GCN Video Shows Shallow Rim Wheels Climb Faster Than Aero Wheels

Triathlon Forum
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This GCN Video was posted about a month back where they did a test of climbing a 5.6% hill at 325 watts average using shallow rims and then deep section rims on the same bike (16:52 vs 16:55). They found that using shallow rim wheels on the bike was faster than using the aero rim wheels.

This goes to prove what all the pro cyclists already know when they switch to shallow rim wheels for races with big climbs. Shallow rim wheels do indeed climb faster than deep section rims. And the testing didn’t even include having to do accelerations uphill that is typical of bike races.

It is a myth on here that deep section wheels are always faster. The wheels have micro-accelerations when going up hill because there is always the dead spot in everyone’s pedal stroke where no power is applied. The wheels slow down due to gravity pulling down and then you have to micro accelerate it after the dead spot is over. Add that up over a big climb and the gains can be significant, especially if you have to chase down repeated attacks.

A wheel with lower rotational weight will have the advantage going up hill because there is less rotational weight you have to overcome with each pedal stroke. It also explains when people’s cadence and pedal stroke mechanics going up hill is different than on flat ground. On flat ground it takes much longer to slow down if you stop pedaling so the dead spots in everyone’s pedal strokes simply don’t matter very much.

https://youtu.be/lC4OoBp_teg

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This is your Weekend of Troll? :slight_smile:

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No, just stuff that I’ve thought about for a long time but never posted about. I needed to get it off my chest since I read so many posts on Slowtwitch that say the pro cyclists have no idea what they are doing with wheels and it just so happened the GCN video came up on my YouTube feed. I don’t have any more rants.

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This is all supposed to be pink, right? 0.25% difference? Inside the margin of error, don’t you think? And what happens on the descent after you top out? Or the flat before the climb?

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You draft in a pack before the climb. And you have to brake in corners for the descent and most often have other riders with you to draft on the descent/flats so deep section wheels are not as beneficial as you might think. And the finish line is often at the top of the big climb so deep section wheels would actually hurt you when going at max effort up the climb.

And the results are quite significant from the GCN video seeing as everybody on Slowtwitch says you get huge benefits from using aero wheels rather than shallow rimmed ones, even on climbs. Especially from the ones who incorrectly do the physics calculations. You can’t model it as statics, that is totally the wrong method. You have to use dynamics.

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40 is not super shallow… and they are still billed as aero rims… those C40’s

I expected them to throw out some C24’s or something.

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That’s hardly a “test.” It was two rides. With no controlling for variance in power during the ride; simply average power overall. Further, there were no reasonable steps taken to identify possible variations in weather conditions between the runs.

Further, they had tires and tubes mounted on both wheels; given what we know about variance with tire construction, the difference could easily be due to simply to variations in tire/tube construction.

And, of course, there’s the fact that Shimano wheels are no known for being particularly aerodynamic. So you’re taking two relatively similar - C40 vs C60 - wheels from a manufacturer not known for attention to aerodynamic detail and comparing them in a poorly conducted N=1 trial that cannot reasonably be called a “test” under any circumstances.

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40 is not super shallow… and they are still billed as aero rims… those C40’s

I expected them to throw out some C24’s or something.

Message them to do another set of tests. The current test is C40 vs. C60 which is still a big difference in rim depths.

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That’s hardly a “test.” It was two rides. With no controlling for variance in power during the ride; simply average power overall.

There was more controls and legitimacy in the GCN test than from any Slowtwitch approved test. And at least he isn’t using a spherical cow and calling it a flat plate. :slight_smile:

And you can’t expect a real world test to output power like a motor at all angles of the pedal stroke so of course there will be some real world variance, but the average power is the same.

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I don’t care really… I climb with Enve 2.2s. mainly because they are ~1100g…and they are tubs which I trust more on descents anyways.

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The wheels have micro-accelerations when going up hill because there is always the dead spot in everyone’s pedal stroke where no power is applied. The wheels slow down due to gravity pulling down and then you have to micro accelerate it after the dead spot is over…

Has anyone actually tested or modeled this? I’ve heard the micro acceleration theory a million times but never seen any real analysis.

In God we trust. All others bring data.

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Has anyone actually tested or modeled this? I’ve heard the micro acceleration theory a million times but never seen any real analysis.

In God we trust. All others bring data.

I’ve modeled a cyclist with a dynamics model where the micro-accelerations were clearly visible as half sinusoidal waves. But I didn’t bother to check the difference in speed with different wheel inertias. Don’t know where I placed my model but I would be curious to run it again. For these micro acceleration questions, the step time of the dynamics model must be on the order of fractions of the time it takes to complete a pedal stroke in order to properly capture the detail, which I haven’t ever seen anybody in here do properly.

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The wheels have micro-accelerations when going up hill because there is always the dead spot in everyone’s pedal stroke where no power is applied. The wheels slow down due to gravity pulling down and then you have to micro accelerate it after the dead spot is over…

Has anyone actually tested or modeled this? I’ve heard the micro acceleration theory a million times but never seen any real analysis.

In God we trust. All others bring data.

The easiest way to “refute” the micro acceleration argument is to simply apply it to aerodynamics.

I.e., it’s clear for that steady-state acceleration, aerodynamics trump weight. Which means the same thing is true for “microaccelerations” of the wheel aerodynamically.

In other words, if you are going to account for the minor accelerations of mass due to the wheel incrementally slowing down, you also need to account for minor accelerations of the airfoil. We know that a more aerodynamic wheel accelerates faster.

And you end up right back where you started.

The microacceleration theory only could be valid if relatively minor accelerations of mass mattered but relatively minor accelerations through a fluid do not. That makes no sense.

I’ve never seen anyone model out the complete system - aerodynamics and mass, but that doesn’t mean it hasn’t been done. I can find out how discrete Dr. Matthew Godo went when he solved the rotational-translation CFD problem (that Zipp used when developing Firecrest), but I believe that model considered steady state rotational and translational velocity.

The hardest part about modeling this is that people don’t all pedal in the same way. There was a guy on the forum - perfection - who maintained that Bernard Hinault (IIRC) had developed some sort of pedaling style that allowed him to be “more efficient” and that this was the real key to becoming a faster cyclist.

But sort of like how the whole “circular pedal stroke” thing has died off as people realize that it’s not actually better, you’re talking about an inconsistent model. And in that way, the proof is sort of in the pudding. If microaccelerations were really a problem, the faster climbers would have more circular pedal strokes, but they don’t. The most circular pedal strokes belong to mountain bikers, and it’s for a single obvious reason - traction.

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The easiest way to “refute” the micro acceleration argument is to simply apply it to aerodynamics.

I.e., it’s clear for that steady-state acceleration, aerodynamics trump weight. Which means the same thing is true for “microaccelerations” of the wheel aerodynamically.

In other words, if you are going to account for the minor accelerations of mass due to the wheel incrementally slowing down, you also need to account for minor accelerations of the airfoil. We know that a more aerodynamic wheel accelerates faster.

And you end up right back where you started.

BS. You totally misrepresent science. You say the real world has to act this way because you say so when the real world evidence says otherwise. Science is suppose to explain what happens in the real world, not dictate to the real world how it’s math and physics should behave. You have everything backwards, including your so called refutation. Have you ever even modeled micro-accelerations using the physics model of a cyclists at timesteps of ~0.01 sec?

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You draft in a pack before the climb. And you have to brake in corners for the descent and most often have other riders with you to draft on the descent/flats so deep section wheels are not as beneficial as you might think. And the finish line is often at the top of the big climb so deep section wheels would actually hurt you when going at max effort up the climb.

And the results are quite significant from the GCN video seeing as everybody on Slowtwitch says you get huge benefits from using aero wheels rather than shallow rimmed ones, even on climbs. Especially from the ones who incorrectly do the physics calculations. You can’t model it as statics, that is totally the wrong method. You have to use dynamics.

The video shows that there is no measurable difference between the shallow and deep wheel. The error in the power meter alone is +/- 2%. Then there is differences in wind. Differences in the exact line he rode. Differences in how he actually applied the power over the duration, even if both averaged exactly 325W. The error on that test is AT LEAST 4%. 16 times higher than the measured time difference. So this test, if it were repeated many times with the same results, shows that to the extent that equipment can measure it, the wheels are exactly the same up the climb.

Also, if you really want to talk about physics, use the correct term. What you are talking about is rotational moment of inertia. I bet the rotational moments of inertia of these two wheels are extremely similar. The deeper wheel might be slightly heavier, but the average radius from the center of rotation of that mass is smaller than it is for the shallower wheel, which at least in part makes up for the extra weight.

Also, what Jordan says - aerodynamics still matters. When you are going slowly it does not matter as much as when going fast, but when you are comparing to the effects of micro-accelerations of two wheels with very similar rotational moments of inertia, it will be very significant even at low speed.

To suggest that the inertial effects of the wheel on this climb is significant compared to aerodynamic differences on the descent or flats is pretty silly - even when you consider braking in the corners (which both wheels have to do) or drafting. Aerodynamics still help you, even when you are drafting. And for must of us on this forum, drafting is not something we do.

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They didn’t equalize the weights so the C40s are 150ish grams lighter. I am guessing that the micro-accelerations are less of an issue than the weight difference. I am guessing that climb is roughly 1000 vertical feet. I don’t remember the rule of thumb for time saved per kilo, but I bet the 0.15 kg explains most of the difference.

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Well, seems you know everything about physics and mother nature must be wrong. No use funding science research any longer or checking if you are even modeling the physics right or at the proper integration time steps.

Even between very low profile wheels, there is a significant difference in the moment of rotational inertia:

Look at the difference of what Velonews found just comparing wheels with rim depths of ~24mm (let alone what we would find for the moment of rotational inertia for deep section wheels):

http://www.velonews.com/2008/07/bikes-and-tech/calculating-a-wheel’s-moment-of-inertia_157317

As you can see, the Zipp has the lowest weight and the lowest moment of inertia. Its rotational inertia is the same as if it weighed 270 grams, all concentrated at its outer edge. Sounds like a fast wheel, all other things being equal (which they never are).

Interestingly, the Shimano wheel is considerably heavier than the Bontrager in both front and rear, yet it has a lower moment of inertia. And the Shimano wheels share the same rotational inertia with the Reynolds wheels, which are lighter yet. This indicates that the Shimano’s rim and the outboard ends of its spokes are lighter. The Shimano’s and Easton’s rotational inertias are the same as if they weighed 300 grams, all concentrated at the rim’s outer diameter, while the Bontrager’s rotational inertia is the same as if it weighed 340 grams, all concentrated at its outer rim diameter.

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They didn’t equalize the weights so the C40s are 150ish grams lighter. I am guessing that the micro-accelerations are less of an issue than the weight difference. I am guessing that climb is roughly 1000 vertical feet. I don’t remember the rule of thumb for time saved per kilo, but I bet the 0.15 kg explains most of the difference.

That’s a valid explanation but then it would mean weight is more important than aero on a climb that was only 5.6%, which is heresy around here that will get you tarred and feathered.

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Well, seems you know everything about physics and mother nature must be wrong. No use funding science research any longer or checking if you are even modeling the physics right or at the proper integration time steps.

Even between very low profile wheels, there is a significant difference in the moment of rotational inertia:

Look at the difference of what Velonews found just comparing wheels with rim depths of ~24mm (let alone what we would find for the moment of rotational inertia for deep section wheels):

http://www.velonews.com/...nt-of-inertia_157317

As you can see, the Zipp has the lowest weight and the lowest moment of inertia. Its rotational inertia is the same as if it weighed 270 grams, all concentrated at its outer edge. Sounds like a fast wheel, all other things being equal (which they never are).

Interestingly, the Shimano wheel is considerably heavier than the Bontrager in both front and rear, yet it has a lower moment of inertia. And the Shimano wheels share the same rotational inertia with the Reynolds wheels, which are lighter yet. This indicates that the Shimano’s rim and the outboard ends of its spokes are lighter. The Shimano’s and Easton’s rotational inertias are the same as if they weighed 300 grams, all concentrated at the rim’s outer diameter, while the Bontrager’s rotational inertia is the same as if it weighed 340 grams, all concentrated at its outer rim diameter.

What are you even talking about? What scientific research am I denying is required? It is likely that I do a hell of a lot more experimental scientific research than you do. You are holding up this test as showing something it does not because you want it to. That is the opposite of science. I have no idea what point you are trying to make with the list of mass properties of the wheels…

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I do not think that anyone is going to argue that shallow wheels will climb better in a pure climbing race. You still have to ride to the hill most of the time and then back to the start so the aero wheels will perform better overall.

Pure uphill race I am going as light and shallow as possible.

If I was govern by weight restrictions my choices would be different.