Spooky Spokes

I had a front wheel spoke break at the weekend, which turned out to be rather more dramatic than it should have been. It appears that the spoke snagged on one of the brake calipers (dual discs), bent, and then beat the crap out of one of the brake hoses and while the brake didn't actually fail there was a loss of some brake fluid. On another bike I lost numerous spokes in the rear wheel, which had a drum brake and such events were little more than a nuisance since there was nothing for the spoke to snag on. Searching the web I've found quite a few instances of broken spoke drama, mainly involving rear wheels with disc brakes: some where the brake lines were damaged and others where it appears the spoke was driven into the rim with obvious consequences for the integrity of the inner tube.

Stock Commando wheels with single disc brakes are probably safe, since on mine, at least, the spokes closest to the caliper are "swept back", as it where; so they would tend to be deflected by the caliper rather than snag on it.

I'm not familiar with the different lacing patterns of spoked wheels, but from the ones I've had chance to look at it seems that whereas on one side the outside spokes might be swept back, on the other side they are swept forward and hence prone to snagging and capable of further mischief.

Is this a known issue with spoked wheel/disc brakes? Does anyone familiar with wheel building know if wheels can be laced to minimize the risk of broken spokes snagginng?

One suggestion made to me is to tie pairs of spokes together with safety wire where they cross (almost touching), but I'd have to be desperate to go that route, I'd prefer a solution that didn't involve adding 10 or 20 finger-piercers.

Gary

I have laced up a few wheels, and I still dont grasp patterns. I have copied existing wheels.
I do know a thing or 1000 about safety wiring.
One thing we used to do to prevent finger piercing is to end the wrap with a rosette instead of a simple fold over. The tail of the wire is buried under the rosette.

I tried to take a picture of it but my phone camera was having a hard time focusing. But I think you can get the point.
It takes a little time to master, but once you do, you will not go back. Safetying 14 sets of fuel nozzles on the Pt-6's sucked, but being able to run a gloved hand over them and not getting snagged didn't.

I don't know if it is common but those disc side spokes are a hole lot more stressed than the other side due to the drastic offset.

Just having some rims laced at present for Bike # 2 project by well respected restorer of wire wheels , cars and bikes, he recommends CAD plated spokes , and as mentioned shorter straight spokes take a lot more stress in the front disc model C'do wheel due to the huge offset. His reasoning is that the CAD plated spokes have more give(flex) especially if racing a bike, stainless steel ones tend to harden with use and eventually become brittle.
Regards Mike

Brooking 850 said:

Just having some rims laced at present for Bike # 2 project by well respected restorer of wire wheels , cars and bikes, he recommends CAD plated spokes , and as mentioned shorter straight spokes take a lot more stress in the front disc model C'do wheel due to the huge offset. His reasoning is that the CAD plated spokes have more give(flex) especially if racing a bike, stainless steel ones tend to harden with use and eventually become brittle.
Regards Mike

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I'm not sure how much flex you get or want; on the bike I lost the spoke on this weekend everything is very tight. The insides of the fork sliders have been shaved to provide about 1/16" clearance over the discs and that spacing puts the inside edges of the calipers almost in contact with the spokes; in fact there are witness marks to show that contact occasionally does takes place. Nonetheless the spoke didn't fail due to contact with the caliper (at least not directly). It failed at the normal location where it bends to mate with the hub. There, I guess some flexing takes place every revolution and fatigue is the issue. I once had some Titanium spokes in a wheel with a mismatched hub and rim, they had to be lightly "sprung" into place. It was not a happy combination, those things were popping all the time.

Gary

Its old bicycle practice to wrap wire then soder it solid at the spoke cross points. I Will be doing that on Peel SS pokes, to not get spoke whipped. if her spokes got any tighter the spoke would twist or the nipple treads fail. Do ya have to re lace the Norton front to get space to replace?

ttp://www.avocet.com/wheelbook/wheelbook.gif
I have this wheelbuilding book, which explains that the ties around spokes
were originally to keep spokes on penny farthings from flopping around
when they break. The author thinks it really isnt necessary to do this on modern wheels.

Click to expand...

On my race bike I have a Brembo calliper which is very close to the spokes. I filed a couple of millimetres from the back of the calliper to give it clearance.

If the chief issue is fouling the brake line, perhaps a guard for the line is something to spend some time on.

After reading a bit on, mostly, bicycle related websites I figured that what I needed was a "mirrored" spoke pattern. All patterns are either "identical" or "mirrored".

You have an "identical" pattern when the wheel looks, well....., identical when viewed from either side. That means that if the outside spokes on the left hand side sweep back from rim to hub (relative to the sense of wheel rotation) then the outside spokes on the right side sweep forward. The pattern is identical , but wheel rotation reverses between clock-wise and anti-clockwise depending on which side you are looking at.

You have a mirrored pattern when the sweep angle of the spokes , relative to the sense of wheel rotation , is the same whether viewed from left or right.

The mirrored pattern seems to be rare on motorcycles, but I reckon it is the safest and best where dual discs are concerned, allowing the outside spokes on both sides to sweep back from rim to hub, so that if a break occurs at the normal location (the hub) the broken spoke will tend to be swept aside by the caliper rather than snag on it, become bent, and wreck havoc!

It probably doesnt help you much, but I have/was/am looking at twin discs and have a Harley hub. These are laced slightly differently with all of the spoke ends towards the outside of the hub, Im guessing this may have been to get a bit more clearance.

Another thing you could try is having a hard brake line to the top of the slider which can be tucked well out of the way easily.