BMC TMR01 vs. Giant Propel

[sawyer]

Yes, it is a complete mis-understanding of scientific method.

I would not be so comfortable airing my dirty Ys in public but people never cease to entertain.

I do agree completely with airwise with respect to bike feel though. I had two Giant TCRs and to me (and two other mates who had them) they felt like complete planks ... dead ... and demoralising to ride. Though some people love them and no doubt they test well for something in a lab.

And you do hear this said about many of the aero frames so far.

So it could well be that for some people, many of the aero frames to date have negative characteristics that outweigh the aerodynamic benefit vs. good non-aero frames.

That's a respectable point of view. But doesn't contradict that they are more aerodynamic.

[airwise]

In a wind tunnel

There were lots of parts that Ferrari tested last year in the wind tunnel that produced increased downforce that disappeared in the real world. Same for Mclaren this year. And these guys are REAL experts with enormous budgets.

It is perfect scientific practice to demand empirical, peer reviewed data to back up manufacturers' claims. I'm surprised so many seem to confuse the latter for the former here.

[Pharmstrong]

Isn't Specialized's new tunnel built with testing bikes within a group in mind?

[airwise]

I look forward to the data. I do wonder how much of it we'll see though unless it can be used positively by marketing but maybe that's just cynical.

At the moment Specialized claim that the savings when "drafting" are in the region of the same percentage as when not. But they don't offer a percentage for when not - just a wattage figure. They don't say drafting where and they don't state the affect of drafting. Therein lies some of the genius of a marketing department interpreting data. Sounds great - in reality means probably one or two watts at best.

[Zigmeister]

Well, since the Felt AR FRD isn't even going to be available until after January, maybe not an option if you want a bike in the next 9-12 months until they are out in the wild.

I'm looking for another bike to switch from my Scott Foil. Biggest complaint, the ride is absolutely brutal. Every vibration comes up through the handlebars and seat. Only with tubulars and carbon bars did the ride become tolerant, but I'm done with tubulars personally, so the ride is still harsh.

Plus, looking to move to Di2...it is difficult to find the Propel Advanced SL in the wild also in the size/color I would like...so I guess what I'm saying is, availability is an issue with all of the newest frames out, unless you want to pay full retail on a frame from the store...I don't.

[NGMN]

I'm with sawyer. You ride the bike, look at the data, apply grains of salt; and then make a choice. There's never going to be pear reviewed literature. There will continue to be loads of manufacturer and third party data, which peopl will need to read with what they feel is the right amount skepticism.

[sawyer]

In a wind tunnel

There were lots of parts that Ferrari tested last year in the wind tunnel that produced increased downforce that disappeared in the real world. Same for Mclaren this year. And these guys are REAL experts with enormous budgets.

It is perfect scientific practice to demand empirical, peer reviewed data to back up manufacturers' claims. I'm surprised so many seem to confuse the latter for the former here.

Well, it would be if reliable testing on the road was possible. Right now it's not.

Fair to say to balance your point that isolating characteristics in the real world is often impossible/very hard and without knowing the detail that might also apply to your examples - what they think they are seeing could be confounded by other factors. in aeronautics and car manufacture labs (e.g. wind tunnels) are used extensively, so it is a respectable technique for establishing performance that even if it can never exactly predict real world performance, does tell engineers something important.

Right now it's the best we have for bikes.

[Pharmstrong]

[53x12]

Well, it would be if reliable testing on the road was possible. Right now it's not.

Sure there is. Chung method.


WW is a great place for most things cycling related. Especially WW related. Talking about aero is not one of the strengths that this forum brings. There are other places online where that is done much better based on the collective knowledge and experience of its members.

[sawyer]

Well, it would be if reliable testing on the road was possible. Right now it's not.

Sure there is. Chung method.


WW is a great place for most things cycling related. Especially WW related. Talking about aero is not one of the strengths that this forum brings. There are other places online where that is done much better based on the collective knowledge and experience of its members.

Problem is the Chung method is useless in trying to quantify what are small differences in drag between frames

I'm not aware of any reliable real world technique for accurately assessing the very small (in the big scheme of things) differences in drag generated by frames.

[53x12]

"Problem is the Chung method is useless in trying to quantify what are small differences in drag between frames"

Not true at all. I believe you don't fully understand the use of the Chung method then.

http://bikeblather.blogspot.com/2013/08/aero-field-testing-using-chung-method.html

http://anonymous.coward.free.fr/simkins-egg/Egg%20Brake%20Testing%20using%20Chung%20Method%20Testing%20R6.pdf

http://jasperga.blogspot.com/2009/11/chung-method-is-no-joke.html

http://anonymous.coward.free.fr/wattage/cda/indirect-cda.pdf

"I'm not aware of any reliable real world technique for accurately assessing the very small (in the big scheme of things) differences in drag generated by frames."

Seriously, the Chung method. Lots of great info available online about it. I believe he is even a member on here. Wonder if he will chime in.


http://fitwerx.com/ask-fitwerx-article-archive/your-power-meter-is-the-best-wind-tunnel-available

[sawyer]

53x12 - if you're cycling the bike the inherent difficulties are (1) ensuring accurate measurement of all the different forces acting on the system (rider plus bike) and (2) repeating the experimental conditions, not least the rider movement or line along the road.

The delta we're attempting to isolate is very small.

I don't see that anything you've posted overcomes these difficulties and would allow you to effectively measure real world differences between frames accurately.

BTW, one small point to raise about the tests is that no-one can maintain absolutely constant power output. It is probably impossible for a human being to do. And the measurement from powermeters (and any other equipment) used to measure the various forces isn't accurate enough to allow compensation for this fact.

I could go on - but you get the point I hope.

This all points to the reason why airwise's example of motorcars is a good one, but not in the way he intends. Rider + bike is actually a lot more complex system in this regard ...

[53x12]

Chung method works and has been proven to work multiple times. /discussion. Also you are never going to make a comparison on only one data run. No one does that. That is why you use the same route/lap each time. Follow the protocol given in his paper and it works.

Check here for a recent discussion by guys (like you and me) doing the testing themselves and the solid data they get.

http://forum.slowtwitch.com/gforum.cgi?do=post_view_flat;post=4684817;page=1;sb=post_latest_reply;so=ASC;mh=25

So the comment that "if reliable testing on the road was possible. Right now it's not." isn't correct.

[rchung]

53x12 - if you're cycling the bike the inherent difficulties are (1) ensuring accurate measurement of all the different forces acting on the system (rider plus bike) and (2) repeating the experimental conditions, not least the rider movement or line along the road.

The delta we're attempting to isolate is very small.

I don't see that anything you've posted overcomes these difficulties and would allow you to effectively measure real world differences between frames accurately.

BTW, one small point to raise about the tests is that no-one can maintain absolutely constant power output. It is probably impossible for a human being to do. And the measurement from powermeters (and any other equipment) used to measure the various forces isn't accurate enough to allow compensation for this fact.

I could go on - but you get the point I hope.

Well, you're right about many of your points but not quite about the entirety of the message.

1. I completely agree that no one can maintain absolutely constant power output, and that it's probably impossible for a human being to do. However, this protocol doesn't require that you maintain constant power (or constant speed). In fact, this protocol works best if you have a wide range of power and speed.

2. You're absolutely right that the instantaneous accuracy of power meters can be larger than the difference in drag between, say, two frames. However, this protocol works not across instantaneous data samples but across aggregated segments or intervals of data samples. In that case the instantaneous accuracy of the power meter matters much (much) less. There's also a way to test for accuracy drift across tests, and it's good field practice to do that if you're trying to isolate small differences.

3. You're completely right that real-world conditions can affect the estimates. However, one of the nicest things about this protocol is that you get a diagnostic that tells you when the conditions interfere with a good estimate (like, when a car passes, or a momentary use of the brakes to avoid a hazard, or when the wind gusts). So while it would be great if we could eliminate all those problems the next best thing is to be able to tell when that happens so we can drop the "contaminated results" and re-test.

4. You're absolutely right that there's a detection limit beyond which field tests can't detect small changes in frames but that's also true about all measurement methods. Nonetheless, the detection limit is actually pretty small. The best I've ever seen in an outdoor field test was in a case where the weather conditions were nearly ideal, there was no other passing traffic, the rider was experienced in the method, and the venue was well-suited to getting a wide range of test speeds. In that case the SE on the estimated CdA was around .0006 m^2, or about 0.3% of total drag area. But, admittedly, that was a pretty clean case. The method is also being used in more controlled indoor (velodrome) settings, and SE's of that magnitude are more common. There are frames on the market that absolutely are more than .001 m^2 different in CdA (which would be twice the size of the SE).

[jockalldrick]

I'm not sure if i really beleive that the shape of the BMC is better than an airfoil... or aero at all
But the brakes on it are awesome (strength)
And it did feel rapid