Bicycle Mechanics - Double butted?

I have a spoke question for those of you that build wheels or know a good deal about them. I have built all my wheels with stright guage believing those spokes to be stronger the double guage. I have read a from DT Swiss and Wheel Smith that a 14/15g will be stronger then a stright 14g. There resoning is this, the 14/15g will have the same strengths where connected to the rim and hub yet the thinner middle portion will absorbs hits better allowing the spoke to some what flex relieving the pressure from the rim and hub. I can see the reasoning for this but my question is this, since I do alot of dh would it not be better to have stright guage spokes because it will offer a stiffer wheel that won't flex as much when cornering hard? It seems that 14/15g would flex more and cause your front tire to slide more. Any thoughts?
Slainte:beer:

Have you ever seen a spoke that has broken in the center? They always break at the bend near the head or once in a while at the stress point near the threads. Correct , even spoke tension is the key to good reliable wheels. Spoke tension is the determining factor as to how stiff or rigid your wheel is, the tighter the tension the stiffer the wheel. I've been riding heavily loaded touring bikes with DB spokes without trouble for years. As far as weight savings go, How much weight are you going to save going from 14 ga. spokes to 14/15 DB spokes? My guess is a couple of grams, If you go to the bathroom before you ride you will save more weight. I like using DB spokes, I think they are easier to work with and measure stension more accurately, I also think they build a better, cleaner looking wheel.

I have (had) a pair of cross country wheels built up with DT revolution spokes (15-17-15) - the front has held up fine for 2 years, but the rear spokes started snapping - in the middle - after about 6 months. I've since rebuilt it with straght gauge on the drive side and normal butted spokes on the non-drive. My Big Hit came with DB spokes, and I had nothing but problems - so when I rebuilt I went with straight gauge - no more problems. My thoughts: on the road I have never seen a spoke break in the middle, but if building a wheel for off road, specificly DH, error to the side of over building, I've seen plenty of DB spokes break and kink in the middle.

My guess is your spoke broblems have been related to poorly built OEM wheels, like you said, once you rebuilt them you have had no more problems. I agree there are extreme cases of off road abuse that can justify straight gage spokes. I ride DB spokes off road and have for years without trouble. Straight gage spokes can tollerate sticks and branches better than DB spokes, but other than object damage a properly built and tesioned wheel will do it for most riders.

Originally posted by mrfix
My guess is your spoke broblems have been related to poorly built OEM wheels, like you said, once you rebuilt them you have had no more problems. I agree there are extreme cases of off road abuse that can justify straight gage spokes. I ride DB spokes off road and have for years without trouble. Straight gage spokes can tollerate sticks and branches better than DB spokes, but other than object damage a properly built and tesioned wheel will do it for most riders.

I agree with the OEM wheel statement, but the wheels built with the revolution spokes were custom - Mavic 517 built with King hubs - built by the same person that rebuilt the rear. The guy that built it said he has had so many issues with the revolution spokes (because of the middle section being too thin) that he advises against anyone building a rear wheel with them.

For hard use, you could use a 13/14 butted spoke. This would be stronger in the middle, against twings and branches, but still distribute stress from the shoulder to the middle as butted spokes do.

It depends on the hub, but sometimes 13/14 is a tighter fit in the flange, leading to less wiggle room and less fatigue.

Seems to me he isnt wondering what would be stronger, but what would be stiffer in a DH scenario. I rarely see well built wheels suffer premature spoke breakage regardless of if they were built with straight guage or DB spokes. A decent tensiometer will allow even tension and a long lasting wheel.

Now about stiffness...Straight guage spokes will offer more side to side stiffness in a wheel. Obviously because they do flex less in the center. How much is a matter of opinion. I offer my own experiences though for you. I build my own wheels, have for more than 7 years now and have something like 100 or so to my credit. A few years back I built up a super light set of wheels for a cross country/epic bike. I used the 15/17 DB in the front and 14/15 in the back. My spare set of wheels utilized the same rims and hubs as the superlights, but also used straight guage spokes. Lace pattern was also the same, cross 2 in the front and cross three in the back. I weigh 200lbs and am super agressive and noticed a big difference between both sets of wheels. In the back I had a "vague" loose feeling when applying alot of torque going up hill, while in the front noticed that holding a precise line in technical sections at speed or in downhill sections was noticably more difficult. After some thought on the matter, I increased spoke tension in the wheels by 10 percent and some of the problems went away, although the light wheels were never as precise as the work horse wheels. In the end I decided that for every day riding I would always prefer a stiffer, if slightly heavier wheelset. For racing, or days I just really want to go fast, I would use the light wheel set .

That's just my personal experiences and you can read into it what you want, but were I you I would build the wheels a bit stiffer. A cross 3 pattern in front is the only waty to go for a DH bike or even for a double duty DH/freeride bike. For DH only I would put straight guage on. Alot will depend on your wieght, riding style and terrain where you ride. For a double duty bike you could get away with 14/15 DB if you had a higher tension and a cross three pattern.

Chuck

OK, it's time for a mechanical engineer to enter this discussion....

A straight-gauge spoke is stronger than a DB spoke, but is more likely to fatigue and break at the head (hub end). This is because the thinner section in the center is more elastic, and, therefore, because of greater stretch, the forces on the head bend are smaller, thereby reducing the likelyhood of fatigue failure.

To make a simple test, you could load a 14 gauge straight spoke and a 14/15 DB spoke with a progressively static load. The DB spoke would fail first, likely in the center, from tensile failure.

On the other hand, if you were to load them cyclically with a load a bit lower than the endurance limit for the material the spoke is made from (as expected on the straigh portion of the spoke), the DB spoke will last longer. The straight gauge spoke will suffer a fatigue failure, most likely at the bend of the head of the spoke.

Since it's a set of DH wheels, I think the longer fatigue life of top-quality double-butted spokes is an academic question. The wheels are likely to get rebuilt every 2 years or less anyway, right? I would go with the raw strength and rigidity of quality straight 14ga spokes in that scenario.

Maybe I'll add one more bit of my opinion... the spokes should make it well into the heads of the nipples to discourage the barrel of the nipple from breaking off of the head, particularly for a wheel that might get side impacts (such as wheelchair rugby) or get things caught in them (such as DH). I think good wheelbuilders will start over if they find that they're not getting good thread engagement, so that's probably not something to worry about... but you can always check the built wheel by looking at the heads of the nipples to make sure the spokes are long enough to make it to the vincinity of the bottom of the screwdriver slot.

Thanks for all the replies. Since I am Clydesdale and I end up rebuilding my wheels every couple of months I will opt for the stright guage. Every ones info is much appreciated. I have never broken a stright guage at either end, always in the middle from either a rock or large stick.
As I am writing this it is making me think, would not a set of 13/14 db spokes offer the same rigidity of a stright 14g?

Slainte :beer: