I'm using the values gives on the Roues Artisanales site



So you think that the truth most likely lies in the opposite direction to all evidence accumulated so far?



No it's not, that's a rule of thumb... it will depend on what sort of aero and what sort of rolling resistance we're talking about. The measurements suggest the cross-over occurs much higher for wheels and tyres



No, I haven't. The measurements on Adrien's site claim the aero drag was reduced by almost exactly 1.95 times between 50 & 30km/h regardless of wheel type. That makes it a mix of linear & quadratic.

At 50km/h, the measurements (for what they're worth... if you've got better, go ahead...) suggest 23W for Boras, 33.2 for Ksyrium ES, so 10.2W different at 50km/h, or 5.2 at 30km/h (or, by fitting a general quadratic through those two points and zero, 7.7W at 40km/h).

Now from the RR tables, at 30km/h, Michelin Pro Race 2: 29.2W, Veloflex (best of the tubulars) 34W, so 4.8W.

Hence siding solo at 30km/h you are pretty damn close to break-even: 0.4W in favour of veloflex + Bora vs Ksyrium + Michelin.

Rolling at 50km/h and assuming RR stays constant so that dissipated power increases linearly, the RR losses would differ by 8W, just slightly more than the differences in aero losses at 40km/h.

So if running in a pack reduces aero drag by about 10km/h worth (which is probably conservative, given time vs distance results for a pack vs ITT), then using an $80 pair of Michelins will give more benefit than a $2200 pair of Boras.



Actual numbers above...



I think this is probably true: my point was to bring up the "a lot that is not accounted for"

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Graham

The thing is there isn't anything new in these wheels (apart from them throwing away one of the big advantages of tension spoked design). They do basically work in the same way as "old" deisgns, thus you can analyse them in the same way.

Maybe they are stiff enough since the carbon spokes are stiffer than standard steel spokes. However remembering we are concerned about weight here, it would be possible to use a carbon spoke half the size and weight if they were pre-tensioned and so the spokes on both sides helped to support the load.

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No scales on the trails

You could do it. Hypothetically, just glue all the spokes on one side. Flip the wheel so they're at the bottom, and support it around the rim. Hang a weight from the hub and glue the other set of spokes in. Remove weight.... done.

However it should be remembered that stiffness and strength are not the same. Pre-tensioning will double (well, probably less for a glued spoke wheel) the stiffness, but actually decrease the ultimate strength (since any impact is on top of the pre-tension). So cutting back on materials may not be the go...

That, btw, is the reason you don't see spoked wheels on (serious) road-based motorcycles anymore. Getting stiffness was ok, avoiding catastrophic failure under high lateral loads was another. I was at one of the last big meetings in Australia where they were used and I remember several wheel failures and one death

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Graham

I'm thinking that "spoke tension" for wheels using carbon or carbon / kevelar spokes isn't as relevant as we're making it out to be...


Carbo spokes, made as LW build and use em, don't need "tension" to be substantially solid structures. And unlike more traditional wheels, the build process doesn't require the hardware to settle in to place and then get loaded up in order to be functionally stiff.



And I'm not sure that anyone has ever a problem with a set of lightweights not being stiff enough anyway...

That's the beauty with Lightweights... You can get close to the weight, but no traditional (or even a few new designs) spoked wheel is equal in stiffness (wind up and lateral) and weight...

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charles@pezcyclingnews.com

So you've obviously talked with the manufacturer and know the wheels' design completely from an engineering point of view, then, right? Or are you just postulating based on what you think you see?

I couldn't find the "bunch effect" numbers you mentioned on Adrien's site. Do you have a link to the numbers?

Oh yes, I'm just postulating based on seeing a rim attached to a hub with spokes which won't take a compression loading. Not really relevant what the manufacturer thinks he's doing, as it won't make such a structure work any differently.

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No scales on the trails

Not argueing, just asking...

What "Big advantage" do Lightweights "throw away" with regard to tensioned spokes?

Lightweight's design and material choice doesn't require tension to function the way standard wheels do...

In fact, it could be said that "tension" is more a negative than positive as it's creating stresses all over the wheel in order to hold it's shape and stiffnes where the lightweight design doesn't have to put in place in order to function extremely well.

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charles@pezcyclingnews.com

That is an essential point. Failing to engineer a design according to the materials used would be a massive design error. Just as CF frames have caused everyone to reevaluate what is considered light and strong, CF wheels need to be evaluated based on the current materials in use and the requirements those materials bring to a given design. What is being seen and learned now is that CF doesn't have to be implemented just like Al, steel, Ti, or whatever. It can be used completely differently.

Further, it's a huge mistake to throw around figures or demands for stiffness, strength, and etc. w/out quantifying exactly what stiffness is needed for a given design. Making something stiff for the sake of being stiff is a stupid endeavor. A well designed product is as stiff as it needs to be, as strong as it needs to be to meet it's performance targets. It does not have to meet some generic "wheel's must be built like this" ideal.

I didn't want to reply in this thread since some of you are taking it very seriously, as if it was a question of death or life but I'd like to add my 2 cents.

From the wheel cross test I've performed, the Lew wheels are indeed the flexiest laterally and frontally. They are far more flexy than any other wheel ever tested. Since years, every manufacturers focused on stiffness at all cost, Lew Racing does not and want to explore new horizons.
Lew Racing claims the low lateral stiffness is not a problem since it will not be significant while riding, accelerating, etc... this, because of the triple flanges.
The center one transmits the torque and prevents the rim from moving to the left and right because of the pulling spokes.
However, on a standard wheel (any wheel with two flanges), there are as many pulling spokes as pushing spokes. Thus the position of the rim is kept while accelerating. The only motion of the rim we can see is caused by the angle the rider is doing with the ground (i.e. standing on the bike). This is directly represented by the lateral stiffness, and it really can be a problem since the rim will touch the brake pads (the deflection is very important) and thus, slow you down.

The wheels, front and rear was incredibly flexy. The spokes bent a lot, always taking the same shape, both from lateral and frontal loads. This is caused by the small cross section of the spokes that doesn't resist a lot to the loads. However, since they are pretty elastic, the resistance of the wheels should be high.
About spoke tension, it's indeed close to 0 if not 0. It doesn't really matter.


@alienator: about the stiffness, yes it is very important, almost at any place of the bike. Mavic performed serious tests with stiff and flexy components, same super powerful track guy, same position, etc... the stiffness of the components allow the rider to exploit his full potential while reaching the maximal hearth rate. With less stiff components, the rider can't exploit fully his potential. You can contact Mavic if you want to know more. They perform thousands interesting tests.

@pez: Lightweight wheels are not obligatory stiff. I rode the Obermayer Generation 2: they were very flexy. I had both the Obermayer Generation 3 and Standard Generation 3 at the test and my feelings were simply verified although the full carbon spokes are claimed to bring an extra 30% stiffness.


In term of inertia, the Lew VT1 obviously kicked every other wheels.

The aero was correct but nothing exceptionnal.


I hope to ride the wheels before writing my report in the magasine... I'll thus be able to do my own opinion beside the static tests.

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RAR wheels
Roues Artisanales

That's a blanket statement that cannot be supported. Stiffness needs are a function of design and engineering requirements. They are not absolutes. Such an idea--that more stiffness is always better--flies in the face of good engineering principles. Where is the Mavic data published?

It is not published, but I'm sure you would like to contact them to know more. Feel free to drop them an email or give them a call.
You will see all the test they perform: strain gauges eveywhere on the bike, with camera attached to the bike to record the rim deflection between the brake pads, powermeters, hearth rates, etc...

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RAR wheels
Roues Artisanales

I'm sorry if i'm 'pushing you' but I don't quite understand your review above. Are you saying the wheels are 'stiff' enough or not. I mean stiffness in terms of touching the rims.

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Colnago extreme-C Scott Addict SL

@alienator:
That is not what Adrien said. He did not say "stiff is always better" as an absolute. It is the same argument you and I had in a previous post where you insisted on the argument as if i said "stiff is always better" which i didn't. He didn't either.

Rim deflection......interesting. Doubly so since Mavic has claimed that both stiff rims and less than stiff rims can deflect between pads. Hmmm. Seems like a confused message Mavic is trying to market.

Test data from a company are lot like white papers: they need to be take with an appropriately sized grain of salt. It doesn't matter whether that company is Zipp, Calfee, LEW, Mavic, or whoever. The only data they're bound to release is data that supports their position or product. That's a completely different scenario than doing work that is to distributed as refereed scientific work, wherein you're bound to include data that not only supports your theory, but any data that doesn't support your theory. Moreover, you're bound to describe in detail how you collected your data so that other can replicate your experiments to either support or refute your results. Again, that is something that companies are not required to do when they are feeding the public--be it directly through ads or through journalists--what they want the public to hear.

I seriously doubt that Mavic would release data that didn't support their conclusions, and I doubt they'd describe in detail their testing procedures and test setups so that others could duplicate their tests.