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Show Notes
In this week's episode, Randall has Josh Poertner on to talk aerodynamics. In a wide-ranging conversation, the two touch upon Josh's time as Technical Director at Zipp, involvement in the development of computational models for rotating wheels, early collaboration with Cervelo founders Phil White and Gerard Vroomen, founding and leadership of the product brand Silca and The Marginal Gains Podcast, and ongoing consulting work with elite athletes and teams.
Silca Website
Marginal Gains Podcast
Episode Sponsor: Logos Components
Join The Ridership
Automated Transcription, please excuse the typos:
Silca - Josh Poertner[00:00:00] Craig Dalton: Hello, and welcome to the gravel ride podcast, where we go deep on the sport of gravel cycling through in-depth interviews with product designers, event organizers and athletes. Who are pioneering the sport
I'm your host, Craig Dalton, a lifelong cyclist who discovered gravel cycling back in 2016 and made all the mistakes you don't need to make. I approach each episode as a beginner down, unlock all the knowledge you need to become a great gravel cyclist.
This week on the show, I'm handing the microphone back to my co-host Randall Jacobs.
Who's got Josh Portner, the CEO of Silka on the shout out a wide range in conversation about the sport and high performance. Many of you may be familiar with the storied Silka brand. It's been around for close to a hundred years. But josh took over back in 2013 with a mission of merging the highest quality materials and craftsmanship with cutting edge design and manufacturing
When you visit the Silca website, you notice a tagline, the pursuit of perfection, never settling, always improving. And I think that embodies how Josh approaches the sport. . So I'm excited to pass you over to Randall to dig into this conversation. Before we jump in i want to thank this week sponsor logos components
Yeah, I've been itching to get back on a set of six 50 B wheels, and I've been waiting for my logo's components, wheels to arrive. They literally just arrived last night and I'm super stoked. But yet disappointed because I have to go away for the weekend and I won't be able to actually ride them
until sometime next week. I chose the Atara six 50 B model. As you know, I'm sort of big on the big tires, big fun philosophy. So I've been eager on my unicorn, which I've been riding on a 700 SEASET for a while now. To get into the six 50 bees again and see what a six 50 by 50 combined with that rock shock fork is going to yield for me on the trails here in Marin. You guys may remember.
Me sitting down with Randall, talking about what makes a great gravel wheel set and everything that went into these logos component wheels. I encourage you to go back to that conversation because whether or not the logo's wheel set is for you or not. I think Randall does an excellent job of teasing out.
All the various considerations. You should be having when considering buying a gravel wheelset,
It is no small expense when getting into a carbon wheel set, but the team at logos has endeavored with their direct consumer model. Uh, to make it as affordable as possible and make them as durable and high performing as anything out there on the market. I written wheels designed by Randall for the last three years. So I'm super excited.
To see his latest vision come to fruition. With these new wheels and I'll have them underneath me soon enough. I encourage you to check them [email protected]. Randall's also an active member of the ridership community. So if you have questions for him, feel free to join us over there at the ridership and connect with other riders. I seen people paying that their wheels have arrived so you can get some real, real people answering your questions.
About whether they're enjoying the wheelset and how they perform, et cetera. And I'll have more on this in future additions.
At this point. I'm going to hand the microphone over to Randall. And i hope you enjoy this conversation with josh
[00:03:30] Randall: Josh Portner, thank you for joining us on the podcast. This is a conversation I've been looking forward to for quite some time. Some deep bike nerdy is probably about to ensue, so, uh, let's dive, let's hope. Dive right into it.
[00:03:43] Josh: Well, thank you for having me.
Always, always up for some deep bike. Nerdy. I like that.
[00:03:49] Randall: So a number of our listeners will already know who you are, but just give folks a high level summary of what you do now.
[00:03:55] Josh: Oh gosh. So I own Silca, um, or I own Arrow Mind, which, uh, owns the Silca brand and trademark, um, and, and all that that entails.
And then we also have a, uh, we own Marginal Gains, which is a podcast and a YouTube channel. And, um, Yeah, our goal is to, a mind works with a lot of pro riders, pro teams, world tour teams. Um, you know, we do everything, Excuse me. We do everything from, you know, performance consulting, uh, modeling, uh, you know, setting up our record attempts for people or, or helping them design our record attempts.
Um, you know, we do tire pressure work with pros. We do equipment choices for teams. We think some of the most interesting stuff we do, um, is around where like, uh, teams or national federations don't trust the equipment they're getting from somebody. And they'll come to us and say, you know, the, you know, bike brand X says that this does this, and our writers don't think so.
Can you tell us what's true? And. We'll find a way to make that happen. So we, we've had some pretty interesting ones of those with, uh, particularly around the Olympics with the national federations. You know, no, nobody wants to have another Under Armor speeds skating suit, uh, situation, , right? Where all the, all the athletes think something is true and therefore it becomes true and, and nobody knows.
And so, um, you know, so we do a lot of that. Arrow mind does that, essentially. And so that's a lot of the performance work I was doing in my old world. I was technical director at ZIP for almost 15 years. Um, and, and then Silca is the product arm of the company. Uh, that's probably how, you know, most people know us.
You know, we make pumps and tools and, and, but we also make a lot of crazy things that people look at me and go, Oh, where the hell did that come from? Well, that probably came from some project or another. We did it in the Arrow Mind side of the business, Um mm-hmm. . So that's how we've gotten into sealants and lubricants and 3D printing and, and all sorts of other craziness.
Right? That's sort of how the one flows into the other. And then, you know, Marginal Gains is a podcast and, and YouTube channel where we talk about it all and, and we, we typically with a, a team or a company have like a two year. Secrecy period on a technology. And then after that we can do something with it and, and talk about it and tell the story.
So, you know, it's always, it's always fun to go through those periods where like, Oh, thank God we can talk about that now, . Cause you know, we're talking about it internally all the time. And, and you're like, Oh, can we put that in the podcast? I don't know. So, so that, that's what I do now. We, I, I play with bikes basically.
[00:06:34] Randall: Very, very cool. And, um, when you talk about the consulting work you do, is this kind of full stack performance consulting, is it very a focused, is it all technical sides, including say, like bearing drag or, or things like this? Is it, um, obviously positioning falls into Arrow Nutrition. Like where, where do you, ooh, where does your domain physiology start?
[00:06:57] Josh: And I draw the line at physiology, you know, there's a whole, there, there are people who are, are like my equivalent in that world. And, and my God, I can never even dream to. You know, clean their shoes. So, um, no, you, you need someone to talk physiology, you know, And I'll, I'll pull my phone out and we'll call Allen Li or somebody, you know, Yeah.
With a bunch of contacts. But, uh, you know, Alan's one of my favorite go-tos for things like that and be like, Oh dude, I've been over my head help . You know,
[00:07:21] Randall: he, he's, um, he's actually been on the pod before, but Craig interviewed him, so I might bring him on in the future to do, you know, my, my more kind of nerdy type of interview.
Alan's great. Yeah, no,
[00:07:31] Josh: he's, he's a lovely guy. He's a lovely guy. And, and I just love, I mean, he, you know, like I find myself pretty quickly sometimes getting into places where people's eyes just glaze over, like, what the hell is this guy talking about? And, you know, I love that Alan can do that to me in about 30 seconds, you know, we're talking about the stuff that he does.
You're like, Oh, whoa, shit, way over my head way. I, I didn't even recognize the last four words that you used in that sentence, . And, uh, so it's, it's awesome to be able to be surrounded by people with that. But no, you know, we. The stuff that they come to us for. I mean, you know, when I left sip and started soak, of course everybody and their brother, you know, came and said, Oh, design us a wheel.
I'm like, well, like I can't do that for a couple years. But also I'm kind of just done with that, you know, like I've lived that life. I, you know, it, it was fun. But, you know, we, we continually updated wheels for 15 years, but it, it really is kinda like doing the same thing over and over again, you know? And, and so it just wasn't fun for me.
So, you know, they'll come and say, um, you know, help us design this cockpit, or we, we do a lot of, with our, our in-house, uh, 3D titanium printing, we do a lot of custom cockpits for, uh, teams, riders, things like that. You know, where we laser scan the rider, get the position, lock that down to the wind tunnel, design the part, 3D print it, um, you know, stuff like that, that, that's really exciting.
We, we'd get a lot of, you know what, um, You know, help us optimize for this time trial at the tour or the Olympics or whatever, where, you know, what tires should we run and we can, we have systems and tools and, and spreadsheets and a million other things that we can, um, Yeah. Help, help them determine. And then a lot of times we, you know, we get companies coming to us, um, really just wanting to know, like, you know, if, like, which of their sponsor products should they use and when should they go off sponsor?
You know, you'll see that a lot at like, the tour where, excuse me. Um, you know, like they, they ride the sponsor correct product, you know, 98% of the time, and then they're gonna sneak it in here or there when it's really critical. So, you know, what, what are those really critical points? And then, you know, if, if they're gonna risk getting in trouble or outright get in trouble, like it needs to be worth it, right?
And so they might come to us with like, okay, you know, we need. I need a time trial tire for this rider for this day. You know, what should we do? And, and we'll help him with that. But yeah, you know, if you, if you were a, a brand, uh, or a world tour team there, or approach our athlete that wanted to go to the win tunnel, you know, you might pay us to come along.
Um, a lot of what I do too is kind of fun is just act as like a fly on the wall in these team to sponsor interactions. You know, I think I was probably at half a dozen wind tunnel tests last year where I really had pretty much nothing to contribute other than being the neutral third party in the room, um mm-hmm.
you know, so that everybody was comfortable that everybody was. Comfortable .
[00:10:26] Randall: Well, I would imagine there's a mix of the, uh, the political, if you're talking about, you know, what should be using our own sponsors gear versus slipping something else in all the way to, um, balancing the competing goals of say, like comfort and pure power output on the bike versus aerodynamics.
Um, if you're talking about a time trial position. Yeah.
[00:10:47] Josh: Oh yeah, for sure. And, and I think even down to, you know, and I think as much as we love to talk science and testing and, and try to be as scientific as possible, I mean, this stuff is really, it's emotionally hard. It's politically hard. It's, you know, companies will bring new equipment in, they're with their engineers.
I mean, those guys and girls want that stuff to work so bad. And you know, sometimes you just see things coming out where, Oh yeah, that's clearly faster. And you're like, Well, actually, the way I would interpret that is it's probably about. The same, um, or mm-hmm. , you know, let's, let's rerun that test or, um, you know, it's always, I don't know, it, it, they, they like, people like to get themselves in these loops where, you know, Oh, we did this and it's 10 seconds faster and it's that, And I feel like back in the, you know, when I was with zip, we did this a lot during the Lance Armstrong area and he was writing our disc and, and we were coming in as consultants for the first probably five tours or whatever.
And um, you know, every wind tunnel test you'd get to the end and they would have this chart that's like, we just made him 90 seconds faster. And it's like, look guys, that. There is no 90 seconds faster. I mean, you know? Mm-hmm. like, like that is not gonna happen. You know, you, you just did a whole bunch of stuff that's not sustainable that he can't hold his head like that.
Mm-hmm. that helmet tails gonna come off the back, you know, I mean, cuz he, people do things like, Oh, oh, the helmet tail moved, rerun. You're like, Yep guys, when you ride in the real world, like the tail's gonna move. Like you don't, you know, people like to, they select data, um, without even realize they're selecting data.
And so, you know, it is, it's just good always to have a third party in the room. Um, you know, it's kinda like funny story, you know, back to, you know, my zip days, how Firecrest came about, you know, Firecrest was literally the name of the prototype that, that kind of blew all of our minds. And the reason the prototypes had weird bird names was that we had to double blind them across engineers because you just didn't want anybody.
Kind of, you know, having an effect on their product, right? I mean, we all, you know, we all fall in love with our children, right? . And, and in this world, like you, you can't love your children. Um, and you have to be willing to kill them when they're not good. And, um, you know, we would do this double blind thing where we would like assign them all a number and then we would assign bird name, these bird names a number, and then we would randomize it and then they would get all put up.
And then nobody really knew whose idea was what, when you were in the tunnel. Um, that's necessary, right? Cause you're, you know, you can be your own worst enemy at that stuff. I think we've, you know, we've all been guilty of that a time or two in our lives. But, uh, you see it all the time, particularly in these performance, um, improvement coaching type things where, you know, people just wanna will something into existence even when it's not.
Yeah.
[00:13:38] Randall: Well, and I can see, um, you know, the marketing oftentimes has it much more, uh, presented, much more like a, you know, this is just, it's physics. It's more, it's more exact, it's more, um, it's more controlled. And, um, there are competing variables, particularly when you have, you know, a monkey in the middle.
You have to, this, this, you know, this animal needs to be comfortable. This animal needs to be fueled, This animal needs to be able to control this machine through a varied environment. And that varied environment may be varying in real time if weather changes or things like this. Um, and so there's just all these competing interests.
And so when you see, you know, I often laugh at like, You add up all the different arrow benefits that, you know, different companies claim for components and you should be doing. Right. Right. You know, you might be looking at, um, uh, relativistic effects potentially at some of the speeds you'd be able to achieve.
Uh, Jen, just like how, how many watts can be saved. Totally. Being a little bit facetious there.
[00:14:37] Josh: Yeah. No, no, it's totally true. I mean, and I still have this photo somewhere, I think I even showed it a couple years ago on social media. But as this, this really great photo that I love that ended up, um, on the wall at the Texas A and Wind tunnel, but it's me with next to Lance Armstrong, um, in the, what became the Nike Swift spin suit, um, that had been flown down there from, you know, Seattle.
And it's, uh, oh God, the guy in from his book college or whatever he calls him, and then a guy from Nike, so it's the four of us. And I'm kind of standing there like doing, you know, like pointing at something on his back and it, like, a college student took it for the school newspaper and then they had him autograph it and it ended up on the wall.
And so like, Oh, that's me. You know, it's kind of funny. But, but the real story there was that suit, you know, they were paying like 3000 bucks a meter for this suit. They'd been putting it on a mannequin in the tunnel. I mean, it was gonna save three minutes per 40 k. And you're just sitting like going, guys, like, I, I mean, just quick doing the math, like three minutes for Lance Armstrong, you know, like the guys already, That's not possible.
And, and of course we get it. We put it on him. Um, the whole thing, you know, it, it's, it's cool, it's fancy, it was very red and it does nothing. I mean, it literally, we were, and the Nike people are there and they're like, Oh, that's not possible. It, it can't do nothing like whole. Let's run it again. Okay. Now get 'em out of it.
Put 'em in the normal suit. Run that one. You're like, it, it just doesn't do anything. And, and they just kept going. Well run it again. Well do this. Let's, let's close pin it up. Let's tighten it. Let's, do, you know, I mean, I bet we, we lost two hours trying to make that stupid thing look like it would do anything.
You know, And again, it's, it's just people being people and we've all done it. But
[00:16:21] Randall: I hear like something of stages, of, stages of grief. Like, you have your baby and like first it's denial, and then you, then you have bargaining. Yeah. Yes. Put so much into this. Yeah, that's exactly,
[00:16:32] Josh: that is exactly what it is.
And, and you know, the, the crazy reality with that one was, you know, three months later at the tour, they launched it anyway, and they said it saved three minutes and he , you know mm-hmm. . And we, we. It, you know, I just had to laugh. I mean, I remember, you know him, you know, winning whatever one of the time, trials by like a minute and like going, No.
So Nike's essentially saying he would've lost that time trial by two minutes had it not been, had he not been wearing that suit. Come on guys. Um, yeah.
[00:17:00] Randall: Well, and I think that, that maybe that's, um, you know, headline number one from this interview is don't believe everything you read, especially if it's coming from a party, has a financial interest in it.
[00:17:10] Josh: That is true. That is true. Yeah. I, I, I tell don't, don't even believe yourself. Right? I mean, truly like you, you are a bad, um, a bad predictor of things and, and you're a bad feeler of things and nobody wants to admit that. Um, but it's just true. You know, that's, I've been preaching that gospel for, for years.
But, you know, I mean, 90, I, I would say 90% of the things you. That you feel when you're on your bike. Total, total crap. Um, and, and we know that cuz we, we've done blind testing with riders. I mean, like unbelievable world class rider. And if you blind them to what they're actually riding, they can't tell you almost any Yeah.
Um, you know, all that perception, but still, but the stories away, the
[00:17:56] Randall: stories we tell ourselves are powerful. There is a strong placebo effect. Oh, for sure. Uh, for sure. But it has to be acknowledged that that is the placebo. And if you actually had those beliefs about things that had genuine benefits, you would get both, You would get the actual
[00:18:11] Josh: benefits.
Yes. The, the most powerful thing in the world is a placebo that actually works. Right. , where you get, it's like a, it's a double whammy benefit. Um, and so yeah. That, that's where, you know, I mean, in a nutshell that's a lot of what, you know, I've made my career doing right, is trying to help, help sway people towards the, the, the placebos that, that actually do have a, a, a benefit for them.
[00:18:34] Randall: So this has the conversation going in a slightly different direction than I was anticipating, which I'm really enjoying. So I've been, I've been diving into this lecture series from this guy Robert Sapolsky at Stanford. It's on, um, the, uh, uh, behavioral biology, and it's looking at all the different ways in which studies go wrong.
And so there's like, you know, beliefs about something, uh, for a long period of time, you know, eminence, people in the field, uh, promulgate these, you know, these ideas. And then it's shown that, you know, the study was, was not, uh, taken, uh, done properly or what have you. And so I'm curious, let's dive more into things that go wrong in the study of aerodynamics and, um, maybe kind of the edge of, say, human performance where interfaces with aerodynamics
[00:19:17] Josh: Hmm, ooh.
Interest. So, I mean, a, a good. I would say career defining for me, example of that was, um, you know, we, from like 2009 to 2012, we were really all in on developing, uh, CFD for the, for bicycle wheels. And it, it just wasn't working right. Everybody was talking about it and showing papers, and, but I mean, it just, the reality was like the CFD just never looked like the wind tunnel.
The curve shapes were different. The data was, we're, we're talking It
[00:19:47] Randall: wasn't mid, mid
[00:19:48] Josh: nineties, right? Oh, no, Mid, mid late two thousands. Yeah. Like mid, late, late
[00:19:53] Randall: thousands. Okay. Yeah. And you're not using, you're having to develop something ground up or you're having to, uh, adapt something from Desso or, or one of these bigger
[00:20:02] Josh: vendors.
Yeah, So I think the question at the time was, you know, how do you, how do you really properly model the spinning wheel in, in flow that's also translating, right? And you look at. You know, all the CFD stuff with aircraft, um, you know, there's no rotational flow, you know, and then you look at, there's special models that people have built to look at, like, um, turbine jet, turbine engine combustion or whatever.
But those are incredibly unique. And they're also, you know, there's RO flow rotating, but in a different access and Yeah.
[00:20:36] Randall: The F1 guys perpendicular access.
[00:20:38] Josh: Yeah, exactly. Exactly. And so, and then you got the F1 guys who weren't really modeling, um, they were modeling the rotation of the wheels, but they were doing it by modeling a rotational component at the surface of the tire.
So you were, you weren't essentially like spinning the wheel, you were just saying, Oh, there's a induced rotation a about this surface. Um, which has been in the, the solvers forever. So
[00:21:02] Randall: in interesting, this is taught because the, those wheels are traveling so quickly, especially the top of the wheel. If you're doing 200 miles an hour, the top of the tire is traveling at 400.
And so you're having sign significant turbulence at that interface, right? Well,
[00:21:15] Josh: and you, you have like Magnus effect, right? You're actually getting pressure differential top to bottom, um, you know, from , the direction of the wheel spinning. And so, you know, we, we could do stuff like that pretty accurately, right?
You know, you could look at the, you know, a rotating baseball and, and predict the direction that's gonna curve. I mean, things like that were possible. But, you know, every single, and, you know, my God, I used to get, I still do occasionally, but I, I used to probably get 20 PhD papers a year from kids all over the world.
Um, you know, Oh, what do you think of my paper on, you know, CFD of bicycle wheel? And we're like, Oh, it's beautiful pictures, but your data's crap. Um, . And it just wasn't figured out. And, and in 2009, I, I met a guy, Matt, uh, Godo, who's a triathlete, but he also worked for a company called FieldView. And they had built all of the CFD automation for, uh, Red Bull F one, um, and probably half the F1 grid, but his, his big account was Red Bull.
Um, and he, I met him at Interbike and he had a paper that he was working on. He said, I think, I think I might have figured this out, but I really need to be able to like, Like, build a wind tunnel in the computer and then look at it so we can directly compare them back and forth. And, and so we, we did that.
We published a paper at the a I a, which was at MIT that year, and it went over really well and people liked it. And we published another paper the next year, um, at, at the a i A conference. And that went well. And then we got this big grant, like an $80,000 grant from Intel, um, to really tackle this problem.
Cause the, the head technologist at Intel at the time was a guy, uh, Bill Fry Rise, and one, one of the coolest guys I ever met. Um, you know, the kind of guy who, whose resume just has like a five year period that says like Los Alamos , like,
[00:23:01] Randall: okay, you're cool. You know? Yeah. Yeah. Not, not allowed to talk about it.
What do you do? Yes. Uh, yes, exactly. .
But,
[00:23:08] Josh: uh, but he was a cyclist and he was some senior, somebody at Intel. And, and, um, And they, they gave us this money and we, we, we really went hard at this and we ended up developing a, essentially all of the little nuance details. Uh, we did it in star ccm. We post processed it in field view.
I think we processed it on like a thousand cores, which for 2010 was, you know, a lot. Right.
[00:23:33] Randall: Um, and these are, these are, um, CPUs and not GPUs for that era. Right. A lot of the stuff of that era GPUs now, right?
[00:23:40] Josh: Yeah. Yeah. I remember we, yeah, I mean, that was the beginning of, uh, that was the beginning of the cloud.
It was pretty cool, like 2008, 2009, people were still traveling. I remember at one point in that process there was discussion that like, we might have to travel, um, to, Oh God, what is it? The, the university over there in Illinois had a huge, had like a 1200 core machine and they're like, Okay, we, we might have to go there and, and buy, you know, two days of time.
And then as that was happening, cloud. Kind of the beginnings of cloud was there. And I remember we, we met a guy who had a cloud thing, and they had just been bought by Dell. And, uh, we were at a conference and he's like, Oh, no, you know, with our, our thing, What was that called? But, uh, with our thing, you, you can just do it like up in the ether.
We're like, Whoa. You had never heard of that before. Yeah. Um, it was just exciting times and, and, uh, but, but we, you know, had this great team. We pulled it together. I mean, that's really where Firecrest came from, right? It was, it was largely designed using, um, Hundreds of iterations of capes predicted to be fast, uh, using this cfd.
And, and ultimately we won. We, we became like, I think the first non university and non-governmental group to ever win a, uh, uh, innovation excellence award from the Supercomputing Society. So it was pretty cool. Salt Lake City's like this huge super computing conference and you know, it's like darpa, this and university of that.
And it was like these four guys from this bike brand and, you know, was, uh, it was a pretty cool experience. But, but in that, so that's like a huge tangent. No,
[00:25:17] Randall: no, this is, this is great. And, and just to take a, uh, stop for a second, CFD computational Fluid Dynamics software that is used to model complex multi-variate systems where there's second order effects and, you know, fluids and, and things like this.
So anyone who's not, uh, who's not with us on that, like complicated software for complicated system models, in your
[00:25:39] Josh: ideal world, it's like a wind tunnel on your laptop, right? In the, in the George Jetson's version of things. It, it's the wind tunnel on the laptop. And in the reality of things, it's kind of more like, eh, it's about as good as guessing most of the time.
But, but, but sometimes it's really good at finding certain really specific things. So I won't, uh, I won't knock it too hard, but why the thing I wanna
[00:25:59] Randall: dive in a little bit
[00:26:00] Josh: here. Oh, go ahead. Yeah, yeah. Well, let me, so let me finish the, the thing that we discovered in this process that was super cool. Um, was that once we had all of these transient, we were solving for all these transients, um, and we really started looking at not just like the, you know, the, the side force or the yaw force or you think of um, you know, the whole thing with like wheels and handling, right?
This all came out of this project cuz you could, you could predict the steering torque on the wheel, which, you know, none of the balances being used to test wheels at the time even had torque sensing, right? You had drag side force and lift, but none of them had the rotational components in there. And so that for us at first was like, oh shit, we've never thought about torque cuz we weren't measuring it.
Right? It's sort of one of those, yeah, like you've biased your study all along, but then the big one was looking at the predicted, um, data and there were all of these, uh, harmonic effects. and we kind of looked at each other and we're like, Oh my God, every wind tunnel you've ever been in, Right? The first thing everybody discusses is, you know, what's the, what's the, the time across which you're taking the data and at what frequency?
And then you're averaging that data, right? Cuz we're all after a data point. And you could look at the tunnel data and the CFD data, and when you pulled them out of their point form into their wave form, essentially you could see the harmonics kind of lined up, the frequencies match when, oh shit, we've been averaging out a really important piece of data for 30 years.
You know, this harmonic thing is big. Like what's your,
[00:27:39] Randall: your standard? So it's operating on a, it's operating on a frequency that is smaller than the sample rate. Or how
[00:27:46] Josh: was it essentially? Essentially we were just idiots and we were just, we were just time averaging the all of that out. Right. I mean, it's, you know, if you need to Okay.
Any wind tunnel you, you went to in the world and be like, Oh, well, we'll take, we here, we take data for 30 seconds at, you know, whatever, a hundred hertz, 60 hertz, 120, or whatever it is, and then we'll, we'll take an average. Oh, okay. That, that's fine. Got it. You're averaging out in there is real, um, uh, like amplitude changes, uh, largely due to vortex shedding is, as it turns out with bicycle wheels.
But a lot of that high frequency handling stuff, particularly as wheels get deep, um, , sorry, I'm in, uh, I'm in our studio, which is off of our kitchen and somebody's lunchbox just, just leapt off of the top of the
[00:28:34] Randall: refrigerator. Um, yeah, sometimes I'll have a niece or nephew come in screaming, so No worries.
Yeah. So, but,
[00:28:39] Josh: uh, but no, we, we realized there, there was a, a. About a factor of five difference in amplitude between wheels in terms of that, those oscillating effects. Right. Which typically it's just, it's generally vortex shedding. And the CFD can predict that really well, right? Where your little pressure builds up, sheds off, sets off a counter rotation that sheds off.
Um, but as a, as a cyclist, you, you feel that as the wheel, you know, kind of oscillating left to right. Um, and we, and let's, let's for 20 years, you know,
[00:29:12] Randall: Yeah. So you're just taking the, the lump, you know, 30 seconds averaged out data and saying, Okay, it gives you this amount of benefit and you're not seeing those.
Um, I mean, really what we're talking about is, uh, you know, instability that may. Or, you know, otherwise result in, in control issues on the bike. And I want to take a moment to just like, define some terms, uh, because not, you know, many of our listeners are not overly technical. Um, but uh, I think some of these concepts are easy enough to get your head around, like, so, you know, describe at a very high level you're talking about vs.
So, you know, maybe describe lader flow and flow attachments and vortices sheddings. How, how does this, how does this, uh, how can you understand this without a, a technical background?
[00:29:59] Josh: Oh, those are awesome questions. Okay. So Lader LaMer flow is kind of what you. What the, the world wants you to think of in the wind tunnel.
You see the wind tunnel picture and they've got like the, the 10 lines of smoke and they're all kind of flowing together cleanly and beautifully. That's, that's meant to, to evoke lam or flow, right. That if you were to drop a, a smoke or a particle in there, that they would all flow in lamini, you know, like sheets of paper.
Um, yeah. Uh, so, so
[00:30:29] Randall: it's going in a straight line. Smooth,
[00:30:31] Josh: controlled, Predictable, yeah. Flow. And it, it follows the contours of the thing that it's flowing against. So,
[00:30:38] Randall: so kinda like water flowing down a river sort of thing. It's not perfectly laminate, but it's all going roughly in the same direction. And there's not a lot of water
[00:30:46] Josh: in a pipe disturbance, you know, would be in a pipe better example, presumably pretty laminate, right?
And then you start to add stuff, you know, water in the river. Now you're, you're, you know, you've got a rock and now all of a sudden there's a disturbance and it starts to swirl. Um, and so you, you get into, you know, more complicated types of flow. I, I think the, the big ones, you know, for us to think about are, you know, most, so most drag that we deal with comes from, um, uh, pressure related things.
So you either have like the, the high pressure on the front of the rider, right? The wind that you're pushing into this when you stick your hand out the car window, right? The mm-hmm. the air you feel hitting your hand, you know, that's, uh, that's a pressure drag, uh, in the positive direction. And then you have the flow, the vacuum in the back.
Yeah. The flow will detach off of the object and that'll create a vacuum behind. And so that's a suction drag, um mm-hmm. . And then when you have something like vortex shedding, it's when, uh, the, the. Description I ever have for vortex sheddings. If you've ever driven an old car with, uh, like the metal antenna on the hood, you know, at some speed on the highway, that antenna starts vibrating, oscillating sideways, which is like the last thing on earth you think it would do, right?
Like your brain's like, well, it should just keep bending backwards with speed. Mm-hmm. , why is it going sideways? Well, that's that you get this thing where you have a little, uh, a little curl of flow will kind of detach more on one side than the other, and that creates a side force. Mm-hmm. . But in doing so, the suction that that has now left behind will pull a similar vortex from the opposite side.
Mm-hmm. . And that creates an opposite side force. And so you get these, see an oscillation, you get these oscillations and uh, you know, that's, it's huge in architecture and mm-hmm. , it, it's why you see so many of those super tall buildings or kind of have pyramid shapes or might have some sort of like, feature that spirals down them to, to kind of break that up.
I, I
live
[00:32:46] Randall: in Boston. We actually have, um, a skyscraper here that was flexing so much, the windows were popping out. This is, you know, decades ago. And, you know, it's still, you know, they have this like funnel of air that's going through there and just the nature of the shape of it and how air gets funneled in, it was causing enough torsion to, um, you know, cause window de bonding.
Um, so yeah. That's crazy. Uh, so then, you know, think applying this to the bike and particularly a wheel, um, you know, this is the biggest effect is, is presumably your front wheel where you're having this oscillation, this shift in pressure from one side to the other at a very high, high level, um, that's causing instability.
It's making it so that you may lose control of the bike. It's not predictable.
[00:33:34] Josh: Yeah. Correct. Correct. And, and the, the other thing we learned through CFD that it was doing, which is not obvious until you think about it, but so you think of the. So you might have, say it that the trailing edge of the front half of the rim, you're, you, you set up a little vortex shedding situation.
Mm-hmm. . Um, and so you've got a little side force, but it's kind of at the, the trailing edge of the rim there. Right? So it's got a little bit of leverage on your steering, but the other thing that's happening is that alternating attachment and detachment of flow, um, changing the side force, but you're a side force at an angle.
So there's a lift component, right? Which is how the drag is being reduced. And as that happens, what, what's also now changing is what we call like the center of pressure. And the center of pressure. You think of like the wheel from the side, like, like the sum, the aggregate of all the, the arrow forces on that has a center point about which it's balanced.
It's kinda like a center of mass. Um, you know, so it's, it'd be center of pressure. Well, that center of pressure when you have. Shedding happening somewhere that's now moving forwards and backwards and very
[00:34:40] Randall: rapidly
[00:34:41] Josh: as well. Potentially, Yeah. Rather rapidly. I mean, and, and when you really look, look in on it, it, the frequency actually can be quite close to, um, the, uh, speed wobble frequency, right?
Which is somewhere in that like three to four hertz range. Uh, which also happens to be really close to the frequency of human, uh, shivering, which is kind of cool's why you're more likely to, to speed wobble when you're really cold. Um,
[00:35:05] Randall: and not everyone just push will have experienced speed wobble. But if, you know, if this is basically your, you, you hit a certain resonant frequency of, of the frame based on the frames geometry, uh, the head tube angle, the what are the factors that go into that,
[00:35:20] Josh: Uh, it's top tube stiffness is big and so, yeah.
Yeah. And it's actually this speed wobble's. Interesting. It's. It starts as a residency issue, but it's really a, it's a hop bifurcation and, um, a hop B. Okay. And so, yeah. And so what you have in a hop, uh, bifurcation is you essentially have two st two stability, um, would be the best way to think of it. And you are jumping from the one to the other.
And so like, right up until that, so the
[00:35:48] Randall: system wants to be in one state or the other, but not in the middle
[00:35:51] Josh: and there's no middle. Right. And, and what's, what's so cool, like, like early in, um, uh, early in covid, you know, we were all talking about this, you know, what is it the are not value, the, you know, like if it's above or below one.
And when you, you line that out that are not, when are not crosses one, it's a hop bifurcation that looks just like the speed wobble, bifurcation, I mean the graph. It's amazing how like, cool those things, you know, mathematically you're like, Oh yeah, that's exactly the same as this. It's just here, it's in a, you know, you get the exact same graph if you're looking at, um, Uh, wing flutter in an aircraft, uh, in the wing tunnel.
Mm-hmm. , similar bifurcation problem, but yeah. So you, you, you have essentially two states and the system can get tripped from one end into the other. And in the one the bike is stable and wants to go straight, and in the other it wants to oscillate because each oscillation mm-hmm. is setting up the, the counter oscillation.
Um, and so like, it, it's, you know, in resonance it's more of like a runaway you, you think of like the, how that's tradition. Yeah. It amplifi forcing. Yeah. It, it just keeps growing and growing and growing. Um, and in this one it just, it, it, it's not growing and growing, but it just trips you into this spot where like it's really bad.
Um mm-hmm. and it will just shake the crap outta you at the front end. And um, and in fact motorcycles quite
[00:37:07] Randall: scary. The high performance motorcycles will sometimes have a steering damper for this very reason. Um, because you'll, yeah, you'll get these speed wobbles. And so the damper is essentially making it so there's some exponentially increasing resistance.
Um, I, I know you know this, I'm explaining it for our, our audience just in, you know, cause again, I wanna keep bringing it back down to earth, but, you know, having just like your, your suspension, you don't just have a a just a spring, you have some sort of damping circuit so it doesn't feel like a pogo stick.
Um, which is a related effect. Um, but, uh, very cool. And are not for our listeners as well.
[00:37:47] Josh: Funny. I hadn't thought about that. I haven't thought about that in like two years as we were talking like, Oh, I remember now. That was, uh, yeah. Yeah, that was, uh, But what or not was the, um, Oh shit. It was the. The contagion ratio or whatever, like how, how many people, each person would transmit to mm-hmm.
And so if it's, which makes sense, right? If every person's gonna transmit it to 1.1, it grows. If you're gonna transmit it to 0.8, it, it dies. Um,
[00:38:12] Randall: so the analogy here is that, that the increasing amplitude of that, you know, those pressure differentials, sending it to the, the system to one state or the other and causing that increasing oscillation, Is that a exactly correct characterization?
[00:38:26] Josh: Yeah. Yeah, exactly. Like you, you can take it right up to a line, um, and you don't have a problem. And then as soon as you cross the line, you're in a different state. Mm-hmm. . And, and that's where I think, you know, speed wobble for those of you who've experienced it or chase tried chasing it on a bicycle, um, you can solve it sometimes with like, the stupidest stuff.
Um, you know, one of the, the common ones is to just put a little bit of like, um, like, like a heavier bar tape or a little bit of lead weight in like your, um, Uh, your plugs. Mm-hmm. . Mm-hmm. . You can oftentimes change it with a tire pressure or a different tire cuz you can add just enough damping at the contact patch.
Um, that it just pushes it up high. You know, if, if, cause typically what people will find is like, Oh, it's, I'm totally fine. Then I hit, you know, 38.5 miles an hour and all hell breaks loose. Well. Mm-hmm. , you change the mass at the top of the system a little bit and maybe you've now pushed that point out to 45 miles an.
but if you never go 45 miles an hour, you've affected, that's not a problem. Right? Yeah, yeah. Like, oh yeah, I
[00:39:28] Randall: fixed it. I think another example that people may have experienced too is like, uh, sometimes you'll have an issue with your car that, you know, won't notice except that certain speeds and it's because of those speeds.
There is some, you know, oscillation that's happening. If it's a tire and balance or something in your drive train or the like. Um, you know, I've, I once had a vehicle that was really good up to 60 and then like 60, 61, it was problematic and then it would smooth out a bit after that and it was just like this wobbling effect that would balance out beyond that, that speed.
Um, alright, so then bringing things back down to earth. Um, this is delightful by the way. I, I could do this all day, . Um, and I, I hadn't quite appreciated. Um, the, the basic r and d and like basic science and tool building that you were involved in. Uh, so. That's, its its own topic. That's probably not one for, for a podcast of this particular
[00:40:22] Josh: def.
Yeah. I, I will say on that, I think that's the part that I think never, you know, the marketing never really tells that side of the story cuz it's just too complicated. Yeah. But if you're, if you're out there and you're, you're into this stuff, like that's the fun stuff. Like, I love launching product and, and the product itself.
But like, that crazy journey to get there is usually like, that's where all the fun is happening. And, and, and typically cuz we're, you know, you're doing it wrong, like 90% of the time you're like, you know, it's just can be months or years of like, we suck, you know, this doesn't work, we're getting our sasses kicked.
And then you, you know, if you persevere long enough, you will come out the other end and it's like, wow, we, we needed all that stuff. Like, we needed to get our heads handed to us over and over again, or we never would've figured this stuff out. Um, Yeah. I really, really enjoy that part of, um, of, of technology development or whatever you wanna call it.
[00:41:16] Randall: Yeah. Basic, like real basic r and d right down to building the tools that you need to do the r and d you want to do, um, Right. . Yeah. Very cool. And obviously like the compute power and the, the algorithms available and, you know, the switch to GPUs and all these other things that have, um, changed since you were developing that make it such that today's models are both vastly more powerful and still yet trivial in complexity relative to the system itself.
[00:41:44] Josh: Yeah, totally.
[00:41:46] Randall: Yeah. Um, well let's dive into some more practical topics. So let's talk about like, alright, so a lot of our listeners we're the Gravel Ride podcast, right? So thinking about that particular experience, um, what should, what are, what is worth, um, a gravel rider thinking about. Uh, with relation to arrow.
Uh, so things that can be done that will improve aerodynamics, but then not take away from the ride experience that a lot of riders are after, particularly when they're going to grab, you know, they wanna be comfortable, they wanna have a good time, they wanna have good control over a variety of different terrain and so on.
So what are the arrow? Um, and, and they don't wanna look silly, so they might not be, want wanting to wear a skin suit or something like that. Not that it looks silly, but, but you know, a more, a more serious enthusiast type of rider. Uh, what are the Yeah, what are the things to think about?
[00:42:36] Josh: Oh, gosh. That's, that's a good question.
Um, I mean, I think it really depends on, on what. Th the particular rider, you know, is after, I mean, are you, are you racing? Do you wanna go fast? Do you wanna not get dropped? Mm-hmm. , um, you know, do you need to carry stuff? I mean, I would say one of, one of the big ones that I, I just see and, and you know, we, we make a ton of stuff in our company and one of, one of them being bags.
And, you know, we're constantly accused of not making bags that are big enough. And so I've been on this mission for a couple years of like, you know, what is in there, , Like Really? Mm-hmm. what's in there. Yeah. And it is amazing to me just how much crap people are carrying. You know, you, you open some of these monster seat bags, it's like, man, just because you bought it doesn't mean you need to fill it or use it.
Um, you know, it, and, and absolutely there's, there's like time and place for it. But, um, you know, I. Some of the stuff like that, like, Oh, okay. You've, you know, do you, you show up on the local gravel right here and you know, people look like they're, they're almost like bike packing, like mm-hmm. , you just don't need, you know, it, it's a 40 mile loop, you know, that starts and ends at a bike shop.
Like, you, you don't need to bring a bike
[00:43:49] Randall: shop with you. Well, you, you need your