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Straight 14 or DB 14/15 Spokes, which is stronger?(19 posts)

Straight 14 or DB 14/15 Spokes, which is stronger?roaddog
Feb 16, 2003 6:28 PM
At 220 lbs I occasionally experience broken spokes using Ultegra hubs and Open Pro rims with 32 spokes on the rear. The LBS says use straight 14 guage spokes instead of double butted 14/15.
How could there be any difference in strength since the thickness at the critical point at the bend is the same?
In which failure mode?Kerry
Feb 16, 2003 6:46 PM
Since spokes nearly always fail at the head (bend), there is not much point in worrying about the thickness in the middle. In fact, butted spokes are better at distributing stress, so they are recommended for stronger wheels. Your LBS is speaking BS. The only reason to go with straight gauge spokes is to save money.
re: Straight 14 or DB 14/15 Spokes, which is stronger?bobobo
Feb 16, 2003 6:50 PM
14/15 spokes are stronger if they are DT because they are forged in the center section of the spoke unlike the straight gauge spokes. Lots of guys think a straight gauge spoke with a lower number is automatically stronger than a butted spoke with a slightly higher gauge number. Not true! DT themselves say that their 14/15 butted spokes are stronger than their straight gauge 14's for example.
What I have heard isAmbishawn
Feb 16, 2003 6:54 PM
The double butted spokes have more elasticity meaning they strech more and return to there normal length. I suppose this is subject for debate. I assume that DB spokes would make mabey an entire wheel stronger by reducing stress on the rim. I'd consider a 36 spoke rear wheel set up. The wheel will only weigh 16 to 18 grames more. Be sure you have a good wheel builder put it toghther as that may be part of the problem. Also not only is more of your weight on the rear wheel but the rear wheel has a mechanical disadvantage because of the dish requierd to accomdate the 9sd cassette. Not to mention the torque of hard out of the saddle sprinting and climbing. As far as breaking spokes is concerned I'd assume a straight gauge 14 might be a little stonger. 36 spokes and a good wheel builder is for sure stronger.
The true culprit is.......DaveLobster
Feb 17, 2003 6:17 AM
I have a friend who is a little lighter than you, and had similar problems with an identical wheelset. My suggestion, which you may find hard to believe, it that the HUBS are the problem.

Ultegra hubs have 2.6mm spoke holes. This makes them easier to lace in a production environment. Dura-Ace and most pricy non-OEM hubs use a 2.4mm hole. Since 14 gauge spokes are 2mm at the bend (same for straight gauge or butted), this give the spokes room to move about. On every revolution of the wheel, the spokes move back and forth in the hole, and work harden themselves. Finally, you hit a bump, and the spoke breaks at the bend. This is accelerated on a poorly built low-tension wheel.

The solution is amazingly simple - have a custom builder rebuild the wheel with tiny copper spoke head washers (and proper tension).

Check Gerd Schraner's book "The Art of Wheelbuilding" if you think I am full of it. -DaveW
The true culprit is.......curlybike
Feb 17, 2003 8:38 AM
Since I started using the washers on all hubs that require them, the incidence of broken spokes has dropped to zero. For some reason it is hard to convince the owner of the wheel how important this is, especially since I do not charge extra to do it. The weight is nil. The final answer for me is to tell them, "no washers, go someplace else". I am the one that has to fix the wheel after the spokes break, so I want them to last. It also looks bad for me when it happens.
Washers?chipnseal
Feb 17, 2003 6:39 PM
Hey Curleybike,

Where do you buy the washers?

Thanks!
QBP or Ochsner n/mcurlybike
Feb 17, 2003 8:38 PM
A mechanical engineer adds his $.02 worth:Alexx
Feb 17, 2003 7:08 AM
The quick answer is that the stright gauge spokes are stronger in tensile strength. This is a no-brainer, but not always the same thing as asking "which spoke is more reliable?"
Most spokes fail at the heads, due to fatigue, not due to ductile failure. At this point, the spoke is experiencing bending forces. A DB spoke, which stretches more in the center, will reduce the amount of bending forces, and therefore increase the life of this one critical part of the spoke.
so, the answer to your question is twofold: A wheel with straight spokes will be stonger right out of the box. A wheel made with DB spokes will probably last longer.
And another thingEric_H
Feb 17, 2003 9:13 AM
Since most rear spoke failures are fatigue related, on the non-drive side, it makes sense to use a lighter gauge spoke like the DT Revolution on this side. The increased elasticity of the thinner spoke will spread the load across more spokes, as eacg spoke passes through the contact patch of the wheel and is unloaded. Plus, the relative tension in the thinner DB spokes is higher than that of a straight gauge spoke.

I had a wheelset built with DT 14/15/14 all-round and I had broken spokes on the non-drive side. I rebuilt the non-drive side with DT Revolutions 14/17/14 and I have had no problems. I plan to use Revolutions on any future wheel builds, on the non-drive side. I think they are too weak torsionally to use on the drive side and the spoke wind-up would be very difficult to deal with.
Not in my experienceAlexx
Feb 17, 2003 1:13 PM
Most rear wheel spoke failures are on the drive side! If you have problems with non-drive-side failures, then you should try spoking it semi-radially. This cuts down on non-drive failures enormously.
The failure mode: always at the bend thru the hub flangeroaddog
Feb 17, 2003 7:35 PM
The drive side spokes were breaking about every 1000 miles.
But then a non-drive went at 500 miles. The lacing is 3 cross both sides which I understand is strongest (except for 4X which I've never seen). I guess I'll look for 36 hole rims and stay with 14/15 DB. Thanks to all.
The failure mode: always at the bend thru the hub flangecurlybike
Feb 17, 2003 8:45 PM
This rate of failure is generally due to a wheel that is to lightly tensioned. Since you need to pay for a rebuild anyway you should opt for a 36 hole with a higher profile rim, built by a competent builder that will put enough tension on the spokes. You might consider the Velocity Aerohead OC which has an asymetric drilling to reduce effective dish. This allows less differential in spoke tension.
The failure mode: always at the bend thru the hub flangecurlybike
Feb 17, 2003 8:50 PM
Also the spoke holes in an Ultegra hub are 2.6 mm which is too big for standard spokes and they will break sooner. You can either build the wheel with DT Alpine 3 spokes which are 2.3 mm at the elbow or use the little brass washers that DT sells for just such a situation.
try mixed spoking!Alexx
Feb 18, 2003 7:01 AM
One of the strongest wheels I own is my touring bike wheel, 36 spokes, 4x drive, 3x non-drive, DB spokes all around. This wheel is an old 6-speed, but hasn't had any troubles at all.
For a more heavily dished wheel, try mixed spoking-like a 3x/1x or 3x/2x combo (for 36 spoke wheels), or even a 3x/radial for 32 or fewer spokes. This will allow greater stress on the non-drive spokes. This should solve the fatigue problems associated with your wheel, because this way the non-drive spokes won't go slack as easily. As a result, fatigue won't happen as quickly, if at all.
won't a stronger rim help?DougSloan
Feb 18, 2003 8:41 AM
If a rim is less forgiving vertically, won't it prevent spokes from de-tensioning and fatiguing as much? Maybe a CXP33 or something even deeper would help.

Doug
Stronger rim allows higher spoke tensionKerry
Feb 18, 2003 4:40 PM
Higher spoke tension will largely eliminate fatigue induced spoke breakage (at the head). You're right that even with equal spoke tension a stiffer rim will reduce spoke breakage because it effectively spreads the stress over more spokes. However, you'll get a much larger effect by increasing spoke tension. This is true for any rim, as there are few rims on the market that truly limit spoke tension (AC 350 perhaps?).
Stronger rim allows higher spoke tensionkoala
Feb 18, 2003 8:14 PM
Speaking of light rims, Rolf has a 1250 gram clincher wheel called the elan coming out that uses a 365 gram rim. With the paired spokes (and fewer of them) doesnt the tension have to be so high that this wheel has to be for lightweights only? The website does not directly answer the rider weight question but gives the many faceted it depends on a number of factors and ask your lbs.
probably high tension, but maybe compensatedDougSloan
Feb 19, 2003 2:01 PM
Higher tension isn't per se bad, is it? They may have larger, stronger alloy, improved attachments for the spokes, which could handle the higher tension.

Nonetheless, any gorilla out there should know better than to attempt to ride 1250 gram wheelsets.

Doug