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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [BergHugi] [ In reply to ]
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BergHugi wrote:
Looking at tests of the recumbent community, they often observe an increase of Crr with speed

Yeah. I've seen those claims, too. I'm sure that at very high speeds it does matter. The question is whether on a velodrome at more usual speeds whether the speed dependence is large or small.

I have a couple of data files from streamliner speed runs at Battle Mountain. There are a couple of anomalies but, as a whole, it appears that the speed dependence of CdA and Crr isn't huge in speeds from ~40 to ~75 mph (~65 to ~120 km/h).
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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I┬┤m going to test with top cyclists between 45-50km/h.

Copy text from this article "Simulation Model for Road Cycling Time Trials with a Non-constant Drag Area
"
: "The Martin model can be modified to account for variation in CDA with variations in the Reynolds number of the air flow. To do this, the model must use the effective wind velocity parallel to the riding direction given a certain yaw angle, to return the correct drag area for those conditions. For this model, these values were obtained through wind tunnel testing"

I understand for this that Cda calculated is only valid for the same velocity. I can read in other papers that is one of the limitation of wind tunel test. Cda is high at low velocity and low at high velocity. Then we need to report cda value allways at specific velocity.

About Crr is also dependent of velocity I should test Crr at target velocity.

Anyone can explain or link how do accuracy test of Crr in velodrome?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [cyclistgo] [ In reply to ]
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cyclistgo wrote:
I┬┤m going to test with top cyclists between 45-50km/h.

"Simulation Model for Road Cycling Time Trials with a Non-constant Drag Area"

Thanks. That's an interesting paper. I see they did their field tests with speed (and gradient) measured by GPS (and the power meter was a Stages).

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I understand for this that Cda calculated is only valid for the same velocity. I can read in other papers that is one of the limitation of wind tunel test. Cda is high at low velocity and low at high velocity. Then we need to report cda value allways at specific velocity.

They report a dependence of CdA on wind tunnel speed that's huge: there's about a 5% difference (for both riders) in CdA between 9 and 13 m/s (about 32 to 47 km/h). That's puzzling.

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Anyone can explain or link how do accuracy test of Crr in velodrome?
I can understand now why you're worried.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [BergHugi] [ In reply to ]
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BergHugi wrote:
Did not do many tests with my test rig yet, but I saw a slight increase of Crr for a Schwalbe pro one TT from 0.0016 to 0.0018 increasing speed of the wooden drum (d = 90cm) from 20 km/h to 60 km/h .Loooking at tests of the recumbent community, they often observe an increase of Crr with speed

Cool... is your test rig posted somewhere?

Very low Crr... I've been getting ~.0025 with Vittoria Pistas at slow speed. That's on a road though.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [rruff] [ In reply to ]
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rruff wrote:

Cool... is your test rig posted somewhere?


Not yet. I will write a paper when every thing is fine i.e. when the results are bullet proof and when I have the time to write. In the mean time look at the picture.

rruff wrote:

Very low Crr... I've been getting ~.0025 with Vittoria Pistas at slow speed. That's on a road though.


Yes, I measure generally low Crr values. But tests are on a smooth wooden drum (I want to be as close as possible to a wooden track surface), results are corrected for drag to spin the drum and the wheel, and results are recalculated / corrected for a flat surface.

Last edited by: BergHugi: Jun 5, 20 0:08
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [rruff] [ In reply to ]
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I understand RChung, that the best option is not try to calculate Crr on velodrome, is get data from roller test, or from data tables from https://www.bicyclerollingresistance.com/road-bike-reviews?

If I decide to get data from other experiments, how should I convert or adjust this factor of Crr to my test? For temperature?

I┬┤ve been reading about aerodynamic very different things...
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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RChung wrote:
cyclistgo wrote:
Cda is dependent for velocity only for Reynolds number?

Um, maybe I made things more complicated than I should have. The essential piece is: over the speeds at which we usually ride, CdA is not dependent on speed. If it were, we wouldn't be able to predict pwer for speed based on wind tunnel tests that are done at a single speed.

I would add that in terms of pressure drag yes (eg. components, bike frames, wheels), but friction drag the CdA will change (skinsuits etc.) even over 35-50kph.

Regarding Crr round a velodrome you can do it with the TAS kit but as mentioned above it's really hard and you have to devote entire sessions to doing just that. We did some for a recent bit of data correlating things with wind tunnel and Crr data (see herehttps://www.aero-coach.co.uk/...mics-of-racing-tyres[/url] ).

Low 0.002s for Anadia is the correct value. Local temperature can vary quite a bit - gets really really hot there in the summer.

AeroCoach UK
http://www.aero-coach.co.uk
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [Xavier] [ In reply to ]
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Xavier wrote:
RChung wrote:
cyclistgo wrote:
Cda is dependent for velocity only for Reynolds number?

Um, maybe I made things more complicated than I should have. The essential piece is: over the speeds at which we usually ride, CdA is not dependent on speed. If it were, we wouldn't be able to predict pwer for speed based on wind tunnel tests that are done at a single speed.


I would add that in terms of pressure drag yes (eg. components, bike frames, wheels), but friction drag the CdA will change (skinsuits etc.) even over 35-50kph.

Regarding Crr round a velodrome you can do it with the TAS kit but as mentioned above it's really hard and you have to devote entire sessions to doing just that. We did some for a recent bit of data correlating things with wind tunnel and Crr data (see herehttps://www.aero-coach.co.uk/...mics-of-racing-tyres[/url] ).

Low 0.002s for Anadia is the correct value. Local temperature can vary quite a bit - gets really really hot there in the summer.

Thanks for your answer Xavier. ┬┐What are you mean with TAS kit? ┬┐Aerodynamic system TAS? I understand that TAS is also regression on real time.

We are going to stay also in Valencia in August-September and I┬┤m thinking in get data from test roller, one for concrete and another for wooden, and control stable all variables along test for get the most accuracy Cda in velodrome and Crr in test roller. Same pressure, same tyres and same velocity, and adjust for temperature and weight.┬┐Could be this a good idea? ┬┐Which limiting factors could have this methodology?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [cyclistgo] [ In reply to ]
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cyclistgo wrote:
I understand RChung, that the best option is not try to calculate Crr on velodrome, is get data from roller test, or from data tables from https://www.bicyclerollingresistance.com/road-bike-reviews?

If I decide to get data from other experiments, how should I convert or adjust this factor of Crr to my test? For temperature?

I┬┤ve been reading about aerodynamic very different things...


No, I'm not sure that's the *best* option. Crr differs across velodromes, so whether that's the best option depends on if you can get away with transferring Crr values from another testing situation, and that depends on how precise you need to be.

The purpose of models isn't to fit data, but the test of a model is. If you think that Crr (and CdA) vary with speed, the thing to do is to test it. Our current model of drag forces (slightly simplified to get rid of the potential and kinetic energy terms and assuming no wind) looks like

Watts = Crr * m* g * v + 0.5 * rho* CdA * v^3
or
Force = Crr * m * g + 0.5 * rho * CdA * v^2

So the test to determine dependence of Crr on speed is to estimate the coefficients of a model that looks like

Force = A + B*m*g*v + C* v^2

and see whether the coefficient B is different from zero. The problem is that you also think that C is speed dependent, so interpreting B may be hard -- but at least you'd know if dependence was an issue. You might also be able to vary m to separately estimate a Crr dependence and a CdA dependence, but I have to think on that a bit more.
Last edited by: RChung: Jun 5, 20 7:27
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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Thanks RChung. I need to think in your answer, interesting.

Which variables change on Crr measure in roller for the same material of the track to be different?

If from my point of view regression method is not valid for consider that we have one Cda for one specific velocity, also for Crr, which could be other alternative method for measure Cda and Crr with high accuracy?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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RChung wrote:
cyclistgo wrote:
I understand RChung, that the best option is not try to calculate Crr on velodrome, is get data from roller test, or from data tables from https://www.bicyclerollingresistance.com/road-bike-reviews?

If I decide to get data from other experiments, how should I convert or adjust this factor of Crr to my test? For temperature?

I┬┤ve been reading about aerodynamic very different things...


No, I'm not sure that's the *best* option. Crr differs across velodromes, so whether that's the best option depends on if you can get away with transferring Crr values from another testing situation, and that depends on how precise you need to be.

The purpose of models isn't to fit data, but the test of a model is. If you think that Crr (and CdA) vary with speed, the thing to do is to test it. Our current model of drag forces (slightly simplified to get rid of the potential and kinetic energy terms and assuming no wind) looks like

Watts = Crr * m* g * v + 0.5 * rho* CdA * v^3
or
Force = Crr * m * g + 0.5 * rho * CdA * v^2

So the test to determine dependence of Crr on speed is to estimate the coefficients of a model that looks like

Force = A + B*m*g*v + C* v^2

and see whether the coefficient B is different from zero. The problem is that you also think that C is speed dependent, so interpreting B may be hard -- but at least you'd know if dependence was an issue. You might also be able to vary m to separately estimate a Crr dependence and a CdA dependence, but I have to think on that a bit more.

what would it be in this case A, B and C?

I can find here https://www.tiresciencetechnology.org/....2346/tire.20.190207 that Crr have non-linear relation for velocity above 45 km/h.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [cyclistgo] [ In reply to ]
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cyclistgo wrote:
RChung wrote:

So the test to determine dependence of Crr on speed is to estimate the coefficients of a model that looks like

Force = A + B*m*g*v + C* v^2

and see whether the coefficient B is different from zero. The problem is that you also think that C is speed dependent, so interpreting B may be hard -- but at least you'd know if dependence was an issue. You might also be able to vary m to separately estimate a Crr dependence and a CdA dependence, but I have to think on that a bit more.


what would it be in this case A, B and C?

Well, I was simplifying. In the usual Martin model, A is an estimate of the quantity Crr*m*g and C is an estimate of the quantity 0.5*rho*CdA. In this case, you'd be testing to see whether B is non-zero. If it is, you'd have to do another test to determine whether it's non-zero because of speed dependence of Crr, of CdA, or of both. I was thinking that would require some variation in m, since rolling drag is affected by mass but CdA isn't.

And, of course, VE is actually designed as a diagnostic for these kinds of things -- and it's pretty sensitive.

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I can find here https://www.tiresciencetechnology.org/....2346/tire.20.190207 that Crr have non-linear relation for velocity above 45 km/h.

That's interesting. I'd like to see how they tested. As I mentioned above, I have some data on actual speed runs at Battle Mountain and if the dependence of Crr on speed were large I think it would've shown up. (I was actually kind of surprised when I first saw the data because I was expecting to see a "regime" change in Crr and CdA but I didn't).
Last edited by: RChung: Jun 5, 20 9:10
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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We really need a "Paper Police".

Not saying their paper is invalid but I would love for someone to check it out

I recently had to take a paper, take the raw data and dissect how they came to such flagrantly wrong results. Which they published. All user error.

There has to be a better way to review/comment get some of this stuff retracted

Again, I am not targeting this specific paper or saying it is wrong, I just now question every paper that I read.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [marcag] [ In reply to ]
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marcag wrote:
Again, I am not targeting this specific paper or saying it is wrong, I just now question every paper that I read.

I thought the paper several posts above that did field tests with GPS speed and gradient and a Stages power meter was kinda fun.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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RChung wrote:
...GPS speed and gradient and a Stages power meter...

I noticed you noted that. :-)

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [cyclistgo] [ In reply to ]
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cyclistgo wrote:
Thanks for your answer Xavier. ┬┐What are you mean with TAS kit? ┬┐Aerodynamic system TAS? I understand that TAS is also regression on real time.

TAS is the real-time Track Aero System developed by AndyF for Alphamantis/Garmin.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [damon_rinard] [ In reply to ]
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damon_rinard wrote:
I noticed you noted that. :-)

Do you know me, or what?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [BergHugi] [ In reply to ]
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BergHugi wrote:
Yes, I measure generally low Crr values. But tests are on a smooth wooden drum (I want to be as close as possible to a wooden track surface), results are corrected for drag to spin the drum and the wheel, and results are recalculated / corrected for a flat surface.

Nice! I don't know what instrumentation you are using, but I wondered if it would be best to determine the inertia of the system and derive Crr from the rate of change in speed. Would be better than some hacks at least (like measuring motor inputs) and would be simple and consistent.
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