I've got a few different topics that are generally about wheels, so I'm going to do something unusual for me and cleanly divide them into discreet chapters.
Part of the reason why Lasers and CX Rays are such good spokes that they are crazy strong in tension, but they act like springs in compression. As an experiment, line three spokes - one straight gauge, one 2.0/1.5/2.0 double butted (like a Laser), and one CX Ray. They should all be the same length. Stand them up, and press down on the top of each one until the mid section bends. The straight gauge spoke pretty much doesn't bend, while the 2.0/1.5/2.0 bends pretty readily, and the CX Ray bends with just slight pressure. This illustrates two things. First, the straight gauge spoke transmits any compressive pressure that it receives. This means that it is going to stress the nipple, stress the spoke flange on the hub, and stress the spoke head. A spoke that is overstressed in compression will eventually break at an end. Second, when you pushed down and it hurt your finger before it bent - that force would go into you when you rode that wheel. Butted and bladed spokes give a less jarring ride than straight blade spokes.
Butting also makes spokes stronger. "Isotropic" means that a material is equally as strong in any direction, and its counterpart is "anisotropic." Anisotropic things are stronger in some directions than others. The process of butting the spokes (in which the middle part of the spoke is swaged, or mashed down between two rollers) makes the spoke stronger along the spoke than across it by aligning the grain of the metal. Much the same thing is accomplished when they work the blades shape into a CX Ray, although the process is a little different. A CX Ray has a tensile strength (pull the ends until it breaks in the middle) of 1600 N/mm2. That's pretty much hook it up to two tractors heading in opposite directions and floor it strong. But if you pulled it apart perpendicular to its length, it would be less strong. So it takes strength from one undesirable direction and puts it into a desirable dimension.
Spokes that go slack eventually break. It's REALLY REALLY hard to break a spoke in tension, but in compression they aren't that hard to break. Continuously repeat our little exercise above, compressing the spoke, and after a few hours the spoke head will break off. Cycle fatigue, it's a killer.
CX Rays and more heavily butted spokes can be more stretchy than straight gauge or less heavily butted spokes, despite their greater ultimate strength. We are rolling out with some news about alloy wheels soon. Nothing earth shattering, we are just refining our product line, but one of the things we've been asked to do and wanted to do was introduce a lower spoke count alloy rimmed wheel. We love alloy wheels, but they can feel a little squishy with lower spoke counts (I'll talk about this a lot more in following installments of this). Velocity coming out with an off-center ("O/C") version of their A23 really helps, as it makes the wheel's geometry just a whole lot better. Another thing we are doing is lacing the drive side with Race spokes. Race spokes are heavier duty versions of Lasers. They allow us to get just a bit more tension on the non-drive spokes (every little bit counts), and provide a bit of extra lateral stability (alas, at a small cost of decreased vertical compliance - don't worry there's still some of that). We're hardly the innovators here, as this is a trick that people have been using for a while and is still in use today (Cavendish's wheels happen to be built this way), it's just that this is the first wheel we've made that can really take advantage of this technique. The aerodynamic costs are nil, as the drive side rear spokes are well hidden from whatever chopped up wind they might be exposed to, but the Race spokes do add a catastrophic 16 grams (my tongue is in my cheek now) to the build weight. And yes, I did just very strongly imply that we are doing a 20/24 A23-based build with CX Rays and Race on the drive side and they are awesome. So there. If I keep eating like I did all weekend this will be a bad choice for me.
Following parts to follow.
5 comments
So apparently an awesomely strong and reliable alloy wheel, that also happens to come in under 1500g yet doesn't cost a fortune, isn't worth it in people's minds because it has too many spokes?Once you offer this low-count A23, will the FSWs as they exist today still also be available?
Awesome!We exchanged emails about this build a few weeks ago. I am most certainly interested.
Joe – Life is like a box of chocolates? The could well have been the original motive for butting. The butted section is a great strain relief, although my experience (one area in which I'm very happy to have a limited firsthand data set) is that spokes are more likely to snap at the head. Threads are rolled on, not cut in (thread 100 spokes and there will be basically no shaved material accumulated after) which probably still leaves a stress riser there. But if you size the spokes correctly then the loaded part of the threads become part of the unified spoke/nipple system, which is probably a profound stress riser but I've never seen a spoke break right at the hub side of a nipple. I've seen some nipples break at the head, which is general a sign of too short spoke length and often compounded by wheels forced to live life in an electrolytic bath of salt, grit, grime, and nastiness. In any case, whatever the original motivation was for butting spokes, it's a good thing it happened because they work awfully well for a lot of different reasons. Keep your wheels clean people! Thanks.
I've always heard that the Forrest Gump's mama explanation for butted spokes is moving the thinnest and thus most likely place to break from a sharp edged stress riser in the spoke threads to the smoothly profiled mid point of the spokes.
Chris – We're ready when you are.Mike – No alloy wheel options will have been harmed in the making of the new one – current FSWs will still be around, and will have some nice enhancements (like the O/C rear rim). For each and every wheel and for each and every rider there is an ideal spoke count. Some people are really really into the fashion of low spoke count wheels, and those are not the people we're responding to with this. But our tester for this new build is a lighter (but incredibly strong) rider who's using them for commuting. He's been treating them like rented mules for a couple of thousand miles and has pronounced that they work pretty much perfectly. But I'll discuss spoke count more in one of the installments of this series.