Spoked Wheels Maintenance
About 45 years ago, manufacturers were making predictions about how much longer the spoked motorcycle wheel would be with us in the face of the advent of the alloy-cast wheel. I think it's fair to say that they all got it wrong... because spoked wheels are still here.Part of the argument against spoked wheels was that they're high maintenance compared to their alloy-cast wheel equivalent, but sometimes the fact that you can maintain the wheel and not simply throw it away because it's bent is a big advantage – which is why off-road and most adventure motorcycles have spoked wheels.
I've never laced a wheel up myself because I've always known at least one person that would do it for me. But, like wiring a motorcycle, once you've got your head round it, acquired a few tools, and sourced the stuff you need, it's less aggravation than you'd think, which is fairly obvious given that spoked wheels are mass-produced.
From a adventure bike building point of view, the advantage of spoked wheels is that you can lace the rime size to another rim size. Changing the rim size is, however, a little ambitious for a first attempt; the rim needs to be drilled to suit the hub, spoke lengths need to be worked out, and so on. Bearing that in mind, speak to your wheel builder before cutting the hub out of a wheel you want to modify so that they can make a note of the spoke pattern, whether or not the rim is centered on the hub, and anything else they need to know. Then you can paint, polish, or powdercoat your hub to your heart's desire before having it laced to a new rim.
Spoked wheels work because all the spokes are under tension. If you tried to prop a motorcycle up by putting a spoke underneath it, the spoke would just buckle because it's too thin to take a load in compression. But you probably could hang a respectably-sized motorcycle off the same spoke without snapping it, as long as you took some care about how you attached the ends because they work in tension.
So the spokes under the hub in the wheel don't support the weight of the motorcycle; rather, it's the spokes at the top that take the load. This load is trying to flatten the rim into an oval, but to do that, the 3 and 9 o'clock areas of the rim would have to move away from the hub, which puts the spokes at those positions in tension, and stops the rim from moving. The spokes at 6 o'clock aren't taking any weight and the nipple on the spoke would just pass through the hole in the rim if the rim tried to move towards the hub.
With a steel rim and spokes, then, there is a degree of 'spring' in the wheel, but hitting potholes and such like can pit a flat spot in the rim which leaves some spokes loose – thus when the loose spokes reach the top of the wheel, the hub is unsupported until it drops enough to take up the tension in the loose spokes. That over-stresses some of the spokes at 3 and 9 o'clock, which can cause them to stretch and the whole web of tensions will start to unravel.This is where the maintenance bit comes in. With the wheel off of the ground and free to spin, then the spokes should be under the same amount of tension, so the idea is that they should all make the same sound when tapped with a metal rod. That's tapped, not battered.
Not all of the spokes in a given wheel are going to be the same length, and spokes of a different length will make a different sound. Before plinking around the spokes, the rim should be checked to make sure it's running true. Holding the tip of the metal rod near the rim and spinning the wheel will quickly show if that's the case or not. A certain amount of out of true is usually permissible – check the service manual for a value.
A slightly loose spoke or two and no significant run out means it's probably okay to tweak the spoke or spokes up the same sort of value as the rest, but recheck shortly afterwards and make sure nothing further has happened. Excessive run out and a lot of loose spokes will usually mean either a rebuild or a replacement wheel.
When a nipple is tightened, then the end of the spoke will move towards the inner tube. If the wheel was specially built, the ends of the spokes will have been ground flush and any adjustment will make the spoke protrude, creating the risk of a tire puncture, so the tire should be removed and a check made.
The thread on a spoke is a rolled thread, formed with rollers under pressure, not cut with a die. With a cut thread, the cut is a stress raiser and offers somewhere for a crack to start; rolled threads reshape the grain of the metal rather than cutting away the excess and are much stronger for this sort of application. This means that cutting down a spoke and 're-tapping' the thread is a really bad idea.
The number of spokes in a wheel is normally a number that divides by four, and then divides into 360. Because you have half the spokes on the left side, and half the spokes on the right side, and then the spokes on each side are angled to take either the braking or the driving loads, this gives four groups of spokes, which may be identical, or may all be different from each other. The spoke's diameter (or gauge) length, and the angle of the head on the fixed end varies, as does the way the head is formed. The number of spokes in each set will normally be the same and divide nicely into 360 because no one really want to be drilling holes a weird number of degrees apart.
