Tuesday, December 23, 2008

Swimmin' with pros

Managed a cracker of a swim today at East Boundary pool.

Got invited to a session with Van, Rob Harris and Maddog - fairly tidy swimmers to say the least.

400 WU then

10 x 100 on 1:15 (made the first 3 then averaged 1:16/1:17 for the rest)

400 easy

10 x 100 on 1:15 (made 1 then averaged 1:16/1:17 for the rest).

400 CD

3.2 Km cranked out in around 50 min. 12:50/km and 9:30/750m along the way.

Oh yeah, Van and Rob H were sitting on 1:03's without too much trouble...

Edit: Rob and Van both went on to score 2nds and 3rds at Pier to Pub and Sorrento swims in Jan 09.

Sunday, November 23, 2008

New rolling resistance data

Biketechreview.com has new tire rolling resistance data out this last week which has re-tested tubbies that have been *properly* glued.

Turns out:

[spoiler]The best tubbies are faster than the best clinchers when properly glued.[/spoiler]

Data is here: [url="http://www.biketechreview.com/tires/AFM_tire_crr.htm"]biketechreview.com[/url]

Top 6 least rolling tires: number at the end is watts of resistance per wheel

[spoiler]1 Vittoria EVO Corsa Crono (20) Tubular X 20 11.5
2 Velo Flex Record Tubular X 19 11.6
3 Bontrager Race X Lite Pro Tubular (22) 11.8
4 FMB Silk Tubular (23) Criterium Tread X 24 11.8
5 Vittoria Ultra Speed (20)/Mich Latex tube (18/20) 21 11.9
6 Bontrager Race X Lite Pro (23)/Mich Latex tube (18/20) 23 12.0[/spoiler]

What is properly glued?

[quote][spoiler]It seems now more important to achieve a ~ 100% bond to the base tape - the light gluing I initially used must have allowed some slipping resulting in higher Crr.
The test in 2007 was on a Vittoria Crono mounted on a Sub 9 disc using 3 coats of Mastik 1 glue on the rim and 2 coats on the tire (~ 2 tubes of glue per wheel).
The tire tested out at a very low Crr, significantly lower than the first test with light Continental gluing. I have repeated the test on several Cronos with similar results.
Additionally I have tested other tires with "the same" gluing processes and have seen similar and better results as compared to the light gluing tests.
Rev 8 adds those results plus identifies the glue process. I would estimate that the Crr lightly glued tires might improve by ~ 0.0003 - 0.0004 when properly glued.
Definitions - Properly glued => Mastik 1 - 3 coats on Rim, 2 coats on Tire Lightly Glued => Continental - 2 coats on Rim, no glue on tire
Note on Definitions - in some cases I've tested tires supplied on others wheels and glued by shops - I've identified those cases as Properly Glued.[/spoiler][/quote]

There ya go - no excuses in Adelaide!

Tuesday, August 12, 2008

Monash Wind Tunnel testing

Monash Wind tunnel tests

Wind tunnel testing for lesser mortals

About the Monash tunnel

The tunnel has a working section up to four metres high and 12 metres wide, making it the biggest in the Southern Hemisphere and large enough to fit a small truck. It can produce winds of up to 180kmh. The tunnel has a team of dedicated staff and costs in the order of $10,000 per day to hire out to commercial enterprises wanting to obtain data.
The tunnel has played host to a variety of elite sports people over the last few years including Cadel Evans, Australian down hill ski team, Australian skeleton team (like luge, but head first) and others. The wind tunnels have also been used to test the aerodynamic forces of cars, V8 Supercar teams and the remodelling of the Spencer Street train station.

David Burton (Monash tunnel staff) in the control room for the tunnel
How it works

A balance in the centre of the tunnel has four electronically sensitive pressure sensors underneath a rotating plate, when the wind blows over the object mounted on the plate, the pressure it causes on the sensors can be interpreted as a drag reading. The plate can be rotated to allow for testing different angles of yaw. The whole apparatus measures in milliNewtons (one Newton is about 102 grams, 1 milli Newton is 0.1 grams) and is highly repeatable. A bike is mounted to front and rear supports on rollers which allows the cyclist to pedal and have the wheels move.

The session had been organised by Raoul Luescher (aka transitions:Whodesigns), who has worked for a considerable period with the AIS and other aero experts such as John Cobb. At $500 a throw, not cheap, but hopefully of benefit. transitions:Dalai, transitions:fishboy and a track cyclist (let’s call him Mr X) had ponied the cash and were eager to see what a day in the tunnel could do.

The first hurdle is the legal agreement - sorry guys - can't tell anyone the data - which does make it more challenging to publish results. The reason for this is to prevent bike and or other companies getting free data which they would otherwise have to pay 000's of dollars for. Fair enough - they sting us for the bling so, make em pay to convince us to buy their gear.

Legal agreement out of the way, and coffee consumed. Time to get a bike in.

Fitting Dalais ride into position: Few minor adjustments with the jigsaw!

Whodesigns adjusting the front wheel to get it into position.


Dalai was first and had to have a few running adjustments to the tunnel apparatus to get it to fit ... his P2 was a very short 92cm axle to axle which necessitated a quick run with the jigsaw to get the rollers close enough together to fit the rig.

First job is to balance the rig with the rider in it - meaning holding very still in the same position while the sensors are set to the zero point with no force being applied. Then start up the fans ...

40kmh doesn't sound that fast, but is a bit of a blast if you walk from the calm side of the tunnel into the 40 kmh air stream. The other issue is it can get a bit cold... particularly if you are just wearing a tri suit.

Baseline position readings are taken still and pedalling for your "standard" aero position, then Whoey sets out trying to find you some more speed.

Generally, unless you are interested in effects caused by rotating wheels, the measurements are taken in a still position. The bouncing nature of the pedalling action affects the readings on the pressure sensors and it is easier to spot trends while remaining as still as possible.

The drag figures are visible inside the control room from the tunnel floor, so while the cyclist can't see the drag currently (they would have to turn their head, kinda defeating the purpose), the staff directing have a pretty good idea of what the numbers are and what to try.

First test was Dalais hands moved back to mid aero bars, instead of gripping the bar ends - no good! More than 10% additional drag over gripping the end of the bars.

Quite a few other tests were done, swapping one position or piece of equipment at a time, and gradually reducing the drag each time. According to whodesigns, a very effective way to go fast is to find an aero position and adapt to riding it - this is what Chris Boardman did for the 1 hour time trial - a record that is still standing.

Some other changes included flattening out Dalai's back, and getting him to turtle his neck a bit more.

We also had him have a go at the big range of helmets we'd assembled:

L to R: Bell Meteor II thanks transitions:AndrewT, Limar Speed Demon, LAS Chrono (back) thanks transitions:Freak, Limar Chrono (front), Giro LA TdF special (back) (whodesigns), Giro Advantage2, Uvex FP2 thanks transitions:Otter.

The final position was close to a 50 watt reduction in drag which is the difference between riding 38.5 and 42 kmh at the same power. Pretty astounding really, and no way that $500 spent on ANY bling would ever get you that fast, that quickly.

One of the later (more aero) tests for Dalai

Next up was Mr X testing a track bike and various wheel combos at a much higher fan speed of 55kmh (275 rpm, but much chortling in the control room when they almost set the fan to 2758 rpm). Being at higher speed than the 40 kmh for Dalai, the drag readings were a lot higher. Mr X's tests included seated and sprinting positions, and finished with a series of wheel tests which showed that one particular wheel combo was at least 1% better than another.

Finally Fishboy gets to have a go, and after extensive testing (1.5 hours) in the breeze, manages a very slight improvement. Turns out the swimming shoulders have got to go, and as soon as I figure out how to do this and still be able to swim, I'll be right on it.

Edit: Some positionals of fishboy shot by Dalai
Baseline (before) - good view of the rotating plate too.

Testing LA TdF Giro - shame you can't buy these!

So was it worth it?

Without any doubt, the testing in the tunnel will give you a competitive edge that (at the moment) few other people will have. If you are more than moderately serious about riding the bike fast, then my advice is to get in there! Whoey has suggested that there will be some more of these days in the future.

Thanks to transitions:Whodesigns for organising the day, and David Burton and the top engineering team at the tunnel.

Aero gems - courtesy of Tunnel time with Whodesigns

  • Cancellara's Olympic time trial was awesome, put 30 seconds into Larsson (2nd) on the last descent at speeds close to 100kmh.
  • It's not about the bike - it's about the rider on it. A Cervelo in the tunnel had 10 units of drag.
    A track bike had 15 units of drag.
    A cyclist on the Cervelo had 380 units of drag.
    Endless arguing about this bike or that bike being more aero is pretty pointless, it is about how the cyclist sits on it that counts.
  • Find an aero position and adapt your body to ride in it -
    that is what Chris Boardman did for the (still standing) 1 hour record.
  • Minute, tiny, seemingly insignificant position changes can bring about big improvements in drag.
    Dalai's hand change from aero bar end to aero bar climbing (gripped half way down) was a big increase in drag (roughly 10%).
  • When tired, it is even more important to ride aero.
    Sitting up, moving around etc all less aero and more taxing than your best aero position.
  • For best results with an aero helmet, try to close the gap between the underside of the helmet tail and your shoulders.

Saturday, June 7, 2008

2008 ITU Triathlon Sprint World Championships - Vancouver CAN

Epic race. Very bittersweet.

Trained my arse off for this and thought I had potential to do well, just not sure how well ...

Race day fn cold again, 7C air, 11C water. Up at 5am get down to transition and put the gear in, pump the tires on the bike. Ran back to check junior female race start to make sure I had the measure of the procedure. Course starts on the beach in a line and heads pretty hard right, so pays to be in the first few through the entry check in to get possibly up to 50m advantage on the start line. Retreat to hotel room and perform a warmup to AC/DC on the iPod.

Luckily in my previous life as a cross country skiier I had plenty of experience in racing in miserable conditions - it wasn't actually sleeting so I figured it couldn't be that bad! Leave hotel at the latest possible time with race clothing of race singlet under 2 tri suites, plus wetsuit half on and jog to race start tent. Keep jogging on spot in race tent, forgo warmup swim (good decision), realise guys are entering the chute for the start procedure, shit myself and sprint to get in there. Spend 10 minutes waiting in the chute, noticing how the GB'ers seem to favour oversize swim masks that must have the drag of an anchor while racing, not to mention make them look really stoopid. Glad to be living on a large, relatively warm island, amongst a nation of swimmers.

Get through the chute - see name on screen and run down to the start line on the beach - top 6 or 8 guys at the favored end of the course. Dip hands and face into water and hope this suffices to stop shock. Try to stay calm.

Luckily I'd watched earlier waves and the lack of a hooter or horn was evident, some people had been missing the start, there were marshalls standing behind us with red flags raised for the start. Stand watching the marshall over my shoulder to make sure I get some cue to go. Hear something, take 3 steps and a racing dive and go. Swim a bit straight to find clean water and immediately have someone swim over my legs, turn a bit more right and try to ease into the swim thinking cool, calm thoughts while every pore screams murder at the sudden assault of the cold and shuts down. Someone goes out hard and I immediately respond before thinking Oops can I do this pace? Back off just a little but maintain speed. Guys start falling off left and right, 2 guys ahead, 1 to the side. Get round first bouy and find a lane rope pointing off in the direction of bouy 2. Get on it and get into a better rythym, trying to keep breathing calm and stroke strong. Fk, it's cold. Still in touch with the top 2 guys - realise I'm at the front of the swim pack at the worlds and feel pretty good about it. When will this frikking swim end? Supposed to be 750m, must seriously be over 1km (Edit: Google maps says 1.05km) Get another bouy down, still few to go, about 40m behind leader and 20m behind second. Finally hit the beach and manage to stand up - dizzy as buggery and unco as well. 3rd out of the water in 16:46, 51 sec down on the leader, and 4th right on my shoulder. 16:46 for 750m? Gotta be joking - I'd swum 10:25 last Aussi season for 750, and wasn't growing barnacles out there.

Get through transition some how with out falling over - grass is sodden and very slippery. Awesome Aussi support once people can see your race suit - even get some first name calls from a few people, can't see anyone, just keep going hard trying to get brain unfrozen. On bike and get into variable pacing strategy my coach had worked out for me. Because of the hills in the course (including 1.2 km of 4.5% uphill) it is faster to vary effort to apply more power to the hills and less on the downhills. The plan was breaking the course into 6 sections with different watts for each section ranging from a pretty easy 170w to a more nasty 270w climbing. Had painstakingly inscribed this onto the face of the Ergomo with a fine tipped permanent marker. The variable pace plan was 59 seconds faster than riding the course with constant power output, but if you go too hard and blow, well, thanks for coming.

Warm up a bit on the first climb, and get through the rough as guts sections as well. The disc is singing the sweet song of speed on the downhills, and doesn't feel that bad on the ups - I was riding one of the few discs - most people opt for deep rim or even shallow rim wheelsets - I guess the size of the climb freaked them out, even though 75% of the course was flat or downhill. Swoop down the hill passing everyone in site, and line up for lap 2 - when I hear wap, wap, wap coming from the machine. Look down, realise tape covering the valve hole had come unstuck from the wetness, and was making me look like a complete n00bie. Determined not to tarnish the team image of beer and vegemite swilling tri freaks, I wait till the top of the small climb, stop and yank the tape off. Get going again, but 15 seconds lost.

Feel a bit warmer on the second lap, and get higher power out during the climb. Descend like a madman, at over 60kmh, gaining valuable time, and starting to really enjoy proceedings. Approaching the base of the descent, legs pumping in my best Tor Hushovd impersonation to blast by some pommie when the dreaded sound every cyclist fears occurs - pssschht! God, please let it be the other guy. Keep going with the power down and everything still feels OK, maybe it was the other guy, make it round the corner and realise the front has detonated and is going down. Faark! Currently in third, 44 mins in, 6.8km to go on bike, 1:34 down on the leader, with chasers closing hard and no spare (if you have to change a spare in a Sprint race you're done anyway - even if I had a spare, my hands were so cold it would have taken a week to change it). Luckily I'd put goo in the tubby, and it wasn't totally flat, just about 40 psi. Almost have a hissy fit as I realise that something you work so hard for more than 8 months might not go the way you want. Get over that 3 seconds later and decide to go for it anyway. Get the weight off the back to lighten the pressure on the front and gingerly nurse it through several turns, no real turning ability at all. Bottom out the front rim on several bumps and begin to worry about descending. Climb the big hill for the last time, power is OK, and speed is not too bad. Hopefully not loosing too much time. Big breath time for the downhill - turns out not too bad - can roll with weight off the front and take a sweeping, slow flowing line - actually descend at about 50kmh keeping pace with a few pommies - they need to HTFU. Make it to dismount line with great relief, legs not feeling too bad either. 1st 2 laps 12:48 (cold!) and 12:10, slowing to 14:06 with the flat, 1:54 slower for nursing the bike round the last lap, but power only a tad lower.

Head into transition, try to get shoes on, actually get helmet off (which is a relief seeing junior girls couldn't) and head out on the run. Legs feel great, but arms are soooo cold. Settle in to nice pace and form and get the pain flowing. Passed by a Scot at warp speed, keep looking for Michael Pratt AUS to come storming by. Great support from Aussies and others, final turn around appears, 1.2 km to go and no-one behind that looks fast - maybe I can do well in spite of the flat. Keep the hammer down on the long downhill to the finish, manage to grab an Aussie flag before the finish chute and hold it aloft in a frozen claw, so, so happy to have made it over the line.

Run not a PB, but fast enough to hold on to 9th, 5:33 down on Aussie Richard Woods who takes the title with a +2:56 margin over Simon Gowen (GBR) and
Frank Boyne (GBR) +3:58 in third. Realise that the 1:54 deficit on lap 3 on the bike would have put me +3:39 behind the winner and into third place by a comfortable 19 seconds. Aaargh. Our 4th 40-44 member, Brett Starkey finishes 16th about +8:19 down on Woods. My time of 1:19:44 is the slowest sprint race time I've posted for about 4 years, but the easily the most satisfying, under the worst conditions.

Michael Pratt DNFs on the run for some reason, and a glorious Aussie 1,2,3 is twice denied.

Sitting in the recovery tent, sipping hot soup and wrapped in a space blanket all I can think about is what might have been, the Gold Coast in 09, and how nice it will be to be warm. Game on!

Sunday, May 18, 2008

Aero test - helmets - final

[b]Final results for helmet test 1:[/b]

OK, after a lot of analysis, playing with different stats and error methods here are the final results for Helmet Aero test 1 between the Specialised Decibel, Giro Advantage 2 and Limar Crono 05.

I've also readjusted the data to take into account that the rolling resistance should be the same for all groups of data (since it was... same wheels/tyres for every test). This was done by plotting all the helmet data collected as one series and generating a combined linear trend to get the rolling resistance offset, and using that combined offset for each dataset. (Google Wattage group was some use after all).

The graph also plots the amount of error (SE) for each set of data (plotted as +SE/-SE). (These are the little black bars extending from each data point). At slower speeds the error from each data point overlap the other trend lines (not what we want), but at higher speeds this is not the case (this is what we want).

The graph plots force against the velocity (speed) squared in order to get a linear line, no easy way to force the data through the same rolling resistance offset otherwise.
This means it's harder to read, so the results below are included in the easy to digest format that shows how much time you could expect to save, and your time on the course.


Now does anyone want to participate in Helmet test no 2, which should be able to test a much wider variety of aero helmets (providing we get loaner donations of lids for a week or so).
I'd also be interested in anyone else with a proper power meter (SRM/powertap) that would like to help run tests, can't hurt to have some different riders have a crack at the test protocol either (plus you'll get good info on your drag profile that might allow you to go faster with a few tweaks). And finally, if anyone has got any strings with indoor velodromes, now would be a good time to let us know!

Results: At 200 watts: 0 degrees yaw (ie a calm day).[/b]


Av KMH.....35.5......36.1......36.9

time on course (hh:mm:ss)


time savings over using Decibel (hh:mm:ss)



Saturday, May 17, 2008

Wattage showdown

[quote=fishboy,May 12 2008, 07:57 AM]1- Yes. Was waiting till the dust settled on Wattage for a consensus to be reached (if that is possible!). All that will happen in the end is that we should be able to say it is 95% or 99% certain that the aero differences do exist between these helmets, and the variation is not occurring by chance.
2 - No idea, but that banner seems to chase me around transitions.
Wattage debate has degenerated into a smackdown between Robert Chung and Andy Coggan. Billed as the prize fight of the non tunnel aero testing methods, I'm not sure its going to help ...

[quote]Andy Coggan
More options May 17, 12:37 am
From: Andy Coggan
Date: Fri, 16 May 2008 07:37:06 -0700 (PDT)

On May 15, 11:57 pm, Robert Chung wrote:

> On May 15, 8:28 pm, Andy Coggan wrote:

> > So why did you essentially dispute me when I said that it wasn't?

> Cuz I can?

Well, hmmm. You can't possibly mean that you'd abuse your position of
authority to imply that you can do things that you can't actually do.
So, you must mean that you think that calculating a pseudo-elevation
profile allows you to identify sources of variability in ways that
can't be accomplished by other means. Assuming that's correct, I'm all
ears...in fact, why not start with my wife's velodrome tests, and tell
us all exactly why her power-vs-speed relationship varied slightly
across the different efforts?

Andy Coggan [/quote]

Sunday, May 11, 2008

Wattage debate (isn't there always!)

Debate currently raging over on Wattage as to how to derive some statistical measure of significance on the results. Hmmn, opened a can-o-worms...

[quote]From: Robert Chung
Date: Wed, 7 May 2008 11:09:10 -0700 (PDT)
Local: Thurs, May 8 2008 4:09 am
Subject: Re: Aero Testing Sheets - Update (Chung & Regression Methods)

> On May 7, 12:04 pm, Robert Chung wrote:

> > Andy (Coggan): with the regression method, using the proper model specification
> > always dominates.

> But (somewhat rhetorically) what is the "proper model specification"?
> The two alternatives are mathematically equivalent, the physics don't
> really help you decide, and the argument could be made that a power
> meter is just as much a force (torque) meter. To me, then, it comes
> down to how errors in the underlying measurements impact the precision
> of the CdA estimate, and that's what I can't decide (since the noise
> isn't necessarily "white", I don't think that a simple uncertainty
> analysis will suffice).

Since this is rhetorical, you almost surely already know the answer
but for those who don't, Andy's right, the physics models don't help,
and the mathematics are equivalent. What's not equivalent is the
statistical model. The underlying linear regression model is unbiased
and efficient (i.e., lowest variance) when the Gauss-Markov
assumptions are met. The "usual" regression model (where one regresses
W/v on v^2) will produce inefficient (though consistent aka
asymptotically unbiased) estimates because of heteroscedasticity.
However, over the range of v we usually see for these kinds of field
tests, I expect the efficiency loss will be relatively small. The
bottom line is that it's slightly better to use whatever the PM
reports rather than to transform the variables, though only very

BTW, you're right that the errors aren't "white." Note, for example,
systematic holes in the SRM's speed reporting. [/quote]

Wednesday, May 7, 2008

Helmet goes to heaven

Suffered a setback with the demise of the control Specialised Decibel. It has gone to helmet heaven. Thankfully, no-one injured or otherwise damaged in the process.

Also been consorting with stats nerds to try to get a proper test established so that when we do a big run with a bunch of helmets, we can say "good stuff, there really are differences between these lids, and the variation didn't happen by chance".

Now, anyone got any strings they can pull at indoor velodromes in Melbourne?

Sunday, April 27, 2008

Stats and other schtuff

Hmmn. Spent the last day reading up on stats - great way to pass the time :blink:

In any experiment there are 2 possible types of error: systematic and random.


Ergomo isn't factory calibrated properly
Offset is incorrect for temperature
k- factor in Ergomo is incorrect

Systematic errors affect all samples collected.


This run had more/less wind than that run
Goofy couldn't hold his aero position in this run or that run
Height up or down the bank was not constant
Too close behind another cyclist on the track and run was draft affected
Temperature varies between trials
Left/Right leg imbalance changes total reported watts

Random errors affect some samples collected.

Because the systematic errors affect everything the same way, we can probably discard them if we are only looking to show a significant difference between 1 helmet and another. In this case systematic errors might be important if we really want to know the difference at [i]exactly 200 real watts[/i], not what the test Ergomo unit reports as 200 watts.

Random errors are much more sinister. Maybe the difference between 2 helmets is due to solely random error, and not because 1 is more aero than another. This we don't want.

Still thinking ...

Friday, April 25, 2008

Aero testing helmets - comments


Hi Fishboy,

Interesting thread, I have done similar stuff in the past and also spent time in wind tunnels. There are a lot of uncontrolled variables in outdoor testing, hence the increased use of wind tunnels.

I have a few questions:

How do you verify the calibration of the Ergomo, in my experience they can be a bit random?

How are you sampling the data?

What is your calculated total error for each run?
Aero testing is very individual. It has been my experience that a helmet may be fast on one person but slower on another.


Yep Ergomos can be a bit random, and in fact there are studies (at the Saris web site) that confirm this; there is also no verifiable external test you can perform like on an SRM to ensure accuracy.
The BB unit in question is new and was properly installed to spec. It performs accurately in high climb tests predicting speed vs. weight on certain grades.
Every test I've done allows offset calibration to take place after stabilisation of temperature - all the above tests were conducted with the same offset value. So yes, it is possible that the measurement instrument is not as accurate as it could be, but short of heading off to the tunnel, it should be capable of producing some results. In fact this was one reason for trying these tests - could you actually see a difference between certain types of equipment/position without having to resort to a tunnel.

The data is sampled by looking for sections of constant speed and velocity, where the initial and final velocities are the same. Because it is on a velodrome, the data chosen must be more than 400 metres in length to ensure that at least one full lap of the 'drome is completed. This ensures that if there is some slight wind all angles into and away from the wind are covered (all tests so far conducted with no wind). Average power and speed are recorded and plotted.

By total error do you mean TE = Bias + Z*SD? And what value would you recommend for Z?

And yes, aero [i]can [/i]be highly variable. What works for one person might not work for another. I've stated that a few times through this discussion. But in general terms it is still applicable. The fact that the test data shows an improvement of 0.5 to 1.0 kmh at 200 watts by using an aero helmet is an important finding that people without access to their own tunnel and R&D staff would be interested to know. I've achieved that same result 4 or 5 times now over the course of the last year with testing, and results backed up with racing, so I'm pretty comfortable that this is on the money. And if the choice is aero wheels at $2500-3500 or a helmet for $200 that achieves the same benefit, again, I think people would be interested to know.

There is so much crap that goes on with aero testing manufacturers claiming this much time with this and this much time with that. I'm convinced that most manufacturers don't actually have that much idea what is actually going on (some notable exceptions), but the reality is that saying something is 'tunnel tested' is good for biz. For every tiny bit of data I've collected from every wind tunnel test that I've been able to find, the test result has often depended on who was running the test. As Cervelo says: "We're happy to finish second in tunnel tests paid for by someone else."


This is so true, you know what, the really interesting data never gets published, the best stuff I have seen in the tunnel will never get published.

Don't even get me started on CFD!!!!

By total error I mean the sum of all the errors, often this is bigger than the difference you are trying to measure so it becomes uncertain if you are really seeing a trend or not. Repeat trials can help, as can use of a control.

As I said it gets really hard to control the variables especially outdoors, so apart from the Ergomo, there is frontal area, rolling resistance, ambient conditions etc etc.

Congrats on the time and effort you have spent on this.

Tuesday, April 22, 2008

Aero testing #3 - results

[quote=fishboy,Apr 24 2008, 01:02 PM]Test number three this morning. Limar Chrono 05 v Giro Advantage 2 with taped vents. Subjectively, don't think taping has helped improve the situation, but need to run the data.
Better get to the LHS (local hardware shop) and get some duct tape.

Turns out that with the vents taped the Giro Advantage 2 performs exactly the same as the Limar. Kind of surprised me - how can 5 pissy little vents on the front of the helmet result in 0.9-1.0 kmh slower speed at 200 watts??? :blink: Should repeat this test with vents taped and de-taped to make sure.

So the first rule of aero helmets would seem to be: [quote]Buy aero helmets without vents in preference to ones with vents.*[/quote]
And the second is: [quote]If you have vents on an aero helmet, tape them.[/quote]

* Sure, if you think you're going to have a hot head, get one with vents, and ride that bit slower.

Here's the data:


Also interesting to note that this test with done with different clothing to last time - looser (but warmer) jacket which is not skin tight. This jacket is responsible for dropping the speed at 200 watts from:

37.1 and 38.1 kmh for Advantage 2 and Chrono (test 1)
37.1 and 37.9 kmh for Advantage 2 and Chrono (test 2 - same clothes as test 1, skin tight)


36.0 kmh for both helmets (test 3) - looser jacket, non skin tight

Aero testing #2 - similar results to earlier test

[quote=fishboy,Apr 21 2008, 09:28 PM]
Here it is folks:

I've just realised that the original test done between the Chrono and the Advantage is almost the same results as the second test.

The first test had average kmh speeds at 200 watts of: 37.1 and 38.1 for Advantage and Chrono
Second test at 200 watts: 37.1 and 37.9 kmh for Advantage and Chrono

So even though first trial used a disc and H3, and the second 36 spoked training wheels, the magnitude of the difference between the helmets was almost identical.

This is very good from a repeatability point of view, not so good from an aero wheel point of view - why spend $3500 on wheels if a $200 lid does the same job!!!!

Monday, April 21, 2008

Aero testing #2 - final results

I've been riding in the wrong helmet most of the season... :(

At least that is what the data says.

The simple assumption that new = better isn't necessarily so.

Here it is folks:

Orange and pink are the Specialised Decibel (least aero/non aero helmet).
Next best is the red circle of the Giro Advantage 2 (more aero).
Best is the Limar Chrono 05 in green (most aero).

I did have 2 outlying data points over 46 kmh, but I omitted them because it added more noise - probably cause power delivery at those higher speeds is a bit hit and miss (it's hard to control the application of 430 watts in a controlled manner - at least for me! - and hard to sustain that power for a long enough period that the speed stabilises.

So time savings; how much:

200 watts

Av KMH.....36.6......37.2......37.9

time on course (hh:mm:ss)


savings (hh:mm:ss)

Seems amazing that the choice on an aero lid can save you over a minute in a Sprint race, and more than 10 in an Ironman...

Remember this is based on 200 watts - if you are faster than this, it is even more important to have an aero lid!

Grain of salt time:

Are the results accurate? You tell me. Carefully designed experiment - careful test protocol, careful evaluation of results. As accurate as I can get.

Repeatable? Possibly. The whole experiment needs to be done again, and maybe a third time before we can see that it is repeatable and therefore 'admissable as evidence'.

Believable? Why is the Giro slower than the Chrono? Well the wind tunnel eyeball test confirms:

- The Giro has front vents, the Limar has none
- The Giro is taller and wider at the front than the Limar

both these factors should hurt the Giro


the Giro has a longer tail, and side burn covers that should make it lower drag than the Limar.

Would you get the same time savings if you used these helmets?

Possibly. This data is based on a 188cm dude on a P3C in a pretty aero position. If you aren't like that then the magnitude of the savings might be different. In general terms you are likely to have lower drag and faster times with the same helmets as shown above.


- More helmets
- Indoor venue (although wind less than 10kmh doesn't seem to have affected control runs to a measurable extent, particularly in the important business zone of 36 to 41kmh)
- Wind tunnel comparison to validate??

Any other suggestions?

fishboy ;)

Sunday, April 20, 2008

Aero testing #2 - results

Ok Got the control runs analysed.

And its good - both separate runs with the non aero helmet are very close together!
So the concern about the extra wind in the second trial seems not to be a problem.

Here's the graph:

Certainly the area between 32 and 41 kmh is very similar from both trials.

Will get to analysing the other two aero helmets soon, but probably not today.
The process is a bit tedious and if I'm gunna do more of this I think I might write a program to do the analysis. 5am swim training .... :unsure: :sleepy:

Saturday, April 19, 2008

Aero testing #2 - results

OK, Second test completed this morning. No results yet - will try to get online today.

Managed to get a full run of speeds for:

1. Specialised Decibel (non aero)
2. Limar Chrono 05 (aero)
3. Giro Advantage 2 (aero)
4. Specialised Decibel (non aero)

Unfortunately there was a bit more wind at the end of the test, will see if that affects the data. Dead calm at the start. Runs 1 and 4 should be very close together on the graph. If not ... maybe indoor velodrome time ;) . Also used spoked training wheels instead of disc/H3 to try to prevent any wind on that gear lowering CdA.

Subjectively, at speeds over 40 the two aero helmets felt significantly easier to maintain speed than the non aero lid. Max speed was about 50kmh.

All the other parts of the test were OK - constant Ergomo offset at beginning and end, consistent use of the selected speeds, consistent riding position (head up looking 15 m in front of the bike, still shoulders held in same position, knees just brushing the top tube all the time, same seat position, stayed away from drafting other track riders).

Thursday, April 17, 2008

Aero testing #2 - results

Here's the test data (piccy): Still working on the real results (time consuming :( )

Aero testing #2

Tomorrow mornings weather is looking OK (calm, but probably cold again).

I think I'll try another test to try to improve on the first set of results (since I'm not sure I believe them...)


[b]3 helmets: [/b]
Specialised Decibel (Non aero)

Limar Chrono 05 (aero)

Giro Advantage 2 (aero)

[b]Test protocol:[/b]

Ergomo offset 30 min after bike is in ambient


Run order (to save a bit of time, recovery on slower speeds, cause you need to try to keep power delivery really even). This time the speeds will be taped to the bars to make sure the X-axis data points are the same for each helmet.


(so that's a run of >60 sec for each speed for each helmet, 21 runs total)

Ergomo offset afterwards (hopefully same offset).

If it turns out that these two trials are OK, and we can see real differences, then it is worth taking the trouble to collect a set of helmets together and do a more extensive test.

BTW both Otter and Jester PM'd me - obviously keen to add further performance enhancement to each arsenal at their disposal. :lol:

Wednesday, April 16, 2008

Aero testing #1 - results


Holy Cow Batman - we do have some results. But before we get all excited, maybe we need to RETEST, just to see if the results stays the same (ie is the experiment is repeatable). Wouldn't hurt to tighten the test protocol so the numbers are the same eg. 26, 32, 36, 38, 40, 42, 44, max.

Here is the graph of the data:

Shows about a 12 watt reduction in drag at 40 kmh by using pink helmet, compared to orange helmet. And guess which helmet takes an additional 6-10 seconds in transition (ie get on your head)?

Now who wants to hazard a guess as to which is Limar Chrono 05 and which is Giro Advantage 2?

I'll post the answer tomorrow to allow some guessing time.

Aero testing #1


Location: Carnegie Velodrome
Date/Time: 16-Apr-2008 0645
Weather: Clear, calm, 8 deg C

Weather Moorabbin airport:


Bike + rider weight: 91.7 +/- 0.5kg

Ergomo Power meter
Stabilised at ambient temperature for 25 min before offset
Offset calibrated before test: 983 offset value
Offset calibrated after test: 983 offset value (no change)


Ride at constant power and speed for 2-3 laps of the velodrome
Choose range of speeds from 25 to max capable KMH eg.
25, 28, 30, 34, 38, 40, 42, 44, max.

Ride on blue line of track (ie same distance up the bank) to prevent changes in potential energy.

Change aero equipment and repeat test using same protocol above.

Download power file, isolate sections of speed with same initial and final speed > 60 seconds in duration, calculate average watts in this section of data.

Plot data using fancy spreadsheet (Coming soon).


What? You want results? Just kidding - working on these right now and will post when completed (soon).