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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 09-21-05, 08:35 PM   #1
GetOutOfNJ
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Spoke tension?

I'm building my first wheel set (the back is done, the front is in the works) and I'm wondering what tension the spokes should be. When I true a wheel, I usually just flick them with my finger and listen to it, but I feel like I might as well learn to do something more pro. I have access to a spoke tension-o-meter, but what tension should it read? I'm using mavic ma3 rims and double-butted spokes in front, straight in back. I weigh 135 lbs.

Also, I was discussing this issue with my friend at the Bike Library-- Should fixed gear back wheels use heavier spokes than normal, or only straight spokes, for the extra strain? Should the spokes be more tense? Does a tense wheel mean a stronger wheel?

thanks.
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Old 09-22-05, 08:03 AM   #2
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The tensiometer will include a chart for converting the deflection readings to tension. If you don't know your spoke gauge, there should be a little measuring tool in there. For butted spokes, use the narrower width as that's the part of the spoke you'll be deflecting.

100 kgf is the general guideline, I've taken to building a little higher (110) lately even though Mavic has a reputation for spoke pull through. Look for between 10 and 20 percent variation from your average tension. So if you're shooting for 100 kgf, you want your tension to be between 80 and 120 or 90 and 110, depending on how exacting you are. In fact, if you really want to be pedantic about it, you need to measure all your spokes and take the average. So if you're talking 100 kgf +/- 20% but half your spokes read around 80 and the other half are coming in at 90, then you've got an average tension of 85 kgf, far below your target tension. You'll need to bring the whole wheel up. Park has a nice spreadsheet that will help you keep track of average tension and does some fun graphs with it.

There's no special requirement for spokes on a track wheel versus freewheel. Higher tension does translate into stronger wheels. Basically the guideline is to build with the highest tension that your rims can reliably handle without the nipples pulling through the rim surface.
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Old 09-22-05, 01:09 PM   #3
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Seconded, on all counts. Also, I would add that double-butted spokes are actually more resilient than straight ones, due to their increased springing effect.
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Old 09-22-05, 02:17 PM   #4
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I have a question about the comment "Should fixed gear back wheels use heavier spokes than normal, or only straight spokes, for the extra strain?"

I've always thought that a fixed gear or SS wheel was stronger due to being symetrical (sp?). Shouldn't this be enough to combat any additional issues of torque from the center of the wheel?
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Old 09-22-05, 02:22 PM   #5
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Quote:
Originally Posted by Cynikal
I've always thought that a fixed gear or SS wheel was stronger due to being symetrical (sp?). Shouldn't this be enough to combat any additional issues of torque from the center of the wheel?
Based on a complete lack of authority, I would tend to agree, if only because of the lack of dish and the presence of symmetrical tension.
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Old 09-22-05, 02:34 PM   #6
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The primary argument for going to double-butted from straight-gauge spokes is spoke fatigue. Now fatigue is something that develops, in a reasonably well built wheel, after 10-15 thousand miles or more. Who's ever going to ride a wheel on the track that much? On the track, excessive spoke crosses and double butted spokes both lend to lateral (sideways) flexibility that's comfortable on the road and prolongs the life of the spoke, but is largely irrelevant on the track. You really want not just the best torque transfer, but also the best lateral stiffness so you can attack a banking without being concerned about your wheel flexing and feeling unstable under you. For that reason, I've shifted to building all the track wheels for our team and for others with radial fronts and 3-cross rears -- no 4-cross rears, no crossed fronts -- and with 14-gauge straight gauge spokes (unless someone requests an aero spoke as an alternative).

For road fixie riding, it's a somewhat different ballgame. Compared to a typical road hub, you are far ahead in the game -- you don't have the extreme dishing on one side of the rear wheel and if you have a high-flange hub you have better support and attack angles on the spokes. A straight gauge spoke can last you for a long, long time. But a double-butted spoke will still last a bit longer (25000 miles instead of 20000?) and will feel more flexible and comfortable to ride. The harder you are on your wheels, the more double-butted spokes are appropriate on a road fixie.

Tension-wise, Mavic recommends 950 n-m for pretty much all of their rims. That's pretty low compared to what a good wheel build really needs (it barely is enough to pull all spokes into common tension) and many mechanics bump up to 1100 n-m or higher without problems. Mavic uses rim extrusions that are quite thin and aren't any thicker at the spoke hole; they depend on the ferrules to hold the spoke nipple in place, but the ferrule actually requires a bigger hole in the rim, and the whole thing develops a bit more of a tendency to pull through. Ferrules are not necessary except to deal with very thin-walled rim extrusions. That's why rims like Velocity's, various superb Araya tubular rims (like the R-40 and R-50) and so on do not have ferrules and actually outlast a Mavic. I'm not knocking Mavics -- they are great rims and I love to use them -- but it's just about design compromises. You save a little weight with a ferrule and give up reliability. Buy a heavier Mavic and the problem goes away. Anyway, if you're doing a Velocity Deep-V or Pro-Elite, you can easily do 1400-1450 n-m and not even blink; I've built them quite a bit tighter and never had a problem. You'll never break a spoke with excessive spoke tension -- the rim will fail first. The longitudinal tension on a spoke just isn't even close to what it takes to break it. Only fatigue will break a spoke, and tension too low can allow it to bend back and forth more, leading to workhardening and an earlier break.
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Old 09-22-05, 03:07 PM   #7
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dang. some knowledgeable folks here.. and i've got trouble just keeping my boys true!
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Old 09-22-05, 08:08 PM   #8
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yea there is some hard core knowlege here. I just tension mine up till they are tight by feel. I will squeeze a pair of spokes and if it is tight enough then it feels like if it were sharpened it would cut my hands. Not very scientific or engeenering like but works for me.
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Old 09-22-05, 08:43 PM   #9
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Suggested reading: The Art of Wheelbuilding by Gerd Schraner

The Bicycle Wheel by Jobst Brandt

Enjoy.
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Old 09-23-05, 06:42 AM   #10
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Quote:
Originally Posted by GetOutOfNJ
I'm building my first wheel set (the back is done, the front is in the works) and I'm wondering what tension the spokes should be. When I true a wheel, I usually just flick them with my finger and listen to it, but I feel like I might as well learn to do something more pro. I have access to a spoke tension-o-meter, but what tension should it read? I'm using mavic ma3 rims and double-butted spokes in front, straight in back. I weigh 135 lbs.

Also, I was discussing this issue with my friend at the Bike Library-- Should fixed gear back wheels use heavier spokes than normal, or only straight spokes, for the extra strain? Should the spokes be more tense? Does a tense wheel mean a stronger wheel?

thanks.
I've been following advice on tension from here all year. And I am happy with the results.

http://www.bikexprt.com/bicycle/tension.htm

Essentially the idea is that the tension of a spoke of certain length matches a musical pitch when optimally tensioned, so if you have a good ear and a tuning fork you can go a long way on but a little.


cheers


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Old 09-23-05, 07:54 AM   #11
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I highly reccommend the Schraner book for the novice wheelbuilder. Brandt is very technical.
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Old 09-23-05, 08:15 AM   #12
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Jobst has a rant on wheelbuilding by tone (versus simply matching tension in an existing wheel).

http://yarchive.net/bike/spoke_tone.html
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Old 09-23-05, 03:46 PM   #13
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Quote:
Originally Posted by bostontrevor
Jobst has a rant on wheelbuilding by tone (versus simply matching tension in an existing wheel).

http://yarchive.net/bike/spoke_tone.html
Jobst might be right.
I got the hint from Sheldon Brown's article: http://sheldonbrown.com/wheelbuild.html#tensioning
Apparently he used it before he had a guage.



cheers

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Old 09-23-05, 05:33 PM   #14
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Yup, Sheldon's a trustworthy guy and I know John and he's no dummy either. On the other hand, Jobst is...well...Jobst.

Who's right?

LET THE STEEL CAGE DECIDE! SUNDAY, SUNDAY, SUNDAY!!
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Old 09-23-05, 06:17 PM   #15
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i just finished a build using all the geeky gadgets i could get my hands on, (tensiometer and the park spreadsheet) and it was a blast (if you're into that sort of thing).

got those puppies up to about 130kgf and they seem to be pretty happy so far.

(i also found sheldon's method of stress-relieving to be more fun and less physically wearing than brandt's).
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Old 09-24-05, 03:14 PM   #16
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For those wheelbuilding geeks out there, check out this tensionometer:

http://fullspeedahead.com/fly.aspx?l...xid=49&pid=162
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