Can we just dispatch with the Spinal Tap references already?
We're beginning to see the inevitable conversion to 11 speed hubs, with White Industries being first out of the gate. Fans of White Industries will immediately notice the revised hub shell spacing. Real notice-niks will also see the loop of masking tape around the (still as awesome as ever) titanium cassette body - in order to use 11 speed hubs with 10 (or fewer) gears, you'll need to use the spacer between your cassette and the hub. 
In order to accommodate the wider cassette of Shimano 11 speed, White (and I'd guess most others to follow) have more or less shifted the hub shell 2mm to the left along the axle. The profound thing that this does is to decrease the bracing angle of the drive side while increasing the non-drive side bracing angle. There's no two way about it, this creates a challenge for wheelbuilders. Because the non-drive side spokes, because of the wider angle, will pull the rim off center so much more than a drive side spoke for any given spoke tension, the trick is two fold; keep the drive side stable, and get enough non-drive side tension to keep the non-drive spokes in tension.
It's probably pretty easy to visualize that the steepr the angle of the spoke from the hub to the rim, the less side to side stability that spoke is going to naturally provide. Increasing tension doesn't do much for you (more on this in a bit), but there are a couple of things that you can do. One is to use a heavier gauge spoke. This is when the REAL wheel geeks will start talking about Young's Modulus and eyes the world over start to glaze and roll back in heads. Simply put, a steel bar is going to do a better job of stiffening a poor angle than a thin wire spoke - hopefully that's pretty easy to visualize. So you put a heavier gauge spoke on the drive side and that helps.
Another thing to do is to add more spokes - the "many hands make light work" theory at work. The pictured wheel is 32 spokes, and is built for an aggressive rider who isn't all that heavy. In this case, I stuck with Lasers (instead of going to heavier gauge Race spokes) because I think that the wheel is sort of kind of borderline overbuilt for him at 32 spokes. Race spokes would have added weight that I didn't necessarily think was beneficial.
My magical number for non-drive tension is somewhere around 50 for a 24 hole rear, and decreases to around 40 for a 32 spoke rear. That's just a tension that I think, and have had proven through a whole lot of wheels built, works. If the non-drive spokes aren't tight enough, they go slack when they are between the hub and the ground. If they go slack, they eventually break. This is why using light gauge butted spokes on the non-drive actually produces a more durable wheel - the lighter butted spokes bend in the middle, reducing cycle stress at the ends. Straight gauge spokes on the non-drive side are a terrible idea.
You need a lower tension on wheels with more spokes because there are more spokes "between the hub and the ground" at every given moment. The bottom of the wheel has more support because of more spokes, so each individual spoke is shouldering less of the load. The distance between spokes becomes relevant here, which is a big part of why deeper section rims need fewer spokes - the distance between spokes at the rim is so much less. Take an 85mm deep rim and put 28 spokes on it, it will be the functional equivalent of a box section rim with 40 or so spokes in this regard.
Non-drive side tension is purely a function of drive side tension. On a Chris King 10 speed R45 hub, I get about 55% of the drive side tension onto the non-drive side. So if I put 120 kpf on the drive side, I get about 66 kpf on the non-drive, which gives me a really structurally sound wheel. Put the same 120 kpf on a hub where you get 40% on the non-drive and you wind up with 48 kpf on the non-drive. Still above my mendoza line, but closer to it. Small variances in non-drive tension are impossible to avoid, which means that you're going to have some a bit higher and some a bit lower (the ability to minimize these differences is part of what makes a good wheel builder good). If the "some a bit lower" get too low, you can have durability problems.
Over time and with tire pressure, spoke tensions gradually relax a small amount, which decreases the margin that you get.
Some lightweight aluminum rims spec a max tension of 100 kpf. If you take the drive side to that max, and get 40% of the drive side tension into the non-drive side, then you have no margin for my 40 kpf tension requirement for a 32 spoke wheel, and you're not close to it for my 24 spoke preference.
We're way over the "eyes glaze over" word count so next time I will talk about how we (November) are a bit insulated from these issues, how we will likely deal more actively with them going forward, how Campy has dealt with this issue up to now and why that's a good solution for their wheels but impractical as an across the board solution, and some of the products we'd love to see in order to respond to these new issues.
6 comments
Speaking of which, my WI-FSW 23s arrived yesterday, complete with extra spacer and masking tape. They are beautiful and amazingly lightweight. Can't wait to give 'em a spin. Thanks again, guys.
Please elaborate on spokes supporting the bottom of the wheel. I thought the spokes above the hub did all the supporting (i.e., the hub it's supported from above rather than being pushed upward from below) and the other spokes were just hanging around hoping to not de-tension too much.
Steve – Those wheels should look awfully familiar. Enjoy them.Baron – Can I take a quick crack at explaining relativity instead? In all seriousness, the only functional thing that counts is the the spokes below the hub get looser and the spokes above get tighter. As the wheel builder, my job is to minimize that cycling.
It almost sounds as if Shimano 11-speed wheels will have a geometry similar to that used by Campy wheels for over a decade now. There's probably a lesson to be learned here.On my last wheel rebuild, which I had a very good LBS do for me, I decided to try Velocity Aerohead O/C rims. This is a "trick" advocated by other good wheelbuilders, so I thought I'd give it a try. So far, so good.I suggest that this rim would be great on the new 11-speed hubs (Campy or Shimano).I had to have my last rebuild done because, after about 15,000 miles, I was getting stress cracks around the spoke holes of the previous Mavic Open Pro rims. Approximately 2/3 of the holes had cracks. The wheel was starting to come out of true, but I hadn't broken any spokes yet. I'm sure that was next up, though.My new build is Phil Wood butted spokes on both sides, the Aerohead O/C, and Campy Record Ti hubs (that have a 12t small cog limit — and who cares, since a 50-12 is still a seriously large gear?); 32 holes. I have a Shimano bike too, but that will remain 10-speed as long as I can get that stuff. As soon as Shimano stops making 10-speed Ultegra levers, I'm probably in trouble.
Mike – I'd say 15000 miles out of a set of rims constitutes excellent durability. That's about 11,000,000 revolutions of the wheel, give or take. Part 2 will discuss some of the other stuff.