Jump to content

The Draft Zone Analysis Thread


Recommended Posts

Well here's a test so we can find out:

 

Open, outdoor velodrome; wind affected if windy, last ride there nearly sent me into the fence with a 70kmh gust.

Whatever wind conditions and angles are there tomorrow.

 

ride for 3 minutes at 12m separation, ride for 3 minutes on the front, repeat.

3 minutes at 40kmh will give about 5.5 laps of the drome, enough to average out specific wind conditions as long as they are reasonably consistent

I have a laser pointer mounted for 12 metre accuracy on the bike in front.

Bike mounted camera to record test protocol.

SRM to record power.

 

Oh yeah, and a 9 x 10km interval session to do.

My guess is I'll have a fair bit of data afterwards....

 

I did do this before, but not at 12m, and wasn't too scientific with regard to distance off the bike in front.

 

I'll report back tomorrow.

  • Like 2
Link to post
Share on other sites

I have data. Will take some time to analyse. Was 12m behind another rider/not behind another rider for a 10km interval this morning at ~40kmh. He's a fairly small guy so the draft benefit would have been less than someone with more "chunk". Not much wind.

 

Laser pointer worked very nicely. Read short on the bends due to the curve and bank, but OK on the straights.

Link to post
Share on other sites

I have data. Will take some time to analyse. Was 12m behind another rider/not behind another rider for a 10km interval this morning at ~40kmh. He's a fairly small guy so the draft benefit would have been less than someone with more "chunk". Not much wind.

 

Laser pointer worked very nicely. Read short on the bends due to the curve and bank, but OK on the straights.

 

If I had the data and there were no markers attached to tell me anything about when you did/did not "draft", would I be able to successfully identify those sections?

 

i.e. a blind analysis

Link to post
Share on other sites

I'd rather not predict anything Rog, just look at the data without any preconceived notions.

 

Alex, blind analysis might work.

I can send you the gpx file if you'd like to have a look.

Have 3 x 10 km intervals (E, M, H) with periods of ~2.5-2.7k leading and following at 12 m as best as possible, except for the last interval where I spent more time on the front.

I have video of the first interval. First 2 intervals relatively calm. By the third interval a definite headwind in operation on one side of the track.

Edit: and yes, no markers in interval for in front/behind, and I haven't told you who started leading.

 

Started pissing with rain and my back tire went flat, so didn't complete the 9 as planned. Not sure if that should be :smile1: or :sly: .

 

Should have some results around 7pm tonight.

Edited by fishboy
Link to post
Share on other sites

I'd rather not predict anything Rog, just look at the data without any preconceived notions.

 

Alex, blind analysis might work.

I can send you the gpx file if you'd like to have a look.

Have 3 x 10 km intervals (E, M, H) with periods of ~2.5-2.7k leading and following at 12 m as best as possible, except for the last interval where I spent more time on the front.

I have video of the first interval. First 2 intervals relatively calm. By the third interval a definite headwind in operation on one side of the track.

Edit: and yes, no markers in interval for in front/behind, and I haven't told you who started leading.

 

Started pissing with rain and my back tire went flat, so didn't complete the 9 as planned. Not sure if that should be :smile1: or :sly: .

 

Should have some results around 7pm tonight.

 

alex AT rstsport DOT com

 

if I get a chance will see what I can see

been a bit busy with normal training stuff, plus building a new website ;-)

Link to post
Share on other sites

OK, very briefly:

 

Alex no peaking till you look at the file I emailed you.

 

Raw data:

 

 

1st 10km interval (Easy, and no wind)

 

drafting @ 12 m

2:31

1.6km

38.9kmh

211 watts

 

in front

2:35

1.72km

40.0kmh

258 watts

 

back drafting @ 12m

 

2:38

1.675km

38.0 kmh

194 watts

 

back in front

 

2:37

1.74 km

40.1 kmh

265 watts

 

Last 10km interval (Hard, and now distinct headwind one side of track, tailwind the other, and cross winds at each end)

 

drafting @12 m

2:33

1.72km

40.5 kmh

245 watts

 

in front

2:35

1.76km

41.0 kmh

276 watts

 

spent most of that interval on the front, so only got 1 repeat in

 

 

 

 

There is a little difference due to the average speeds being slightly off, I'll work those out so they are consistent and provide a real figure in watts saved.

This'll be later

Link to post
Share on other sites

Wow. That is much more of an advantage than I thought it would be. I hear Jimmy Riccitello saying he thought it was 5-10 watts as 10m.

 

Just to confirm that is 12m from back wheel of bike in front to front wheel of bike behind?

Link to post
Share on other sites

In the other thread about speed for an IM rider with modest wattage, there was some discussion about the drafting benefit (or lack of) when there is some gap between you and the rider in front.

 

Fishboy mentioned he would do some test runs at his local outdoor track, collect the power meter data and report back. I suggested he send me the power file with no notes attached, and that I would take a look to see what I could discern from the data without actually knowing what he did.

 

He also asked I not look at the other thread until I reported back, which I haven't done (but will once I've finished posting this). You will all just have to take my word for it.

 

OK, so what did I find?

 

Following are 3 charts. I did this because from the data file, it appeared that Fishboy rode about 35km total, with 3 intervals of ~10km each, with a bit of warm up and short recovery between each interval. So there is one chart for each 10km interval. The speed and average power for each interval was a little different, which each being ~ 20W harder and 0.7 - 1km/h faster than the previous effort.

 

Upon examination of the data, it was clear to me Fishboy's apparent air resistance varied during each 10km interval. Within each interval, there were 4 distinct sections with relatively stable aerodynamics, each of approximately 2.5km in length. In each chart I have indicated on the bottom axis where I think the start and end of each of those sections was, and the columns show my estimated CdA for each of those sections. Note that the CdA numbers won't be absolutely correct since I am making some other global assumptions about Fishboy and environmental conditions, but what's important is the measured differences in apparent CdA - which are quite reliable.

 

 

You will see some blue and red columns, as it is clear that Fishboy's apparent CdA was either "low" or "high" during these sections. Now, this can be as result for instance of being in the aero position, and then sitting up, then back into aero again etc. But for the purpose of this exercise I will assume he rode with another rider on the track, and was either in front of, or behind the other rider. I don't know how far the gap between the riders was in any of the intervals, all I am showing is the estimated difference in apparent CdA between "leading" (red) and "drafting" (blue).

 

Also shown, are horizontal lines, which are the average apparent CdA for "drafting" (blue) and "leading" (red), as well as the difference in apparent CdA between each (the fat vertical double headed arrow).

 

Interval 1:

FishboyTest1.jpg

 

Interval 2:

FishboyTest2.jpg

 

Interval 3:

FishboyTest3.jpg

 

 

So in summary, the gain by drafting was an apparent* reduction in CdA of:

Interval 1: 0.035m^2

Interval 2: 0.033m^2

Interval 3: 0.026m^2

 

In terms of wattage savings for drafting over leading, when riding at 40km/h:

 

Interval 1: 29W

Interval 2: 27W

Interval 3: 21W

 

So, I'll let Fishboy fill in the blanks as to what he actually did. All I can tell you is that whatever it was, there was a definite aerodynamic benefit in play, it was substantial in each case, although in the 3rd 10km run, it was a smaller advantage, but still significant, 20W is certainly nothing to be sneezed at.

 

Also, there was an apparent increase in non draft CdA in the third interval. There can be several reasons for this, such as environmental condition changes, on bike position changes due to riding at higher power and/or fatigue (creeping forward on saddle for instance), change in equipment/clothing and so on.

 

 

 

* I say an apparent reduction, because it's not Fishboy's actual aerodynamics that changes, it's the air flow he is riding through that is changing. What these numbers represent is the equivalent impact of that beneficial air flow in both CdA and in wattage saving terms.

 

 

(note: quick edit for typo, no content change)

Edited by Alex Simmons
  • Like 3
Link to post
Share on other sites

OK, back now - I posted my findings on a new thread called: "The Drafting Thread".

OK, about to have a look at what Fishboy has posted.....

 

Link here:

http://forums.transi...ndpost&p=908298

 

I just looked at Fishboy's post, not sure if I quite follow the order of what's been posted, but if all three 10km intervals were examples of leading, or drafting with a 12 metre gap, then wow. I think you guys might need the 120 metre rule :D

Edited by Alex Simmons
Link to post
Share on other sites

Looks like more than I would have thought, seems 5-10% range?, but 40 km/h ave speed :)

 

When I'm spaced 10m thereabouts on Beach Rd from a guy I ride with (tried this a few times) don't reckon get anything! Can just start to feel it getting a little easier at around a couple of bike lengths (say 5 m). But pretty rough n ready comparison, no PM.

 

(I used to fly hang gliders. The wake/bumpiness/vortices from a glider in front when aloft, and trees etc at ground level if windy when landing, went much further than would have thought, and one of the emphasized risk factors)

Link to post
Share on other sites

And if you had 5 more guys each spaced out in front of the first, the effect would have been even greater, especially on a calm day or with a straight headwind.

 

Maybe that first part of the ride before any wind comes up later in the morning is when it's important to be in that paceline.

Link to post
Share on other sites

Nice work fishboy.

 

I love the use of the ratdog patented laser for the distance measuring.

 

The real advantage comes when your slow out of the water and able to leapfrog long large packs whilst carving through the field.

 

Testing this might be difficult but possible if you have enough mates. a velodrome with a continuous paceline 12 apart and you leap frogging them all.

Link to post
Share on other sites
(I used to fly hang gliders. The wake/bumpiness/vortices from a glider in front when aloft, and trees etc at ground level if windy when landing, went much further than would have thought, and one of the emphasized risk factors)

 

In an indoor 250m velodrome, I can detect in the power meter data the change (lowering) in apparent CdA of a solo rider gradually creating a swirl of air flow, like a toothpick stirring a bathtub. Takes about 10-minutes or so to finally reach a plateau, and it affects things for many minutes after stopping as well.

Link to post
Share on other sites

I'd like Fishboy to confirm a few things, such as:

- were all intervals the same draft distance, or different?

- what was the morphology/aero (approx) of the other rider (small/medium/large)?

- what were the wind conditions, and did conditions change during the session, and in what way?

- photo or location of the track

Link to post
Share on other sites

In the other thread I think he said the rider wasn't big, and that the last one had much more wind.

 

I'd like to see this thread fully updated with all the info regarding this, and then trigold it! Can be referred to every time a drafting benefit question is asked.

Link to post
Share on other sites

In the other thread I think he said the rider wasn't big, and that the last one had much more wind.

 

Well if that's the case, it would explain two things:

- the increase in apparent CdA of the non-draft sections of the third and final interval*

- the reduction in the benefit gained from drafting in the final interval

 

In any case, I can see this becoming a new blog post.

 

 

* having said that, there are occasions when cross wind can actually lower your apparent CdA.

Link to post
Share on other sites

* having said that, there are occasions when cross wind can actually lower your apparent CdA.

 

I was going to ask about the effect of cross winds. What would the results look like if you were legally sitting 12m behind someone in a race but there was a crosswind? Tailwind? Cross headwind? I guess that would depend on the strength of the wind also but say for argument sake it was 20 km/h.

Link to post
Share on other sites

Could the percentage gain for drafting be greater for slower riders?

 

In sailing the wind shadow cast by a spinnaker is longer in light winds than in strong winds where it seems to fill the hole much earlier. Of course even 30kph would be considered strong winds for sailing so the speed we are travelling may be above a certain threshold. However just a question for our boffins.

Link to post
Share on other sites

I do all my riding with fishy and I also have a PM.

And the result speak true to what I have found on the drome. In the other thread i suggested it would be around 20w.

 

However, in race conditions, on rough roads like pt Mac, this will be Lower. I would say around 15 watts saved. Then add in the fact that in an IM you are not going round at 40+kmph, it makes the wattage difference a bit (small bit) lower.

Link to post
Share on other sites

Nice data analysis, Alex.

 

Is aero-coach.com your new, yet to be released website?

 

The data Fishboy gave you from simply a power file for you to do this analysis?

 

 

Thanks, yes and yes. Fishboy simply emailed the power file with no other information (well apart from the fact that each 10-km interval was marked as an interval). Obviously I was aware it was from a ride where he was trying something to do with drafting but I did not know beforehand what he was trying. The test was to see if I could assess anything, determine what he did, for what periods, what the variances were etc. If I was wrong, the I'm sure he'll update us.

 

Armed with the leading edge technology we're bringing to the market, we'll be able to nail these things precisely while riding your bike on the road/track no matter the wind conditions.

Edited by Alex Simmons
Link to post
Share on other sites

I've moved all the posts out of the other topic and placed them all here.

They have come in within time and date order.

 

eg:Alex started this topic but fishboys original posts regarding doing the testing will be first up.

Link to post
Share on other sites

Armed with the leading edge technology we're bringing to the market, we'll be able to nail these things precisely while riding your bike on the road/track no matter the wind conditions.

 

Nice.

 

"Chung-on-a-stick" type stuff?

Link to post
Share on other sites

So from reading this Alex, can one surmise that you could grab someone's run from Calga and work out their CdA if you have their avg power and ride time?

 

You'd need more than that. For a start you need the second by second speed and power data, some other info on the rider/bike mass, weather data, and with that you can make a reasonably good estimate, however unless you are also measuring wind, the precision of this is limited, but yes, I have done exactly that.

 

In the case of Fishboy's data, this is a special case in that we know he is passing the same point (which is at precisely the same elevation) many, many times. This greatly aids in nailing down the estimates and enables us to tease out more info if we really crunch it. For example, once I have the software up and running, we'll be able to auto solve for CdA and Crr (rolling resistance).

Link to post
Share on other sites

Alex,

 

Is aero-coach.com associated with Andy F of Alphamantis Technologies?

 

From their website:

 

Services

We provide cutting-edge physics models of bicycle motion. Our specialists can provide you with insightful turn-key solutions for your team or solo needs on the track or on the road. For pro bike teams and national federations, we can provide systems to monitor your athletes and to create race-specific time-trial pacing.

 

In addition, we provide:

 

team or solo pursuit analyses

pacing tools

optimisation tools

custom sensors

custom hardware solutions

Go faster by riding smarter!

 

Link to post
Share on other sites

Yes, but it's a bit more sophisticated than many will initially appreciate.

 

It's already been used to good effect for one Olympic track cycling team.

 

Not cost-effective for aging (aka old) tech-geek triathletes?

Link to post
Share on other sites

Not cost-effective for aging (aka old) tech-geek triathletes?

 

How much do people spent to attain speed/performance improvement?

 

Many seem happy to spend thousands of bucks on frames and wheels, and then ride an aero nightmare of a position, and/or with other crimes against aero on their bikes or selves. That doesn't seem particularly cost effective to me.

  • Like 2
Link to post
Share on other sites

umm.. hardly conclusive data, looking at it; its a simple case of more speed- more watts. everytime hes out front hes riding faster. there needs to be a consistent speed precisely - this data doesnt show anything that says its easier to sit in the back

Link to post
Share on other sites

You'd need more than that. For a start you need the second by second speed and power data, some other info on the rider/bike mass, weather data, and with that you can make a reasonably good estimate, however unless you are also measuring wind, the precision of this is limited, but yes, I have done exactly that.

 

In the case of Fishboy's data, this is a special case in that we know he is passing the same point (which is at precisely the same elevation) many, many times. This greatly aids in nailing down the estimates and enables us to tease out more info if we really crunch it. For example, once I have the software up and running, we'll be able to auto solve for CdA and Crr (rolling resistance).

 

 

Yeah Alex totally appreciate that. A WKO+ file, bike details, weather (from Calga's ATTA results) and rider weight

 

Doesn't give you the same point of reference (passing the same spot) but you would get elevation gain from the garmin and the 24.5k 1 km markers though as well.

 

Very interesting, i'd be curious to know mine at some point.

Link to post
Share on other sites

How much do people spent to attain speed/performance improvement?

 

Many seem happy to spend thousands of bucks on frames and wheels, and then ride an aero nightmare of a position, and/or with other crimes against aero on their bikes or selves. That doesn't seem particularly cost effective to me.

 

Sorry, let me re-phrase that:

 

Is the price-point for such services geared towards individuals too, or only teams etc?

Link to post
Share on other sites

 

Yeah Alex totally appreciate that. A WKO+ file, bike details, weather (from Calga's ATTA results) and rider weight

 

Doesn't give you the same point of reference (passing the same spot) but you would get elevation gain from the garmin and the 24.5k 1 km markers though as well.

 

Very interesting, i'd be curious to know mine at some point.

 

 

Load your garmin data into this to get a rough idea. It won't mean a whole lot unless you used a speed sensor and little wind but will give you some starting point.

 

I must say Alex I am getting a little excited about what you may be looking to launch.

Link to post
Share on other sites

To confirm:

 

All intervals were the same draft distance +/- 0.3m, 12m front wheel to front wheel.

The intervals got harder (3 x 10km E, M, H)

The wind went from dead calm to moderate on the H interval. Distinct head, tail and cross winds on interval 3 (the H one), possibly more than what Moorabbin airport recorded as there was a rain shower that came through with much stronger wind.

The other rider is small, ~65kg, on a very aero bike, in a good aero position. Probably 0.250 or so CdA. If there was something smaller or more aero to draft off, it would be hard to find.

 

The BOM data for Moorabbin airport, 10km away approx was:

Date/Time

EDT Tmp

 

°C App

Tmp

°C Dew

Point

°C Rel

Hum

% Delta-T

 

°C Wind Press

QNH

hPa Press

MSL

hPa Rain

since

9 am

mm Dir

Spd

km/h Gust

km/h Spd

kts Gust

kts -

08/06:00am 12.6 11.3 11.2 91 0.7 NNW 9 13 5 7 1010.6 1010.5 0.0 08/05:45am 11.9 11.4 10.6 92 0.7 NNW 4 9 2 5 1010.5 - 0.0 08/05:33am 11.5 11.6 10.2 92 0.7 CALM 0 0 0 0 1010.3 - 0.0 08/05:30am 11.5 11.6 10.2 92 0.7 CALM 0 0 0 0 1010.2 - 0.0

 

My weight and bike 95kg.

Crr previously measured many times on this velodrome at 0.0044.

Air density pretty consistent around 1.227.

 

Bike is TT (P3) with H3 front, H Jet Disc rear, eKoi helmet (no vents).

 

Track location is Carnegie Velodrome in Packer Park just near East Boundary Rd and North Road. 363m circuit.

 

Laser pointer was taped to the frame to aim at the back wheel of the rider in front for a 12m front wheel to front wheel distance.

Rig checked after the session and laser was still accurate, so didn't move during the session.

 

The procedure was to ride sections of the interval drafting and non drafting.

It was attempted to hold a constant speed during each section (were aiming for 40kmh, but my front rider went a little slower on the first interval).

In the data I selected above, I ignored the changeover sections where I was passing or being passed.

 

In all intervals I trailed on the first segment, then swapped to the front twice.

 

In all intervals I tried to hold the same aero position. This was very consistent on the first interval, but possibly less so on the final interval.

 

Alex derived these energy savings, and while I haven't cross checked yet, they look about right to me.

 

Interval 1: 29W

Interval 2: 27W

Interval 3: 21W

 

In other words, get in the zone people, especially if its a draft zone shorter than 12m.

 

Anyone suggesting there is no benefit at 12m is totally incorrect, even in head, cross and tail winds on interval 3 there was close to 20w difference - which is significant.

When it is calmer, there is more benefit, which makes perfect sense.

 

There is also a high likelihood that there could be even more benefit that could be found from a bigger test rider in front, being 3rd or 4th wheel, or being closer than 12m.

 

If I have time I'll see if we can test that next week. JimmyK needs to turn up!

 

Over the weekend I'll post the actual TCX file and a picture of the interval data so you can see them.

Link to post
Share on other sites
×
×
  • Create New...