Wheelbuilding: Variable spoke gauge on rear wheels?
 

I'm building up a wheelset with for a touring rig and built the front wheel with a 70s Phil touring hub (36h), DT Swiss TK540 rim, and DT Alpine III spokes. I was planning in building a rear wheel with probably a Velo Orange Grand Cru Touring hub and the same rim and spokes.

I've heard debate on the internet about dishing and spoke tension as to whether you should use thicker gauged spokes on the drive side of rear wheels, or even that only the trailing spokes on the drive side should be thicker gauge. Other than weight difference in spokes, does it really matter?

If so, what spokes would be recommended? Alpine IIIs only come in one gauge to my knowledge, so what spokes should I be using on either side?

Spoke tension stuff gets a lot of debate, but wheels come out fine with all sorts of different spokes and don't need to be built with magic combinations.

If I was using super light weight spokes, like 2/1.5/2 DT Revolutions, I would use slightly thicker spokes just on the driveside. But that's just making up for a slightly fragile spoke, not balance tensions better.


It would be good to know what kind of wheel you are building to advise you. You'll not the Alpine IIIs are intended for Ebikes and that sort of heavy use sort of wheel. What kind of bike are we talking.

It is a Bianchi frame that I am building up as a touring bike. I'd like to be able to load it up pretty well, so I'm definitely looking to build strong wheels.

Another question that came to mind but I haven't heard brought up in these debates is that presumably the spoke hole diameter is the same on both flanges of a rear hub, so thinner spokes on the left side would be a loose fit, which I have heard can fatigue spokes and cause failure.

Is there a reason why you are asking about using lighter spokes for the non-drive side?

I'm sure that you will be able to find people who have successfully built wheels both ways. How are you going to determine whose advice to take?

As long as you use a reasonable number of spoke in reasonable diameters, the wheel should be plenty strong. For touring, 36 or more spokes lightens the load on each spoke while making an (unlikely breakage) less serious to deal with on the road.


The spoke flange holes really don't matter. The spoke is being supported by the head and the hook formed by the bend, not by the circumference of the hole. The main reason spokes break is because the spokes with the heads in weren't properly bent around the flange when the wheel was laced. The J-bend is left under bending tension and eventually cracks because the tension cycles concentrate stress on that point. Alp IIIs are just less likely to break at the heads if they weren't seat correctly in the first place.


If you want to buy some cheap insurance, go ahead and buy Alp IIIs for the driveside and regular butted everywhere else. You might have to work harder getting the thick heads of the Alps to seat properly because they are so thick compared to the center spoke section. Maybe use a non-marring tool or mallet.

Good spoke seating, a rigid rim, enough spokes and appropriate, even tension with frequent stress relieve while building will make the longest lasting wheels. Unless you use delicate spokes, I don't think the spokes matter so much.

Ric Hjertberg, founder of Wheelsmith, thinks people should use spokes with thicker elbows in a lot of rear wheel builds. Because spokes that break almost always break at the elbows, and thicker elbows (2.3/1.8/2.0 for DT Alpine III, 2.2/1.8/2.0 for Sapim Force) add a tiny bit of weight to have about 1.25 times the cross-sectional area at the elbow and thus significantly less likely to break there. For a touring wheel that will see heavy loads, with only 36 spokes, this is probably a good way to go. He thinks this matters significantly more than thinner NDS spokes, and says the value of butted spokes is still largely a theoretical proposition that is nearly impossible to prove empirically. (He engages this more in the comments section of the link above)

I've been very interested in figuring out optimal design for a dished rear wheel, and like the idea of asymmetric rear rims and/or thinner NDS spokes. My sense is that, empirically, it's difficult to show that either of these has the benefits. The most important thing is to build the wheel well, with consistent tension on each side, and tension not too high for the rim.

Every time I see a wheel with spokes broken at the elbows, it is the outside elbows. If DS spoke tension stress was the problem, both elbows in and out would break equally. That's why I think it is primarily a lack of proper seating rather than a lack of sufficient strength.

Yeah, the NonDriveSide spokes are way more likely to break at the elbows than DriveSide spokes. Conventional theory is that this is caused by the loading/unloading cycles which happens with each wheel rotation, or particularly in some areas when the rim flexes while hitting a bump. The NDS spokes are more likely to go slack (de-tension), and this loading/unloading cycle flexes them microscopically at the elbows, which can lead to cracking over time.
Lack of proper seating and stress relieving can make this worse. But under the conventional understanding, even properly-seated and stress-relieved NDS spokes will undergo flexion at the elbows every time the spokes momentarily de-tension.
From other threads I think you're pretty knowledgeable about wheelbuilding, so I may misunderstand your point. Let me know if we're actually in agreement here.

Years ago I heard a claim that Alpines were supposed to make things WORSE, not better.
The reason being that if you bend a thicker piece to the same radius as a thinner piece, the outside face of the thicker piece will have to stretch farther than the outside face of the thinner piece.
This extra deformation could then act as stress risers and starting points for cracks.


It sounds reasonable enough, but the few wheels I've built with Alpines have held up until the rims gave out.


Maybe the rumored superiority of the Alpines comes from anyone being interested enough to get them will also be interested enough to do do a good job of building the wheels.

Note that I'm referring to Alpine III, which is different from the Alpine spoke. The Alpine (to which you refer) is a 2.3mm at the elbow, and otherwise a straight-gauge 2.0mm spoke. The Alpine III is only 2.3mm at the elbow, and otherwise has the most common butted spoke profile: 1.8mm in the middle, and 2.0mm at the threads. The Alpine has no more downside than standard 2.0mm spokes (and elbows less likely to break), while the Alpine III is basically a 2.0/1.8/2.0 spoke but with elbows less likely to break.

I have always used the same spokes on both sides on the rear, either 14 or 15 gauge double butted. I have built wheels for friends who are 280 pounds and don't have problems.

Using extra-thin NDS spokes is one of those things that makes perfect theoretical sense to me, but I haven't gotten around to trying it yet.

Currently, my most "daring" wheel build has been a set of 3-cross 32 with 1.8/1.6/1.8 spokes. If those hold up over time, I may just stick with them as long as DT bothers to make them. :)

The gains from using different spoke gauges for different sides probably aren't worth the hassle. Frankly, you'd see more gains in strength by using an off-center rim.

Doesn’t change the theory I described.
A thicker elbow bent to the same radius as a thinner elbow still has to stretch more at the outside face.

I don't think using thicker spokes on a 36h wheel will make any difference other then maybe making the wheel harder to true. If you are looking for a stiffer wheel I think you would benefit more from high flange hubs.

That's true. I should say I think the theory you described is wrong. Because if it was right, then 15g spokes (1.8mm all the way through) would be more durable at the elbows becuase they don't have as much differential bending when the elbow gets turned to 90 degrees. But as it stands, very few people build with spokes that are 1.8mm at the ends, because they are more likely to break.
(Note: I understand you're not presenting this theory as true, just as something you heard.)

My touring wheel building has been 2mm straight gage, they work fine.. just bring a spare of those on the right drive side.

Only ever broke one , there .. though I brought spares for other 2 lengths left rear and front..


lots of esoteric builds go for the butted ones , and this forum has its fans of those..

Wheelsmith still get 14 with a 13 butt..?





....

First time I heard this theory deeply discussed there was an effort made to find a forum member who worked with metallurgy. The idea was to section a 2.0 and a 2.3 mm spoke elbow and stick them in a microscope. Didn’t work out unfortunately.

Are you sure that this is the reason few people build with 1.8mm straight spokes? I'm not saying you're wrong, I just haven't heard anyone give this as a reason.

FWIW, 1.8mm straight spokes is my personal go-to configuration for most wheels. I'm not a particularly lightweight rider at around 180-185 lbs, and I have been riding the same 32-spoke wheelsets on my road and hardtail mountain bike for about 20 years and tens of thousands of miles, both of which are built with 1.8 straight spokes F&R, and neither of which have ever broken a spoke elbow. In fact the only spokes that have broken were damaged by an overshift. Both wheels are built with brass washers under the heads, which is a best practice for 1.8 spokes in hubs with holes made for 2.0 spokes.

Many many vintage race wheelsets were built this way, or even with 1.8-1.5 DB spokes.

So while this idea about 15 gauge spokes may be theoretically true, for most riders it is of no practical concern. You would have to be both a very strong, heavy, and/or equipment-killing rider, and do equipment-killing mileage before it becomes a problem. And you'll probably have gone through several rims before you start to break spokes from fatigue.

Spokes (Jobst Brandt)

It turns out I was echoing Brandt's sentiments on why spoke elbows fail - they weren't stress relieved, "bent" or "seated" to the flange and end up flexing until they work harden. Hence his dismissal of the 2.34 section spokes.


I don't think any reasonable spoke in a wheel with a reasonable spoke count has any reason to fail from mileage alone, IF it is stress relieved correctly when built. Brandt would wear out multiple sets of rims on one set of 1.8/1.6/1.8 spokes with the only breakage coming from foreign objects.



My personal theory as to why butted spokes are "stronger" is that they move some of the spoke flex from the (unseated) elbow to the thin spoke section which can handle it better. That way the unseated elbows don't work harden as quickly from the tension cycles.

It would be interesting to build a front wheel with Revolutions (2.0/1.5/2.0) on one side and similarly light 1.8 straight gauge on the other and see if there is any difference in longevity. They both would weigh about the same, but have that mass distributed differently.

Only the elbow (and the normal amount of butting on a spoke) is thicker. The center section is 1.8mm and the nipple end is 2.0mm. I've not found them to be any more difficult to work with than any other spoke.

Ah OK I see. I thought you were using a thicker gauge of spoke on the drive side. I see what you're going for.

I could be wrong, but to me it would seem like the energy would get transferred to the hub first and then distributed evenly through the spokes out to the rim. So I think by having a stronger spoke on one side wouldn't help.

Spokes just about never fail through overload, unless you get something caught in the wheel.


So "stronger" isn't the characteristic people are after.
Spokes generally fail by (metal) fatigue, similar to bending a paper clip at the same spot repeatedly.
The characteristic people are after when building with different gauges is endurance, resistance to fatigue.
If you match the differences in cross-section area to the differences in DS/NDS tension, the elbow of the NDS spoke will experience less flex and be less prone to fatigue failure.


The thing to remember here is that sometimes there's very little actual gain by going from "good enough" to "better".


If your wheels stay true and spokes hold up using straight-gauge spokes, the only benefit from thinner NDS spokes is a tiny weight reduction.
Perhaps an even tinier aerodynamics improvement.


And since straight gauge spokes are cheaper and easier/faster to build with, you might as well stick with them unless there's an actual problem you're trying to fix.

But he also rode 6-speed freewheels, making his wheels less dished than the current average road bike rear wheel.
Not so sure he'd make the same statements now as he did BITD.

I would tend to agree with you. I see little value in having thinner spokes on the nondrive side. I don't think it would matter much since the NDS spokes seldom break anyway but I don't see any benefit of tempting fate. There's little to no weight penalty and the wheels end up being a little over built.

And, as I said above, it complicates the build by having to keep track of more parts.