Good catch and I get that. But why can't a rim mfr...lets take carbon for material...develop a lower modulus and thinner walled deep V rim that isn't uber stiff that may rival the flexibility of a lower (shorter) section rim. This would allow reduced spoke count per discussion above as wheel deflection would be closer to the ground and not as prevalent at the top of the wheel near the brake pads.

The knock on some carbon aero wheels made by Rob was...to control their displacement...they don't flex much...you need more spokes. So why not simply reduce section modulus of a deep carbon aero section rim so you can reduce spoke count? Seems like win win.

That makes sense. I guess it comes down to how much radial punishment is required. Lots of clydes riding aroung on 32H Open Pros...generally perceived as boomproof. Other thing is...ride quality. Seems to me a high spoke count rigid carbon deep V rim will have a severe ride. All said, this still may be acceptable depending on the priority of the rider...aero and durable/stiff.

Exactly.....and yet....

Look back at how we used to lace those old thin flexy rims. We used to overspoke the hell out of them. What makes the OP in 32 spoke a combo that almost everyone on forums or in shops recommends? Because the OP is a flimsy rim and once you get 32 or more spokes on it and they are big gauge spokes you end up with a soft riding, durable wheel. Soft riding comes from the rim, durable comes from the spoke count.

Aerodynamics is a punk though. You need the depth for aero. Well....depth, width and overall shape for aerodynamics. The carbon provides the ability to build deep sections at incredibly high stiffness and substantially lower weight than if we did it in aluminum. Less spokes = more aero. Thus you end up in the quandary we are currently in.

I have an old saying - I NEVER lost a single race because I had too many spokes. I have lost every single race I have ever been in because: 1. I didn't train enough. 2. I didn't want it as much as the next guy. 3. I lack any sort of talent needed to win.

YMMV

In general though I find that racers at all levels greatly appreciate how I build when compared to industry standards such as Zipp. Huge difference in stiffness.

Thank you. Sharing your philosophy is greatly appreciated. I have learned alot.

Carbon and AL are very different materials with different structural properties. If you made your carbon rims flimsy enough to give in this way you would open up a whole new book of durability issues.

Clearly the balance. Carbon has much higher yield and modulus compared to Al...and if deriving same force/deflection, by using lower modulus carbon and with reduced wall section...elongation to yield maybe unacceptable.

I think the author agrees with you. What he is saying that a flexy wheel caused by a flelxible rim will behave differently from a flexy wheel having a stiff rim but too few or too light spokes. He is saying if the rim is very stiff but if too few spokes are the problem the rim will tilt at the axis defined by the hub and cause brake rub. If the rim is not so stiff, you may not notice the flex even with too few spokes, because the flex will constitute a bend at wheel's mid point, no brake rub. The "upper" part of the wheel won't be much affected. Yep, more or heavier spokes will work to fix both problems. He is trying to show that stiffening the rim may not do so. So if you are weight conscious at all, once you go with a heavy duty rim you may be screwed as you will still need substantial spokes to prevent brake rub. If you favor high spoke count or heavy spokes, you may be well served to save a little weight in the rim. That will help with the brake rub and won't hurt much elsewhere. That is, as near as I can tell, the principal learning from the article.

Robert

Late last year I built some 58mm deep carbon tubulars for a local racer that I know -- 24h radial laced in front (DT Comp, heads in), 32h 2x rear with a powertap (DT Champ DS, DT Comp NDS). He had the rims and hubs and all I chose were the spokes. They are generic Chinese rims and I was unable to get a spoke tension spec from the manufacturer so I went with the Zipp standard (100 kgf) for spoke tension.

He describes them as feeling a bit "whippy". He's a big, powerful guy -- goes about 220 lbs and when he's on form has an FTP around 350W.

Based on what I garnered from the link and this thread, there's not much more I can do with the wheelset to make it stiffer for him. If I'd been able to spec the front wheel I think 32h would have been the order of the day. I was a little surprised by how much lateral stiffness was attributed to spoke gauge in the article, but I don't know if going to DT Champs all around would make them perceptibly better for him.

Rob, please explain how 2X would help. Doesn't the longer spoke make for a smaller bracing angle? Wouldn't the 2X setup be less stiff than the radial? Are you after something else here?

Robert

Yup. My issue was how he was choosing to explain it. Almost as though they were two different entities...when it's a system. The spokes themselves don't do anything for the stiffness....but the number and how they are laced can and does affect it. I just think that point wasn't as clear as it could have been.

In general I have almost always leaned towards a lighter rim that has a lot of stiffness and then backed it up with the appropriate (in my mind) spoke count. By contrast the industry of prebuilts has a different set of problems. They don't know what rider is going to ride them so they have to over build. Yet the 3 things that consumers care about at the retail level are: how much, how light, and does it look cool. As a result the vast majority of prebuilts have low spoke count for aerodynamics and looks as well as low weight. In order to preserve some system performance they have to put the strength of the system or durability and stiffness back into the rim. Another word for strength, durability and stiffness is....weight.

So - long story short you end up with a wheelset that has a lot of rim weight, is low weight overall meaning that it is actually underspoked and usually feels like a wet noodle when sprinting.

For the longest time when Zipp was using the alloy brake track in the 404 dimpled it was really easy to illustrate this. The rims weighed anywhere from 550-650g each. By contrast a Kinlin XR300 rim is about 465g. An ENVE 45mm carbon traditional clincher is about 430g. Yet Zipp 404 set would compete with other in terms of overall weight. They did this by having a low spoke count, lacings that would reduce weight but not be as durable (the whole radial DS or NDS thing is a bust. Sound theory but bunk in practice - go through the years and see how many times they have changed it from one to the other. They both break spokes) and hubs so light that they failed constantly due to poor stiffness and undersized bearings.

It's the price you pay for a stiff durable rim with alloy braking surface.

They didn't get into the full carbon clincher (firecrest) deal because they all of a sudden "discovered a new resin that is far superior" - rather they had to finally get into the full carbon clincher market because their mixed rims were just too heavy to continue to hold market share and they had pushed the hub and spoke structure too light to sustain. They are still playing catch-up to companies like ENVE. Near refusing still to go head to head with them in aero tests - the one place that Zipp is supposedly king.

Another good example would be Mavic. They use beefy rims that aren't necessarily light or deep/aero as the strength center on overall lighter builds. They could reduce rim weight and add more spokes and have a much better riding wheel. I prove it time and time again when I provide someone a similar weight build that they come back and rave about simply because the weight is at the hub and not the rim and there is an appropriate spoke count.

Oh, that old pick two thing again. I guess, because it is true. But really, isn't that an oversimplification that applies only to the ideologue. You know, gotta have the lightest, gotta have the cheapest... For more reasonable folks isn't there a lot of compromise that makes sense. In fact isn't that what you do for people, find the way to get all three, just not all three to an extreme degree? I like to believe that I can have it light, cheap, stiff and strong, just not lightest, cheapest, stiffest and strongest. The special combination that works for the customer is what custom wheels are all about, no?

Robert

Increasing the "x" increases, albeit slightly, the lateral stiffness of the system. Radial isn't really all that stiff. The bracing angle has little to no change - sure you get every other spoke on the opposite side of the flange but they still cross - making the average bracing angle roughly half the difference between heads in and heads out. In this case he'd be increasing his bracing angle.

Data shows the increase in stiffness with the higher "x" lacing, but that is still relatively small. Even on my high end builds I never build for a sprinter by using radial lacing in the front. Always 2X minimum. The feedback is as it should be as a result.

Exactly. It's knowing how to balance the needed factors that I find is my one of my main "value added" steps in my process. I also find it's really hard to teach.

Understood.

Thanks, Rob. This makes sense. Now I have a project.

I don't think adding crosses affects lateral stiffness much at all. What it does, I think, is add stiffness in the, I'll call it "transaxial" direction. Imagine planting the rim and torquing on the axle on an axis normal to the axle of the wheel. This is the kind of stress the wheel sees when it is turning... The axle is being torqued on an axis normal to the axle by the fork while the rim wants to roll straight. Crossed spoke patterns give the wheel stiffness in this direction and should give the wheel (we are talking about front wheels here) a better handling feeling in a corner. This, I think, comes at the expense of radial stiffness.

Whatever you call it, this is what I'm looking for.

I think that's what my friend wants too. I'm going to suggest relacing his front wheel 2x and see how he likes it. I don't think I can go 3x on a 24 spoke rim.

So few people understand this. My understanding is that:
while higher tension would seem to make a stiffer wheel, the difference in tension increase necessary to stretch a 100 kgf spoke vs. a 140 kgf spoke for 1mm is very small, if any. The purpose of adequate tension is to stretch the spoke enough to prevent detensioning and thus fatigue. Which is the reason that some builders' heavier straight gauge builds fail sooner than a double butted build, tension as you say being determined by the rim and heavier spokes stretch less at the same tension.

However, that last being the case, I don't understand why you don't think a heavier spoke will make a stiffer wheel, all other things being equal, since it will require more force to get a 1mm stretch than a thinner spoke. Is the difference negligible for common spoke gauges?

Good point and that may in fact account for the change in feeling of stiffness between say a DT comp vs a Sapim CX Ray build. In general though the main difference is in the 'primary gauge' - or the amount of material there to begin with. The end shape has an effect on the aerodynamics and the area moment of inertia of the spoke in deflection (something we are not looking to experience), but the rough cross sectional area and the resulting strain from the tension load applied are roughly the same throughout a family of spokes.

In your example - straight gauge spokes - larger area, resulting in a lower strain, lower stretch, and a higher probability of unloading - especially with a heavy rider in a low spoke count. Double butted - less material, lower area, higher strain, higher stretch/elongation, lower probability of unloading. Change that double butted into an "aero" shape. Same area, same strain, same elongation, etc.

The CX Ray is actually made out of a laser spoke though. So less material to begin with - lower cross sectional area, higher strain, higher elongation by a large factor. It was work hardened through the process they use to make it so it ends up with a very high strength and high fatigue life, but trades it off with a bit of brittleness.

Im struggling to see why higher x gets more stiffness.

Ive just looked at a 3D CAD drawing of my wheels using CK hub and RR440 rims (i know thats not what was mentioned earlier but you seem to be talking in general so it should still apply) I

For my wheels going from radial heads out, to 2x, the bracing width increases about 1.6mm per side at the centreline of where the spokes cross and spoke length increases approx 10mm (you need to buy new spokes)

In contrast, going with the approach mentioned earlier of relacing heads in, for my wheels, bracing width increases about 4mm and spoke length remains the same. Adding the benefit of not needing new spokes.

So on the face of it, to stiffen a wheel laced radial heads out, you would be better to rebuild heads in to increase stiffness than going 2x with new spokes.

What am i missing?

The only thing I can think of -- when the spokes are crossed, the deflection of the rim is countered by the netting of spokes rather than just the individuals at the point of deflection. So, for a given lateral force there are more spokes engaged in supporting the wheel laterally against it.

Do you have the ability to model the reactions to a lateral load with the CAD program?

Yes, I kind of agree as you say, on the face of it. You have to make sure your spoke hole drilling and flange design allow this. Some are designed only for radial heads out. If allowed, the crossed lacing does give some improvement despite the longer spokes because 1/2 the spokes are heads in. He says there is data showing the crossed lacing is stiffer. As I said in an earlier post, wheel statics and dynamics are so complex, it is hard not to miss something in a quick and dirty perusal.

Thats a good point about the drilling being compatible - not all hubs would allow it. I guess the other consideration would be the deflection of the flange itself which would be larger with radial and reduced with a cross lace. Not knowing the sectional area of my hub or the exact alloy properties I cant calculate how significant that would be but I would think the bracing angle is far more influential.

I earn a living using finite element analysis, Ive often thought that one day I'll answer some of these questions for myself but I never get around to doing it. Too much like work I guess.

Uh oh, every now and then I get in a mental quagmire where nothing seems to be as it should. I was trying to figure out why crossed spokes give higher stiffness as Rob says when EVERYONE KNOWS higher bracing angle (θ) means more stiffness. So I did the trig. First, as I understand it bracing angle is the angle of the spoke from the vertical at the flange to the rim. Lets say the length of the spoke is h (for hypotenuse). Suppose you want to shift the rim x mm to the right. Then x = Δh(sin θ). Or rearranging, Δh = x/sin θ. Assuming the only way for the rim to move is for the spoke to get longer, then all the force required must stretch the spoke, and the force F will be the change in length multiplied times the tensile modulus m. So F = mx/sin θ. The sine of the angle increases as the angle increases, so as the bracing angle increases, the force needed to stretch the spoke the required length to realize an x mm lateral shift DECREASES. Whoops. How can that be? First it explains why crossing could stiffen the wheel, but it is contrary to what EVERYONE KNOWS. All I can say is that other things are going on. At very low bracing angle there is probably more spoke bending and rotating in the spoke hole than stretching to accommodate a lateral force. Higher bracing angles may produce a more STABLE wheel but not a stiffer one. Think a 90 deg. angle; the only way lateral movement could occur is by spoke stretching. Now think a 0 deg. angle. There would be many more modes of movement besides spoke stretching. The wheel would be infinitely delicate even though in theory there would be no force large enough in the lateral direction to stretch the spoke along its length. Interesting, huh?