I've started commuting to school and back 2-3 days a week this summer to lose some weight and save some $$$ on gas. I have a stock 2005 Trek 7300FX that I purchased new but let sit around until recently so it only has about 250 miles on it in total. I suppose I could be characterized as a super-cylde at 325 lbs. The problem I'm having is that twice in the last 3 weeks, I've broken 2 spokes on the left (non-cog) side of the rear wheel. The first time was on a night ride home and I didn't notice until the next day. I took the wheel in to the LBS to have get spokes replaced and it took 5 days to get my bike back (i'm guessing they are busy right now.) I was not completely satisfied with the job they did, as the wheel seemed a bit out of true when I got it back, but I figured it was close enough and I wanted to get back to riding, so I fgured it wouldn't matter and took the bike home. On the ride home today (only the second ride since I got it back), I hit a bump and heard the "pong" as 2 more spokes popped.
The wheel is a WTB Dual Duty XC 700c (622x17) rim with a Shimano Deore FH-510 VAM hub. My questions are: As a clyde, should I just accept that I'll pop spokes and take it back to the LBS for another round of repairs? The wheel seems to have low-mid quality components, so is it worth repairing the wheel again (probably $27- $25 labor +$1 per spoke?) I'm not afraid to build/ rebuild a wheel myself (although I've never done it,) so would it be worthwhile to invest in a wheel truing stand and the other accoutrements (and is the truing stand absolutely necessary if I just want to replace a spoke or two on occasion?) If I choose to upgrade the wheel, please offer recommendations on a clyde-appropriate 700c rim/ hub spoke combo.
My plan is to keep this bike in service until I hit 250 lbs then I'll treat myself to a new bike, but I cannot fathom that paying $27 every other week and having the bike in the shop for 5 days as being a reliable machine and the best investment I can make until I have lost that weight.
I'm going to cross-post this in the Clyde forum to get their take on things.
Many thanks,
Aeneas

Kudos for taking on the challenge of getting exercise and generally looking for a more active lifestyle.

There's no doubt that the rear wheel usually takes more of the load on most bicycles since we generally area positioned so that more of our weight is to the rear on most bicycles. So that's a factor for starters.

Second is that as odd as it sounds spokes are very tough when under tension. When they break it's mostly because they get loose as they pass over the bottom of the rotation and then get jammed between the rim and the hub if or when the tension goes to zero load. Eventually metal fatigue occurs and they break as they go around the top. We actually are hanging from the spokes around the top half of the wheel when riding.

Now on the rear the drive side has more tension on it so the spokes on the drive (cog) side will almost never loose all their tension. But on the non drive side they run with less tension due to the offset or dish of the wheel. And sure enough it's the non drive side with the lower tension that you're breaking the spokes on.

What I'd suggest is that you find a shop that can build a good wheel and request that they rebuild your rear wheel with good quality 14 gauge spokes and run the build up to a higher tension all around than they usually do. This way your non drive side is running closer to or up around what your present drive side setup has for tension. This way your weight won't let the spokes reach a zero tensile load at any point in the rotation. And that's the key.

You can even test this for yourself. Tap the drive side spokes with a plastic handle screwdriver and note the tone. Do the same to the non drive side. Note the higher tone and try to remember it. After your wheel comes back from the rebuild tap the non drive and see if it's around the same sound as your present drive side.

The reason you need to dump your present spokes is that they have already fatigued from the riding you've done on the bike. It's because they are now weakened that they are all of a sudden letting go. You don't want to trust any of them at this point as even if you get the shop to run up the tension there's an excellent chance that the non drive spokes will just keep breaking. Now the drive side spokes may be all right but for the sake of a few dollars it is false economy to trust them. That's why I say replace them all and rebuild your wheel from the ground up.

That WTB rim looks pretty sturdy from what I see but if the shop recomends a more bomb proof option you may want to consider it at least for the time being just as insurance. There's some nice options now thanks to the 29'er trail bike movement. This is off road riding with tires and rims that are the same overall diameters as the 700c wheels but often build extra sturdy.

I'd suggest using 14/15-gauge DB spokes on that new wheel. The higher stretch of those spokes will ensure that the spokes never lose tension at the bottom of the wheel's rotation.

He'd be better off switching to a thinner NDS spoke and perhaps going to heads-out half radial than by merely increasing tension. That'd do even more to prevent the NDS spoke from going slack.

^^^^

Agree with the last 2 posts and in addition I would recomend spoke washers be used under the spoke heads to minimize the "banging around" that the usual 2.0mm spoke does in a 2.3mm hole when the tension nears 0 on the left side of a rear wheel.

Thank you for the suggestions to this point and for the explanation of bicycle wheel engineering. I remembered that there is a bike coop on campus the president of which I'm friends with so I can probably use the truing stand and other equipment there, and maybe get some instruction as well. Could you suggest a reference, either hard copy or web-based for bicycle wheel construction (yes, I've read and reread sheldon's page) and dynamics? Why are there different spoke gauges and why are the mechanical properties different?
dabac, pardon my ignorance, but could you explain what you mean by "heads-out half radial?"

Thank you
Aeneas

I ride with some 250+ pound guys and from what I've seen my recommendation is for a 36 spoke 3-cross wheel with double butted (DT Competition 2.0-1.8-2.0) spokes, Ultegra or 105 hub, and CXP33 or similar rim.
And, of course, plenty of tension.

Al

I haven't found any web-based wheelbuilding stuff that has as much technical detail as:

The Bicycle Wheel - Jobst Brandt

Spoke gauges are selected based upon weight, load and durability. Thicker 14ga (2.0mm) spokes are pretty standard on common department-store bikes and they're fairly reliable and bulletproof. Thinner 15ga (1.8mm) spokes are favored by racers due to the weight-savings (about 1/4-1/2 lb per wheelset), but they tend to fatigue and fail sooner. But 2-3 years is fine for a racer, even 1-year is sufficient.

Double-butted spokes is a combination and yields weight-savings WITH durability. That's because the most stressed parts of a spoke are at the ends where the bend through the hub occurs; and to a lesser extend, out by the spoke-nipple. So a 14/15/14ga (2.0/1.8/2.0) spoke has most of the weight-savings of a 15ga spoke, yet has the strength of a 14ga spoke. It's actually better than both because it has higher-stretch than 14ga for the same tension. This ensures that it can go through a wider-range of loads without losing tension completely. Losing tension causes the nipples to be loose at the bottom of the rotation and vibrations will loosen them, causing the wheel to go out of true over time. The all-tension/no-tension transition is also harsh on the material and will lead to fatigue-failure sooner than if the spoke were kept tensioned all the time.

A very good spoke to use for clydes is the DT Alpine spoke in 13/15/14ga (2.3/1.8/2.0mm). It has the thickest part at the bend for strength as well as fully filling the spoke-hole in the hub. Yet it doesn't have excess weight and it has additional stretch from the butting. Be sure to pick these up for your new wheel.

"Heads-out half-radial" refers to lacing-up the non-drive side spokes on your rear-wheel. Radial is spokes going straight from the hub to the rim without any tangential angles or crossing. The heads-out means the spokes sit on the inside of the hub-flange. This reduces the angle of the spoke to rim and matches better the angle of the spokes on the drive-side. Matching the angles more results in more similar tensions and more even load-bearing from all the spokes.

Borrow a tension-gauge or have your tension inspected by a knowledgeable wheel-builder. You'll want to have tension towards the high-end of the range for the specific rim you're using. Something around 125-140 kgf. Most stock wheels on bikes are way undertensioned at 80-100 kgr and this leads to faster fatigue failures.

36H is a good start, but DT Revolution (2.0-1.5-2.0) on the NDS would be an even better match. That hub should give about 60-70% of the DS tension on the NDS. With that matched to the cross section of the thinner spoke you end up with a very evenly balanced wheel.

3X is a solid and conservative recommendation, but not as influential for wheel durability as spoke tension and spoke numbers.

The Alpine III does a much better job. It fills the 2.3mm hub hole so that there is less movement. I only build with the Alpines now. I have one set on a rear wheel of a mountain bike that has been ridden hard for over 5 years without any kind of trouble.

Not a bad idea for clyde wheels. I had settled on the current formula just about the time Alpines became available and just hadn't given them a try.

Cool thread with lots of helpful detail!

I'm about to hand a rear wheel back to a friend that I just rebuilt with double-butted DT spokes. She's a small/light woman and was having chronic spoke breakage issues...tells you something about the build quality on low-end factory wheels.

Are the DT Alpine III spokes still available? Harris Cyclery said awhile ago that they're gone forever.

Also, I'd add that a neat idea (which I'll be trying for the first time on my next wheelset) is to use asymmetric rims like the ones made by Velocity...they dramatically even out the left/right tension ratio (to about 85% or so in my build) for the rear wheel, according to Spocalc.

Better yet, go single speed or internal gear and forget about rear wheel dish altogether! (duck and cover)

DT still lists them and you can find them at various places on the net. Here, here and here.

I bow to the suggestions of the others. Some great ideas there and I'd forgotten about the butted spokes being actually stronger in real world use than the single guage spokes.

The heads out deal refers to lacing the spokes so that they are all feeding off the inner side of the hub flange and thus the spoke heads are all on the outside instead of the insy/outsy alternating head pattern on your wheel now. The advantage in this case being that the head out spokes will have a touch more vertical angle and therefore will need that little extra tension to counter the DS side spokes. And since the goal is to try to raise the NDS (that's so much better than typing non drive side each time ) tension every little trick is worthwhile. The only issue is that now you're running radial spokes on the one side and all I've read suggests that the good ol' 3 cross pattern is overall stronger. Perhaps some of the others can shed more light on this semi radial option.

Someone else mentioned the issue with cheapie machine built wheels. It's quite possible that just a new custom built 36 spoke typical 3cross but done with care and attention would be just fine for your needs. Certainly a decent wheel builder can better the output from one of those machines any day of the week.

Again, I really appreciate the advice offered here. I'm having my LBS rebuild the wheel with Double Taper spokes, recycling the hub and the rim. They say it will be done early next week.
I hate being without my bike though... and I still want to learn how to build a wheel, so I'm going to go about my reading and research and begin accumulating the bits I need to build a generator hub for the front wheel. I hope to use the equipment and expertise in the campus bicycle co-op, thus eliminating the necessity to purchase a truing stand right now.
Once again, thank you for your help!
Aeneas

Thanks for the links, cyccommute!

It's too bad that the sizes I need for my upcoming build (a 650B Rivendell) aren't available. I would have definitely gone for the triple-butted spokes.

The only time 3x plays a factor is in torsional strength. Vertical and lateral strength is identical regardless of the number of crosses (really tangential angle), and is based purely on numbers of spokes and tension. Due to the torque-reduction through the gearing, a human generates a miniscule amount of torque at the hub. So little in fact, you actually get minimal wind-up even with an all-radial rear wheel.

IMHO an all radial rear wheel or an all radial disc wheel fornt or rear is bad news waiting to happen. Spokes only have strength in tension and there have to be some trailing spokes (at least a half radial) to absorb the drive torque.

You haven't tried riding an all-radial rear-wheel have you?

No, and for my survival I hope to never have to.

Every wheel building recomendation ever put on paper recomends against it. There is simply no structure built into such a wheel to resist torque. A half radial is as far as I will go.

So everyone is saying, and I don't deny the theory. But given the extreme rarity of people actually building and riding radials all we actually can say is "bad in theory". Unless tested or properly calculated we don't really know if current materials would actually let us get away with it.
What we do know, because it happens with some regularity, is that it's possible to rip a hub flange apart with too high spoke tensions in a radial.

But that's true regardless if it's a radial or a tangential spoke.

Does it really? I'm not so sure. What'll happen with a radial wheel exposed to torque is that as the hub begins to twist in relation to the rim the spokes will begin to increase in tension, just as they would if they were laced tangentially.
The only difference I can see is that with a tangential lace a smaller angular displacement will cause a more immediate increase in spoke tension - i.e. as soon as the hub twists with relation to the rim this will immediately mean that the spoke's attachment point at the hub is displaced along the spoke's axis.
With the radial lace the first degrees of displacement would primarily move the spoke's attatchment point at the hub perpendicularly to the spoke's axis, thus delaying the increase of spoke tension required to move the rim somewhat.

Now, if we were dealing with a system with some slack in it this would definitely be significant. But bike wheels have their whole survival based around the fact that they are heavily pre-stressed.
It'd be fairly easy to test actually.
a)Label your rear wheel spokes. Measure and register their tension.
b)Select your lowest gear, but front wheel against immovable object. Have Friend #1 support you as you get on the bike and put pressure on the pedals.
b)While you're doing your static honking, have Friend#2 measure your spoke tensions.
c) Compare spoke tensions. Unless pedalling causes significant increase in spoke tension radial wheels should do OK in torque transfer as long as the flanges are up to it.

I think that I would be more worried about the dynamic situation. Torque is not applied smoothly by the average rider. Instead it arrives in pulses as the riders power is delivered to the pedals. As you point out in your example, the rim of a radially laced wheel will lag behind the acceleration of of the hub. ( probably by a substantial amount more than that of a wheel with tangential spokes.) In effect this is wrapping up a spring and as power diminishes at the pedals, the spring will in turn accelerate the rim more than the hub as it tries to achieve a ballance point. It would be interesting to chart the sine wave of spoke tension rising and falling with each oscillation. I have a feeling (unsubstantiated by any hard data, just an initial impression based on the small angles involved in the trig functions for radial spokes) that the tensions would be quite high. Leading and trailing spokes may dampen this tendency toward oscillation.

Given the recomendations of the published wheel builders and the even stronger recomendations not to use disk brakes on radial wheels (same torque situation) I for one don't have the courage to put wheels in service that are built that way.

If it turned out to be safe, I would be among the first to climb on the wagon as there are several other advantages to radial spokes that I would like to explore beyond the half radial rear that I currently favor.

A radial front is one thing since the spokes only support the weight loading. At least with a rim brake. A semi radial rear as discussed earlier I like the idea of since you've still got the tangential spokes to suck up the torque. And the heads out sets up the NDS with a little steeper angle. All good.

But a radial disc or drive wheel isn't a good idea at all.

It's from looking at the loading geometry of the spokes. I'd have to draw up some charts to show you but it comes down to the torque multiplication due to the angles involved. A tangental load is running near 90 from the axle to the hub hole and then to the spoke. A radial wheel is running a zero angle that under torque is going to flex to a measurable but small angle. The leverage angles the torque is working with are acting to multiply the resulting tension load on the spokes to many more times what they are required to endure with a tangential setup. Also since the radial angle is zero (as for inline) the multiplying factor is infinite at first and only comes down as the hub torques around within the lacing patter to produce a small tangential angle and the spoke takes up that extra load.

So even if the spokes CAN handle the locads of a pure radial laced rear wheel there is going to be some windup and release in the all radial system rather than a crisp and far more flex free link in the tangential setup between the hub and the tire contact patch.

Basically if you lace up your drive side radially then you're setting up a situation where the torque has a lot stronger leverage ratio and the spokes are going to see a tensile buildup many times more than they would in a regular tangential arrangement. How much? I'm not sure without doing some serious head scratching and would need some numbers to play with. But I have no doubt that it would be very significant.

NO! The wind-up and angle is CAUSED by the torque from the hub, it doesn't GENERATE the torque or the increase in tension. What happens is a dynamic sequence:

1. torque is applied to hub
2. hub winds up
3. flange pulls on spokes
4. spokes increase in tension... up to the point where they even out the torque

What happens is ALL hubs will wind-up until the increase in tension equals the applied torque. The exact amount of wind-up then depends upon the tangential-angle of the spokes coming out of the flange and their tension. So lacings with exactly 90-degree spokes relative to flange will have the least amount of wind-up. On large-flange hubs, this can be 3x, and on small-flange hubs, 4x. Lower crosses like 3x, 2x, 1x, will result in more wind-up for the exact same increase in spoke-tension. It's the torque that causes the wind-up and tension-increase. But that tension-increase is the same in all cases and comes from the force applied at the pedals.


Here's a good start:

1. 250 lbs = 114kg = maximum total-force on pedals for Olympic level track-racer (use 1/2 that for most arm-chair racers here)
2. 170mm = 0.170m = crank-length
3. 114kg * 0.170m = 19.38kgm torque at bottom-bracket
4. 0.288 ratio = 52x15t = gearing used for 100% all-out sprint
5. 0.288 * 19.38kgm = 5.58kgm = torque at rear-hub
6. 38mm = 0.038m= diameter of rear-hub
7. 5.58kgm / 0.038m = 147kg = total pulling force on spokes at hub

Note that this force on the spokes at the hub is the same regardless of the lacing. That's because the force at the hub comes from the force at the pedals, through the crank, through the gearing, to the flange. Now, let's look at how this total force is distributed amongst the spokes:

32-HOLE 4x/3x/2x
32h /2 = 16 = number of pulling spokes
147kg/16 = 9.19kg = extra tension added to each pulling spoke
120kgf = initial tension
9.19/120 = 7.7% = increase in tension on each pulling spoke from Olympic-class sprinter at maximum-exertion

32-HOLE 0x RADIAL
32h /1 = 32 = number of pulling spokes
147kg/32 = 4.59kg = extra tension added to each pulling spoke
120kgf = initial tension
4.59/120 = 3.83% = increase in tension on each pulling spoke from Olympic-class sprinter at maximum-exertion

The thing with radial is that ALL of the spokes becomes pulling-spokes on a rear wheel. What we're talking about here is torsional rigidity. That is, the relative rotation of the hub relative to the rim when any amount of torque is applied to the rear-hub. It doesn't have anything to do with wheel-strength, stiffness or durability. It does have an impact on the "feel" of a rear-wheel when you torque on it. But if you're smooth and have an even pedaling-style (like a track-sprinter), you won't even notice that the rear-wheel is radial or crossed. Gee, I wonder how I know this...

Exactly, that's the only issue we're really talking about here is hub-durability with radial-lacing. You really do want to get a hub with lots of meat on the flange to handle the outward-pull of radial-lacing. And if you want stiff wheels, you want radial-lacing. Check out the stiffness wheels here: Damon Rinard - wheel-stiffness test data. Notice the effect of heads-in vs. heads-out radial-orientation on wheel-stiffness.

Try this... measure braking-distance from 45mph to 0. Then measure how much distance you need to accelerate from 0-45mph and you'll see the vastly different forces on the wheels in power-transmission versus braking. You can also calculate the difference in hub wind-up as well. Problem with such large torques on the hub in radial-lacing is that you end up really wearing out the spoke-holes. And if you have single-sided discs, you end up twisting the hub-center because the left & right flanges will face vastly different torques under braking.

As for your 2nd point, there's really no advantage to radial spokes over half-radial. Just that there's no really any disadvantages either, aside from hub-flange durability.