usefulness of butted spokes on front, or rear drive-side?
 

So butted spokes are nice because they stretch more (since they're thinner diameter in the middle, they stretch more for a given spoke tension than non-butted spokes of the same end-diameter). This means that when the rim deflects when the wheel hits a bump, spokes are less likely to lose tension.
This is particularly advantageous on the non-drive-side of dished rear wheels, where the spoke tension has to be relatively lower because of the dish. Broken spokes usually happen on the non-drive-side of the rear wheel because those are most likely to go out of tension as a result of rim deflection, and over many repetitions the spokes will flex back-and-forth at the elbow and eventually snap there.

I'm talking about straight 14g (2.0mm) spokes compared to 14/15/14 (2.0/1.8/2.0mm) butted spokes - these are the most common forms of straight-gauge and butted spokes.

Now, I'm wondering if there is much point of using butted spokes on the front wheel (non-disc wheel, no dish), or on the drive-side of the rear wheel. In both of these cases, spokes can be tensioned to the max safely allowable for the rim, and there is little to no chance of spokes ever losing tension as a result of rim deflection.
So, I'm wondering how much advantage butted spokes will give in the front wheel or rear drive-side? There are slight advantages in weight and aerodynamics, but are these even remotely relevant?

Thanks for any thoughts here.

I think butted never hurts, and always helps. Even though you can bring drive-side and front spokes to full tension, you still get some benefit from the stretch. If you encounter tremendous lateral forces, like from a crash, those spokes will be less likely to go slack, potentially preventing a taco.

Also, thinner spokes approach full tension more gradually, so you have more control as you bring the wheel to tension.

The downside is the increased windup during build and maintenance, but that's pretty easy to control if you lube the nipples, pay attention, and don't use spokes thinner than 1.8mm.

There's always a load-point when the spokes at the weight-bearing bottom of the wheel will lose tension. It comes down to those unexpected times of high-impact loads that does it. Such as hitting speed-bumps or potholes unexpectedly. Large drainage ditches going across the road can result in some high loads on the wheels causing the spokes at the bottom to lose all tension and rattle the nipples loose. I've had good luck with 1.8/1.5/1.8mm spokes in front and 2.0/1.8/2.0 spokes in the rear.

Fatigue-failures can actually occur with no movement of the spokes. It's the on/off tension that does it. They don't need to flex or move in the holes.

+1

Does anyone have any experience or input on DT Alpine III triple butted spokes? I'm thinking of using them in a build for my mountain bike this spring. The reason i ask in this thread is that my reasoning is along the same lines. For any that are not aware of the Alpine IIIs, they are 2.34/1.8/2.0 where the 2.34 is at the elbow for strength, 1.8 throughout the middle for stretch, spring etc and 2.0 at the nipple. It seams to me like it would be the best overall. I hear they are common in tandem wheels. I want them for strength and durability in a MTB application.

I guess I should say that the load-point is much less likely to be reached in the rear drive-side spokes (and even less likely to be reached for front wheel spokes unless you hit a pothole that's bad enough to bend the rim anyway). So practically-speaking, it seems that most of the gain is slight weight savings, slight aerodynamic benefit, and the satisfaction of knowing that you've "built the wheel right."

waterrockets and DannoXYZ have both raised good points, but I think they are points that matter only at the extremes, whereas butted spokes offer a marked improvement when used on the rear non-drive-side.

Gerd Schraner's book "The Art of Wheelbuilding" states that the 2.0/1.8/2.0 spoke is the favorite of professional wheelbuilders as it relieves stress at the elbow and threaded end better than the straight butted spoke. In fact he calls it the universal spoke for all types of high quality wheels. In fact, the repeated implication in his book (and from many other wheelbuilder sources) is that straight butted spokes are a false economy. They also advise that spoke washers should be used on quality wheels.

For Blamp28, the triple butted spoke is sensible for Downhill, loaded treking, tandems and Heavy riders if you are willing to redrill the hub holes to 2.8mm.

You just have to watch the spoke hole diameter. Most hubs will accomodate them, but not all. Those spokes should last forever.

DTs site says the elbow ends are 2.34mm rather than 2.8mm I have never seen these spokes and assumed that the holes in standard drillings would accomodate 2.34mm. Please let me know if that is incorrect. I am a heavy rider - at least for now and I like to ride reasonably hard so I was thinking that these might be better than the 2.0/1.8/2.0 for my needs. My intent is to use XT hubs, Velocity Synergy Off Center rim in the rear and matching front rim. I thought these spokes would be just the ticket for high strength without loosing the elastic quality of a double butted build. If I would have to drill out the spoke holes, I won't do it. Pleas let me know if you are aware of the standard drilling dia.

Right. But my contention is that butted 14/15/14g spokes matters especially for the non-drive-side of the rear wheel, and not so much elsewhere. I agree that butted spokes are a false economy there, and may be a false economy elsewhere, but it seems as if the cases where butted spokes would be better in those other cases are extreme enough that the rim would probably be damaged anyway, and so there's no practical advantage except on non-drive-side of the rear wheel. Would love to hear responses to my reasoning.

anything that relieves instanious stress due to radial loads (bump) at the elbow will increase the life of a spoke. The elbow of the spoke is by far the most common failure point. This failure is rarely caused by a single event but rather by repeated load/unload cycles and manifests itself as a work hardening of the metal and eventual failure.

I'm thinking that you benefit in all cases from the small amount of elasticity of the center portion of the spoke -- Drive side, non drive side, front - it matters not. My thoughts are that any time you can absorb a small amount of the road shock anywhere other than at the spoke elbow, you reduce the wear and fatigue on that area of the spoke and therefore extend the life of the wheel assembly. The wheel will flex regardless but by giving it a section that is ever so slightly more compliant, you have focused where the flex will occur to a great extent.

I know I read something like that before but I don't remember where. Jobst Brandt wold be my guess. My training partner and I have this informal test going on this. He runs straight gauge spokes on his road bike and I run 2.0/1.8/2.0 Wheelsmiths. He contends that the straight gauge are stronger. i told him about this theory and line of reasoning and he is going to check with his father, a retired metallurgist for an opinion.

Sorry, left this out of privious thread. Spoke holes in Hub are an industry standard of 2.3mm. Possible sloppy over that some but still pretty tight for Alpine III. 2.8 is the recomended hole for those. Because you will be loosing the factory chamfer you will almost certainly want to use washers for this. Else go looking for downhill or tandem hubs already drilled to that size???

OK, I'm sorry for the hijack but I need to know if anyone here knows what the standard hole size is in MTB hubs like XT m760s. Will they accommodate 2.34 SPOKE?

Thanks maddmax, that makes sense. I don't want to go to that much trouble. I appreciate your input.

No. You will need to enlarge the holes. I do it using a press and jig to hold the hub straight. I also chamfer the holes. but you can use spoke washers if you can get some with a big enough ID(The washers I have will not fit on an Alpine.

Right, right, right. But if drive-side rear spokes, as well as front spokes, basically never break anyway, then lowering the instantaneous stress is a phantom benefit. I've only ever seen non-drive-side rear spokes break.

Good input Rev Chuck. I also have no washeres for 2.3 I just assumed that someone must make them as there are washers for 2.0 and 1.8

btw, I know this has been asked before, on these forums, but where does one buy spoke washers? I'd like to use them for a couple of builds I'm doing soon.

spoke washers from DT Swiss are available at Alfred E Bike on the Web. (access to national shared catalog from many different shops) Bags of 1000 for about $20. Lately I've been buying them on Ebay in lots of 200. The ebay listing is interesting in that the seller has different washer diameters. (found the listing at "CT bikes" web store under spokehead washers)

Since I started using washers I have noticed a distinct improvement in my wheels, more uniform tension etc.

One of the explinations that I was given is that if you can install a loose spoke into a hub at the proper angle and feel any end play while shaking it then you should think about washers.

I use 15/16 butted on non drive rear since the tension is so low there. 14/15's are way overkill. For front wheels, straight 15's are a decent way to go - on a road bike anyway, or a lighter MTB rider. They build into a pretty firm wheel while being lighter than 14/15's. I've never had any breakage problems on wheels built this way. Just my opinion (and experience). :)

Well, this is a different failure-mode you're talking about and I'm not sure this is what a spoke experiences. Work-hardening occurs when a part is stressed above its yield-strength, but still below its ultimate-strength. The material enters its non-elastic plastic deformation phase. Repeated stresses at this level will work-harden and crack the material. However, this is not fatigue-failure.

First, the highest stress on the spoke is from tension, being pulled out by the rim. As you apply loads to the axle pushing down, the actual stress on the spokes at the bottom actually decreases. So you never actualy overstress a spoke much more than its tension under normal use. Even when hitting a big bump and causing say... an 800-load on the front-wheel. This load relieves tension on 4 bottom spokes (of 200-lb tension each). This relieved tension is then divided out and carried by the remaining spokes above the contact area (the rim tries to expand evenly all around the part that's not loaded). The remaining 28-spokes then increase their tension by 800/28 = +29 lbs (+14%); not a whole lot given the impact.

So you're right that the on/off load/unload cycles is what casues the failure, but it's fatigue failure, not work-hardening. This can be differentiated by examining the two halves where the break occurs. Work-hardening, like other failures over the yield/ultimate-strength limits will result in deformation of the part on either side of the crack, the part can't be fitted back together cleanly. Fatigue-failures on the other hand are caused by propagation of microscopic cracks due to on/off load-cycles above the fatigue-limit but below the yield-strength of the material. These cracks build up, spread and when they finally meet up, the part breaks cleanly; you can actually re-assemble the two halves with a perfect fit.

As for the OP's question regarding fatigue-resistance of DB spokes. Yes, the left-rear might be the most vulnerable due to its lowest-tension and higher load/unload tension-ranges. However, the other spokes are also vulnerable to fatigue, but just not as much. All this of course has to do with the types of loads and bumps encoutered by the bike. A track-bike can probably get away with 1.7/1.4mm/1.7mm spokes and a 250lb gorilla riding it without any problems. A crit-bike on rough-courses might need 2.3/1.8/2.0 spokes to deal with the impacts of a 160-lb rider bunny-hopping and running over pot-holes and crashed bikes & riders. I think we need to quantify the loads to really answer the question.

Perhaps one is going a bit overboard on the topic of spoke diameter. Butted spokes allow for strength at the elbow while having less rotational mass. Keep in mind a very thin butted spoke has aerodynamic properties that come extremely close to rivaling that of the best bladed/oval spoke. In fact, scientific tests have backed this statement.

A poor mans aerodynamic wheels will have 28 of the thinnest butted spokes on the front. Taking this into account butted spokes do have their place on the front.

Modern wheels do not have the extreme dish of wheels from the past. If you determine spoke length with any of the modern programs you'll find that drive-side and non-drive-side spoke lengths are often the same or within .5-1mm. At one time it was common to have different thickness spokes on the opposing sides of a rear wheel to 'balance' the tension. Perhaps my vast experience is faltering me but I recall a majority of rear spokes broke on the drive side......

My advice is this...if money is no object use butted spokes on both wheels. The thinnest on the front and the appropriate diameter in the rear to match your rim/hub selection and your body weight.

If money is an object...2mm DT's all around.

Jim......2,000 plus wheel builds and counting

Just about all the wheels that come in with broken spokes are rears, broken on the drive side, at the hook. Usually straight 15 and anodised black.

washers