lifeinajug

I'm building some wheels for a friends tourng bike and need to use 18 296mm spokes and 18 294mm. Is it sound to mix butted and strait guage spokes if all sg are the 296 and the butted are 294. At first I thought no because the spokes would stress differently, but since its on a rear wheel each side would already have different stresses so now I'm on the fence. Can anyone clairify?

Thanks
travis

G piny parnas

i would use DBswiss all around--- straight guage for the front maybe..... the length does not matter to me-- the angle of the nips--- the length of the nips--- SS nips these matter to me
how you put it together.... if its a quick repair what you are doing is fine.....

TimJ

I can't imagine how it would make any difference. The tension is going to be so different on either side I don't see how a butted spoke being slightly more elastic would effect anything because, again, the tensions are so different to begin with.

WNG

Shouldn't be a problem.
The DB spokes will be more beneficial on the DS of the rear hub.
SG spokes: NDS will be stressed so little to begin with, that the resilience/springiness of DB isn't required.

wmodavis

Not sure what you mean by the number '18'. Likely it has something to do with spoke diameter. Spoke diameter is usually referred to by either guage such as 13, 14, 15, etc or directly in mm. I'm not aware of an 18 guage spoke and if there is one it would be way too thin for my taste - less then 1.5mm. If you were abbreviating 1.8mm by omitting the decimal point than that's a good size. Mixing would be OK but not sure why you'd want to. You must have some reason to suggest it. DB spokes are better all around than straight so unless you have some strong reason/preference otherwise put DB all around especially for touring since frequently that means carrying heavier loads. DB would be better also if rider is on the heavy side. In either case I wouldn't go any lighter than 15 guage (1.8mm). You didn't mention if the wheels go on bike with rim or disk brakes. Disk brakes put a much greater stress on the spokes.

G piny parnas

this is a point I would like to learn a bit more about( I am searching now)
does a disc brake put more "stress" on a wheel?
does a disc brake not put un-even stress on a wheel?

I am curious because I think I will attempt to build a front ss 700 and run a hydrolic line--
can somebody give me a quick reference maybe for technique or decent hub/rotor set up.thank you
many of you are very respectful and knowledgeable.......

Retro Grouch 

Building a wheel is a fair amount of work.

It doesn't sound to me like you have a lot of experience. If that's the case, my advice is to be sure that you're starting with a straight, round rim and the right spokes. Working with mismatched parts makes the job more difficult and reduces your chances of getting a good result.

carpediemracing 

18 I think refers to the number. 36 spoke, wheel, 18 of each size. Writing "eighteen" instead of putting the number may have clarified it but that's not important.

Some folks will argue that you should use straight spokes on the drive side, others will claim butted spokes are better. I regularly use different thickness spokes on either side of a rear wheel. Reynolds uses round spokes and brass nipples on the drive side of the DV46s I have, and aero spokes with alloy nipples on the non-drive side. The wheels work fine.

Either way, if you're building a wheel to get trashed (that's how I'd view a touring bike wheel), I'd build it the way you have it now. Then rebuild it when the rim gets flat spotted.

cdr

Al1943

I assumed that the OP means 18 spokes on the left and 18 spokes on the right for a 36 spoke wheel. It's common practice to use a larger diameter spoke on the driveside rear, but that would be the shorter spokes, the reverse of what the OP has proposed.

Nessism

It's good building practice to use lighter weight spokes on the non drive side since the tension is lower there. Using too thick a spoke on the NDS will result in the tension being very low on these spokes which can lead to breakage since the nipples can unscrew on their own.

wmodavis

I do not see how using thick spokes on the NDS can result in lower tension. The tension is determined by tightening the NDS spokes with the tension required to counteract the force on the DS spokes to properly dish the wheel. The force the DS spokes pull to the left must be equally opposed by the NDS spokes. Spoke diameter is not in the equation.

dabac

It's lack of resolution in everyday language, and it's actually two types of tension being discussed here. One is the kind that is exerted between spoke nipple and spoke bend, the other is the tension the spoke is experiencing as divided by cross section area of the spoke.
A thin spoke can pull equally hard at the hub/rim as a thick spoke, but the thicker spoke will see less tension by cross section area than the thinner spoke.
And this is important, as tension by scross section area determines how "springy" the spoke will be. A thinner NDS spoke will see higher tension by cross section area, remain "springier", have less opportunity to go slack and be less prone to break due to fatigue than a thicker spoke in the same position.

lifeinajug

sorry about the confusion with "18" I was meaning the number of spokes. I've built a fair amount of wheels and happen to have sone left over spokes, but have never mixed sg and db on a single wheel. I'm also typingon an ipodshich could cause some confusion.

Thank for the help
travis

wmodavis

I should have read more carefully. Now when I read the original post its hard to see why I so badly mistook what you said. My bad!

And tension is tension. Don't quite understand "the tension the spoke is experiencing as divided by cross section area ". Are you talking about something like pounds per square inch? Mechanical Engineering literature doesn't refer to tension per square inch, only tension. If I'm wrong please direct me to an authoritative source.
I believe it to be better to use double butted spokes on the rear DS because of the greater elasticity and the chance of a DB spoke loosening under loads is less.

dabac

Not really. Suppose you were to take a 2.0 mm spoke and a 1.8 mm spoke, hook them to the rafters and then hang 100 kgs of weights raided from your neighbor's home gym in each of them. Both would be under 100 kgs of tension, but the 1.8 mm would be more stressed because of its smaller cross section, the tension in the material would be higher than for the 2.0 mm spoke.

Exactly! (apart from that we're pulling instead of pushing...) English isn't my first language, it might be called strain, or load, rather than tension.


It's usually held to be the other way around, I'm afraid.
Bike wheels are pre-stressed structures, and the key to pre-stressed structures is that the working load/stress should be small compared to the stress already built into the system.
Say you're running 100 kgs on the DS and 70 kgs on the NDS, then you hit a really bad bump that momentarily compresses the rim enough to lose 35 kgs of tension. That's about 1/3 of the load for the DS but half the load for the NDS.
So you see that if there's one side of the wheel that needs help to keep the tension up it's the NDS.

But the place where you need the greater elasticity is on the NDS. By going to a thinner spoke on the NDS the greater elasticity will allow it to shorten more w/o going slack, thus avoiding/postponing fatigue/unscrewing issues.
Also, the lower tension there will put both spokes on a more similar "pounds per square inch"-value than if you were running same gauges on both sides. And with the same "PSI" both DS and NDS spokes have pretty much the same chance of contracting w/o going slack when the rim deforms.

If you were to draw a graph over wheel quality vs build configuration you'd probably find that it hasn't got a peak but more of a rather wide hump, and there simply aren't enough wheels breaking under known and repeatable conditions for a single winner to be easily crowned.
It can be fun to hunt for "the perfect wheel", but in reality the observable differences between "perfect" and "serviceable" are small indeed. And once you've found "good enough" there really isn't much point apart from the entertainment value to continue searching for "the best".

The bottom line is that for an average-looking rider doing average-looking riding on an average-looking bike the structural margins are so big that with a decent build quality pretty much anything goes.