Emergency wheelbuilding problem - leading spokes too short? Pic.
 

Hey all,

I just started lacing up a Miche 36h rear track hub (fixed/fixed, no dish) to a 36h Mavic Open Pro. Gene Spicer from Spicer Cycles and myself both independently calculated that the spokes should be 288mm long for 3x lacing (I used spocalc, he used shop software).

So I've been following Sheldon's guide, and installed all of the trailing spokes on each side without a hitch - when I was done, the hub was nicely centered in the wheel, and even the dish seemed right (yes, the spokes were still pretty loose - I still have about half of the threads showing). I could even hold the hub in my hand at this point and spin the wheel straight.

However - as soon as I tried to lace the first of the leading spokes, they don't seem to reach anywhere near where they should go! If I lace the spoke to cross three other (trailing) spokes on the same side of the flange, the leading spoke is short by a good 2 or 3cm. It's not b/c some of the nipples aren't seated in the rim all of the way.

It does seem as though it would fit in a 2x pattern, and that would be a disappointing mistake, b/c I want this to be 3x. But I don't think both of us made the same calculation error (I just checked again).

I've read and re-read the instructions a million times, and they make perfect sense to me - I just don't see why the hell this is happening.

Advice is very appreciated.

http://i35.tinypic.com/120jdck.jpg

In this next image you can see that it is crossing three spokes, as Retro Grouch suggested:
http://i34.tinypic.com/30stw0m.jpg

Are you sure that you're counting the crosses right? On a 3 cross wheel the forst cross is at the hub flange.

The only way I got close to useful wheels (My wheels are still works in progress) is I got a copy of Jobst Brandt's book, 'The Bicycle Wheel' and between it, Sheldon's Essay, and Wheelbuilding Videos on You Tube I was able to figure it out. I also started with a front wheel to work out the basics.

Thanks, but again I've read a few how-to's and I understand the concepts, I've just never heard of this happening. (Note that I did not ask 'How do I learn how to build a wheel' - this is a specific problem.) Also, as I mentioned, this is a fixed/fixed rear hub with symmetric dish on both sides (no dish), therefore is no more difficult than a front wheel.

Now that I've had a chance to see the photos, it looks to me like your spokes are too short. Your trailing spokes look too perpendicular to the hub for a 3 cross wheel. I'm thinking they should be leaving at more of a tandent.

How did you determine the ERD?

I hope you're wrong. If I was holding the wheel for those pics, I could twist the hub more counterclockwise to make the spokes cross at more of a tangent.

Looks to me like the already laced spokes are off. If you take the three spokes that you're crossing, there are three holes between the 1st and second, and two between the second and third.
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Scratch that. The lighting was playing tricks on my eyes.

Looks like the spokes are too short for a 3-cross.

Did both you and the LBS make independent measurements and calculations? Or just independent calculations off of the same set of measurements?

Loosen the spokes more and give the hub a big damn twist.

And since it's a Mavic rim, did you notice in the notes on Spocalc next to the Mavic rims that the program uses conventional ERD which is = to Mavic's NSD + 3mm. So I hope you didn't use Mavic's numbers

That's not right. Leading/trailing should be symmetrical, and they very obviously are not.

http://www.terminalvelocity.demon.co...uild/4by2l.gif

svtmike: I'm not going to lie, the shop and myself both used the same set of measurements.

Bob: I did notice the notes in Spocalc next to the Mavic rims, however, I read many threads on the matter and not one person knew what that was about. Can you explain?

So yes, I ultimately did use Mavic's number. However, even if I calculate with the extra 3mm, I only get spokes that are 1.5mm longer, which rounded = 2mm. It doesn't look like that 2mm would give me extra length I need.

Or would it, since that 2mm would change the amount I could twist the hub, etc.?

Damnit.

I'm guessing here, but NippleSeatDiameter to me means the nipple/rim interface diameter measurement (the "bottom" of the head of the nipple). Unless I'm remembering wrong, ERD is measured to the "top" of the nipples. The assumed nipple head is 1.5mm in thickness.

I haven't done a wheel in ages, but...All the spokes are the same length, right? If so, the ones already laced should be the same distance from their spots on the rim as the one that is "too short" in the picture. I.e. if one is too short, all are too short - if you have the hub twisted the right amount and they are crossing in the appropriate pattern. No?

Yep, your spokes appear to be too short. The only thing I would suggest is to rethread each nipple only 1 turn and see if this gives you enough slack to twist the hub and get the cross spoke to reach. I kinda doubt it, but it's worth a try. Everything you've done so far looks right anyway.

Nope, you laced up the "leading" spokes first, not the "trailing" spokes. Sheldon calls them the ones on the inside of the hub-flange. I prefer to lace up all these heads-out spokes first because it's a lot easier to manipulate the heads-in leading spokes to do the crossing later. No messy bending and weaving needed.

Looks like spokes are too short as all the nipples on the laced-up spokes are fully seated. Try it again with 2x and I bet it'll be right on. Also helps to tighten each nipple only about 2-turns at first; just enough to hold, but will give you enough length to fully twist the hub. Makes it easier to get that 1st crossed spoke in.

You're a bit confused - those are in fact trailing spokes, not 'leading' spokes, as leading spokes face forward towards the direction of rotation (like my leading spoke that is too short).

However - you are right in saying that Sheldon generally laces the trailing spokes on the inside of the flange (opposite of my wheel), but this is a fixed-gear wheel, about which he says: "In the case of fixed-gear or coaster-brake wheels, it is better to lace the opposite way, because a derailed chain is more likely to get jammed by backpedaling in these cases."

He also says, "Note: This is not an important issue! There is a sizable minority of good wheelbuilders who prefer to go the other way around, and good wheels can be built either way." There is also this thread on BF with various opinions regarding this issue.

The more I look at it the more it looks like a 3X/2X mix-up. Try moving the heads-out spoke in the pic to the next vacant hole clockwise and see how it fits.

I might be able to make 2x work, but I recalculated the spoke lengths (3 cross) using an ERD of 605 (instead of 602) and a flange diameter of 59mm (instead of 60mm) and I end up with spokes that are 2 or 3mm longer than what I bought.


Do you think 2 or 3mm longer spokes would be enough to make these spokes reach?

Offhand, no. But it's a tough call to make based on your pic. If you look at your lower pic you can see how much you'd need to rotate the hub clockwise before the heads-out spoke head will be aligned with its corresponding heads-in spoke that's already in place.

I coubt it. It looks like you have already twisted the hub enough to almost seat the nipples and you have about 10 or 15 mm left (guessing). If I were you I would try a 2 cross pattern and see what happens. It is only a front wheel, after all.

dabac, thanks for the reply. Which spoke is the corresponding heads-in spoke, the one 180 degrees away on the same flange?

LarDasse - it's a rear wheel, on a fixed/fixed hub.

If you look at a cross-laced wheel you'll notice that (on each side) you'll have pairs of spokes that run almost parallell to each other. For a 3X there should be 6 holes at the hub between these paired parallell spokes, so simply count off 6 holes counter-clockwise to see which heads-in spoke your heads-out spoke in the pic should run "parallell" to.

For 2X you should have 4 empty holes between the spokes in the "parallell" pair.

I don't like using the term 'leading' or 'trailing" just because of this confusion. The real issue here is one of heads-in versus heads-out on the spokes. When you install the heads-in spoke first, it gets really difficult later when you install the heads-out spokes. You end up having to thread the spoke through already-crossed spokes on the opposite side and have to bend the spokes severely in order to thread them through the opposite site. It's better to install the heads-out spokes first, then do the heads-in ones later.

+1

You're trying to connect to the wrong spoke hole. In the upper picture, rotate the short spoke either 4 or 5 holes counterclockwise. (I think 5, but hard to see from the pic)

That would be a 2-cross. He's trying to do a 3-cross.