And is the answer different between "I will take this round spoke as a drop-in for the next 100km until the next town where I can expect to find a suitable bladed spoke" versus "I will ride that wheel as it is until the end of my trip, however long that will be"?

PS: The touring thing is only the framing story for the question of mixing of spoke types. I'm not interested in opinions or discussions about which wheel builds are best for touring.

PPS: Loosely related: Is it ok to use one odd spoke for a wheel build?

Answer 1

Intuitively, it seems like different spokes might respond differently to identical tensions and cause a wheel to be more "volatile", so to speak. So, a wheel with straight-gauge spokes with a single, say, aero spoke would seem more likely to fail at that point, immediately transferring failure forces to nearby spokes.

Practically, I weighed about 315 pounds when I started mountain biking. I rode wheels built on Sun Rhyno Lite rims. When I broke a straight-gauge spoke, the LBS had only butted replacements. I bought several, just in case I had to do this again, and replaced the broken spoke. I rode that wheel for 6-7 more years without the slightest problem, and still have it in my garage.

Anyway, long answer short: IMHO, drastically different spokes might be a problem. Reasonably similar ones do just fine, according to my experimental results. I never used the extra spokes, but I still encourage you to get some!

Answer 2

"Conventional" spoke is a term that can use more specificity. What matters for the purpose of having a wheel that you're less likely to be stranded with is whether it's built with a hub and rim interface that take standard spokes. Secondarily, there's a standard for straight pull heads that all the spoke producers have products that conform with, but walking into a shop and expecting them to have them in the length you need is unreliable. Real shops at the very least should have straight pull 2mm blanks and a Hozan cutter, but there are plenty of bad shops out there.

Replacing a bladed spoke with a round one in and of itself doesn't matter.

The potential negative or harmful situation you can get into has to do with replacing a good butted or butted-then-flattened spoke with a heavier gauge round one, i.e. you broke an Aerolite and got it replaced with a straight gauge 2.0 (DT Champion etc). One of the chief advantages of good light spokes is they distribute loads better and thus reduce or delay the rim developing fatigue cracks. Slotted hubs were more common in the past and are still around, but these days a lot of the wheels with aero spokes in the first place have CX-Rays, Aerolites, and others with the 2.2mm-ish flat profile that allow them compatibility with normal hubs. These are among the lightest, most elastic type of steel spoke. They often go along with a rim that would be less than ideal to pair with chunkier spokes. That said whenever I'm in this situation and don't have an aero spoke on hand to offer and the rider doesn't want to wait for one to come, I feel no compunction about offering a 2.0/1.8 round butted spoke.

The risk in question here is minor or negligible in a lot of situations, but not others. It's not something I'd recommend doing to a light, low-spoke-count rim for longer than needed, though the actual probability of a crack resulting is hard to predict.

Answer 3

Since all spokes are made from only one type of material (steel), the only thing that matters here is cross section. A steel wire with a certain cross section has a certain spring constant.

If you replace a spoke with one having different cross section, then the spring constant differs. This is unlikely to be a major issue, but it could still affect the durability of the wheel at this point.

Let's assume you have a wheel with spokes that spring only a bit for a certain amount of force. If you now replace one spoke with one that springs a lot (so small cross section), it will distribute a huge amount of the load it would have on a wheel with only that spoke type to neighboring spokes. This is entirely fine. The spoke will experience less changes in load, so it will be very durable, the nipple is very unlikely to self-unscrew.

In the other direction, the situation could be more problematic. If you let's say have a wheel with 1.8mm/1.6mm/1.8mm spokes and install one Alpine 2.34mm/2.34mm/2.0mm spoke, the difference between 1.6mm and 2.34mm is very large. The sole Alpine spoke experiences far more changes in load than it would experience in a wheel with only Alpine spokes. Thus, the Alpine spoke is the most likely point at which the spoke could snap in the wheel, or at which the nipple could self-unscrew.

For bladed spokes, the only parameter that matters here is the cross section. Is it small (like with spokes 1.6mm at middle), or large (like with spokes 2.34mm at middle)?

Of course, bladed spokes can have other bad effects, like the spoke could twist too much during tightening. But it does that in every wheel, both for wheels having only bladed spokes, or for wheels having 35 normal spokes and 1 bladed spoke. So when mixing different spoke types, the only problem is that you install one very heavy gauge spoke on a wheel with 35 spokes with light gauge, which could cause problems at the heavy gauge spoke.

Overall, if you like a durable wheel, you should select a spoke with as little cross section in the middle as possible, but not so little cross section that tightening the spoke to final tension is impossible. 1.5mm is probably not fine, but 1.6mm is probably fine. However, 1.6mm spokes are only available in 1.8mm/1.6mm/1.8mm format, whereas if you select 1.8mm, you can choose Alpine III (2.34mm/1.8mm/2.0mm) which has a better match at the 2.34mm end to most hubs available these days. So even though 1.6mm makes more durable wheel, 1.8mm causes less damage at the hub spoke holes.