Many of you have asked if we have aerodynamic data on our Trakk frame compared to competitors - and of course we do, since great design work requires a point of comparison. Our goal was to make a bike fast enough to win at an Olympic level while being affordable and maintainable enough for the Friday night local scratch race, and you can't do that without knowing what "fast" means!
But we haven't shared it publicly, until now. So why now, and not before? For one, I did some bragging to my local velodrome (JBMV) folks recently, and will never live down the good-natured teasing if I don't. But more importantly, we finally have the context to be confident our data is accurate. Stromm believes very strongly in truth in science (and for me specifically aerodynamic science), and until recently, we had a few question marks about our early wind tunnel testing. In this article, I'll talk about those questions, why we're confident in our answers to them now, and finally share the tunnel data you're here for.
Sure, it looks cool, but does it represent the reality you demand from your gear?
First, the main questions that gave us hesitation originally:
1) How did the prototype's surface finish (it was 3D-printed and sanded) affect the tunnel results?
Check out that fork finish - not exactly production smooth!
Surface finish that's rougher than the finish product changes drag in complex ways - it adds friction drag (since a rougher than production surface means more friction between frame and air), but that same friction drag also increases mixing of the air, which can reduce pressure drag. Which of those two impacts is stronger can vary with yaw angle and tunnel speed, and is hard to characterize.
Recent results from our road frame tunnel tests (with both rough and smooth surface models) have helped us characterize the impact in the tunnel to a high degree of confidence - enough for the aviation industry, much less cycling!
2) How accurate are our predictions between the tunnel and the real world?
Chung testing is helpful in determining how much the more turbulent tunnels and more laminar real world behave, but it's very hard to get specific yaw-dependent data, which is what we need to validate our computational simulations of the track frame.
For that, ideally you need tests in two tunnels of different levels of turbulence - and thanks to Tour Magazin's road bike tests, we now have that, and then can use it to predict to an even slimmer error margin the difference between the real world and the wind tunnel.
Road bike design hasn't pulled us away from our roots in the velodrome - it helps us design for track even better.
3) What other biases or unknowns might there be in our data?
As you'd imagine, knowing all the things above is critical to the design process, and we've done our best to do them well years ago. But the last and final missing piece was that all of these tests were run by me, Ben, Stromm's aerodynamicist.
Introducing the biggest remaining unknown unknown in our design and test process - yours truly!
I'm fairly experienced with high-end aerodynamic design, and with wind tunnels specifically - I've tested in tunnels at everywhere from 25 mph to Mach 5, from cars, bikes, and ground vehicles up to commercial, tactical, and even hypersonic aircraft. I've been trusted to bring online, characterize, and calibrate nationally critical wind tunnel facilities that are literally impossible to replace should there be a serious mistake. Multi-billion dollar decisions for aircraft programs have been made based on my aerodynamic estimates. But critically, I am also human, and therefore still potentially fallible.
How? I'm inherently biased, and I think a certain way. While I do my utmost to run our tests such that my personal hopes can't impact the results, without fully double-blind testing it's still possible that I could influence the results whether intentionally or unintentionally. And if I haven't considered an important factor that could affect results, I probably haven't considered it in any of our tests, and therefore none of them will reveal that potential inaccuracy. Tour Magazin's independent results convinced us to within a single watt that my bias wasn't misleading us, and that my methods weren't skewing our data from the truth. It took any unknown unknowns due to me, and made them known.
What You Came For
With this sub-single-watt confidence in our entire engineering design process, we are finally satisfied that releasing our Trakk wind tunnel data is both accurate and truthful. Without further ado, here's what you came for. I've scaled the data to two track-relevant speeds for your convenience, and we've provided a concrete comparison point via the previous best-in-class frame. I'd estimate we have a roughly similar (and perhaps in some cases greater) advantage over any frame not explicitly designed for a national team, but this provides something very well known to compare to. For legal purposes I have to mention that Argon of course is not affiliated with us nor do we own the rights to their marks.
These results are using a Mavic wheelset as pictured above, Vision bars, and otherwise representative gear transferred between each frame for consistency, and include the effects of the lower-body drag reductions that are our frame's hallmark performance advantage, all in a Tour Magazin-esque lower body mannequin setup with the exception of static legs. The exact drag wattage number is for a frame and wheels alone, but includes body reductions in that number.
A few interesting (to me at least) observations: you can tell I explicitly designed this frame for stability and speed on an outdoor velodrome, with the much more gradual stall characteristics (above ~10 degrees) and greater sailing effect (above 2 degrees). Selfishly, I wanted a bit of home field advantage for us when at Jerry Baker and Hellyer, and the sailing effect at the lower yaws still helps even indoors due to bike movement! You can also see the results of the extreme low yaw optimization we did for Olympic level indoor events in that zero-yaw data point. Always cool to see what you intended to happen on a computer play out in real air!
If you have any questions, feel free to reach out via our website contact forms - it'll come directly to me, Dave, and Stephen to answer!