sondelux spoke lenght for 20" wheel. HELP!
 

I am having a hard time calculating the spoke length I will need for building my new Sondelux dynamo hub into my 20" Sun CR18 rim (ertro 406).

Any help would be greatly appreciated as i need to order the spokes from overseas!
Thank you!

what are the measurements for the hub and rim that you've gotten?

also, what is the spoke count?

spoke count is 36.
The measurements for the hub are 50mm flange to flange, 27mm from axle to holes. I know the well on the rim is 17.5mm, but I cant figure out the radius (short of dis-assembling the wheel and measuring it with a tape measure, but I am not ready to do that as i still need to ride the bike until the new spokes arrive!).

I can't remember the ERD for CR-18 20", but it's not 389mm, like on the website.

If I remember correctly, the ERD for a 406mm CR-18 was around 392mm.
but this is on my rim, so yours might be different as it's most likely a different batch.

found an online spreadsheet that states the ERD for the Sun CR18 406 rim is 395.
should I trust this? Oh, and spoke count is 32, not 36 as i mistakenly typed above.

CR-18 20" is typically 392 / 393....that's what the last two I've measured came out to.

Give me the Shimano part# for the hub - I'll calculate for you..

=8-)

uh, oh! I went with 395 and ordered 180mm spokes, per the formula than came with the hub that said: L = r2 - 17.5mm. I hope I didn't make a mistake, they should arrive tomorrow!

BTW: it is not a Shimano hub, it is a SONdeluxe from Nabendynamo.com

Okay...I'll go look up the hubs from that manu...and add to my database...brb.

=8-)

Assuming the spokes are the guage the hub holes are expecting I get:

184.86 or 185.00mm for a 36H 3X setup with SONdelux and CR-18 20"

R=392 (CR-18)
r=54 (SONdelux hole-to-hole diameter...)
c=25 (SONdelux flange offset...)
x=3 (crossings)

see http://www.mrrabbit.net/wheelsbyflemingapplications.php and download the spreadsheet to calculate yourself...

=8-)

188.00mm for 32 holes...

=8-)

Don't panic...2X 32 hole is 178.68mm...so you MIGHT get way with using 180.00mm for 2X if you ordered the spokes already...spokes will go to the top of the nipple for sure...with luck - no further.

=8-)

ai ai ai!
well, nothing to do but wait for the spokes to get here and see!
thanks for your help!