As I keep working on updating the potentially revolutionary pipeline for video of cyclist to 3D model to CFD aero drag test for my new beta service https://wind-tunnel.ai I keep running interesting tests and sharing them here and a few other places (Slow Twitch, Reddit, they do First go up on the Insta@windtunnel_ai).
This one is really just a quick peak because I only tested one speed and one yaw, lone rider, vs a rider drafting a rider, measuring the forces each one has to overcome from the wind specifically.
Iām already working to scale and try to answer this at many yaw angles, 3 speeds, perhaps different rider size configurations, maybe even more riders, etc.
So, how many watts does the rider Pulling SAVE from having someone else Draft?
This is a quick test to ensure the setup was configured properly. More detailed comparisons and much more data are on the way!
Results at 0Ā° Yaw, 22.4 mph (~36.0 km/h)
Rider Scenario
CdA (mĀ²)
Power (W)
Approx. Reduction from Lone
Lone Rider
0.26
159
ā
Front Rider
0.24
150
~6% less
Rear Rider
0.17
105
~34% less
Why does the front rider also gain?
The trailing rider āfillsā the turbulent wake, reducing the low-pressure zone behind the leaderāso everyone wins!
(Test subject is ~5ā7ā (~170 cm), ~145 lb (~66 kg). Stay tuned for more speeds and yaw angles!)
Much appreciated, Iām trying to run these tests to add value to the post and yeah, I mostly post on Insta and Gravel Subreddit, and have just started making a few on SlowTwitch.
Although Iām not really trying to āsellā it so to speak, Iām the developer, not a business/marketing guy. Iām just excited and want to show it off from a technical point of view, answer questions, take feedback, etc.
I saw something similar a couple of years ago. Will be interesting to see how your results compare, and if there are surprising differences as yaw, speed, rider sizes change.
This is a fascinating chart. Iām also curious about the effects at very low mtb speeds, aero bars on front/back rider, the effect a third rider causes, echelons, different rider sizes and more.
Iām also going to add some vehicles and get to modeling that as well, but again, good find.
Iām interested in this, as this is most of my riding. Iāve seen modeling before that the % change in aero drag as CdA changes is the same - so aero matters - no matter the speed.
But at lower speeds, the absolute wattage savings is lower, so doesnāt sound as impressive at higher speeds. Plus, at lower speeds, aero as a percent of overall drag is less, so aero savings lead to less time percentage savings vs at higher speeds. But I have only a qualitative understanding of this (I think).
Iām riding Moab Rocks at the beginning of April, and am not planning to optimize for aero. I wonder how much time Iām losing as a result?
First, Iām just testing some of these things (like 15mph mtbing) because I canāt find data from anyone else and it interests me.
Second, a common misconception is that slow speed aerodynamics optimization isnāt worthwhile, but, if looking at Triathlon as an example, the slower athletes spent much more time on the course than the pros. Even though the watt difference in aero gains is lower, they end up saving minutes while pros might just shave a few seconds with similar optimizations.
Third, Iām jealous, Iāve been dying to go back to Moab! Iāve only been there once, and I was a terrible mountain biker, now, Iām ā¦ slightly better, and it was such an incredible place!
Itās impressive what youāve come up with so far!
Still wrapping my head around the ā4 cables less make 0,3 watt differenceā example another example could be full aero one piece integrated cockpit vs traditional round bar+stem+cable or 40cm vs 38cm vs 36cm bar widthā¦
Just a little suggestion for your examples:
At first glance your examples seem to have too low wattage required against what you would normally expect. It only becomes clearer when you see the comparatively low rider height and weight and the riderās aero position.
I think your examples and marketing would benefit from making these more relatable like 180cm 75kg rider on the hoods for example.
This tallies with my personal experiences of trying to hold a steady speed in a 4-up team time trial.
Being the tail gunner felt harder than being the ā3rd placeā rider. Watts fluctuated but generally 15 to 20 watts less from what I could tell - running circa 270 watts in the draft of the 2nd rider.
This was counterintuitive to my initial expectations.
What AlSO made a difference (quite noticeable) was who was behind me.
We did some practice runs and the obvious benefit of drafting a big unit (6ā5ā tall 210lbs) was in stark contrast to our smallest team member (5ā7ā tall 135lbs).
What I didnāt expect was to find that having the bigger guy behind me made it easier than the smaller guy (go figure?).
The problem is, Iām 5ā7" 135lbs and I have a twin (who does front-end work on these projects), heās similar, and weāre both aero obsessed, so it always comes out so aero, and it tracks for us, we test rigorously.
Weāve had some customers, but without explicit consent I wouldnāt touch their models for anything post worthy.
If youāre a bigger person and want a few free tests that I could uses in examples, just let me know!
Also, I canāt just scale up the models, because the rider is āattachedā to the bike, and the bike wheels (as an example) remain a static size for most rider height/weights.
another example could be full aero one piece integrated cockpit vs traditional round bar+stem+cable or 40cm vs 38cm vs 36cm bar widthā¦
