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Old 04-08-06, 06:41 PM   #1
vw addict
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spoke strength differences.

Biggest difference between lacing up my new disc wheelset with 2.0/1.8 butted's instead of just 1.8 straight gauge? Will it make a big strength difference with the butted spokes, or just save some extra weight?
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Old 04-08-06, 07:36 PM   #2
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The butted spokes will be very slightly heavier than the straight gage, and will build a more durable wheel.

EDIT: This applies ONLY to the specific spokes (2.0-1.8mm butted vs. 1.8mm straight gage) in the OP.
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Old 04-08-06, 09:14 PM   #3
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They will be over 20% stronger than straight guage 1.8 mm spokes. They will be slightly lighter and the wheel will have slightly less lateral stiffnes than straight guage 2.0 mm, but not enough to notice.
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Old 04-08-06, 09:35 PM   #4
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Quote:
Originally Posted by vw addict
Biggest difference between lacing up my new disc wheelset with 2.0/1.8 butted's instead of just 1.8 straight gauge? Will it make a big strength difference with the butted spokes, or just save some extra weight?
Exactly what do you mean by "strength difference"?

When spokes break, 95% of the time it's at the elbow. The rest of the time it's right where they go into the nipple. I've never ever seen one break in the middle.

Butted spokes put a little more material where they break and leave it out of the center section where they don't break.
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Old 04-08-06, 10:29 PM   #5
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Again see: http://www.sheldonbrown.com/wheelbuild.html and scroll down till you see a section dealing with single butted, double butted, triple butted, and aero.

Then there's Jobst Brandt at: http://yarchive.net/bike/spokes.html There's more on this site about butted vs straight if you want to read it...I would.
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Old 04-08-06, 10:38 PM   #6
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Butted 2.0/1.8/2.0 spokes are stronger than straight-gauge 1.8mm spokes. And as Retro Grouch points out, they're stronger where it matters - at the elbow and the nipple.

What's interesting here is that these butted spokes actually make for a stronger wheel than straight-gauge 2.0mm spokes - because the center section flexes more, which means lower max forces at the nipple and elbow, and on the flange and the rim.
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Old 04-08-06, 10:59 PM   #7
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This is from Sheldon Brown at: http://www.sheldonbrown.com/gloss_sp...spoke_patterns

Spoke
One of the wires connecting the rim to the hub of a bicycle wheel. See my article on wheelbuilding.
A conventional spoke has a swaged head, like the head of a nail, to keep it from pulling throgh the flange of the hub. Immediately after the head the spoke takes a right-angle bend, also known as the "elbow" of the spoke. (See also straight spokes) The outer end of the spoke is threaded, and a special nut called a nipple fits through the rim and screws onto the spoke threads.

Traditionally, most bicycles have had 36 spokes in each wheel. British bicycles, for years, used to use 40 spokes in the rear, and 32 in the front. This was a better system for the consumer, because the strength of the wheels was in better proportion to the stresses on them. It makes things easier for the manufacturers, however, to use the same number of spokes front and rear. This results in a front wheel that is needlessly heavy, and/or a rear wheel that is not as strong as it should be.

In the last few years, 32 spoke wheels have become increasingly common. Manufacturers tout this as an advantage, because it saves a very small amount of weight (they don't mention that it is also cheaper!) For most cyclists, the reduced strength and repairability of 32 spoke rear wheels is a greater detriment than the very tiny improvement in performance they offer.


Then read this site for another opinion: http://yarchive.net/bike/spoke_count.html
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Old 04-09-06, 07:19 AM   #8
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Originally Posted by timcupery
Butted 2.0/1.8/2.0 spokes are stronger than straight-gauge 1.8mm spokes. And as Retro Grouch points out, they're stronger where it matters - at the elbow and the nipple.

What's interesting here is that these butted spokes actually make for a stronger wheel than straight-gauge 2.0mm spokes - because the center section flexes more, which means lower max forces at the nipple and elbow, and on the flange and the rim.
Replace "stronger" with "better able to resist fatigue failure" or simply "more durable", and we'll be in agreement. (see note at bottom for clarification)

Also, the max forces at the nipple, elbow, flange, and rim are not altered by changing the cross-section of the spokes. The maximum force that all those parts of the wheel see is brought about by the spoke tension when the wheel is built initially. The forces on all parts of the wheel (except for the structure or "meat" of the rim) actually decrease when that part of the wheel is loaded. So the spokes see the maximum tension (applied during building) for most of the wheel's revolution, and then the tension decreases when the spoke rotates around to the bottom of the wheel. It is this oscillation between maximum tension and less tension which causes spokes and nipples and sometimes the rim's spoke holes to fatigue and fail. The greater the difference between maximum and minimum tension, the faster the fatigue.

The effect of butted spokes is to keep the decrease in tension (when the spoke is unloaded at the bottom of the wheel) to a minimum. So just as a crude example, a straight-gage 2.0mm spoke might see tension varying between 100kgf and 50kgf, where a double-butted 2.0-1.8-2.0mm spoke might see tension varying between 100kgf and 80kgf. Since the tension in the double-butted spokes only changes by 20kgf every revolution of the wheel, as opposed to the straight-gage spoke whose change is 50kgf every revolution, the double-butted spoke will fatigue much slower and have a much longer service life.

note at bottom:
(A straight-gage 2.0mm spoke is actually stronger than a double-butted 2.0-1.8-2.0mm spoke. It is also more stiff. The tradeoff is that it has a shorter fatigue life when built into a wheel.)

EDIT: A wheel should be able to be built with less spoke tension but the same durability when using double-butted spokes. I just realized that may have been what timcupery was saying.
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Old 04-09-06, 08:53 AM   #9
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Incredible replies guys, thanks.
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Old 04-09-06, 09:04 AM   #10
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In the last few years, 32 spoke wheels have become increasingly common. Manufacturers tout this as an advantage, because it saves a very small amount of weight (they don't mention that it is also cheaper!) For most cyclists, the reduced strength and repairability of 32 spoke rear wheels is a greater detriment than the very tiny improvement in performance they offer.
I've got to take issue with Sheldon here. Modern wheels with 32 spokes are at least as durable and strong as previous wheels were with 36 or even 40 spokes. Current materials and production methods have improved so much that there is no the need for high spoke count wheels except for loaded touring or tandems. The 36/40 spoke British wheels Sheldon mentions were less durable than modern 32 spoke wheels.

Broken spokes, except for accidental damage, are now rare. I've gotten 30,000+ miles on several 32 spoke wheels and never broken a DT or Wheelsmith stainless steel spoke. My riding friends and family members have similar experience. That was not true with the older plated spokes even with 36 hole wheels.

As to repairability, 32 hole rims and hubs are now so common that finding anything else, particularly higher count, is difficult.
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Old 04-09-06, 10:11 AM   #11
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Juicemouse: good explanation of how a butted spoke can stretch a greater distance for a given decrease in tension than can a spoke with a fatter center.

I agree with your on the terminology of "more durable wheel" as opposed to the generic, easy-to-misinterpret term, "stronger." Thanks.


As for the number of spokes in a wheel, I'm in agreement that it makes sense for the rear to have more than the front.
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Old 04-09-06, 10:21 AM   #12
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Originally Posted by HillRider
Broken spokes, except for accidental damage, are now rare.

As to repairability, 32 hole rims and hubs are now so common that finding anything else, particularly higher count, is difficult.
I'd have to dispute the first statement, at least to a point. I've done tech support on some big rides and, after flat tires, broken spokes are still the #1 problem. It's true, however, that you don't see people carrying spares around with them like they did in the old days so I'd agree is't less common than it used to be.

As for 32 hole rims, my advice for anybody doing significant travel with anything else is to make sure that your front and rear are the same. I have a tandem buddy who saved a tour by relacing his 48 spoke front rim onto his rear hub and buying a 32 spoke front wheel to complete his trip.
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Old 04-09-06, 10:40 AM   #13
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Quote:
Originally Posted by Retro Grouch
I'd have to dispute the first statement, at least to a point. I've done tech support on some big rides and, after flat tires, broken spokes are still the #1 problem. It's true, however, that you don't see people carrying spares around with them like they did in the old days so I'd agree is't less common than it used to be.
I'd put some of the broken spoke incidents you reported in the "accidental damage" category caused by hitting an object in the road, like a rock or a pothole, pretty hard. The shock can be quite severe and I wouldn't be surprised if many of the broken spokes were accompanied by a damaged rim.

Also, how many of the broken spokes occurred on low line or even department store quality bikes? These typically don't use high quality spokes like DT or Wheelsmith. Big rides tend to draw a wide range of riders and an equally wide range of bike quality. I've ridden one RAGBRAI and 15 GOBA's and some of the bikes that show up are appalling.
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