David Snyder wrote:
There are performance differences attributable to flange size, but it's durability and building issues more than on-the-road performance that I'm referring to. Firstly, addressing the latter issue of wheel performance, smaller flanges build stiffer wheels. This I learned from Ric Hjertberg a few years back, while he was a consultant for Shimano. So, from a rim durability standpoint, the low flange hub wins, and the sprinter, too, may prefer wheels built on low flange hubs.
The added flex in a high-flange-hubbed wheel is caused by the flanges not being fully canted to match the spoke's bracing angle. Thus, tension in the spokes flexes the flanges local to each hole toward the centerline of the bicycle.
With added flexibility from the nipples inward, rims are subject to being more easily bent. The added flexibility does however lend a more even stress distribution among spokes, increasing the fatigue life of the spokes and also of the rim's nipple sockets.
I have yet to quantify any differences in wheel building or spoke replacement ease attributable to larg vs. small flanges, but I would intuitively give the nod here to larger flanges. I like big flange hubs anyway so I had to say that.
I doubt, no I'm 99.9% sure, that there are any quantifiable "cushioning" effects that larger or smaller flanges lend to "ride quality".
David,
Very interesting post. If Mr. Wheelsmith says it's so, it's probably so. The question this leads to is how significant is the effect of flange flexibility? While it makes sense on paper, is there any evidence that spoke and nipple socket fatigue life are enhanced? It's hard to imagine a hub flane felxing all that much without quickly failing, but then again, spoke tension might vary significanlty with small elastic movements in the flange (consider the small change in effective spoke length imparted by one revolution of a nipple and the associated significant change in tension).
Another question that comes to mind was whether the supposed increase in wheel durability was the intent of the design, or just a happy coincidence. Or, it may be that large flange hubs were determined by experience to build a more durable wheel, yet noboy really knew why.
John Hurley wrote,
Maybe I just missed it, but didn't see any comment on the obvious fact that a larger flange diameter results in more widely spaced spoke holes, which reduces stress in the flange. It would also allow the use of more spokes, if that was an objective.
If you were inventing the wheel, the question of flange diameter would be resolved in terms of spoke hole spacing. This would be a function of the number and diameter of the holes, the amount of force to be expected at each hole, and the strength of the flange material.
John,
Very good points. I think the idea that more holes can be drilled into a large flange is a perfectly reasonable motive for making large flange hubs. Another benefit is that more spoke crossings can be achieved without the spoke heads interfering with adjacent spokes, as sometimes happens with 4x lacing on small flange hubs, especially with low spoke counts. On the other hand, neither your point about spacing of holes or this other point about crossing, explains why flange size, in and of itself, would make a performance difference. But that may be just the point! It may be that large flange hubs just allow configurations that are impossible with small flange hubs, configurations that DO make a difference in performance, or were at least historically thought to make a difference.
One thing to consider from our modern perspective is that spokes in the old days were (I'm told) nowhere near as reliable as they are today. Perhaps minor differences in wheel configuration were mostly about extending spoke life, which is now less of a concern. I don't think I'd ride goofy/cool raidal fronts as I do on my newer bikes if all I had to use was 1950's French spokes (or modern Hoshis!).
Tom Dalton Bethlehem, PA USA
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