How I lowered my CdA from 0.225 to 0.203 with on Road Aero Testing in search of Free Speed

[jennacaer]

Ok, lots of aero talk these days so I figured I would share. I totally got sucked into the aerodynamics and CdA obsession (though not quite water bladder down my trisuit level of obsessed). I’ve always worked towards a fast looking position on the bike and spent years working to achieve what I thought was “free speed.” While I don’t have a pro-level FTP, I usually have some of the fastest bike splits so figure my CdA couldn’t be too bad.

This year, I’ve shifted focus from Ironman to Duathlon to switch it up for a year (threshold work, yuck, but probably good for me after all of the years of Ironman focus). I quickly realized I can’t run nearly as fast as the other women doing duathlon so I wanted to see if I could get as aero as possible to use my bike handing and aerodynamics to make up for my run on the bike especially with a 40km bike instead of ironman it means I can go more aggressive.

Initially, I did some aero testing at a velodrome in Houston, where my CdA was 0.225 on my Factor Hanzo—decent for an age grouper but with room for improvement. After getting a new Argon E-119 Tri+ Disc bike, I wanted to see if I could get faster (and make sure it was at least as fast as my Hanzo)

I reached out for recommendations on aero sensors and was pointed towards the GiBLI Aero Sensor, which promised on-road testing without needing a coach or complicated data analysis. They said I could do aero testing on my own without a coach, I was a little skeptical, I am a triathlon coach but do not have experience with aero testing. Thankfully it turns out with their app it was super easy to set up and get rolling with some tests.

Initial Tests: Tested my Factor Hanzo with a race setup, showing a CdA of 0.216. Inspired by Lionel Sanders, I adjusted my aero bars from a 25-degree angle to 10 degrees, dropping my CdA to 0.208. That was a surprisingly significant gain—over 3 minutes in an Ironman.New Bike Tests: On my Argon, with identical wheels and aerobars, with a retul fit to set up the bike almost identical position wise to my Hanzo, the CdA was 0.217 at 25 degrees and 0.205 at 10 degrees. It showed position really matters a lot, 2 different bikes and very similar numbers.Stack Height and Reach: went out another day and played around more to see what it would do to CdA
Stack height: High (0.219 CdA), moderate (0.216), low (0.210).Reach (both with low stack): Moderate reach (0.208), long reach (0.205).No Surprises here, long and low is faster for me.Final Tweaks: By making my elbows more narrow with a long reach and low stack, my CdA dropped to 0.203. From my starting point of** 0.225**, this improvement could shave almost 2 minutes off a 40km duathlon bike leg, or hey if I can hold it over Ironman would be over 8 minutes

It’s an aggressive position but went back to my bike fitter afterwards and looked at all of the numbers with the Retul system and while it is super aggressive, for 40km shouldn’t be a problem, and I had no issues holding it on my last 2 hour ride. Would I do this position for an Ironman? Maybe, maybe not, we will see how the body adapts, but that’s not the goal this year. Next up I’m going to start testing equipment for those last few percentage points, let me know if you want to hear about those tests. Super impressed with how easy it has been to test with the GiBLI G10 sensor, it actually takes into account elevation and wind direction and has GPS on board so the only external sensor I need is a power meter.

[Former_User]

awesome - were you able to use lactate, SmO2 for effort to see how the changes also affected power production. Could then use BestBikeSplit to see how the change in power production and change in CdA affect race performance… and then there is figuring out how the change in position on the bike affects the person’s run. Possibly: smo2 sensor on gluts and separately on quads, see how changes in bike position affect muscle recruitment and test pool of subjects with treadmill ramp test after bike effort to find correlation of muscle recruitment on bike vs run performance. easy peazy 😂

I use experienced athlete feedback to get as close as possible. Curious to hear Marcag’s thoughts: if you hypothetically had a triathlete who had sub 1:50 bike split ability and their position had been optimized for power and their perception of their off the bike run performance and they had done a good job closing off the gap between hands and face with an aerobar with a solid underside…, aside from clothing, helmet and gear choices, where do you start?

and feel free to weigh in on the above proposed methods for controlling for effort, and empirically assessing the effect of bike position on run performance.

[jennacaer]

You have no idea how much I would love to geek out with all of that!

Really at the end of the day, the biggest changes from my original position on the Hanzo that I’ve raced well on were dropping the aero bars to a 10 degree angle - that wont affect much on the run and power output, and it feels more comfortable. That made the biggest drop in CdA.

The things that may affect power is my previous set up was I was in between the moderate and low stack on my new position, so I am about 1cm lower in the front than I was before. The longer reach is just under 1 cm longer than my previous set up.

So not massive changes in the stack and reach, it turns out other than the aero bar angle I was pretty close to the right position and I’ve raced well on that set up in Ironman and Duathlon. But I would so love to go deep and test the metabolic and power implications of the difference in positions.

Racing this weekend in a race I did last year in the previous set up so will see how everything compares on the race course!

[littlefoot]

Pretty cool. Gotta say, glad you can hold that-I definitely wouldn’t be able to.

Another idea to help you…upgrade your shoes. The Velovetta’s that are sold by a poster on here tests faster than your bonts, as well as the giro empire laced versions. I bought some elastic laces via recommendations from posters here for an easy in and out for transitions. You can get them in multiple colors.

https://www.amazon.com/dp/B01GYSDRRE?psc=1&ref=ppx_yo2ov_dt_b_product_details

[jennacaer]

I’ll check those out, thanks!!

[erbrown]

Congrats! That’s a solid improvement.

What cockpit do you have on that Argon? I still haven’t bit the bullet on something to get me further out front but it looks like you have a FastTT aerobar with some type of baseplate, just curious what you ended up with.

[jennacaer]

You nailed it, it’s the FastTT bars with the universal plate they sell and the adjustable angle piece. Really mostly bought from them because they made it so easy to figure out what adaptors I needed to fit it on my bike and how to install it. Happy with the results though and it was easy to just get a different plate to stick it on my Argon.

[Engner66]

Solid improvement, great job… Long gone are the days when I could ride in a similar position, twenty years sitting on a desk while neglecting strength and flexibility training, my back hurts just looking at such an aero position.

Would be curious to see a photo of the “high stack” 0.22 CdA position if you have one for comparison.

[mathematics]

Nick - For the lactate and muscle recruitment stuff, wouldn’t the ideal be to first find the most aero position and then just get used to it? As long as the position isn’t something crazy you’d expect that with a few weeks (months maybe?) dedicated training the output should nearly level out with cardiorespiratory output. I’m sure it’s a sliding scale kind of thing, but I can’t imagine threshold watts from one TT position to another being too terribly different. Seated climbing position to aero tuck sure, but conservative TT to aggressive TT seems like something you could just get accustomed to.

[Former_User]

Nick - For the lactate and muscle recruitment stuff, wouldn’t the ideal be to first find the most aero position and then just get used to it? As long as the position isn’t something crazy you’d expect that with a few weeks (months maybe?) dedicated training the output should nearly level out with cardiorespiratory output. I’m sure it’s a sliding scale kind of thing, but I can’t imagine threshold watts from one TT position to another being too terribly different. Seated climbing position to aero tuck sure, but conservative TT to aggressive TT seems like something you could just get accustomed to.

getting comfortable being uncomfortable was definitely a thing at one time.

with guys I’m working with doing 1:51, 1:53, low and sub 4 hour bike splits, I just don’t think that’s the path forward. for example, in the OP, I see a position really behind the bb and on the rear of the saddle. If I put folks in that position, guaranteed they’d be on the nose within 5 miles into the bike leg due to naturally wanting to be in a more powerful position, and the cda gains are out the window. That real world element is needed, imo; knowing what actually happens on a TT bike in the real world and that power lost due to naive low cda positions on the bike don’t just become adapted-to with time and then power returns, in my experience.

Others are welcome to weigh in, but for the moment, the proof is in the pudding. Curious and open to see what can be done to make further improvements with these people on my saddles. but one thing I can say, that won’t include naive positions on the bike.

[marcag]

awesome - were you able to use lactate, SmO2 for effort to see how the changes also affected power production. Could then use BestBikeSplit to see how the change in power production and change in CdA affect race performance… and then there is figuring out how the change in position on the bike affects the person’s run. Possibly: smo2 sensor on gluts and separately on quads, see how changes in bike position affect muscle recruitment and test pool of subjects with treadmill ramp test after bike effort to find correlation of muscle recruitment on bike vs run performance. easy peazy 😂

I use experienced athlete feedback to get as close as possible. Curious to hear Marcag’s thoughts: if you hypothetically had a triathlete who had sub 1:50 bike split ability and their position had been optimized for power and their perception of their off the bike run performance and they had done a good job closing off the gap between hands and face with an aerobar with a solid underside…, aside from clothing, helmet and gear choices, where do you start?

and feel free to weigh in on the above proposed methods for controlling for effort, and empirically assessing the effect of bike position on run performance.

Last year at the Moxy Summit I did a talk with a fellow STer (Ryan) on this subject. I think the presentation may still be on the Moxy site. I will ask. My portion of the presentation was on the aero testing. Ryan’s portion was questions on if Sm02 could be used to see changes.

The thing I like about outdoor testing vs the tunnel is the rider can assess if it’s easier or harder (sometimes). Example one pro rider (Kirists Neilands), when testing we raised his stack, no aero gain or loss. “Krists, does that feel easier ?” . “Nah not really”. Go up another 2cm, same. Another 1 started raising CDA. “But Krists, doesn’t it feel easier ?” …“nope”…OK…slam him down to where he started. “Holy shit that is way harder”.

A really good process is to measure the possibilities and then let the rider do long rides in that position. Example, everyone’s favorite triathlete (the guy with his own thread), found the “fastest” position in the tunnel. Two months later he races Oceanside in the 2nd fastest position. He couldn’t hold the fastest position or at least it wasn’t worth what we had measured as the difference.

The guy that just podiumed at the Dauphine. We first tested him at Silverstone : “Derek, that changed cost you 2watts”. “Hell I’ll pay those 2 watts. I’m sure I can generate 10 more”.

Then we get into the whole conversation of “OK, it’s not ideal but if it’s 10watts…”. What if the 10 watts measurement is wrong ? I double and triple check everything when confirming position changes that will impact power production. Same with neck pain…There are ways of getting more confidence in the measurements. Not everyone does that, they are happy to see a good number even if it’s wrong.

[Former_User]

Then we get into the whole conversation of “OK, it’s not ideal but if it’s 10watts…”. What if the 10 watts measurement is wrong ? I double and triple check everything when confirming position changes that will impact power production. Same with neck pain…There are ways of getting more confidence in the measurements. Not everyone does that, they are happy to see a good number even if it’s wrong.

Can you provide clarity around this?

An aside and something interesting imo - most amateurs would be more comfortable in the positions seen used by Ditlev, Long and Foley.

[Hanginon]

.

[marcag]

Then we get into the whole conversation of “OK, it’s not ideal but if it’s 10watts…”. What if the 10 watts measurement is wrong ? I double and triple check everything when confirming position changes that will impact power production. Same with neck pain…There are ways of getting more confidence in the measurements. Not everyone does that, they are happy to see a good number even if it’s wrong.

Can you provide clarity around this?

An aside and something interesting imo - most amateurs would be more comfortable in the positions seen used by Ditlev, Long and Foley.

What I meant is if you test 2 positions and they say 10w difference, before you make a significant change position, you make sure that 10w is accurate.

There are things I see in those pictures that I would double check if I had the data, just to be sure.

[Former_User]

The effective sta’s in those pics (bb to pubis/ischium on saddle) are all slacker than 81 deg. Mid race, nearly everyone I measure migrates to 84-85deg. so, I set people up there and typically 82 at low power and that’s achieved by merely scooting back on the saddle a hair and if the ride is easy, we bring the cups back 5mm pre ride to avoid back pain. Testing cda with these super slack effective sta’s is unrealistic, imo.

[Former_User]

What I meant is if you test 2 positions and they say 10w difference, before you make a significant change position, you make sure that 10w is accurate.

There are things I see in those pictures that I would double check if I had the data, just to be sure.

👌

[mathematics]

Nick - For the lactate and muscle recruitment stuff, wouldn’t the ideal be to first find the most aero position and then just get used to it? As long as the position isn’t something crazy you’d expect that with a few weeks (months maybe?) dedicated training the output should nearly level out with cardiorespiratory output. I’m sure it’s a sliding scale kind of thing, but I can’t imagine threshold watts from one TT position to another being too terribly different. Seated climbing position to aero tuck sure, but conservative TT to aggressive TT seems like something you could just get accustomed to.

getting comfortable being uncomfortable was definitely a thing at one time.

with guys I’m working with doing 1:51, 1:53, low and sub 4 hour bike splits, I just don’t think that’s the path forward. for example, in the OP, I see a position really behind the bb and on the rear of the saddle. If I put folks in that position, guaranteed they’d be on the nose within 5 miles into the bike leg due to naturally wanting to be in a more powerful position, and the cda gains are out the window. That real world element is needed, imo; knowing what actually happens on a TT bike in the real world and that power lost due to naive low cda positions on the bike don’t just become adapted-to with time and then power returns, in my experience.

Others are welcome to weigh in, but for the moment, the proof is in the pudding. Curious and open to see what can be done to make further improvements with these people on my saddles. but one thing I can say, that won’t include naive positions on the bike.

Really interesting. I def fall into the old school tough it out category for a lot of things. Like marcag was getting at, doing long runs may be an ideal compromise between the two. Holding something for 20min isn’t the same as 4h, but ding 4h runs isn’t a tenable test protocol either.

I have to wonder if we’ll start seeing a more iterative year-to-year position process. We already train building on years past, maybe it’s not the worst idea to build a little position a little more aggressive every year, staying just on the edge of what you can hold. Obviously the easier sell is getting faster in a day, but gradually moving lower and narrower should (mostly) continue to gain.

[jennacaer]

That’s probably been one of my favourite things about using the GiBLI is getting that real world info for how I really ride.

I can ride with it in training and use it almost like a power meter (except CdA instead of watts), outside of testing, and when I’m putting in 20-30 minute efforts over something like a 2 hour ride I can just hit lap and see what the CdA average is during those laps. So I can see through a longer ride what the difference is as I fatigue and what it looks like at race pace.

I would do those laps without CdA data visible just to see what my actual position at race pace is CdA wise.

Next up the race this weekend I will have it running to see what the data says race day, it will definitely be higher with a lot of corners and a no passing zone, but get some insight into what it is in a race situation and if my position degrades significantly over the 40km.

[jennacaer]

I absolutely agree, I’ve been doing a lot of testing and over a few days, going back and forth between positions in different conditions to see if a crazy windy day vs. a calmer day made drastic differences.

For this I showed the lowest numbers because they sound the best (yay social media), but between 3 days of testing in various conditions with the stack height and reach, and testing the aero bar angle over 2 different bikes, and 3 days it was all consistent enough for me to feel confident in the difference.

[jennacaer]

Nick - For the lactate and muscle recruitment stuff, wouldn’t the ideal be to first find the most aero position and then just get used to it? As long as the position isn’t something crazy you’d expect that with a few weeks (months maybe?) dedicated training the output should nearly level out with cardiorespiratory output. I’m sure it’s a sliding scale kind of thing, but I can’t imagine threshold watts from one TT position to another being too terribly different. Seated climbing position to aero tuck sure, but conservative TT to aggressive TT seems like something you could just get accustomed to.

getting comfortable being uncomfortable was definitely a thing at one time.

with guys I’m working with doing 1:51, 1:53, low and sub 4 hour bike splits, I just don’t think that’s the path forward. for example, in the OP, I see a position really behind the bb and on the rear of the saddle. If I put folks in that position, guaranteed they’d be on the nose within 5 miles into the bike leg due to naturally wanting to be in a more powerful position, and the cda gains are out the window. That real world element is needed, imo; knowing what actually happens on a TT bike in the real world and that power lost due to naive low cda positions on the bike don’t just become adapted-to with time and then power returns, in my experience.

Others are welcome to weigh in, but for the moment, the proof is in the pudding. Curious and open to see what can be done to make further improvements with these people on my saddles. but one thing I can say, that won’t include naive positions on the bike.

Really interesting. I def fall into the old school tough it out category for a lot of things. Like marcag was getting at, doing long runs may be an ideal compromise between the two. Holding something for 20min isn’t the same as 4h, but ding 4h runs isn’t a tenable test protocol either.

I have to wonder if we’ll start seeing a more iterative year-to-year position process. We already train building on years past, maybe it’s not the worst idea to build a little position a little more aggressive every year, staying just on the edge of what you can hold. Obviously the easier sell is getting faster in a day, but gradually moving lower and narrower should (mostly) continue to gain.

This is exactly what I did over the last 10 years. I work with a bike fitter who started as a bike fitter and then went back to school to become a physiotherapist and now that is what he does is combine the two to do bike fits and treatment with how your body moves in mind.

I’ve slowly gotten into more aggressive positions over the years as I become stronger and more mobile to support those position changes with targeted strength and mobility work.