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Discussion in 'Cycling Equipment' started by alex001, Oct 12, 2003.
do radially spoked wheels make you more aero? are they stronger than conventially spoked wheels?
A quick search on google should clear this up. Radial wheels connect the hub to the rim in a straight line, which makes the wheel stiffer but is also weaker and less efficiently transmits the twist of the hub out to the rim, so you better not have them on your back wheel.
Info from http://www.exploratorium.edu/cycling/wheel2.html
But it does look cool on the front. I also used to have raidal non-drive side but that didn't work out too well.
Radially they're stiffer and just as strong, but the difference is so slight I don't think you can actually feel it. Laterally, they flex more and I don't think they're as strong. Aerodynamically, I would think they're identical. However, they save you about a spoke's worth of spinning weight. I guess this would add up to about 0.05 mph for a 28/32 spoke wheel on the road.
Although I use a radially laced front wheel on the road, you won't see me using one on the trail. On fast corners, I feel the extra flex but it isn't particularly disturbing. A poorly built three-cross will still flex a lot more than a well built radial. I'm a strong climber too, so I'd rather not experiment with a radial non-drive rear either. I like having a few more pulling spokes.
On the mountain bike, I'm much happer using stiffer handlebars, stems, shocks, and wheels. I've started building my own wheels rather than succumb to the fascination of radial lacing and the possibility of having my front wheel wander. I'd rather stick to anal retentively well built wheels with 28/32 spokes in three-cross pattern and save the weight elsewhere.
Your assertion about radial spoking lateral stiffness is not correct.
You can read more on this at Sheldon Brown's Rinard page at URL:
I would agree with you conclusion on 3 cross wheels.
Durability is the positive key differentiator.
The discussion on radial spoking is interesting, but reading the original question, I wonder if alex001 wasn't looking for information about bladed spokes, and simply got the terminology bungled.
If so, the answer is probably just as debatable. I don't think anyone can doubt that a well-designed and well-aligned bladed spoke is more aero than a traditional spoke; I'm not sure what the data out there tells us about the strength or stiffness of bladed spokes, in general. Because there are fewer manufcaturers producing bladed spokes, it probably ends up being a matter of the manufactuer's process and materials, as well as how the design is implemented by the wheelmaker.
There are wheels out there with proprietary rim/bladed-spoke setups out there that carry reputations of being fragile, and just as many that are hailed as tough.
If this about oval or flattened spokes, that is a different question.
According to Jobst Brandt in his book "the Bicycle Wheel":
"Twist continues to be a problem in use because the spokes are subjected to unscrewing forces from raod shock. With so little torsional strength they gradually turn crosswise to the wind and need to be continualy adjusted." That would be bad news as the desirable aerodynamic benefit would be lost. I built a set of bladed spoked wheels and didn't experience any turning, once I spoke aligned, tensioned, stress relieved, and tension balanced.
In know that my one set of wheels doesn't contain sufficient data to refute Jobst.
In the next paragraph Jobst continues:
"Both oval and flattened spokes are made from unbutted spoke blanks and have good or better tensile strength in the flattened part as the original spoke."
There ya go. Good info, David.
I have had bladed radially laced front wheels and never experienced any twisting. Also Ksyriums and the Dura-ace wheelsets have bladed spokes and I don't get any twist on them. As long as the wheels are built with a bit of locktite in the nipples then they should not be coming undone.
how about radially laced and bladed? thats what i meant
Ahh. Well, the first half of these posts deal with radial lacing; the second half deal with bladed spokes. Someone even mentions the Ksyriums, which are radially-laced and bladed.
How about if I restate the lateral stiffness issue this way:
Radial stiffness is better for radial lacing but torsional stiffness is greatly reduced. The additional strain on shorter, radial spokes is higher under lateral stress than it is on longer, three-cross spokes. More strain means more fatigue. Leaving the spokes a little loose to mitigate fatigue results in less lateral stiffness. Lacing them up a little too tight results in reduced durability.
Let's see if I have the rest of this argument, not entirely my own, right:
Stainless steel is ductile and does not exhibit a distinct yield point. When they're tightened beyond a certain threshold and put under a dynamic load, spokes will just keep stretching. Because of this and the strain issue, the line between too loose and too tight is much finer for radial laced wheels.
I'm just a programmer with a wheel fetish. Are there any mechanical or materials engineers out there with an opinion? Does Jobst (I need to get his book) offer any more insights?
As far as bladed spokes go, I'm sure they help but I don't know how much. Maybe I'll lace up a set next fall just to find out. Do you think the difference would be more or less than 0.1mph? Would I even notice?
Bladed versus round spokes:
A 10 Gram decrease in aerodynamic drag yield a .11 second lower time per mile. The only solid information I can find is this:
18 aero spokes, aero rim, 18mm tire: 149 grams
18 round spokes, aero rim, 18mm tire: 206 grams
You would save roughly .55 seconds per mile using aero spokes versus round spokes.
All data from High Tech Cycling, Second Edition. Adapted by permission from C.R. Kyle, 1990, "Wind tunnel tests of bicycle wheels and helmets, "Cycling Science 2(1):27-30
As a side note: Sheldon Browns radial wheel information is in-correct.
Alex, the answer to your question is YES, they are more aerodynamic.
Rinard and Jobst are the engineers. Jobst Brandt's book is worth the read and I keep it handy for reference.
I still think you might get more out of the radial lacing story by reading Jobst's book.
Rinard's testing shows that lateral stiffness goes up when spoke tension goes down until the spokes are totally slack. There are some charts that show force versus elongation in Jobst's book that help understand why the lateral stiffness works the way it does.
On the correct tension issue, Jobst has more for us to learn than I can explain here. The specific rim involved comes in to play as far as the ideal tension in the particular build.
How much will bladed spokes help is dependent on many factors.
How fast are you going?
What is the wind vector? Are you drafting or riding solo time trial?
What are you comparing them to? ( Revolution 15/18 spokes have significant less frontal area than 14 G spokes, etc.)
0.55 seconds per mile ~ 0.05 mph for me and the majority of my riding partners. About the same effect as losing a spoke's worth of spinning weight. Giving up beer, losing the extra five pounds that go with it, and trading in my sport touring frame for an actual racing frame would have a much more dramatic effect than using both radial lacing and aero spokes.
My last word. I promise.
Don't the downward pointing spokes go totally slack or very nearly so in the real world? Rinard does not appear to be applying a simultaneous radial load to simulate this in his measurements of lateral stiffness. With his fixture the upper spoke(s) near the point of load are resisting the rim deflection while the lower spoke(s) are still working to increase it. Although I think his method is valid for evaluating the relative lateral stiffness of similarly assembled wheels, I wonder if a good portion of the effect he is measuring is due to the rounded stress/strain curve of stainless steel and not the real world lateral stiffness of the wheel as spoke tension is increased. His curve, after all, is within 4% of flat for about six turns of tension. It actually corresponds pretty well with the elasticity of stainless steel from from zero tension to ~0.2% proof stress (~0.5mm of elongation). In any case, it does not correspond with my limited experience with spoke tension and lateral stiffness. One turn too tight or too loose may not affect lateral stiffness, but the effect of six turns would be profound.
As the other portions of Rinard's article point out, there are many other variables that also affect lateral stiffness. It would not be a good general practice to loosen spokes to attain more lateral stiffness. We don't want to spokes to ever go slack. We should compromise some lateral stiffness to attain spoke tension that is ideal for the spokes and rim involved in the paricular build.
There is a paragraph "Finding The Right Tension" in Jobst Brandt's book that covers this topic.
My goals of having the wheels stay true and durable seem to be attained when I carefully follow all the methods and procedures in "the Bicycle Wheel" by Jobst Brandt. The book also has equations and results of their use for Torsional Elasticity of Spoking, Spoke Elongation from Tension, Torsional stiffness of Tangential Spoking, Torsional Stiffness of a Typical Hub Shaft, Torque Transfer to left side of hub, Rim Compression from spoke tension, and constriction force of inflated tire on the wheel.
I tested one of the front touring wheels I built to see the affects of backing off 6 full turns from the ideal tension in the wheel.
I road it 100 miles around town.
1. I couldn't feel any difference in the wheel. I think that my Conti Top Touring Tires may mask any discernible differences in the wheel.
2. The wheel stayed true.
3. None of the spokes unwound further. I marked the spoke/nipple interface to check for unwinding.
4. I noted some rim expansion, but I didn't measure it.
I returned the wheel to it's ideal tension after the test.
The wheel involved uses 36 3 cross DT Competition 14/15 DB spokes on XTR 950 hub and Bontrager Fairlane rim.
I tried the same test, with the same results on a 26" front wheel using XTR 950 hub, 32 DT 14/15 spokes 3X, and Mavic D521 rim.
thanks ,you have answered all of my questions
I wont speak for the engineers, there are the experts. My limited knowledge of wheel building, 2000+, has taught me a few things, most of which has been discussed here already.
A few things of note are:
DT revolution spokes may have less frontal area than blades but its the shape of the bladed spoke that makes them more aerodynamic.
The bottom spokes of a radially laced wheel do in fact loose tension. How much tension they loose is relative to the overall tension of the entire wheel.
Radial wheels are harsh on equiptment. I couldnt count the number of broken hub shells and rims with pulled through eylets I've seen.
If we go back to original questions.....I think we've established they are more aero, albiet its negligible for most of us. Are they stronger? Well, if you look at the most stressfull riding I can think of...track riding....they are used in that application. Are they stronger? I would never commute of tour with them...they are to harsh for that type of riding and they cant hold those types of cargo like loads.
Very interesting discussion. I've really learned a lot of new things about wheels.
This may seem at first to be off topic but I don't think so; it would help illustrate what is being discussed. Let's take two popular high end wheel sets, such as Ksyrium SSC SL and Eurus, which are presumably using state-of-the-art thinking.
It appears both use radial on the front wheels, which makes sense from the discussion- no problem.
However, the rear wheels are, at least partially, tangential. The Ksyrium appears to have radial on one side, opposite to the free wheel I think, and tangential on the other. The rear wheel of the Eurus looks like it has tangential at least on one side and maybe both.
On real wheels, how does mixing the type of spoking, i.e. radial or tangential, come into play on the back wheels? Does it make sense to mix and how should they be mixed, i.e. which side should have radial and which tangential.
What does the types of real wheel spoking on the Ksyrium and Eurus, if different, or any other brands, say about their respective handling or ride characteristics?
Thanks for the education!!
From my personal experience with a radially spoked wheel on the front of my work bike (bike courier), i broke less spokes but ended up destroying my hub when one of the flanges broke. When i took it to the bike shop they had seen similar instances of this happenning to radially spoked wheels, so it may save you spokes, but cost you more in the long run. Get a shimano 540 wheel either way.