Tandem Cycling - Rear wheel lacing
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03-08-04, 12:30 PM
I would like to have an extra set of wheel built for the tandem. These wheels will not be used for touring, just for fast ride. What are the recommendations for rear wheel lacing? Is 4 cross really worthed or 3 is enough. Exotic pattern??? All input are welcome.
03-08-04, 02:18 PM
What's the total team weight?
How many spokes?
What type of rim?
High or Low flange hub?
All of the above would factor into a decision on what type of spoking pattern to use. In general, for a go-fast wheelset, a rear 36h wheelset laced 3 cross using double-butted spokes is more than adequate for most teams at or below a team weight around 325lbs. The key to ending up with a strong and reliable set of wheels is using high quality double butted spokes and the attention to detail of the wheel build, i.e., making sure the spoke heads seat securely in the hub and without binding, achieving proper spoke tension and stress-relieving the spokes.
03-08-04, 03:56 PM
Sorry for the missing info. It was too obvious to me. I always use double butted spoke and wheels are properly and evently tensionned. This is the basic for a long lasting wheel. I was more concern about the lacing 3 vs 4 cross. I think the number of cross is more related to transmitting rotationnal power from the hub to the rim than the actual rigidity of the wheel. Radial wheel are very rigid but are very poor to transmit power from the hub to the rim. Because tandem have more HP on the pedal than a single I had a tendency to believe that 4 cross was required. On the other end there are single rider with a lot of HP that ride on 18 or 24 spokes wheels. In my case, I am going to use 36H rims/hubs, 14/15/14 DT spokes, low flange Hub and our team weight is around 300 lbs (riders only). I am not decided yet about the rim but it is going to be a V rim.
03-08-04, 05:44 PM
Although I don’t have much personal experience with custom wheel building for bicycles, but I have built many wheels for off-road motorcycles. Most of the time custom wheels were built as the standard wheels came laced cross 3 and we changed to cross 4 with the same number of spokes. The additional spoke length of a cross 4 pattern allows the wheel to flex a great deal more (or also said to be more “springy”) and thereby is more durable in long endurance (Baja 1000 style) races. Cross 3 is much more rigid and allows a better transfer of power however, the more rigid wheel is more prone to failure in those types of conditions. I don’t think this addresses you post directly, but I though this might give you a bit of a different perspective on the effects of lacing patterns.
03-09-04, 07:36 AM
I think the number of cross is more related to transmitting rotationnal power from the hub to the rim than the actual rigidity of the wheel.
Let me back into my recommendation with some rules of thumb:
24h & 28h hubs = lace 2x
32h & 36h hubs = lace 3x
40h hubs = lace 3x or 4x
48h hubs = lace 4x or 5x
1. Low vs High Flange - You may find you need to use fewer crosses with a high-flange hub due to spoke head interference at the hub.
2. For go-fast wheels, fewer crosses are better as they make for a wheel that increases in tension in a linear fashion and is uniformly more resistant to lateral loading, i.e., they are a bit more stable under aggressive riding conditions.
3. For touring, more crosses are better since they will produce a more compliant (comfortable riding) wheel.
4. Stress relieving the spokes will yield a wheel that is far less likely to have spoke failures due to fatigue than a wheel that is only properly tensioned.
03-09-04, 08:07 AM
The 4 cross pattern (on a wheel with 36 or more spokes) will transmit torque more efficiently than 3 cross since the angle that the spokes make with the hub will be closer to tangential. The vector resulting from a three cross lacing pattern will not be quite as efficient, but it will be close enough on a 36 that I doubt if you will be able to tell the difference in wheel longevity, assuming you tension the spokes properly and, as Mark said, properly stress relieve the spokes and seat the heads on the hub. With either pattern, all the power will be transmitted from the hub to the rim. The difference is that with the 3 cross pattern, the hub will deflect rotationally (wind up) a miniscule amount before the full torque is transmitted. This amount is not likely to be detectable to any but the most sensitive instruments and I doubt that it would impact the lifespan of the hub. The 3 cross would be a tad lighter, of course.
On thing that I can only theorize about is the fact that as you approach true tangential spoking, that two adjacent spokes on the hub approach 180 degrees of angle with respect to each other. With the small amount of aluminum between adjacent holes, it seems like the localized stresses would be larger than if the spokes were angled out at a smaller angle. That situation would place reactionary stress in a direction where there is more non-perforated material to allow the localized stress concentrations to be lessened. I'm not sure if this will eventually manifest itself as a difference in fatigue failure between two identical hubs. The fact that hub failures are not a common mode of wheel failure (except in radial lacing situations) leads me to believe that the differences are too small to be of concern.
Of course you know that this does not apply to front wheels since the spokes transmit no torque. However, many hub manufacturers state that tangential lacing voids their warranties since the stress patterns from radial lacing can lead to premature fatigue failures of the hub. In my opinion, a two cross pattern is a good compromise for minimal weight penalty without sacrificing longevity when using these hubs. Some hubs are designed for radial lacing and of course, for them, this caveat doesn't apply.
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