Which descent are those numbers taken from? Are they the first or the second.

Realistically with two climbs and one descent before the first and only time check it is a very real possibility that Cont just out climbed everyone and was actually losing time on the first descent.

both descents together.

all timechecks are here:
http://www.letour.fr/.../aso/stage-1700.html

Contador was fastest up the first climb, and extended that lead on the 1st technical descent

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I have a Venge. It handles perfectly. Best bike I've ever owned. I'm light, ish.

But Jack/Josh, 1 question: What is all the hub-bub about having these deeper wheels in the back? Doesn't the frame block much of the wind resistance (especially on an aero road frame). I use deeper up front and smaller on the back because of the aero impact of the frame, and with the lighter wheel on back I can accelerate faster. Am I dumb?

It affects Cd. Sometimes significantly.

You're only dumb if you keep repeating the same mistakes.

Yes, aero matters more up front, but even in the rear, you will accelerate faster with a deep wheel than a shallow one generally.

Bikes sometimes handle funny with a deep front shallow rear, but if you wanted to keep weight minimum for a hill climb and weren't worried about handling that would be a reasonable approach.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

You are on that point...

Besides, having more side surface area aft tends to help stabilize a bike in crosswinds...

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http://bikeblather.blogspot.com/

So you are saying, from purely an acceleration standpoint - one would be better off with a 1000g, 60mm wheel (all up weight), vs. a 750g, 30mm deep wheel in the rear? Can you point me to the data?

Possibly (depending on the aerodynamics of the 2 wheels)...but, at worst, you won't accelerate slower to any noticeable or measurable degree.

This might help: http://www.slowtwitch.com/...nd_Inertia_2106.html

There's also this: http://www.slowtwitch.com/...ailbag_-_4_3767.html

Look near the bottom of the article for the input from Josh Poertner at Zipp for stuff like this:

"Also of note is that once rolling, bicycle accelerations are very low, so while those super light wheels feel amazing in the parking lot, that parking lot or stoplight acceleration is likely the highest rate of acceleration you'll see during the whole ride; the rest of the ride will be dominated by aero factors. We have done physics modeling around [Mark] Cavendish and found that even if you model the rim weight at zero, the improvement gained due to inertial effects during peak acceleration is a fraction of the gain found [by changing wheel choice for aerodynamic purposes]."

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http://bikeblather.blogspot.com/

You should play with the modeling software at Analyticcycling.com, but there are few if any cases where you can take any 2 real products, one being aero and the other being light, and find that the acceleration benefit of the light one outweighs the aero benefits of the aero one. The problem with light wheels is that your brain can perceive a difference, but when you try and quantify it with data, it is super tiny. The aero gains on the other hand have been processed out by your brain in the first few seconds of your ride...almost nobody feels it, not really.

The other thing to remember is your expectation. We do these really great blind ride tests with different wheels and it is really amazing how terrible humans are at perceiving actual differences when riding. We completed one recently where the rim weights varied by 100grams per rim and the aero difference varied by 20 watts at 30mph, and stiffness varied by a factor of 2 with one wheel at 30N/mm and one at 60N/mm lateral and radial stiffness varied by 2x but doesn't matter. Riders can't see the wheels and have no computer or data on board.. In the forms the riders fill out, pretty much nobody gets it right and almost every wheel was the most favorite of one tester and the least favorite of another. As soon as we began identifying these features, then everybody starts trying to revise the history...it's just human nature to want to be right.

In the end, the aero effect of the rear wheel is reduced 30-50% when compared to the front depending on the frame design. So if a front wheel design saves you 1 watt over some baseline, then the similar rear comparison generally saves you 0.50-0.70watt. Since acceleration effects are so minimal for bicycles, this almost always plays into the favor of the more aero wheel until the weight deltas become ridiculously large. The other thing to remember is the percentage of time spent doing different things. This is one of the hardest things we discuss with protour riders. Often times the key climb or acceleration they are worried about is only a few km long and when the acceleration happens the speeds are reasonably high. 80% of most climbing stages are spent on the flats or descending, and lately we've seen downhill attacks and such that unbelievably favor aero. This decision should be easy for them as ALL the bikes generally weight 6.8kg, so the difference is purely rotating vs static weight and weight position. Aero should pretty much always win, but rarely does. Ultimately is it so hard because the bike with lighter parts seems so much lighter (in their minds), but of course is exactly 6.8kg.

I had a very interesting discussion on this topic with the Schleck brothers after the 2010 TdF where Contador attacked as Andy had a chain problem. The math here was really simple. Had he been on 404's compared to Contador on 202's he almost certainly would have caught Contador on the 22km long decent down to Bagneres du-Luchon, instead, he was only able to maintain the ~40second gap. The mental state of the riders here is that 'I might have been dropped on 'heavier' wheels' but in reality, the bike would weight 6.8kg regardless and since a large percentage of the mass of the rims is at the inner diameter..and the spokes are shorter, the inertial difference is relatively small...small enough to be more or less meaningless even during steep climbing. Ultimately they more or less just didn't believe it...

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http://www.SILCA.cc
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It's much harder to help those with cognitive dissonance.

Josh/Tom/Watts dude -
Awesome. Thanks for taking the time.

I think the rationale is that you want your wheel to matter when it matters most. The benefits from the aero wheel while riding in the prelude to the climb are negligible, its a sub-threshold effort and you aren't racing aggressively. The light wheel matters much more when you are accelerating on that 12% pitch than the aero wheel when you are cruising in the pack. You say speeds are reasonably high but they are doing those climbs at less than half the speed that you test your wheels. At your test speeds you claim claim a few seconds advantage over 40km--these guys ride uphill, outside of the draft for maybe a quarter of that distance, and that is an extremely generous estimate. What's the real aero benefit there?


What the math doesn't account for is the fact that Contador is a really good descender and despite the fact that Schleck outweighs Contador by 5 kilo, he is a crap descender. If he losses time because he he has to use his brakes more than Contador, the deepest rim in the world won't make him faster.

I'm not an aero luddite but on the aero/weight issue I'm still a bit of a skeptic. I really want to believe but after watching the Tour this year I couldn't help but notice that none of the contenders in the mountains rode deep wheels. Why is that? Are they really all so science averse and rooted in backwards cycling tradition? The whole peloton? Aren't SKY all about attention to detail and embracing the science?

Even ON the climb, the aero of a deeper wheel outweighs the weight of the deeper wheel for pros. Especially when you can get to the minimum weight the uci allows anyway. Contador for instance could use 404s front and rear and still be at the minimum weight..on a venge!

The only rational reason you would not run 404s in that case is because you are worried about handling. (and sometimes that is why they don't)

That is not Contador's reason for not doing it though.

Sky has added complications in that

1. their frame sponsor is the heaviest frame in the tour, by a lot

2. their wheel sponsor, shimano, doesn't have a great selection of super aero wheels.

I would suspect, that if sky had zipp or hed as their wheel sponsor, and specialized as their frame sponsor, you would see different equipment choices in many cases.

But, the idea that heavy wheels are extra penalty due to inertia, especially on climbs, is very entrenched, and the nerd a team highers to do equipment tech isn't going to have the weight to tell froome to fuck off and ride a 404, you know?

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

That's because it is real! Rotational inertia is physics! Its a fact. The question is not whether there is a penalty but if it is a negligible one. Similarly I was questioning the real advantage of aerodynamics when you are crawling up a hill. It's a question of acceleration vs. momentum. You are saying that inertia is minor to the point of irrelevant and if you are talking about riding at a steady speed on the flats I 100% agree with you. Even riding uphill at a steady clip I probably agree with you. BUT when I really want whatever benefit my wheel is going to provide it is during that 2 or 3 minute balls out, 500 watt crux part of the climb. When I'm trying to break it open (or more likely not get broken). In that scenario I am an aerodynamic shit-show; out of the saddle, swinging the bike around bobbing my head from side to side, making donkey noises, doing the paperboy, trying to sprint up a steep grade but maybe only going 15 mph, what the hell do my aero wheels matter there? I am accelerating and decelerating with every pedal stroke but barely going fast enough to make aero wheels matter. Is that scenario one in which rotational inertia matters more? I don't know where the tipping point between momentum and acceleration happens. I guess someone who is good at math can figure it out pretty easily but in a bike race this the scenario where I want my wheels to deliver.

Also, re: SKY wheel selection. I'm certain I saw a Velonews article showing Froome's bike with a nonsponsor lightweight climbing wheel. No reason he couldn't have gone with another nonsponsored deep rim if he thought it was the better option.

My understanding is that Froome did his bike change BEFORE the split point at the top of the climb while most everybody else did their swap after the split point. If correct, that would artificially give Froome a much worse split than Contador. More likely is that Contador and Froome were more or less even before Froome did the bike swap. Still the same deal though as he gave up around 10 seconds with the bike swap and then took around 20 back on the descent. But Froome also had a monster gear on the TT bike that was probably more effective than whatever Contador had on that final wide open descent.

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Kevin

http://kevinmetcalfe.dreamhosters.com
My Strava

I think if anything, this is an argument for the heavier wheels. The higher rotational inertia will smooth out the accelerations/decelerations.

For certain types of efforts on short hills, you might even want heavier wheels even without the aero benefit, since they will cause you to decelerate slower (assuming you hit the hill with a reasonable speed).

(this is all assuming the total bike weight stays the same)

Gonna play a little devil's advocate with the modelling... You noted that at speed, rim aerodynamics matter more than rim weights when it comes to acceleration. Does that still matter in a tight draft, when a sprinter is accelerating to close a gap first, then come around (running in: a common trick in a sprinter's repertoire)? In that case, because of the draft, effects of rim aerodynamics become reduced - could this reduction be significant enough that differences in rim weights become perceived again?

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___________________________
Chewie
Slowtwitch Aeroweenie since '06

Momentum is a zero sum gain. All the energy you are conserving with a heavier wheel is there because you put more energy into the heavier wheel in the first place.

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Styrrell

I really want to believe but after watching the Tour this year I couldn't help but notice that none of the contenders in the mountains rode deep wheels. Why is that? Are they really all so science averse and rooted in backwards cycling tradition? The whole peloton? Aren't SKY all about attention to detail and embracing the science?

Protour riders have been doing the same thing for a long time.

Yes.

Not quite, but most, yes.

Yes, but you still have to overcome rider predjudices.

A 400 watt FTP means you might have been winning despite your equipment choices, not because of them. On a TT where they averaged almost 25 mph you had people picking weight over aero. That right there is all you need to know.
Chad

I was thinking more in terms of a road race, where it's not going to be too onerous to put out the extra watts to get up to speed on the flats, so when you hit the hill, you have a bunch of extra momentum over all the other cyclists.

The extreme version of the idea would be to have a flywheel on your bike you can spend all race sitting in the pack putting out extra power spinning it up to thousands of of rpms, then at the opportune moment, you engage it to the drivetrain and take off.

Even drafting, you are still more aero. Since rim acceleration is pretty much all perception and does not affect performance then there is probably never a time when a lighter but less aero wheel will outperform a heavier aero wheel at ProTour speeds. The modeling shows that you need an 8 percent grade for "light wheels" to outperform "aero wheels." Now, they certainly hit those grades on occasion, but for the other hundred miles of riding the aero wheels have been outperforming light.
Certainly in a sprint, light will never be better than aero because those guys are super fast.
Chad

Even riding uphill at a steady clip I probably agree with you. BUT when I really want whatever benefit my wheel is going to provide it is during that 2 or 3 minute balls out, 500 watt crux part of the climb. When I'm trying to break it open (or more likely not get broken). In that scenario I am an aerodynamic shit-show; out of the saddle, swinging the bike around bobbing my head from side to side, making donkey noises, doing the paperboy, trying to sprint up a steep grade but maybe only going 15 mph, what the hell do my aero wheels matter there? I am accelerating and decelerating with every pedal stroke but barely going fast enough to make aero wheels matter.

If this moment happens on a grade greater than 8 percent, then the weight of the wheels will start to make a difference, but the rotational inertia will not. You are not accerating and decelerating in the way you describe, no matter what your brain is telling you. Now, how long does that grade have to be for it to matter on the weight issue? Well, a wheelset one pound heavier will lose you 14 seconds from the bottom to the top of Alpe D'Huez. Thats about 1100 meters/3500 feet. So for your five minutes of crazy hard riding you might climb 400 feet if you were really fast and the heavy wheel was a 2 second penalty. Meanwhile the rest of your ride it was saving you energy by being faster/more efficient. Sometimes its hard to believe the numbers, but if you have done enough riding with a power meter you can find out the truth for yourself. Inertia doesn't matter and weight matters very little.
Chad

If the effects of inertia are essentially negligible, wouldn't that also apply to the idea that heavier wheels roll faster and maintain momentum? Doesn't seem like you can have it both ways. If light wheels aren't easier to spin up, heavy wheels can't be easy to keep going at a certain speed.

Yeah, that's totally true. I was mostly just talking about the theoretical. I don't think that in the real world, the difference in inertia for regular vs. deep wheels is enough to matter at all, but I've never really looked into it.


I'm not sure if you mistyped this. If your speed is constant, then staying at the same speed would require the same power with heavy wheels as with light wheels.

If the light wheels are easier to spin up, then they are also easier to spin down, so you wouldn't coast as far if you stopped pedaling at the base of the hill.

But it does depend on how the models were constructed right? I was interested to know if there were situations at high speeds that may not have been unaccounted for in the modelling where differences in rim weight could be perceived. A cyclist saves 20-30% of drag when drafting behind another cyclist (up to 40-50% when in a peloton), but given that wheels get a lot closer than riders, I'm guessing that wheel aerodynamics might be even more affected in a peloton?

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___________________________
Chewie
Slowtwitch Aeroweenie since '06