Spoke length puzzle
 

I've been thinking of building up some wheels on a set of high-flange Normandy hubs. So I went to Edd, the ever-handy spoke length calculator and selected the Normandy high-flange front, then the Sun CR-18 27", 3x, 36H. The spoke lengths it computed were 295.4mm left, 295.1mm right.

:twitchy: The hub data shows it to be symmetric, as I would expect. I would expect the rim to be symmetric too. So why the .3mm difference???? :twitchy: :twitchy: :twitchy:

That doesn't sound right. Mistake in the data base? Just took a look. Too weird.

The Sun CR-18 27" is listed (on the EDD calculator) as having an offset spoke bed of 1mm... as far as I know that's incorrect, and that's where the difference lies.

Using Spocalc & Spokechart, I come up with 296+

You always round down anyhow so it matters not. 36 @ 295mm will do it.

On a double wall rim, I'd rather be 2MM long than 1MM short.

I built a pair of 27" CR-18's over the Winter and wish I'd ordered 1MM longer spokes than what the calculators showed.
Using the info provided (and Spocalc), I'd personally order 297's.

I suppose so, but it wouldn't be short. It's not guessing, it's simple math.

So I understand, and of course the .3mm is insignificant. But it shouldn't be there at all!

On the other hand, the last time I've bought spokes from my LBS the guy disappeared in the back to measure my hub, came out with a bunch of spokes, and they were a mm or two short. I suspect he forgot I'd said 32H, not 36H, or maybe he just screwed up. Anyway, the point is, those calculators and accompanying databases aren't always correct. I measured the Normandy hub and came up with slightly different values, not terribly different but enough to make me think I'd measured it wrong.

I'm thinkin' I should check spocalc or spokechart or both or all of the above. Or something.

I use a couple of the online calculators and I always measure my hubs and rims to make sure I like the values that are in the data bases. So far out of 30+ wheel builds I have only had to reorder spokes once because they were too short. And still don't know why. :P

Aaron :)

Parheps humon errer..?-)

I do, however, tend to question spoke length calculators. Sometimes they are bang on, other times, not so much. Again, I suggest, perhaps, human error on my part.

I don't expect spoke calculators to be bang on, but they are most of the time. The difficulty is in the rim measurements. Rims vary from one batch to another, and they're hard to measure, too. They may be a bit out of round before they're laced up, making measurement inaccurate.

I agree the rims can be the issue. I typically take at least 4 measurements, 8 if I am being anal and average them. I use the two spoke method for measuring rims. I have two spokes of a known length, they get put in opposite holes on the rim and measure the distance between them. Most rims I have done are usually +/- 2mm for ERD.

Aaron :)

Perhaps parsnips? Some would consider parsnips to be human error. :D

Personally, I use 294-295...

Fwiw, I used the Edd calculator for my 700c CR-18s and the spokes came out a few millimeters too long. I was able to build the wheel just fine but the spokes were sticking out the back side of the nipples(later confirmed by some friends also lacing up CR-18s).

I would double check the measurement. Aside from that, the Edd calculator database has been pretty good.

Jim, I believe the spoke lengths are correct as given, assuming your fork is bent just so.

I see. So the wheel won't work on a Colnago, is that what you're saying?

If it was simple, I wouldn't need Edd . . . . :D