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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [tetonrider] [ In reply to ]
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10m normally.

I re-read what I wrote and I can see that it's easy to misinterpret. Sorry. The reported wind speed will be higher than the wind speed at bike height.

Developing aero, fit and other fun stuff at Red is Faster
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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RChung wrote:
I think they're at 10m.

I have a Kestrel 5100, which reports rho. The wind meter doesn't read quite as low as I'd like (sometimes it says there's 0 wind when I can feel a tiny breeze) but it's still pretty handy.
I think the Kestrels require at least 0.6m/s to record an air speed value. That's pretty significant in terms of power demand, ~20-25W.

http://www.cyclecoach.com
http://www.aerocoach.com.au
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [AlexS] [ In reply to ]
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AlexS wrote:

I think the Kestrels require at least 0.6m/s to record an air speed value. That's pretty significant in terms of power demand, ~20-25W.
The "operating range" of wind speed is 0.6 m/s and up, but I think (?) I've seen values below 0.6. I don't know how accurate the sensor is below 0.6, though.

In track & field, the maximum wind for a legal record is 2.0 m/s. Since I started thinking about bicycle aerodynamics I've come to realize how windy that is.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
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Total newbie question here, but.... lower on the Aerolab graph is "better" CdA, correct? For example, this run would be higher CdA at the start, then it got better, then worse again? Or do I have that backwards? Thanks.


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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [2wheels] [ In reply to ]
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2wheels wrote:
Total newbie question here, but.... lower on the Aerolab graph is "better" CdA, correct? For example, this run would be higher CdA at the start, then it got better, then worse again? Or do I have that backwards? Thanks.


You can answer your own question by moving the CdA slider to see what impact it has on the section where VE trends down and where it trends upwards. IOW adjust it so that the other sections (series of laps) are "levelled out".

Keep in mind that depending on what you did (or didn't do) this is telling you the difference in apparent CdA between those sections of the ride. What actually caused the plot to head one way or another could be various things besides a change in CdA.

http://www.cyclecoach.com
http://www.aerocoach.com.au
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [2wheels] [ In reply to ]
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Downsloping = 'faster',or as Alex points out,'might be 'faster.

I did some testing today and found that one bike was way slower than the other, to discover that the rear brake housing was too short and pulling brake on ,ever so slightly as a I cornered,which I happened to be doing a lot of.

I have found a great venue but it requires riding in quite tight circles,and it seems that the CRR goes up a lot as the speed increases,It is not cambered.
I'm struggling to work out if there is a formula I can apply for test sessions done at different speeds.
Does anyone have any rules of thumb?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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Tight corners can be a bit like braking: noticible but tricky to account for. How long are the corners? One simple option is exclude them, if you can.

Developing aero, fit and other fun stuff at Red is Faster
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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I think most peoples instinct is to carry as much speed as possible from a natural race mindset. I've found that coasting to a near crawl in the turnarounds helps produce nice, consistent results.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [SkippyKitten] [ In reply to ]
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I can't remove corners as I follow a ~130m oval,which I estimate has two 25 metre straights and and a turn radius of ~13 metres,so a lot of turning.
The height of the 'hills' on the aerolab plot goes up by over 50%from a very low speed(say 8kmh) to the speed I can do consistently(~28kmh)

The location is great as I can almost eliminate wind,but am madly frustrated by the apparent altering crr with harder cornering.

If I want to tease out smaller cda changes ,then I need to go faster.....
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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so this is how the plot looks like as I change speed but keep position.
The difference in drag seems way in excess of what you would expect due to extra G force.
Does this imply lots of extra rolling resistance due to increased tyre slip angle?
the numbers after speed show the CRR i'd have to choose to level those sections up,with CDA remaining static,but as the speed drops the crr number looks totally unrealistic(ie a CRR of 0.00005 won't level the plot at 20.3kph)
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
so this is how the plot looks like as I change speed but keep position.
The difference in drag seems way in excess of what you would expect due to extra G force.
Does this imply lots of extra rolling resistance due to increased tyre slip angle?
the numbers after speed show the CRR i'd have to choose to level those sections up,with CDA remaining static,but as the speed drops the crr number looks totally unrealistic(ie a CRR of 0.00005 won't level the plot at 20.3kph)

Is this a running track, by chance? If so...what's the surface material?

http://bikeblather.blogspot.com/
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [Tom A.] [ In reply to ]
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No,it's a pretty nice smooth 'tarmac' surface( in a part underground car park,so low wind conditions)
The surface is also very flat,with no discernible camber.My phone suggests under 1 degree slope.

As I go faster ,I obviously have to lean more ( so my CoM is travelling a smaller distance),but I try to keep on the (imaginary) blue line.

I see earlier in the thread that AndyF said ignoring cornering effects (for a velodrome)would overestimate crr and underestimate cda by 2-3%.My data seems way different.

Any ideas(could it be bearing related,or my wheel rubbing brakes on leaning?)?
The same effect is noted with two different powertap wheels and different frames
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
No,it's a pretty nice smooth 'tarmac' surface( in a part underground car park,so low wind conditions)
The surface is also very flat,with no discernible camber.My phone suggests under 1 degree slope.

As I go faster ,I obviously have to lean more ( so my CoM is travelling a smaller distance),but I try to keep on the (imaginary) blue line.

I see earlier in the thread that AndyF said ignoring cornering effects (for a velodrome)would overestimate crr and underestimate cda by 2-3%.My data seems way different.

Any ideas(could it be bearing related,or my wheel rubbing brakes on leaning?)?
The same effect is noted with two different powertap wheels and different frames

OK...never mind then.

I did some trials once on the HS running track, which has a "cushy" surface. There were some weird non-linear effects on Crr with varying speed...which makes sense, if you think about it.

http://bikeblather.blogspot.com/
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [Tom A.] [ In reply to ]
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Could my graph shape be to do with non linear crr?
this image below shows this for cars ( I don't know the provenance)
it looks more linear at higher pressures and between 40 & 100 kmh.
Not fantastically relevant to most STers,but could this affect estimates of power required to climb steep hills?

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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
so this is how the plot looks like as I change speed but keep position.

The difference in drag seems way in excess of what you would expect due to extra G force.
Does this imply lots of extra rolling resistance due to increased tyre slip angle?
the numbers after speed show the CRR i'd have to choose to level those sections up,with CDA remaining static,but as the speed drops the crr number looks totally unrealistic(ie a CRR of 0.00005 won't level the plot at 20.3kph)

Factors that will change with speed on the curves
  • Locus of body with lean. Either body takes a shorter route or your wheels take a longer route as you compensate. Either way, you have some "interesting" speed adjustment factors to implement. Your data input is wheel speed?
  • Apparent yaw angle, even in still air.
  • Rolling radius of tyre may vary with lean angle? Nothing as severe as a MotoGP bike, but maybe something
  • Crr change due to lateral forces
  • Crr change due to road speed. Think the variation in the car tyre chart is to do with the carcass deflection at contact point failing to return to nearasdammit round by the next rotation, this would surely be less on a bike tyre at much lower speeds
I'm lacking in maths here - the magnitude of the change is shown by the curvature (change in slope) of the trace, not the slope? It appears to change less at higher speeds, though the speed itself does not ramp so fast as the test distance increases. Odd that it appears almost flat at 16.4 as well as 29.5
From a protocol aspect, is it better to test slow to fast, or fast to slow? Gut reaction says it would be easier not to change position going fast to slow, though the whole speed range isn't physically taxing here. Are you cornering comfortably at the higher end of the speed range?
Which way do you have to trade CdA vs Crr to get a flattened trace?
Last edited by: dontswimdontrun: Sep 24, 17 5:38
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dontswimdontrun] [ In reply to ]
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I've run the average speed and watts per interval thru a calculator
this one:https://www.gribble.org/...g/power_v_speed.html
and the numbers make sense from 25kmh upwards ie,at the parameters on the GC screenshot-all give CdA ~.325-.330
below that speed the CdA needs to be massively reduced to make it add up,ie I'm getting too much speed for my watts.

So .I am guessing,-a) different CdA and/or Crr at low speed,or more likely(?) the (wired) PT is overreporting watts
I have ignored centripetal force and centre of mass travelling a shorter course so far,as these are much smaller effects.
AndyF has reported somewhere,if you ignore these effects ( in a velodrome)you'll mis-estimate by 2-3%.

I do have another (wireless ) PT ,so can try again with that wheel,and was thinking of doing some tests with my trainer at varying speeds to see if Crr is linear.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [kevinkeegan] [ In reply to ]
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kevinkeegan wrote:
Could my graph shape be to do with non linear crr?
this image below shows this for cars ( I don't know the provenance)
it looks more linear at higher pressures and between 40 & 100 kmh.
Not fantastically relevant to most STers,but could this affect estimates of power required to climb steep hills?

Doubtful. Most references for bicycle tires over typical speed ranges show basically no speed dependence.

Car tires have a significantly different construction than bicycle tires.

http://bikeblather.blogspot.com/
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [AndyF] [ In reply to ]
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Hi, just wondering if there was a consensus on whether there is any difference in using a wheel-magnet based speed sensor (e.g. a GSC-10) vs a hub-based accelerometer one (e.g. the newer Garmin ones)?

I thought I'd read somewhere that magnet ones were preferable but I'd rather avoid shifting my GSC-10 around between bikes if possible. Thanks!
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [awenborn] [ In reply to ]
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The hub based ones are not precise enough for VE testing.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [GreenPlease] [ In reply to ]
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GreenPlease wrote:
The hub based ones are not precise enough for VE testing.

Genuine question, is there anything to back up that statement?
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dangle] [ In reply to ]
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dangle wrote:
GreenPlease wrote:
The hub based ones are not
precise enough for VE testing.


Genuine question, is there anything to back up that statement?


Have a look at the plots here:
https://www.dcrainmaker.com/2014/05/garmins-spd-cad-magnetless-sensors.html


And this sentence:
"So would I recommend the speed sensor from a data standpoint? For most riders, they realistically won’t likely even notice the noise. Ultimately it’s giving you the basically same speed (albeit with a bit of noise that’s barely noticeable), and it’s giving you basically the same distance. But really for most folks would use GPS outside anyway, so it’s really just indoor training where you might be using some sort of app that utilizes speed.
But there are some use cases where I wouldn’t recommend it. For example, if doing aero testing (such as with Alphamantis), this speed sensor would be a nightmare and skew the data too much. Same goes for any other scenario that relies on incredibly clean and high fidelity speed sensor data. If you’ve never put those words together in the same sentence before, then you likely don’t fall into that camp. Also of note is that I haven’t done any mountain biking. While the cobbles I do have can throw a wrench in things, so can rocks and stumps. So just keep that in mind if you’re looking to go on trails instead."

You have so much other unknowns to control/check that you will not take the risk of using magnetless speed sensor or GPS speed. Use magnet speed sensor. And wired sensors would be even better.

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Last edited by: bugno: Sep 25, 17 14:00
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dangle] [ In reply to ]
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I'm not expert. I read your question and did a bit of research because I'm interested in doing some testing and I have the magnetless speed sensor.


I found these three paragraphs at the end of the Speed sensor section on DCR's review for the new sensors in 2014 (link below).



Quote:
So would I recommend the speed sensor from a data standpoint? For most riders, they realistically won’t likely even notice the noise. Ultimately it’s giving you the basically same speed (albeit with a bit of noise that’s barely noticeable), and it’s giving you basically the same distance. But really for most folks would use GPS outside anyway, so it’s really just indoor training where you might be using some sort of app that utilizes speed.

But there are some use cases where I wouldn’t recommend it. For example, if doing aero testing (such as with Alphamantis), this speed sensor would be a nightmare and skew the data too much. Same goes for any other scenario that relies on incredibly clean and high fidelity speed sensor data. If you’ve never put those words together in the same sentence before, then you likely don’t fall into that camp. Also of note is that I haven’t done any mountain biking. While the cobbles I do have can throw a wrench in things, so can rocks and stumps. So just keep that in mind if you’re looking to go on trails instead.

Like anything else, it appears to be a balance between convenience and accuracy. If you want super-high accuracy – go with the magnet. But for most folks, it’ll likely be a wash.


https://www.dcrainmaker.com/2014/05/garmins-spd-cad-magnetless-sensors.html


Not sure if this also applies to Aerolab testing.


Sounds like a bit of a bummer. I may have to dig up my old GSC-10.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dangle] [ In reply to ]
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dangle wrote:
GreenPlease wrote:
The hub based ones are not precise enough for VE testing.


Genuine question, is there anything to back up that statement?

Yup, check out DCR's review and look at the speed data. It's not off by much but it's off by enough to screw up a VE test.
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dangle] [ In reply to ]
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dangle wrote:
GreenPlease wrote:
The hub based ones are not precise enough for VE testing.


Genuine question, is there anything to back up that statement?


Thanks for the replies. I had just been a hardcore lurker in this thread until today. I really only care about A:B testing, so it's precision that I'm after vs. accuracy. After perfectly matching two B runs last week, I was feeling good until seeing these links. Thanks for contributing to a great thread.

Edit: The DCR link above also said that he was using it on a big Powertap hub (transmitting it's own info) and Saris/Cycleops said that it was likely causing interference. DCR said he would have an update in the Edge 1000 review after trying it on a different wheel. I clicked over to that and the speed sensor data is WAY cleaner and he said he had no problems recommending it now. The exact page is here. The exact text is below:

********************

In my initial testing in my earlier post I saw some oddities with speed and noisiness of the data using the new sensor, compared to traditional magnet-based sensors. Garmin did some poking and believed it was due to the new sensor being installed on a PowerTap hub, which they believe may have introduced some electronic interference. So instead, I moved it to both a different wheelset, as well as to the front wheel. In doing so, here’s the data I saw on about a 90 minutes or so ride:

(Note: Data is in wheel rotations, in order to ensure everything matches exactly, it’s not in precise speed which is simply a function of the wheel circumference)
Here’s a smaller section (1,000 to 1,800) zoomed in:

And, zoomed in one step further (250-500 of the above chart):

As you can see, it’s far cleaner now, and I’d have no problems recommending it.
*************
This would lead me to believe that there's no reason the magnetless sensor wouldn't work. Or more accurately, it may invalidate the reasons above against using the magnetless sensor.
Last edited by: dangle: Sep 25, 17 14:31
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Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [dangle] [ In reply to ]
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dangle wrote:
dangle wrote:
GreenPlease wrote:
The hub based ones are not precise enough for VE testing.


Genuine question, is there anything to back up that statement?


Thanks for the replies. I had just been a hardcore lurker in this thread until today. I really only care about A:B testing, so it's precision that I'm after vs. accuracy. After perfectly matching two B runs last week, I was feeling good until seeing these links. Thanks for contributing to a great thread.

Edit: The DCR link above also said that he was using it on a big Powertap hub (transmitting it's own info) and Saris/Cycleops said that it was likely causing interference. DCR said he would have an update in the Edge 1000 review after trying it on a different wheel. I clicked over to that and the speed sensor data is WAY cleaner and he said he had no problems recommending it now. The exact page is here. The exact text is below:

********************
...
And, zoomed in one step further (250-500 of the above chart):

As you can see, it’s far cleaner now, and I’d have no problems recommending it.
*************
This would lead me to believe that there's no reason the magnetless sensor wouldn't work. Or more accurately, it may invalidate the reasons above against using the magnetless sensor.

Indeed, thanks for pointing out. I would check nevertheless the data from any magnetless sensor to see if it is noisy or not (because of interference or vibration) if I used one...

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