Weight Weenies
* FAQ    * Search    * Trending Topics
* Login   * Register
HOME Listings Blog NEW Galleries NEW FAQ Contact About Impressum
It is currently Sun Dec 17, 2017 3:40 am

All times are UTC+01:00





Post new topic  Reply to topic  [ 27 posts ]  Go to page 1 2 Next
Author Message
PostPosted: Thu Jun 23, 2011 6:19 pm 
Offline
User avatar

Joined: Wed Oct 31, 2007 10:32 pm
Posts: 8509
Location: Los Feliz, Los Angeles, California
Hello -

I was thinking this morning (while waiting for a conference call) about how to properly test for the aero qualities of a frame. The reason why I'm wondering this is because we have at this time an odd debate about various claims for aero.
-Apparently we're told that some frames are proven with a rider on top, yet others claim to be more aero... but with no rider testing it in the wind tunnel.
-Apparently we're told that some wind tunnel tests were performed with a dummy, others with a rider in motion.
-Apparently we're told that at certain yaw angles this frame performs better than that frame... but the problem here is we have no idea how likely a wind yaw angle actually exists on a course, and according to the National Weather Service Bureau (US), the yaw angles are measured at a certain height above the ground, which is not necessarily the height at which a frame sees wind.
-Apparently we're told that now wheels are designed specifically with the frame in mind.
-And that, despite all this, the rider is the greatest signifier in the aero qualities of a frame.

So here's my modest proposal:

1. Take a hill that is straight in its descent. At this time the steepness should be enough to allow for gravity to be significant, but it does not have to be terribly steep. The road ends into a flat section, again with no turns.
2. Each frame is equipped with the same handlebars, same stem type, same saddle, same crank type, and unless brakes are specific to the frame, same brakes. Same pedals. There is no chain. Rear and Front Derailleurs are attached as normal. Cabling is normal as well. The rider only has the ability to brake. Wheels are kept constant, tires are kept constant, tire pressure kept constant.
3. The rider is the same for all tests, same clothes, same helmet, same glasses, same set up. Tests are conducted within one week's time (see next point) to ensure minimal accounting for significant change in rider weight.
4. Rides are conducted within the same two hour time window on each day. This is to account for dramatic changes in the weather/wind which would affect the ride conditions between tests. All testing is conducted within one week in which the local weather at the site is predicted to be stable.
5. Rider starts at a marked line/point at the top of the hill. There is no pedaling, rather the rider is held at the start Track style, then released.
6. Rider descends in a straight line with feet on pedals in 3-9 position, same body position kept across all descents.
7. Each test is marked for the total length of descent until the rider comes to a complete stop. This distance is from a marked point at what is agreed to be the initial absolute 'bottom' of the hill.

This will possibly determine the true aero qualities of a frame in real world conditions... or as close as possible.

Additional criteria:
A. This would take a team of personell to perform properly. A team would need the bikes ready at the top of the hill. A second team would be available to catch the rider when they come to a complete stop (or are unable to maintain balance while moving in a straight line due to reduction in speed and maintenance of position on bicycle). A third team would need to immediately rush the rider back up to the top of the hill as fast as possible to get in as many frame tests within the two hour window, and immediately follow the rider back down the hill. A fourth person would need to record distances accurately.
B. I don't know of anyone really able to afford all the bikes frames in the world, so this would necessitate cooperation from the manufacturers. I have a feeling that many would hesitate to offer a frame for testing however as this would be a scenario which challenges marketing ability.

Thoughts? (Feel free to break it down, I'm genuinely fascinated by testing methods... scientific background/upbringing :mrgreen: )

_________________
Exp001 || Other projects in the works.


Top
   
Posted: Thu Jun 23, 2011 6:19 pm 


Top
   
 
PostPosted: Thu Jun 23, 2011 6:57 pm 
Offline

Joined: Thu Nov 10, 2005 5:31 pm
Posts: 3844
My question is how much time did you have while waiting for this conference call.

I would be up for this as I have three bikes that are almost set up exactly.

_________________
BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5960g/13.13 lbs


Top
   
PostPosted: Thu Jun 23, 2011 7:31 pm 
Offline

Joined: Tue Nov 20, 2007 7:18 pm
Posts: 621
1- You have to take into account that once you are descending the yaw angle changes. It decreases until you reach the terminal velocity and then increases until you stop completely and depending of the type of the hill (length, gradient...) and the wind speed that day, this fact will improve some bikes' data and make other bikes data worst depending of the averaged yaw along the descend. Not all the bikes are designed for the same yaw in mind

2- I don't agree with the non-pedaling aspect. Some bikes are better than others (those with a recessed seat tube for example) with a rider pedaling on it

_________________
http://cds-0.blogspot.com


Top
   
PostPosted: Thu Jun 23, 2011 8:15 pm 
Offline
User avatar

Joined: Wed Oct 31, 2007 10:32 pm
Posts: 8509
Location: Los Feliz, Los Angeles, California
in-reply:

1. Yes, of course the yaw angle changes. That's part of the experiment. The yaw changes will be the same for all frames going down this descent. The test is against a frame's true ability to travel against air in real world conditions.

2. The reason the pedaling aspect was left out is because if it were left in we add further complications: how many pedal strokes were taken? At what power? Some immediate and easy critiques that would negate the findings would be in the lines of "Oh, on this descent the rider pedaled more" or "Pedaled harder" and so forth, which adds to the speed achieved at the point of crossing the bottom line, which lends to the distance achieved. By removing pedaling altogether we are eliminating additional sources of power/speed to the equation. The maximal speed achieved on the descent, which affects the distance traveled, is achieved by the frameset on its own (or as closely as possible in by isolating extra factors which are kept consistent across all tests).

In a good two hour time span within a stable weather forecast the likelihood of dramatic changes in wind is highly unlikely. If that is the case the testing crew would take note. I would assume that the testing crew will measure wind at top and bottom points for each round, if anything to verify the consistency of testing conditions.

_________________
Exp001 || Other projects in the works.


Top
   
PostPosted: Thu Jun 23, 2011 8:30 pm 
Offline
in the industry
User avatar

Joined: Sun Dec 16, 2007 9:33 pm
Posts: 713
Location: Luxembourg / Sweden
A basically sound idea. In the automotive world they call it 'coast to stop'. To my best knowledge it is used by some hypercar manufacturers to asess drag.

_________________
rolobikes


Last edited by andy2 on Thu Jun 23, 2011 8:50 pm, edited 1 time in total.

Top
   
PostPosted: Thu Jun 23, 2011 8:40 pm 
Offline
User avatar

Joined: Sat Jun 26, 2010 11:43 am
Posts: 458
Is there any need to accommodate the weight differences between the frames? It can be even up to 300grams between the lightest and the heaviest and when you are only using gravity to get down that might interfere. I have no clue if there is any validity on what I am saying, I am just thinking out loud here.

_________________
Planet-X Nanolight HM - 5.63kg


Top
   
PostPosted: Thu Jun 23, 2011 8:47 pm 
Offline
User avatar

Joined: Thu Sep 25, 2003 9:11 pm
Posts: 859
Location: SC, USA
Errors in testing would outway the contribution from the frame. The frame has such a low fraction of the overall drag that the accuracy of a field test would make it significant challange.

Regarding coast down tests, I like the idea, but pedalling tests on a velodrome would be more accurate. On a velodrome you can vary your power output and measure speed, thus by slope/intercept, you can detremine drag and Crr. With more data points (than a single coast down) you can create a farily accurate measurment tool that might have a chance to differentiate between frames... maybe. The hardest part by far is keeping your body the same for every data point. The body is such a large fraction of the drag, that a tilt of your head could mask the effects of a frame!!

If you are interested, someone posted a Excel sheet calculator that meausred air density, speed, and power for different laps, and calculated the drag and rolling coeffecients. I'm pretty sure I downloaded that workesheet, but gosh if I remember from where. It could have been another forum.

_________________
:-) Toys-R-Us


Top
   
PostPosted: Fri Jun 24, 2011 3:01 am 
Offline

Joined: Thu May 17, 2007 2:23 am
Posts: 189
Robert Chung method:

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

Coast downs can work but the PM meter method seems more robust. Coogan blogged about some tests he ran recently. Also spoke about this at USA Cycling clinic.


Top
   
PostPosted: Fri Jun 24, 2011 6:21 am 
Offline

Joined: Fri Nov 19, 2010 3:05 pm
Posts: 36
Just to say our club has an annual free-wheeling competition ( social, not serious! ).

It's down a hill, then you coast up a hill the other side, and the one who gets furthest wins.

I came second this year, I'm convinced it was because I had a helmet on, the winner took his off.


Top
   
PostPosted: Fri Jun 24, 2011 6:33 am 
Offline
User avatar

Joined: Wed Oct 31, 2007 10:32 pm
Posts: 8509
Location: Los Feliz, Los Angeles, California
Perhaps we need both Velodrome and Coasting tests?
My question about the velodrome tests lies in the environmental air: there is *no* wind of any kind, in any direction, at all in an indoor velodrome. That won't really help for "real world" conditions, will it?

Testing track bikes, that makes sense in a Velodrome. Testing road bikes (or TT bikes) claiming to be aero... that should be outdoors in normal air conditions.

:noidea:

_________________
Exp001 || Other projects in the works.


Top
   
PostPosted: Fri Jun 24, 2011 7:03 am 
Offline
User avatar

Joined: Thu May 03, 2007 10:39 am
Posts: 2585
markc wrote:
Robert Chung method:

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

Coast downs can work but the PM meter method seems more robust. Coogan blogged about some tests he ran recently. Also spoke about this at USA Cycling clinic.



Beat me too it! Chung method ftw.

_________________
"Physiology is all just propaganda and lies... all waiting to be disproven by the next study."
"I'm not a real doctor; But I am a real worm; I am an actual worm." - TMBG


Top
   
PostPosted: Fri Jun 24, 2011 10:38 pm 
Offline

Joined: Fri Dec 15, 2006 7:45 pm
Posts: 4439
Location: Natovi Landing
You need an indoor chute with a dummy, ideally a dummy that be programmed either to pedal or not pedal, move around etc.

That controls for weather and different rider movement variables.

Without doing that, ras is right ... variables outweigh frame difference.

The point to get is that real world conditions are always unique.

_________________
----------------------------------------
Stiff, Light, Aero - Pick Three!! :thumbup:


Top
   
PostPosted: Sat Jun 25, 2011 2:13 am 
Offline

Joined: Thu May 17, 2007 2:23 am
Posts: 189
Worrying about a few grams of drag in an isolated test on singular parts in perfect conditions is not where it's at. Bikes are always ridden with a rider and the rider has to be able to ride (make power) and steer (control) the bike while presenting the minimal drag possible. The best solution is an intersection of all parameters and finding that solution is a real challenge.

While approaches like the Chung method are obviously limited (zero yaw only for example), they are useful for an individual rider who wants to try different positions, components and kit to make comparisons between A and B. It beats random guessing and there are only a few wind tunnels available / affordable that are workable for most cyclists.

The one thing folks need to remember is that you can't see aero. You've got to test. That takes time and commitment. In that way aero weenies are kindred spirits to weight weenies. You can buy solutions up to a point and then to exceed you've got to get your hands dirty!!

Here is my particular addiction:

Image


And you can coast all you want but nothing beats this approach:

Image

WW and AW - both are diseases leading to big time fun :-)


Top
   
PostPosted: Sat Jun 25, 2011 2:19 am 
Offline
User avatar

Joined: Thu May 04, 2006 4:43 pm
Posts: 5415
Location: Wherever there's a mountain beckoning to be climbed
markc wrote:
In that way aero weenies are kindred spirits to weight weenies.
...
WW and AW - both are diseases leading to big time fun :-)
First of all, let's get the terminology straight. It's AeroAirheads, which I suppose could use the acronym AA.


Top
   
PostPosted: Sat Jun 25, 2011 12:24 pm 
Offline

Joined: Thu May 17, 2007 2:23 am
Posts: 189
I'm totally not digging the AirHead idea. Sounds like a cheap frame pump. I'll stick Aero Weenie

:mrgreen:


Top
   
Posted: Sat Jun 25, 2011 12:24 pm 


Top
   
 
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 27 posts ]  Go to page 1 2 Next

   Similar Topics   Author   Replies   Views   Last post 
There are no new unread posts for this topic. Relation between aero drag and power?

in Road

TonyM

14

1367

Fri Oct 06, 2017 6:23 pm

cyclespeed View the latest post

There are no new unread posts for this topic. Campagnolo SR ITA BB cups installation method

in Road

karhu

14

735

Mon Jul 03, 2017 11:15 pm

AJS914 View the latest post

There are no new unread posts for this topic. Bottom Bracket Drag

in Road

Ltoddokc

10

1491

Wed Oct 18, 2017 12:32 am

youngs_modulus View the latest post

There are no new unread posts for this topic. Drag in BB-R9100 bottom bracket

in Road

savechief

7

1003

Wed Jun 14, 2017 11:20 pm

pdlpsher1 View the latest post

There are no new unread posts for this topic. Weird bearing drag at high speeds ??

in Everything wheels

LouisN

6

744

Mon Jul 03, 2017 12:54 pm

bm0p700f View the latest post


All times are UTC+01:00


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited