Bicycle Mechanics - Rebuilding a wheel on my commuter - Straight Gauge or Double Butted?

So in about a year and 1300 miles I've broken 2 rear drive side spokes on my Novara Randonee commuting to work. It's a Tiagra hub laced with 36 straight gauge spokes to a Mavic A319 hoop. I figure I should rebuild it, as I'm out of spare spokes now, and perhaps 2 broken spokes so soon points to a less-than-stellar build.

So I've got a stand, and am ordering a tensiometer. I'm looking to order the spokes, and find that my choices are straight 14ga, or 14/15/14 double butted.

I've read lost of threads extolling the virtues of DB spokes, will they really be stronger in my application? (Touring bike, 220# rider, carrying about 15# in bags on the rear rack)

Thanks in advance

DB wil absorb shock loading (hits on potholes) better.

Db

So if the smaller diameter middle section is more shock absorbent...would a straight 15 gauge spoke absorb even more shock...and be that much stronger? :p

I recall that somewhere on Sheldon's wheelbuilding page he said that butted spokes were stronger than straight guage, even though that seems counterintuitive.

EDIT:

I tracked it down.


Double-butted spokes do more than save weight. The thick ends make them as strong in the highly-stressed areas as straight-gauge spokes of the same thickness, but the thinner middle sections make the spokes effectively more elastic. This allows them to stretch (temporarily) more than thicker spokes.

As a result, when the wheel is subjected to sharp localized stresses, the most heavily stressed spokes can elongate enough to shift some of the stress to adjoining spokes. This is particularly desirable when the limiting factor is how much stress the rim can withstand without cracking around the spoke hole.

# Triple-butted spokes, such as the DT Alpine III, are the best choice when durability and reliability is the primary aim, as with tandems and bicycles for loaded touring. They share the advantages of single-butted and double-butted spokes. The DT Alpine III, for instance, is 2.34 mm (13 gauge) at the head, 1.8 mm (15 gauge) in the middle, and 2.0 mm (14 gauge) at the threaded end.

Single- and triple-butted spokes solve one of the great problems of wheel design: Since spokes use rolled, not cut threads, the outside diameter of the threads is larger than the base diameter of the spoke wire. Since the holes in the hub flanges must be large enough to fit the threads through, the holes, in turn are larger than the wire requires. This is undesirable, because a tight match between the spoke diameter at the elbow and the diameter of the flange hole is crucial to resisting fatigue-related breakage.

Since single- and triple-butted spokes are thicker at the head end than at the thread end, they may be used with hubs that have holes just large enough to pass the thick wire at the head end.

So in about a year and 1300 miles I've broken 2 rear drive side spokes on my Novara Randonee commuting to work. It's a Tiagra hub laced with 36 straight gauge spokes to a Mavic A319 hoop. I figure I should rebuild it, as I'm out of spare spokes now, and perhaps 2 broken spokes so soon points to a less-than-stellar build.

So I've got a stand, and am ordering a tensiometer. I'm looking to order the spokes, and find that my choices are straight 14ga, or 14/15/14 double butted.

I've read lost of threads extolling the virtues of DB spokes, will they really be stronger in my application? (Touring bike, 220# rider, carrying about 15# in bags on the rear rack)

Thanks in advance

I am now down to 200 lbs but, I was 240 for the last 5 years. I use DB spokes on my road and cross bikes. I ride the corregated dirt roads around Boulder, CO on my road bike and the same, as well as, single track on my cross bike. My road has 32H wheels and my cross has 36H with 14/15g spokes. I have more than 15K miles on the road wheels and haven't broken a single spoke. Cross bike 4K miles...the same no broken spokes. I switched because the single thickness spokes seemed to unwind themselves giving an unbalanced wheel. I build my own wheels and run the tension at the upper end of the rim specs (open pro). Everyone seems to have their own formula for building the best wheel. This works for me.
Good luck.

It sounds like you original wheel was way under tensioned. There is no way spokes of any type should fail in 1300 miles unless you are a dreadfully abusive rider.

As noted DB spokes are strong at the ends where the elbow and threads are the usual failure points and thinner and more elastic in the center where stresses are lower.

Double butted are definitely better.

Are you reusing the rim or replacing it?

Better mechanical properties aside, DB spokes lift a wheel from 'Classy', to . . .

'Ultra Classy'.


Regards,
J T

Wow - thanks for all the replies. It's great to hear experiences that are directly relevant. No - I don't think I'm hard on my stuff, I don't ride through unnecessary crap, and any bumps that we do hit (even rough pavement) I come off the saddle and try to lessen. In reply to the poster who asked - I do plan to reuse the rim and hub. I've never had any problems with either, and the rim hasn't needed trued - except after replacing a spoke:-( I guess one never knows how it'll look without any spokes until I delace it, which I won't do until the rest of the parts are inhand.

Sounds like it's pretty unanimous to try the DB spokes. I'll re-meausure this evening (now that I have a nifty park spoke gauge from REI) and place the order.

Thanks again

If the tensiometer shows that the spoke tension of the wheel is too low, the simplest solution might be to replace only the broken spoke and gradually increase the tension of the wheel. That might be sufficient. If another spoke breaks after that, total replacement of spokes would be called for.

The main difficulty with butted spokes is spoke windup, where the midsection of the spoke starts twisting in response to the turning of the nipple. The higher the spoke tension, the more pronounced the windup. It's fairly easy to compensate by developing a feel for how much to over-rotate, then back off; it's usually up to an eighth of a turn. Proper lubrication of spoke threads and nipple seats is crucial. Either straight gauge or butted should be strong enough if properly tensioned.

DB - I'm 200lbs, commute every day over crappy cracked asphalt and cobblestones. They cost a tick more, but if you're building from scratch - make it worth it.

Besides, DB spokes are almost the only bicycle part that is both lighter and stronger at the same time.

Most often it's the non-driveside rear spokes that break because they are the lowest tensioned spokes due to the asymetric flanges necessary to make room for the cassette or freewheel. Adding tension to the non-driveside spokes means that you must also add tension to the driveside spokes to keep the rim centered (dished).

Al