One of the mechanics at work told me that for a rear 29er wheel its best to build it asymmetric otherwise you might lose spoke tension. Followed most of the explanation but then got lost as I can build wheels slowly following instructions but get lost thinking about it, think the idea ips the spokes pull against each other and so won’t lose tension as easily?
any demon wheelbuilders out there explain it simply?

What does he mean by symetric/asymetric?

Singlespeed hubs allow for an almost symetrical wheel by having the flanges roughly equidistant from the center where as normal hubs the drive side flange is close to the center. This makes for a stronger/stiffer wheel, but it’s not like you see 10speed wheels exploding everywhere.

Asymetric rims are available, these are less commmon aftermarket and more usualy used in compelte wheels, these have the holes drilled to one side (the none drive side) so that the drive side spokes are at a greater angle. i.e. the spokes make more of a even triangle shape, and the rim sits to one side back over the drive side.

I’ve only ever built with normal hubs and normal rims with no issues. The non drive side spokes are usualy slacker than the drive side whilst building but I’ve never had issues with the spokes slackening or the rim going out of true in use, spending time releieveing any stresses in the spokes goes a long way to helping that.

thisisnotaspoon you are talking about ‘dish’ and offset of spoke holes.

Generally (as far as I understood it), you want your spokes orientated to oppose the forces at the hub, on a rear disc wheel that means that you build them asymetrically so as to oppose the driving forces on the drive side and the braking forces on the non-drive side.

Top section of this is pretty easy to understand. http://www.peterverdone.com/archive/bikewheels.htm

There is also a good explanation of this in the wheelbuilding section of the Zinn and the art of mountain biking book.

ctznsmith, I think that’s the rough jist of it, I think the longer spokes and bigger wheel exascerbate the problem as well.

Hmmmm, I’d have to have a wheel in front of me to figure that out. I always build my rear’s so that if the chain comes off the spokes push it back out (think that’ a tip from Sheldon’s wheelbuilding site) rather than drag it in towards the freehub and jam it. i.e. the oposite of what shimano says. The rest of the spokes go in which ever way turns out easier at the time, so I’m probably ‘wrong’ 50/50. Might considder it in the future, for front and NDS rear, but I’ve never had a problem. One set of spokes will straighten and the other bend under braking and the King advice implies they’re doing it to avoid the spoeks clipping the disk calliper, so if that’s not happening then I’d file it away under “nice to do’s” like getting the valve hole and hub logo’s lined up.

Although that page does include the following (IMO crap) advice……..

Alloy spoke nipples should always be used. A busted nipple is quick and easy to fix and the weight savings is extreme.

hahahaha skimmed past that advice re: alloy nipples! I agree total crap.

The only reason to do one or the other is for possible clearance reasons – I like the idea of spokes aligned to lift a derailed chain out, but I can’t see that working. If your spokes are loose enough that they move under pedalling or braking torque, they’re too loose.

It doesn’t matter, in other words.

It doesn’t matter, in other words.

Maybe, but then aren’t you ignoring the repeated stress (either tension or compression) that the spokes are undergoing when braking, pedalling which could then lead to spoke failure?

It probably doesn’t matter, however if you’re carrying a heavy load (rider and/or luggage) and you want a ‘belt and braces’ approach I’d do it as there is nothing to lose (as far I can see).

Although that page does include the following (IMO crap) advice……..

as well as using spokes as light as possible. “I’d rather replace the odd broken spoke rather than ride with heavier wheels”

I wouldn’t. I’ll take the grammes, thanks. all 37 of them

The only reason to do one or the other is for possible clearance reasons – I like the idea of spokes aligned to lift a derailed chain out, but I can’t see that working.

It does work, well it has on the few times I’ve dropped the chain down the back, not exctly a scientific test but the theroy’s there and it’s not jammed since I built it that way so I’m convinced.

If your spokes are loose enough that they move under pedalling or braking torque, they’re too loose.

Hooks Law, so you could put 1000N tension on the spoke, add another 1N and it would extend as much as it did the first 1N. But I struggle to see what differeence it makes other than making that side bow in/or out slighlty under braking. as long as the calliper isn’t so close that it catches the spokes, I suppose if they were asymetric it might cause the wheel to shift imperceptibly left/right or twist?

I’ll follow that advice in future, if ony because theres a small degree of sense in what they say and it makes little or no difference to the build process. Apart from the DS rear which I think laceing to not jam the chain is more usefull.

Maybe, but then aren’t you ignoring the repeated stress (either tension or compression) that the spokes are undergoing when braking, pedalling which could then lead to spoke failure?

I think we’re in the teritory of such marginal gains that you’d struggle to break a spoke and point to this as the cause.

I think the logic is that the outer spokes are the les stressed in the build so best to add the braking tension to them. With the exception of the rear drive side where they’ve assumed the pedaling forces are more important. Thus making the spoking asymetrical (i.e. the spokes on both flanges would be facing the same way rather than being a mirror image). Seeing as the hub is pretty stiff I’d ignore that and and do the opposite (take the driving forces through the NDS and the braking forces through the DS) to avoid the chain jamming.

Look at road wheels with radial spokes on one side at the rear, the only problem is different brands arge their’s are best for specing the radial on one side or the other!

I still think it’s a “nice to do” rather than “your wheels will explode if you don’t” point anyway.