# Trailing Spokes - heads In or Out ?



## tom_h (May 6, 2008)

LBS is assembling a PowerTap Elite-Plus hub (Campy) and alloy rim for me. We went with 28 Sapim Cxray spokes and 2X lacing ... I weigh 165 lbs so 28 was an intentional, slight over-design.

I did not state a preference for trailing spoke, heads In or Out on the wheel -- any strong reason to favor one or the other ?

One argument for head out (elbow inside) is:

http://www.sheldonbrown.com/wheelbuild.html#side
" ... _Under drive torque, especially in low gear, the trailing spokes straighten out and the leading spokes bend even more. If the wheel is laced with the trailing spokes on the outside of the flange, the crossing gets pulled outward toward the derailer cage, and in some cases will actually hit against the derailer only under load._ ..."

ie, he's saying trailing spokes should be heads out & elbow inside.

But a paragraph later Sheldon writes:
" .._.__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..._ "

Other RBR threads have indicated Campy builds will have tighter clearance to Rear Der, so the outward flexing on trailing spoke could be a concern, favoring heads out.

However, on Powertap hubs the drive torque is actually transmitted to the left side (opposite cogs), so maybe it's _not_ an issue!

To further confound, Powertap hubs have relatively narrow flange spacing, so trailing spoke head in & elbow out would effectively widen the flange spacing, and reduce lateral wheel flexing.

No doubt the overall workmanship trumps small details like this, but what do you wheelbuilders out there think ?


----------



## Mike T. (Feb 3, 2004)

This is a can of worms that gets debated about once monthly. I go with the Sheldon approach too, for his reason and for one other - the trailing, or pulling spokes, which see the most tension and strain (from acceleration) are on the inside of the flange so if the chain ever derails over the top of the cassette then the leading spokes (forward radiating; lesser strain) take the trauma.

It's true that it's not terribly important as wheels are built both ways and many of us have built wheels both ways. The wheels I got from Zen Cyclery recently were laced with the pullers' heads *in*. And Roland had his reasons, even if he is *wrong*.


----------



## sanrensho (Jan 2, 2003)

I just went through a ton of online research on this issue, after rebuilding an AC wheel that was laced with pull spokes heads in. (I kept the lacing.)

Summary: There are theoretical arguments for lacing pull spokes heads out, but many wheels have been built with pull spokes heads in, and in practice, it doesn't make a meaningful difference.

I would go default pull spokes heads out, but only for theoretical reasons and knowing that it may not make a practical difference.


----------



## Mike T. (Feb 3, 2004)

sanrensho said:


> There are theoretical arguments for lacing pull spokes heads out, but many wheels have been built with pull spokes heads in, and in practice, it doesn't make a meaningful difference.
> I would go default pull spokes heads out, but only for theoretical reasons and knowing that it may not make a practical difference.


Here's the reasoning that's good enough for me. This is the wheel off a mountain bike that I mechanic for a lady racer. I'm the only one who adjusts the rear derailer and before and after this spoke-gouging incident I can't push that derailer, with thumb on the lower knuckle (which exerts far more pressure than a cable) to make the chain derail over the top of the cassette. Of course in mountain bike races there's far more crashing & banging going on and sticks being flipped up, than on road wheels to make the chain derail over the top.

So you can see the resulting spoke trauma. I'll take this on non-pulling spokes over pulling spokes any day.


----------



## sanrensho (Jan 2, 2003)

Nice photo, Mike T.

I've never thrown a derailleur into the spokes in the last 10 years, much less on the road bike, but of course I know it can and does happen (especially in a crash).

In the case of the pictured wheel, though, isn't the end result the same? I assume that you replaced the chewed up spokes instead of leaving them as is. Do you feel that the spokes would have failed during the remainder of the race in which this happened, had they been pull spokes?


----------



## Mike T. (Feb 3, 2004)

sanrensho said:


> .
> In the case of the pictured wheel, though, isn't the end result the same? I assume that you replaced the chewed up spokes instead of leaving them as is. Do you feel that the spokes would have failed during the remainder of the race in which this happened, had they been pull spokes?


I've seen spokes like this many times and I've yet to see one break due to this trauma but that might not be true if it happened to a puller. I just don't know as I've never seen chawed pullers on my wheels. No I didn't replace them (for the above reason); I'll do it at the end of the season.


----------

