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Let's Talk Triplets

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Old 06-14-17, 11:26 AM
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Self Evident
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Let's Talk Triplets

I was contemplating starting a new lube thread, but then I had a better idea:

Triplets!

You see, I built one a few weeks ago, so now I'm an expert, and would like to share my new-found knowledge with the all of humanity. But before getting into the meat of the matter, here's a summary for the tl;dr and ADHD crowds (like myself)...

The "cross" value for an 8:16 triplet, for the side with more spokes, and laced 3X, can be one of two values:

3.1667 or 2.8333,

depending on the base lace pattern, "Type 1" or "Type 2" (illustrated below).

You will also need to enter 32 for the number of spokes into your favorite spoke calculator. This is because the 16 spoke side is essentially 1/2 of a 32 spoke wheel, spoke length wise.

As for the "Type":

"Type 1" seems to be the more common, and basically looks like this:
Code:
 \ | /
  \|/
   *
  /|\
"Type 2" lacing looks a little like:
Code:
\  / | \  /
 \/  |  \/
 /\  |  /\
(Altho the middle three spokes (above the crosses) in a real wheel actually diverge slightly...)


Ok, that concludes the tl;dr portion of this program. If you didn't know that there are two triplet lacings, or just want to know more, read on...


To continue, note that the two lacing "types" are independent of spoke cross. That is, each type can (theoretically) be laced 2X, 3X, etc. But, each cross is adjusted the same amount for a given spoke count (8:16, 12:24, etc...). For the 16 spoke side of an 8:16, the actual cross adjustment value is (+/-) 1/6. For "Type 1", you add the adjustment; for "Type 2", you subtract it.
(1/6 ~= .1667)

Also, in case it's not obvious, the adjustment only applies to the 16 spoke side. The 8 spoke side is simply treated as a 16 spoke wheel, as far as spoke length calculations are concerned.

The formula for the cross adjustment amount is: (@R - @F/2) / @F

Where @R means angle between spoke holes at the Rim, and @F means the same at the hub Flange.

For an 8:16, that works out as: (15 - 22.5/2)/22.5, or 3.75/22.5, or 1/6, as indicated earlier.

The flange angles all assume normal drilling/evenly spaced holes at both rim & hub.

Ok, as the txt art above is a little lacking, here are a couple graphics giving a better view of the two types:

Type 1:


Type 2:




And The Math...
(The following graphics ignore flange-to-center width for simplicity, as it doesn't have any bearing at this point. Also, the "Radial NDS Spoke: is just for reference to show how the hub & rim align.)

Basic wheel:


Triplet Type 1:


Triplet Type 2:



Well, I guess that's it. I thought I had more to say. Oh, I was going to talk about my spoke calculator that does everything, but maybe I'll save that for it's own topic. For now, I mostly just wanted to document all this for the next time, years from now, when I do it again (build another wheel) and can't remember what or why what I did...
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Old 06-17-17, 02:57 PM
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It's a really cool idea -- haven't gotten around to building a triplet wheel yet, since my regular wheels have all been drama-free thus far. Have you seen this thread?

http://www.bikeforums.net/bicycle-me...el-lacing.html
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