spoke length
 

Hi all,

I'm about to build my first wheelset, so I am a total novice. I used spocalc to determine the lengths of spokes to purchase based on my rims and hubs.

Here is my question: if for instance, for a front wheel, spocalc says to use a 294 length spoke, but I only have available a 293 or a 295, which should I choose? And why?

I apologize in advance if this is a really dumb question...

I go w/ the 293. Becasue, it would be better to have 1mm of thread sticking out, and have a properly tensioned wheel, than to run out of threads before the wheel is brought under tension. Really though its only 1mm, you could probably get away with either.

Thanks for the reply! So does spocalc assume that the end of the spoke will be centered in the nipple at the correct spoke length?

not centered, even w/ the end. You want as many threads engaged as possible

So if I purchase spokes that are longer than spocalc indicates, the tip of the spoke could puncture the innertube?

If you're using a deep section rim, it's unlikely that the ends of the spoke will be a problem, especially if you use a decent rim tape such as Velox; what is more likely to be a problem is that the nipple will run out of threads before there's sufficient tension in the spoke. I would go with shorter rather than longer spokes.

- Wil

I guess this is what is confusing me; if I buy shorter spokes, aren't I going to run out of thread engagement sooner than if I have longer spokes?

Nope - the threaded length is usually around the same on all spokes; if you use a longer spoke, the nipple will be hard against the end of the thread and no amount of turning will increase the tension. You could of course cut extra threads in those spokes which needed it, but one of the reasons for the threaded length being the same on all the spokes is that it provides the builder with a good starting point when starting the truing/tensioning part of the wheelbuild.

- Wil

+1

I would like to extend the question regarding the precision needed.

From what I gather, it sounds like one millimeter in either direction should work.

Not necessarily, best to go 1 mm short. The problem is not what you do with the end of the spoke, the problem is running out of threads at high tension. Some double butted spokes, like Revolutions, actually stretch.

Al

You would think, but on my first build I went 1mm too long on DS rear and never quite got the spoke tension I needed. If you have to choose go short.

I have just been looking into this very thing. I picked up the parts to build a wheel from a reputable local builder/shop owner and he gave me spokes that, from Spocalc, were 2mm too long. He told me that this is how he does it all the time and it works fine. This made me do some checking of the wheels I had built previously - here's what I found:
In my somewhat limited experience, the perfect sized spoke will end up with the spoke end even with the bottom of the screwdriver slot in the nipple. This is true whether straight or butted. The stretch of a butted spoke is not a significant factor when determining spoke length. There is more variance in a set of the same sized spokes than there is between a tensioned straight or butted spoke. (2mm straight vs. 2.0-1.8-2.0)
1mm over length comes flush with the top of the nipple.
The nipple bottoms out on the threads when the spoke sticks through the nipple by about 2mm.
This means that a spoke that is ~3mm too long will bottom out.

Always use new spokes and nipples. Always use spoke prep or linseed oil. An old, dirty, or dry spoke or nipple can bind when building, making it impossible to achieve proper tension. Also, if the spokes are cut on an abused spoke cutting machine or by someone who doesn't know how to use it, the threads may be buggered and bind up while building.

Note that the threads on a spoke are rolled, not cut. This work-hardens the metal, which makes stronger threads. It also makes the threads stand proud of the original spoke thickness. If you could find a die to cut threads on a spoke, it would weaken the spoke and the threads would not be as deep, no good.

From all this, 1mm in either direction makes no real difference. I personally prefer to lean towards the longer spoke for more threads engaged. A little more than 1mm long is ok if it is a deep section rim with no danger of the spoke puncturing the tube. 2mm long is usually ok, but much longer than that and variances in spoke length and machining of the rim can cause spoke bottoming.

When determining spoke size, look at the actual length from your spoke calculator. Some of them will automatically round up so that a 281.2 shows as a 282. Then you go to the next size available up, 283, and you end up with a spoke that is nearly 2mm too long, which just may cause problems in the case of skinny, weight weenie spokes.

OK. This is helpful.

Wish me luck guys/gals.

-G

The DT Swiss calcualtor actually rounds down with Revolution spokes. 281.2 would become 280. I've had spokes bottom out that are the correct calculated length. I'm dealing with that on one wheel now. The hub, spokes, and rim are all DT so there was no chance of a calculation error.
Always round down.

I would agree. It's better to have slightly more tension on a short spoke, than have one bottom out with insufficient tension as the nipple runs out of thread. Shorter is better (despite what all those unsolicited ads would have you believe…)

- Wil