Crack the Code
Crack the code to everlasting wheels.
What’s the biggest overlooked feature in wheel building? Do you use it to your benefit? I bet not, but even still, you could probably use a reminder. Hint: it’s about spokes.
Facts
#1 – The single biggest weakness for cost conscious wheels is spoke breakage (also for many high performance wheels as well).
#2 – Spokes break overwhelmingly at the elbow (hub), secondarily at the threads (rim).
Ouch, broken elbow.
#3 – Stronger spoke material, larger spoke numbers, and thicker spokes decrease a wheel’s tendency to break them.
- Material – good spokes are made of virtually the same material, often from the same sources, so stronger material is not much of an option.
- Number – is decided by hubs and rims whose narrow offerings give builders little choice. Designers pick spokes for aerodynamics, not longevity, these days.
- Thickness – extra rotating wheel mass makes a bike feel sluggish, as if heavier. Excess weight is strongly resisted in wheel components.
Solution: Beefy Elbows!
Builders pick spoke brand and gauge so let’s see what is possible.
Spokes as strong at the elbow as they are at the thread is the obvious solution. Do such spokes exist? Sure. Examples: Alpine (DT), Strong (Sapim), or DH13 (Wheelsmith).
Cartoon heroes Alley Oop and Popeye. Look at those forearms, what great wheel builders they would make. You can bet they’d use spokes with beefy elbows.
Does anyone use them these days? Nearly no one! Ask the makers.
This is ignorance at a level we can’t afford. We need ways to get people on bikes (new or old), persuade them to carry their gear, add features like pedal assist motors, lights, and suspension, and spokes are breaking left and right.
How do Beefy Elbows Work?
The three models just mentioned have 13g elbows (2.3mm diameter) but are 14g (2.0mm dia) at the thread end (so compatible with all rims).
Surprise to many, 2.3mm fit hubs drilled for 2.0. How? The rolled thread of a 2.0mm spoke is 2.2mm outside diameter. Rolling a thread, like plowing dirt, creates peaks and valleys (no material removed). To accept the thread while being spoked hubs are drilled larger, generally to 2.5mm. If you use a 2.3 x 2.0 spoke, the elbow fits perfectly.
Beefy Elbow Example – Wheelsmith’s DH13
Beefy elbow spokes work with 99.9% of hubs and rims intended for standard spokes. So let’s use them!
Beefy elbow spokes cost no more than butted. A set of 32 DH13 (single butted) spokes weighs 7g per wheel (32) more than straight 14g. That’s less than the weight of one spoke and that tiny weight is at the hub where it has the smallest dynamic effect.
How Much Better Are They?
Remember that a spoke’s fatigue resistance is proportional NOT to its diameter but to its cross sectional area.
32% greater cross section area through the J-bend. 32% longer lasting.
That’s a whopping 32% increase for a paltry 7g/wheel. Equivalent to adding 10 spokes to the wheel. Experience shows this one feature can nearly eliminate spoke breakage. Combine with larger tires and you have a solution for every under-built, over-used, or over-loaded wheel.
For a review of the engineering behind spoke longevity, check this nerdy post.
How to Start?
Begin using beefy elbow spokes tomorrow! Tell other builders, mechanics, and product managers at once. Convince spoke companies to NOT drop these gauges the way they dropped many 15g models. Slow sales leads to the end of any product.
Pat yourself on the back for being a wheel guru; knowing cheap tricks, clever solutions, overlooked options; and spreading the word. No flailing around blindly, you’re a confident expert. Prove it by putting beefy elbow spokes to work.
By the way, since too few spoke distributors know about beefy elbows, Wheel Fanatyk now sells Wheelsmith DH13 blanks. Cut them to size with your Morizumi or Phil machines. You are also well served by equivalent products from other spoke companies.
DT Super comp spokes are widely used by many wheel builders, and at ~ 86% the diameter of the DH 13, are plenty stout for many applications. Just ask the Enduro racers…. This seems like a non-issue.
Rico, you are right here: “DT Super comp spokes…are plenty stout for many applications.” High level competition requires good reliability for a predictable (often short) and affordable period. Given the expenses of racing (training, transportation, entry fees, the latest tires, suspension maintenance, medical treatment), wheel costs rate lower. 2.0mm spokes of dependable reliability are plenty for professionals. They will replace their wheels soon due to sponsorships, marginal rims, and crashes. OK, how about the others who are on short budgets or expect ridiculous long life from their equipment? These are not competitors. They outnumber competitors 10000:1. Their needs are well served with beefy elbows, the point of this post.
Beg your pardon, but the statement re. reletive cost does not hold water. The DH13 spoke is only marginally less expensive (at retail cost, anyway) in comparison to the DT Supercomp. And again, the later is widely available and utilized by many wheels builders for amateur (not pro) riders.
Further, the mathematics shown above appear to be in error; 2.3 mm is not 32% greater than 2.00 mm in ‘cross section’…that term (cross-section) typically equates to diameter. So; .3 mm increase from 2.00 mm is .15 or 15%–not 32%.
No debate from me that heavier gauge spokes can produce wheels that are less likely to fail at the ‘elbow’. Only certain details in this post appear to be a bit askew.
No pardon to beg. You are incorrect about cross section. Fatigue resistance and tensile capacity is proportional to cross sectional area, calculated since Euclid, by πr^2. This establishes 2.3mm dia at 32% greater cross section area (mass) than 2.0mm. That is the likely difference in fatigue life between a DT Supercomp and a 2.3mm elbow from the same maker. As regards cost, butted spokes cost the same. The swaging operation is the same whether the spoke is single or double butted, so no economy to single. Glad you’re asking questions, these principles need to be known, hence the post!
Ric, do you have any thoughts on Pillar spoke and their PSR (big elbows) series? Seems a lot of factory built wheels tend to use Pillar so I never gave them much thought, but after a look on their site they seem to have very progressive design.
Off topic: Spent part of the morning on a Moizumi today, and man alive, what a dream! Love using great tools!!
Yes about Pillar. I hope such technique is the general future. It is “upsetting” the metal in forging terms, as is done by a screw maker when the cap of an allen cap screw is made from the thinner rod that carries the rolled threads. Round metal can be decreased in size by drawing or swaging. It is increased by “upsetting.” Heads on nails, etc. There are limits and risks. Pillar’s idea originated with one of their tool vendors listening to a US guy with some theories. Now of course, they claim it as their own, which is entirely the norm in commerce.
Care to elaborate on that last bit? Is their patent of PSR the reason we’re not seeing reinforced elbows on light spokes from the usual three for instance?
I cannot judge patent issues. My impression is their patent would not be defendable as it was provided to them by another party and not an invention. The lack of progressive spoke design (such as PSR or other materials) seems more a consequence of a small number of companies with no urge or ability to rock the boat. Prices are good enough, demand is weak but steady, no one complains. It takes a disruptor to challenge a paralyzed market. In many industries, such a voice is never heard and no change, despite ample opportunity, is seen for decades. Spokes are similarly both serving the industry’s needs and deep in a design ice age. In some industries, a total outsider blows the doors off and the current players disappear. In cycling, there’s no guessing the outcome. Don’t hold your breath.
Ric, Always enjoy your site and blogs! Thank you… With regard to spoke gauge, my personal preference for wheel longevity is 36 x 14/16 gauge. The greater spoke count over 28 or 32, requires correspondingly less tension in each spoke, which in turn places less stress on aluminum rims and hubs, and more evenly distributes “shock” loads among a greater number of spoke resulting from encounters with pot holes, curbs, rocks and the like. Regards, BikinBobS
Hey Ric. What are your thoughts about the triple butted Alpine III or Sapim Force. Both have the larger elbows for added strength but does the triple butting cause any extra stress within the metal of the spoke and possibly lead to microscopic cracks in the metal which could negate any added benefit of the large elbow.
These are good ideas that could lose some of the benefit depending on execution. Butting increases work hardening (a particular issue with stainless). Such hardening is usually harmless in the aero or butted sections of a double butted spoke. The hardness is usually beneficial in the elbow. It makes material more difficult (not impossible) to thread and if it occurred twice, the extra hardness might make for fatigue weakness. If were observed, the maker would want to add an annealing step. Extra cost might be resisted if test results were satisfactory. I don’t see enough of those 2 models to have an opinion on their success. But, in principle, it’s a good idea and any limitations could be addressed.
Ric, the benefits of extra meat at the elbow end are negated by the straight-gauge nature of the spoke at the thread end. The purpose of that but at the thread end is to protect the place with the lowest diameter, which is the thread valley. The diameter there is something like 1.8mm IIRC. By having the spoke shaft at 2mm, the strain is concentrated in the thread valley, By reducing the shaft to 1.8mm or lower, the strain is concentrated on the shaft where the smooth surface provides no stress risers and thus few cracks at either end of the spoke.
I doubt the durability of a 2.3mm – 2mm spoke has been proven, whereas the durability of a 2.0mm – 1.8mm – 2.0mm spoke has.
Making it thicker at one end may make it stronger (but we already have ample strength) but reduces durability, which is what we are after.
Thanks for your thoughts. I disagree. Many believe you cannot make a stronger spoke than 2.0/14G for standard hubs and rims. This type of spoke breaks, usually at the elbow, when overloaded. 2.0-1.8-2.0 is not the solution. What spoke solution is available if you want longer lasting than 2.0? The answer is 2.3-2.0 as I describe. The elbow fits the hub (already drilled to accept the OD of 2.0 rolled thread). You believe 2.0-1.8-2.0 is longer lasting than 2.3-2.0? I am sorry, but you are mistaken.
Ric, I was under the impression that breakage at the elbow was most common on NDS spokes, due to loading/unloading flex cycles which are able to happen because the spoke is at lower tension than DS spokes. Your comment that butted spokes don’t solve this implies otherwise.
Does your comment that “spoke breaks… at the elbow… when overloaded” mean that elbow breakage on DS spokes (which see higher loads than NDS) are just as common as elbow breakage on NDS spokes?
If I read you correctly (here and otherwise), the value of butted spokes is springier ride, but not greater fatigue life at NDS elbows.
All else equal, spoke breakage is greater on NDS spokes due to lower tension and more frequent zero tension moments. Butted spokes should help this problem through elasticity but this cannot be confirmed experimentally so we must accept that the benefit is too small to measure, to isolate from other variables. My contention is that, on a strictly engineering level, the only solidly provable benefit to butted spokes is lower weight. Greater fatigue life, springy (comfortable) ride, better visuals…these have not been quantified to my satisfaction and therefore seem plausible but insignificant. Lower weight is not insignificant.
Ric, one other question for you. You mention that empirical testing can’t statistically differentiate between durability of wheels using butted vs straight-gauge spokes, but it sounds like you are confident that thicker-elbowed spokes do offer decreased elbow-breakage rate.
You’ve obviously built thousands of wheels, which offers you a large data sample. Are there formalized empirical tests you are basing this on as well?
Do these tests include controlling for careful seating/stress relieving of spokes at the flange? For non-heavy-loaded applications (excluding touring, tandems and clydesdales) are thicker elbows mainly valuable for wheels where spokes weren’t seated/stress relieved? Of course everything here is a sliding scale of probabilities.
Re: testing can’t differentiate full wheel fatigue impact of spoke butting, I mean to report that I have not seen this accomplished and have witnessed many sophisticated attempts. Doesn’t mean it hasn’t happened in another proprietary setting. As to elbow thickness and fatigue, all tests I’ve done are not configured for scrutiny. Not aware of such testing in a university/public setting. So many variables, it’s tough to visualize something formal. The relationship between mass and both tensile load capacity and fatigue is direct and most of us have seen the effects when building team or tandem wheels with and without heavier elbows. Heavier elbows resist fatigue better no matter what the preparation (seating, relieving) so optimal wheels should benefit from the best assembly/tensioning AND the thickest elbow that’s practical. Practical = transfers fatigue failure from the elbow to the nipple thread, at which point further elbow strengthening has no effect on longevity. Make sense?
thanks. that all makes sense. multiple quality test designs looking for positives with butted spokes at least means that any real effect size is likely small, even if other proprietary studies have found a statistically significant effect.
I think such a study could be designed, even accounting for the number of variables, but it would require such a large sample size to get through the noise of wire quality variability, and time for wheels to have the chance to fail. So a study large enough to have statistical power would be cost-prohibitive.
Hi Ric,
Excellent article, though I’m obviously a bit late to the game.
Any thoughts on actually building with beefy elbows? The 2.3 J-bend can make hard work of bedding down the spokes along the flange. They just don’t lay down snug like a 2mm gauge.
I recently built up a touring wheel with Alpine 3s and an Shimano LX hub. Had to resort to head washers to get the spokes to set decently. Not sure if that was ultimately necessary, but it seemed to help.
I’d use a lever to set spokes, like the picture here. Not used washers unless the hub hole is drastically too large or made of thin steel. While close contact with the flange is a big fatigue life advantage, bigger plusses are high quality wire and larger cross section.
Just ordered some Sapim Force spokes to build up to some Velocity Ailerons to White Industries CLD hubs. 36h rear, 32h front. Should work out to a very long lasting wheelbuild. Interested to see how the Force spokes build up.
Ric,
I’m kind of stunned at the above comments… Having personally built about 6 touring wheelsets and a TON of Ebike wheels with Mostly Alpine3s I have never had one come back with a broken spoke! Many of the E-bikes are daily transportation.
I’m not sure why any one would say differently if they haven’t at the very least used them on a build. I do still build with mostly 2.0/1.8/2.0 and think for most of my applications they are adequate, but i Never hesitate to pull out the 13/14 when someone whispers E-bike… I don’t believe any wheel is forever though. Especially under those heavy commuter situations, and I’m very curious when/if I will see one of the wheels built with Alpine3 come back with a spoke issue. Have you seen any?
Anyways, haters gonna hate… so keep posting because I really enjoy all the WF Blog posts. Thanks!