Tandem Cycling - Single vs. double butted spokes
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I'm having a freind build up a set of wheels with 32h Deep V's. Chris King up front and a rear XT hub. This is what he has so this is what I'm getting. (and I can't beat the price)
My question is on the spokes. I've read on the forums that it's always double butted spokes for tandem wheels, but now I'm told that going with single butted instead of double butted results in a stronger nipple shoulder (which is where road spokes typically break if they don't break at the j-bend) He has built LOTS of wheels and knows all about even, high ension, etc.
Is this the single bike wheel builder stuff that TG speaks of?
Our team is 265, (stoker @ 100), we have nice roads and do TT's
Please help quickly!
06-28-07, 04:00 PM
My tandem wheels are built with double butted spokes and they hold up fine.
This is what Sheldon writes about spokes:
06-28-07, 04:10 PM
As far as I know there is no such thing as a single butted spoke so I am assuming you mean single gauge or unbutted. (Edit-just found out that there is such a thing, but they are quite rare.)
Spokes on a properly built wheel don't fail from overtension. They fail from fatigue from multiple cycles of loosing and gaining tension as the wheel spins. With insufficient tension or from road shocks, the spoke can actually momentarily loose all tension and the tension goes to zero. This is highly undesireable and leads to premature fatigue failure. Many wheels fail from spoke bed failure of the rim well before the first spoke breaks. You may have seen rims with cracks around the nipple holes.
The benefit of double butted spokes is that the thinner part of the spoke has a little more stretch than a thicker unbutted spoke. When the wheel hits a bump the rim wants to go slightly oval with the bottom deflecting up and the sides deflecting outward. The thinner, stretchier front/rear-facing spokes are more compliant and therefore have more give to adapt to this momentary event. A larger diameter spoke will not be as compliant therefore exerts more force on the rim and will cause the aluminum rim to fail quicker than the same wheel built with butted spokes.
Not that it is a big deal and you can get many thousands of miles with a wheel built either way. The difference in longevity is not huge and double butted spokes are a bit more costly. They are lighter and a tiny bit more aerodynamic but that has never been an influence for me, especially on a tandem.
The deep V is an excellent choice for a tandem rim. Its deep cross section makes it is exceptionally stiff and aerodynamic. For a team of your weight a 32 spoke wheel made with these rims and double butted spokes will last a long time.
06-28-07, 05:17 PM
On our Zona tandem we use Velocity Aerohead rims, with King hubs and double butted Revolution spokes; 32H front, 36H rear. We are a 250- lbs team. Currently have 15,000 miles on wheels, and no issues.
Straight guage or DB? Your decision/choice.
+1 on both the comments above.
The wheelbuilder could possibly mean triple butted spokes. Compared with a double butted spoke the hub end of the spoke is a bit larger diameter to get a perfect fit in the hub while still getting the thread through the spoke hole in the hub. The link to Sheldon Brown above explains in more detail.
As you are probably already aware, other than starting with roughly the right bits, the thing that makes the real difference to wheel's reliability is the pair of hands that put them together and the time they spend to do the job properly, so it's fine to go with what the chap has in stock if you have confidence in his abilities.
For time trialling though, I would be tempted by something more exotic for the front wheel. See some of the recent time trial posts for pictures. A Uni disc or similar for the back wheel would also work nicely.
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