Alien Aurora - broken rear spoke

[jbond]

My much loved and much abused Alien Aurora has broken a rear spoke. These seem to be heavy duty BMX spokes and look like 194mm, stainless, possibly 13 gauge or even 12 gauge. My local bike shop can normally supply custom spokes but his thread cutter/roller doesn't go up to that diameter. Given that Alien has gone out of business, here's the questions. Does anyone know the actual gauge, and does anyone have any ideas on where to get a replacement?

[later]. Looks like 13g 2.3mm straight, 190mm, 5mm nipples. So I've ordered 6 from here.
http://www.tillercycles.co.uk/page2.html#Anchorleader13g
I'll let you know if that worked.

 

[Deleted member 4366]

If you find that more start breaking, get the wheel rebuilt with 14 gauge spokes.

 

[jbond]

It's always slightly puzzled me about this that lighter weight spokes are less likely to break.

 

[trex]

I don't think that there is much difference in probability of breaking spokes between 13 gauge and 14 gauge. Thicker spokes break when compressed or bent but work well in normal circumstance.

 

[Deleted member 4366]

They're more elastic. 14g is more than strong enough, even for very high torque motors. I'm not too sure why they ever used 13g spokes on electric bikes. It was probably just lazy thinking, the idea being that a motor is stronger than a person, so you need stronger spokes than the ones being used without motors. When they found 13g spokes breaking, some even changed to 12g spokes.

In engineering, some things don't follow layman's logic. I was told a story about a big press that someone built. It had a big heavy flywheel on it. The flywheel had an attachment fixed to it, which was basically a plate held on with four bolts. When they tested it, the flywheel cracked at one of the bolts before it got up to full speed. It was obvious that the bolts had something to do with it, so their thinking was that smaller bolts would have less effect on it, They changed the design to 8 smaller bolts to hold the plate on. It then broke at even less speed, so they tried 12 even smaller bolts, but it failed again at low speed. At that point they called in an expert from the local university, who fixed it straight away by using bolts double the size of the originals. Their thinking was that drilling big holes would weaken the flywheel, but actually, it made it stronger.

It's also a bit like your bicycle, where you turn the handlebars left to go right. That doesn't make sense to a lot of people either, but it's a fact nevertheless.

 

[trex]

I agree. I can't think of any no other reason than because they keep drilling the motor flanges for 13 gauge spokes.

 

[johnc46]

Hi. in what manner did the spoke break, was it the threaded portion, the elbow or did the little head pop off the end. I had a number of spokes (10) fail on my Aurora a few months after buying it and they were all caused by the head popping off, I reduced the elbow angle of the spokes so that the head sat more flush to the hub and used a spoke washer, since then no problems. So back to the question, I have a number of rear spokes with nipples brand new which I bought from Jim at Alien, if you need some please let me know.John

 

[trex]

I think the spokes are at risk when they are nearest to the ground. They are compressed. If they are loosened, they'll bow and pop their heads.

 

[mike killay]

I don't see how a spoke can get compressed to any significant degree.
After all, it is pushing against a hole and the only resistance is the inner tube.
I am also not sure why we have spokes with a head and bend.
We would be better off with a plain straight spoke threaded at both ends and ferrules at both ends to screw it into.

 

[trex]

I think this is how it happens. when spokes are loose, you can hear them rattle. Even without a couple of loose spokes, the rim can deform 2-3 millimetres where it passes close to the ground. One of the loosened nipples will eventually catch the inside of the spoke hole and cause the stuck spoke to bow and flex. Over a few miles, the same spoke will bow thousands of time and break.

 

[mike killay]

I always thought that loose spokes do not break, it is the tight ones either side taking extra strain.
BUT
Your explanation is persuasive.
Guess the only way to find out is number all the spokes and ride around with one deliberately loosened.

 

[jbond]

The 13g tiller spokes turned up and they're just right except it looks like the originals are 12g not 13g. I'm drawing a blank on finding another source. There are a couple of places in the USA that do Sapim 12g for BMX but only in short lengths.

johnc46 the head popped off. I've PMed you.

 

[Deleted member 4366]

It'll be OK to use a 13g one.

 

[Tabs]

Yip the 13g ones should be ok,I bust a spoke on my 250w rear hub and couldn't find the correct spokes to replace it, I managed to get a 13g one and it's been fine so far, I also got some spokes from tiller to keep as spares.

 

[jbond]

Well I fitted a 13g one. We'll see how it works out. Probably better than using the old one with the end turned over into a U.