TiHabanero

I know this will light off a firestorm, and for that I apologize, however I see all over the forums the statement that double butted spokes are more durable and less likely to break than straight gauge spokes, but have not seen any data supporting this claim.

What I do have is personal real world experience with straight gauge spokes. All wheels I built for myself have been straight gauge 2.0 Champions, and I have yet to experience broken spokes.

Claiming tensile strength is superior for DB spokes is one thing, but in a wheel tensile strength is not being tested. The movement of a spoke in the hub hole and at the nipple is where I see them break, never elsewhere.

I am looking for conclusive proof in a study format that backs up what I see people putting out there. Not interested in tensile strength or what Jobst has to say about it. I am interested in the flex of the spoke when under load and the fatigue failure rate between DB and straight gauge spokes.

Is there any such studies? Evidence?

shelbyfv

I wish I could remember the name of the poster who related his ongoing argument with DT. His position was that straight gauge was better for bike wheels but he couldn't convince DT, maybe Mavic as well. Anyway, while searching for those threads, I see you've posted this query several times through the years. Since it seems important to you, hope someone has something new to add

velojym

I would suggest you just go with what works.

I'm a clyde (even when very lean), and was having spoke issues with my CX bike from early on. After the guys at Chainwheel re-laced the wheel with DB spokes, I never had a problem after, and I was bunny hopping roadkill on group rides at around 200 lbs.
That being said, now we're comparing a factory wheel with itself, having been hand-laced by someone who is good at what he does. So, straight 14g spokes might have done just fine there too.

However, it isn't flex that the thinner section remedies, it's the ability for it to 'stretch' a tiny bit, taking some of the load off the elbow at the hub, and to some extent off the nipple end.

It worked great for me, but that's yet another real world experience I can't otherwise quantify.

https://www.sheldonbrown.com/wheelbuild.html

terrymorse 

Spoke breakage is not an issue on a well-built wheel, with DB or straight spokes.

But wheels built with DB spokes stay true better. DB spokes are less likely to go slack during use than straight gage spokes. When a spoke goes slack, it’s possible that the nipple will unwind, changing the spoke tension and sending the wheel out of true.

On the the down side, it’s harder to tension a wheel built with DB spokes, because the spokes twist when tightened. When tensioning a wheel with DB spokes, I always use a twist-resist tool to avoid this wind up.

Road Fan

What is a twist-resist tool?

Kimmo 

+1 - I know bladed spoke holders, but what do you use for round spokes...?

DB spokes build better wheels because they're more elastic, thus reduce fatigue failures at the elbows and threads. Doesn't take a study to prove; you just need to know that spokes don't fail from yield, they fail from fatigue.

Moe Zhoost

The engineering arguments for DB spokes being less likely to fatigue and break make a lot of sense. Fatigue is related to both the number of stress cycles as well as their level of stress. Straight gauge spokes will not absorb stress as effectively as DB and thus will reach their fatigue limit sooner (all other things being equal). I think that you will never find a well-designed, real-life study to prove this, though. There are a lot of variables here: lacing pattern, rim strength, weight of rider, surface condition, type of spoke load (tangential, radial, lateral), number of spokes, how the wheel is tensioned, etc.

Most riders will not see a significant difference because the probability of fatigue failure on a well-built wheel, regardless of spoke type, is very low (i.e. millions of peak stress cycles). If a rider were wanting a stronger wheel due to spoke breakage experience, I'd recommend a stronger rim and higher spoke count before worrying about spoke type.

Brocephus

I get the physics argument for DB spokes over straight gauge, but what I'm wondering is if the difference is negligible, or if it's significant and tangible?
These days, my bikes get very low-stress use, just steady paced exercise, on good roads. No off-road, big-air thrashing, and no more road racing with heavy training, interval sprints, etc.
All my wheels are currently straight gauge Swiss DT's. Would I expect to get measurably longer service with DB spokes, or is this basically just an academic/technical argument, at least in my case?

terrymorse 

It lets you clamp onto the spoke to keep it from twisting.



Twist-resist Tool

Nessism

This was always my understanding as well but some very knowledgeable builders over on roadbikereview say no; the spoke tension would have to be drastically low for all the tension to be removed in use, thus allowing the nipple to loosen.

For many years my go-to configuration was 14/15 drive side rear, 15/16 non drive side rear, and straight 15 front. Tons of miles this way and never a broken spoke (road riding only). Anyway, a well built wheel should last a long time regardless of these nit pick arguments over theoretical benefits one way or another.

79pmooney

I don't ride straight gauge spokes, not for spoke breakage but because my rims are less likely to be damaged hitting potholes and the like. Also butted spoke wheels simply feel better on less than perfect roads.

I make zero claim that I have any studies to back this up. But my experience. All of my really long lived wheels have had butted spokes. The store bought wheels are not pleasant rides until I cut out the 14 ga and re-lace with butted. My only claim here is most of 200,000 miles of experience on wheels I built.

Ben

DrIsotope

I have two rear wheels with identical hoops, hubs, and spoke counts. The only difference is, one has straight gauge and the other has double butted. The double butted wheel feels, I dunno... firmer? More consistent? Sometimes I swear the straight gauge wheel feels kinda noodly. The two wheelsets do have completely different tire sizes on them. So could easily be 100% mental.

aggiegrads

I think of it this way: The spokes are essentially springs anchored at each end. If you use really heavy, stiff springs, the connections at the end take all of the stress because the springs do not stretch.

If you use lighter springs, they stretch more, and the stresses are spread across the length of the spring and are not concentrated at the ends.

At the end of the day, reducing the peak stresses at the point where they are most concentrated (the j-bend and threads) will extend the life of the spoke.

cyccommute 

Let’s start with tensile strength. The tensile strength being measured isn’t the wheel but the resistance of the spoke to breakage. Tensile strength measurements of the spoke gives you insight into how much it takes to fatigue the spoke to the point where it will break. Higher tensile strength (or resistance to breakage) will result in a strong, more durable wheel.

Pillar spokes is about the only place where I’ve seen actual measurements of tensile strength of various types of spokes. You have to look at multiple graphs to see what effect butting has on strength but it’s pretty clear when you compare them. For example a 2.0mm (14ga) spoke breaks at 270 kgf (kilograms force which is a really dumb unit). A 2.0/1.8/2.0mm breaks at 290 kgf (about) and a 2.2/1.8/2.0mm spoke breaks at about 330 kgf. They have a 2.3/1.8/2.0mm triple butted spoke that breaks at about 420 kgf. For comparison, their 2.3mm straight spoke breaks at about 360 kgf.

Their charts show pretty conclusively that butting the spokes increases their strength.

cyccommute 

People say this all the time but it isn’t entirely correct. The way the wheel is tensioned is important but materials of construction come into play as well. Spokes can, and do, break because of fatigue. A light rider usually isn’t going to fatigue a spoke but a heavier rider or a light rider who carries a heavy load will fatigue spokes at a faster rate. You can’t put 1.5mm spokes on a bike and expect them to stand up to even a lightweight rider for very long.

I build my own wheels and have always had problems with spoke breakage. When I switched to triple butted spokes about 20 years ago, my spoke breakage problems went to zero. I’m not building the wheels any differently, I’m just using different materials.

AnkleWork

Perform a careful experiment and you will have your proof. Then write a report and you will be published.

Kimmo 

Something folks might want to consider is that during normal use, as in, all the time the wheels aren't being destroyed in a crash, loads on the wheels only decrease tension in any given spoke. Thus sayeth Jobst.

This didn't make much sense to me at first, but when I finally got my head around it, I realised I never quite understood bike wheels until that point. The thing about the hub standing on the bottom spokes even made sense too, believe or not.

Components of a wheel:
Hub
Spokes and nipples
Rim
Tension.

HillRider

This makes no sense. What you are saying is that less material is stronger. A 2 mm spoke has a cross section of 3.24 mm^2, a 1.8 mm spoke has a cross section of 2.54 mm^2. So the smaller cross section is stronger? Perhaps the tensile strength numbers are really given in kgf/mm^2 and the butted spokes are stronger per mm^2 due to cold working.

AnkleWork

Fatigue life and modulus of elasticity are rather more important than UTS.

Darth Lefty 

Spokes are not naturally occurring. They are designed by engineers. Engineers can look at a spoke failure and see what caused it and design against it. They test material samples and predict how they're going to fail in a design. That's where double butted (and all subsequent improved) spokes came from. I'd love to know when they were first used. I'm sure it was far before modern scientific studies of biology or behavior which mostly seem to be trying to find a statistical correlation between data.

If you're not interested in tensile strength, or shear strength, or modulus, or fatigue, perhaps you should be.

Mad Honk 

Cyccommute and AnkleWork,
I get studies from a number of Steel and Graphite tube designers who normally use IE and JG to describe the characteristics of the tubes (EG golf shafts).
What I am hearing is that when you change the diameter of the shaft/spoke at the head end it gives it more strength, and you can thin the tube down in the center but need to bring it back to diameter on the nipple end to regain the strength that occurs in the constant flexing of the wheel while riding. A pretty simple concept. We do it with golf shafts all day long. Bigger diameter at the grip end of the shaft which increases strength where the most loading takes place, and then encapsulating the smaller diameter of the shaft with a large metal hosel of the club head. What I would ask of this esteemed group, is what materials are being used. For example, I can find a very malleable 302 stainless steel, and a 17-4 that is unmovable. Different spokes and different materials from each designer, and the characteristics are going to be different. I spend hundreds of $ every year to get the EI/JG information so I can build a better golf club. I suspect it will be the same with spokes going forward. What happens when we start using carbon fiber spokes in wheels? Smiles, MH

shelbyfv

Well, this doesn't seem to be turning out much different from OP's similar spoke queries in past years. Not really surprising, but I guess you never know....

Kimmo 

Giant did it in the 90s. Then you had Spinergy, Mavic, Lightweight, Reynolds. Probably others too.

AnkleWork

That's a little mixed up. Construct free body diagrams for golf shafts and bike spokes, and you'll begin to see the differences.

davidad

Straight gauge spokes break at about 682 pounds and double butted spokes fail at 640 pounds. The advantage of butting spokes is that the stress is concentrated in the reduced section rather than the nipples or heads.
When I was a millwright helper in the shipyard the bolts on high pressure turbine cases were butted.