I had always wondered why rims with off-set spoke holes where considered stronger. It seems to me like the offset spoke holes would decrease the angle of the spoke making the wheel not as stable laterally.
I always thought that if the spoke holes were angled the right way it would make sense to cross the spokes, this would not work well on a deep v style rim but should be easy enough on a flat wide rim like the Nimbus DJ.
Looks like Fly Bikes has the same idea as me and actually made a rim designed for crossed spokes. Why did this not happen sooner? Is it just that it is harder to build a rim this way and people were used to the same old way of building wheels?
The hub actually hangs by the spokes from the rim and the weakest point on the spoke is the bend at the flange. By crossing over you increase the angle and lengthen the spoke weakening the wheel (if only slightly)
The hub doesn’t hang from the upper spokes–see Jobst Brandt’s engineering studies in The Bicycle Wheel.
But, mtnjeffe is right that the problem is the angle of the spoke elbow at the hub; the reason big rims often have offset eyelets is that any angle at all can put too much pressure on the spoke elbow, causing it to fail over time. You’re right that a spoke with a greater angle would create a wheel with greater lateral stability, and thus there would be less chance to fail catastrophically, but it would make spoke failures much more common.
so it seems to me that cross lacing and having flanges angled in would be the best combo. I have noticed that the flanges on some of my unicycles would angle in after a decent amount of use, I sort of wonder why they don’t make them with the flanges angled to start with.
This brings up something that we were discussing in another thread… I think that it’s about time that someone manufactures a hub with angled flanges. The manufacturing process shouldn’t be that difficult. If a uni hub had appropriately angled flanges, the pull on the spokes would be much more direct allowing the hub and spokes to be much stronger. Different rims and wheel sizes would have different ideal angles, however one hub could be manufactured with an angle that worked fairly well with most wheels. Trials wheelsets should have a hub with a much more angled flange because of the small rim diameter and the harder spoke angle (that hub could possibly work as an option for cross-lacing on bigger wheels). Just throwing out some thoughts, maybe I’m overlooking something, but it seems like a great idea to me.
I guess none of you have ever tried to lace a wheel with a hub that has bent flanges. You have to bend your spokes loads just to thread them through the holes in the hub. Because the flanges point inwards, the spoke holes also point inwards so that when you thread the spokes through they foul with the other flange and have to be bent to avoid it.
It was a UDC CroMo hub that I was building into a second wheel. The flanges were already mostly bent in on the correct angle from being built into another wheel. You have to bend the spokes anyway, I just bent them a bit more and went to the side instead of going directly away from the center.
I can’t find the site, but a company called SYM made a flatland bmx hub which came with spokes that will only fit that hub. The flanges on the hub were designed so that the spokes went into the outer edge of the hub flange rather than in through the side of the flange. The spokes had nipples at each end, and had no elbow, the spoke nipples were to sit in the rim, and in the hub. Perhaps not drawn the best picture, but as I cant find the site it’ll have to do for now, lol.
I have a set of old Spinergy Spox wheels that used a similar system to what Fraggle mentions by SYM, where the adjustments were made for truing at the hub end, rather than the rim end of things. It’s not exactly like the image below, but similar.
Your flanges couldnt have been as bent as mine then (mine were so bent that the flanges were begining to tear off of the axle). I had to bend mine a lot, far more than you do laceing. It scratched quite a bit of paint off the spokes and left them realy bent up.
Angling the flanges in may work on a big wheel but not on a 19"
I didn’t think that they were front only but that is besides the point. I wasn’t so much interested in this particular rim as the concept of cross lacing.
And Mark, why would you re-use a hub that was falling apart? It does sound like it was more bent than mine. My flanges were fairly uniformly about 3mm in from where they were when they were strait.
I have also built up a road bike wheel with (factory) angled flanges no problem.
I haven’t used black spokes so never worried about scratching the paint, might make a difference too.
So… with say a new KH hub cross lacing to a 20" rim would probably warp the crap out of the flanges, or if we had something like an old school Onza hub the flanges would be fine but the outer spokes may have too much stress at the bends.
But if we had a hub with the proper flange angle we could have a stronger wheel.
As for the cross lacing, it does increase the durability very much.
Think of this;
When a wheel takes a hard impact to the ground, the tire first absorbs the pressure, then the rim, then from the rim directly to the spokes. The spokes being centered bend slightly coming from the hub, giving a weak point in which the spoke can bend. The offset spoked holed rims allow the spokes to be completely straight, with no bend or bow at the slightest, giving much more increased spoke, and rim strength.
In other words, the pressure on impact is more evened out.
Firstly, if we’re gong to have technical discussions please look up the difference between force and pressure.
Seconodly, why would a slightly bent tension member be weaker than a straight one? Wouldn’t a spoke that was normally laced, and thus closer in its direction to radial than the cross-laced one have a smaller component of force along its length when loaded radially than one that was at a greater angle to the radial? Doesn’t this suggest the straight laced wheel would be stronger? Obviously the cross-laced would be stronger for side loading, mathematics of course decreeeing that for loading in an axial direction the more angled spoke now has a smaller component of the force running down it the that straight laced spoke. It is effectively the same as increasing the hub flange spacing, which as is well known from cokering creates a wheel which warps less under load.
Having said that, perhaps this would be an ideal solution for those colkeurs who would enjoy the benefits of a wide flange hub, but prefer the narrow hubs for Q-factor etc. This idea, in terms of wheel strength, effectively gives you a wider hub.