TiHabanero

If a motorcycle uses straight gauge spokes, why not on a bicycle? I propose the idea of db spokes as stronger to be a myth. Never have had issues with straight 2.0 Champions, but as soon as I go to 2.0/1.8 db they start to snap at the heads.

PlanoFuji

I don't think anyone claims that double butted is STRONGER than straight gauge, they are lighter and strong enough in the areas they are stressed on a bicycle. Motorcycles are a very different animal (considerably heavier and more power) and weight savings isn't really an issue. Even on a race motorcycle the few grams difference in weight is not going to matter at all.

However, there is nothing wrong with using straight gauge spokes on a bicycle.

krome

The claim is that they are more durable, because the thinned center with gradual transitions is better able to accomodate stress than the threads or the bend at the head. You'll see this design elsewhere in threaded fasteners for some applications. Threads, rolled or otherwise, are a stress riser. Same with bends.

Edit: Also, motorbikes are usually less concerned about weight, and more concerned about wheel failure that the spoke gauges used are probably overkill.

gyozadude

I've had the opposite experience. All my DB spokes have stayed intact and held up quite well over the years. Never a broken head. But straight gauge? I've broken quite a few heads off over the years on standard 14g/2.0mm spokes. I suspect the key is quality of the spoke and tensioning. Not many builders properly tension DB spokes and fail to prep the spoke threads and holes in the rim to allow proper tensioning to occur with minimal twist. But I find the DB spokes to tension elastically and hold that tension so that even with a heavy rider like me, the spoke never gets fully unloaded and reversed into compression, even when I stand and sprint uphill which is when I break most spokes which are the leading (not the trailing ones) on the drive side rear. Also, with DB spokes, they are primarily available under quality brands with good head designs that don't break easily. Some discount/bulk straight gauge spokes I use for super cheap wheels for kids and light riders run about $0.13 each and work great except for clydes where the spokes will break after 1000 - 1500 miles or so. Mr. Rabbit noted that most of the ones I referred to have elbows leading to heads with too great a radius, and in comparing to DT or Wheelsmith, I admit, these are greater radius. My current experiment has been to re-lace the drive side spokes with a small copper washer under the head to fill that tension per suggestion I adapted from Sheldon Brown to see if that can resolve issues of spoke head radius and get these spokes to last longer. I'm just about to enter 1000 miles when I should see more spokes breaking, so we'll see if this helps. but the spokes are straight gauge. I hope it doesn't confuse the point of this thread... DB versus Straight Gauge. But I wanted to inject that spoke quality may have some major impact as well.

sreten

Hi,

DB bicycle spokes have claimed weight and aero advantages meaningless on a motorcycle.

rgds, sreten.

Metaluna

People don't claim they are stronger, but they DO claim that they last longer, due to the increased elasticity of the middle section. This allows the spoke to stretch more for a given tension, lessening the chance of it going completely slack during certain parts of the pedal stroke, which is what causes fatigue and breakage.

So without any engineering knowledge of how spoked motorcycle wheels work, I would suggest we need to at least consider the following possibilities:

a) The lightest motorcycle rim is probably built like a tank compared to the heaviest bicycle rim. Meaning it could be easier to tension a straight gauge spoke enough so that is has the "right" amount of pre-stretch given the loads it is designed to experience.

b) Motorcycle propulsion is a lot different than pedaling in that you probably have a lot more consistent driving torque, rather than hundreds of thousands of cycles of stretch-relax-stretch, so the elasticity of the spoke might be less important.

P.S. I have a wheel laced with straight gauge spokes on the drive side and DB on the non-drive. I forget the rationale for doing this, but it was enough to persuade me at the time I built it I think it had something to do with giving a better balance of spoke tension. Hopefully I won't regret it.

PlanoFuji

Well considering that a well built wheel's (trued and balanced) lifespan exceeds that of the rim's lifespan (from braking wear) I doubt that such possible subtleties matter. But the OP's attempt at myth debunking stated the myth was that DB spokes were stronger than straight gauge. That clearly is not the case.

Ronno6

Motorbkes don't use double butted tubing on the frames,either.
Same reasons.
In bicycle applications, frame tubes as well as spokes, you put the meat where the strength and stresses require it,
and remove weight from where it is not essential.

AnkleWork

I guess you are saying that no _well built wheels (trued and balanced)_ ever break spokes. Also was it ever a myth that DB spokes are stronger than straight gauge?

PlanoFuji

Well barring something damaging the spokes (like getting something caught in them or exceeding their design strength), which has nothing to do with the relative strength of the spokes, then yes that is my understanding.

No, I don't think this was ever a 'myth' beyond the perception of the OP. There is apparently a belief that they are longer lasting (see post #6 ), but that is a different matter.

sreten

Hi,

The drive side always has the most spoke tension, the other side less.

In terms of the optimum tension of spokes you will get a better balance
using skinnier spokes in the non-drive side with symmetrical lacing.

rgds, sreten.

TiHabanero

Alrighty, it seems "stronger" was the incorrect term to use. How about "fatigue resistant"? Makes no sense to me, but I am not a stress analyst or engineer! I do know straight spokes work really, really well in the applications I have used them. I also know from experience that low grade spokes don't last as long as top shelf DT.

DX-MAN

I guess you are reading an awful lot into that other post, as he wasn't saying either of those things. Yes, DB spokes being STRONGER IS a myth; no, no wheel, no matter how well built, lasts forever. Even Gravy had to replace some spokes on his wheels from time to time.

Darth Lefty 

Road motorcycles with any performance pretensions don't have spokes. They have single-piece cast alloy rims. This goes along with having tubeless tires.

Offroad motorcycles still have spoke rims because they fail safe and work well with tubes.

Cruisers have spoke rims for the same reason 1980's Cadillacs have spoke hubcaps.

Drew Eckhardt 

They build into stronger wheels.

When you deflect a rim far enough to make spokes in the area slack it looses horizontal support, can shift off center, and collapse when it springs back.

You can deflect the rim farther with thinner spokes (whether in their center section or entire length) before that happens and take a bigger hit.

If tension is that low the nipples will unscrew and wheel will go out of true long before you have any sort of durability problems unless you've glued the nipples on.

Right. Motorcycle rims are something you wouldn't want dropped on your toes, not 400-500 gram rims you could play frisbee with.

The highest forces come from the rider's weight unloading spokes as they pass the bottom of the rim.

I built one with DT 2.0/1.8mm Competition spokes on the drive side and DT 2.0/1.5mm Revolutions on the non-drive side. It's worked great for 15 years - doesn't go out of true unless crashed, has never broken a spoke, although I've forgotten if it's on the second or third rim (I can't remember if I bent it far enough to suggest replacement on the last hard crash).

Some sort of conventional wisdom suggested that configuration although I think 2.0/1.5 spokes on both sides would have worked as well.

The tension ratio between sides is determined purely by geometry and not affected by spoke gauge.

Given a rim that's not moving to one side (which will quickly eliminate any imbalance) the force vector components parallel to the axle must sum to zero implying equal magnitude between the sides.

A steeper angle means a smaller fraction of tension in the horizontal direction so the drive side has more tension.

Soil_Sampler

Most do, some do not.

https://www.alpinaraggi.it/en/catalog/50339





...mostly because 400lbs and 100 horsepower.

TiHabanero

In plain English, sir. Please, for the common man to understand. Thank you.

Drew Eckhardt 

Yes unless you damage them with an over-shifted chain or other hard road obstacle and provided that you've also stress relieved the spokes. Parts of the elbow aren't taken past the elastic limit during the forming operation and lead to low fatigue life from the high average stress when not corrected. I like to twist spokes around each other at the outer crossing using a brass drift, although other objects softer than the spokes can be used like a plastic screw driver handle or old left crank. You can also squeeze near parallel pairs in a side towards each other (gloves make that more comfortable) and I've heard of one mechanic walking on wheels while wearing tennis shoes. When you do one of those things you take all each elbow past its yield point leaving no residual stress which allows for a lower average stress and extreme number of fatigue cycles.

Jobst Brandt has a set of spokes which have gone 300,000 miles.

FastJake

I don't think anyone's pointed this out yet, but a 2.0 straight gauge spoke has the exact same head size as a 2.0/1.8/2.0 butted spoke. So if you're breaking DB spokes at the head, they weren't tensioned enough.

PlanoFuji

How about this. Any wheel built with the proper number of spokes that are of sufficient size/strength for the desired loads that is built properly (tensioned, balanced, and stress relieved) will last longer than it takes for the braking surface of the rim to wear through. In short, double/triple butted versus straight gauge doesn't matter except for looks and weight.

FBinNY 

One of the earliest makers and promoters of waged (double butted) spokes was the Torington Company of Connecticut.

Interestingly they promoted the concept, not as stronger or lighter, but less expensive.

Understand that the typical steels used for spokes have a shear strength of about 80% the tensile strength. Likewise the thread pf a 2mm spoke has a root diameter of about 1.8mm. So operating under the theory that a chain is no stronger than it's weakest link, any material in the middle of a spoke beyond 80% of the elbow diameter, or the root of the thread (whichever is lower) is wasted material, and a 2/1.6/2.0mm spoke will be as strong as a 2mm plain gauge spoke.

Torrington wasn't as concerned about weight per se, but better use of pricey high strength steels and was selling their butted spokes at the same or lower price than competitors plain spokes.

The info above applies only to strength. However rigidity is a function of the average cross section, so butted spokes build a wheel with flex properties comparable to plain spokes of the thin section.

Lastly is the issue of fatigue, where butted spokes shine. All things being equal, the thinner mid section of butted spokes take up more of the deflections, and so tend to prolong the fatigue life of the ends.

So, no matter how you slice it, the fact that butted spokes are superior when we consider strength, weight & fatigue life is no myth. But fortunately all types of spokes are still available, so you don't have to accept this and can still buy whatever spoke you want.

Bill Kapaun

How long is a MC spoke?
What gauge?
Very different operating conditions, where the MC spoke is, relatively speaking, VERY short.

Myosmith

Your problem isn't that your spokes are butted, your wheel is inadequately tensioned. Due to their compliance in the middle, butted spokes are actually less likely to fail at the head angle than non-butted counterparts, all other things being equal.

MichaelW

Butted spokes and butted steel frame tubing have been (and are) used on motorbikes.
Reynolds tubeing.
SRM custom wheels

Delmarva

Where exactly are you reading that double butted spokes are stronger, more fatigue resistant or some other superlative than straight spokes. Provide a url please. For bikes the double butt design will allow some weight savings while still providing support for wheels and frame. For motorcycles saving a pound in weight is less of an issue.

Here is some spoke information from the folks who actually use them.

https://www.wheelbuilder.com/spoke-information.html